[Bess_GT]

Hi all, This is my first post here. But I've been a frequent visitor here for past few months and I've learned many things from this forum. I'm a newbie in mechanics.

I'm trying to convert the EFI(failed one now, the bike was sitting for many years.) to carburetor and after a hard search out, I got this Mikuni carb from a guy. But I don't know how the carburetor fits in the slot. Please see the attached pics. I'm trying to use the stock Flange and the carburetor is getting stuck between the bars holding the cylinder head assy.

I've seen Otto_Ing(Paul)'s video of the same, but not sure how he did it. Also there are few replies in some posts here about this, but couldn't find anything about this issue.
Earlier I made a quote for conversion kit to Hitchcock, but the Pound to INR conversion makes it much above my budget.

Thanks.
P.S. I've been on this for many months, trying to open the failed fuel pump motor, made it rotate but the pressure in the motor varied after sealing. Trying a second hand fuel pump motor of RE500, which failed after few kms.

[ace.cafe]

You will need to do some fabrication/modification to make things fit.

There is no fuel pump in the carb system. You need a petcock adapter plate to replace the fuel pump at the tank, and use gravity feed for fuel.

[Bess_GT]

Hi ace.cafe,
But the bars that support the cylinder head is blocking the top of carburetor(as marked in pic) . May i know how i could modify that?

[gizzo]

Looks like you'll have to notch the bracket with a grinder to make room for the carb to move in enough. Try making some cardboard templates to figure out where to cut, before you cut the real ones.  Or,  find a piece of tube fits in the stub and use that, and another piece of rubber hose, to move the carb out a little bit. That's probably a less ideal but maybe easier solution. Good luck man, big project for someone just learning to be a mechanic.

[Bess_GT]

Thanks gizzo. Yes exactly that is the issue. I've confirmed this with the Paul's video. https://youtu.be/d4RRMA-r3wY
That is a different bracket.
I will check from where this bracket can be found(also asked Paul in comment)?No lathe at home, hence it would be hard to build new one or grind the existing.

[gizzo]

No angle grinder, holesaw or files?

[Bess_GT]

Nope gizzo. Got a hacksaw blade..but not sure it will cut this metal, but i'll try. May be i will take it to lathe if that don't work.
Paul replied that the head stay bracket came with the hitchcock kit.

[ace.cafe]

Cut the bracket to fit the carb, or maybe extend the inlet manifold if there is the ability to get better fit like that.

It is generally necessary to have tools and some experience to get into a modification process. Getting those would be the first step before starting modifications.

[Adrian II]

I got this Mikuni carb from a guy.

What size? (The carb, not the guy.) What was if fitted to before, this could be important as the settings might need to be changed (different jets, needle, slide, etc).

A.

[gizzo]

It is generally necessary to have tools and some experience to get into a modification process. Getting those would be the first step before starting modifications.

This Δ . You're going to have to invest in a few fabricating tools if you want to be doing that sort of work. They don't have to cost a lot of money. Go on, it'll be fun.

How are you going to notch the brackets in the lathe? Does it have a milling attachment? I've always wanted to have a go on one of those to see how good a job of milling they can do.

[Bess_GT]

ace.cafe : tried connecting it with inlet manifold, but it seems the carb is far too behind. Pls see attached pic (carb-fit).

 Adrian II: Hi, thats what confusing me. The size of the carb is the diameter of the end that connects to manifold? I measured using a scale and its around 32mm. There is a number in main jet like 7 47.5. The bowl has a number 24(pls see attached pic of bowl). Does carb size vary according to engine capacity?is it the diameted or the jet capacity?

gizzo: removed the bracket, pls see attached pic (carb fit). Only left end bracket need to be altered.

New issues: the lock in the flange need to be removed using a blade as its not the size of carb(pic flange-lock)
The throttle cable that came with the carb is having a smaller button lock that will loose out from the plastic hole.  (Pic cable button lock). But i think it could be worked around..not sure though..

[Adrian II]

What you have is a Mikuni VM series carb, they come in all sizes from 22 to 44mm. What I mean by size is the bore of the instrument where the air flows through over the jets. So if the INSIDE diameter of the spigot where it sits in the rubber mounting is 32mm you have a VM32, actually not a bad size for a lightly tuned Bullet.

Ignore the number stamped inside the float bowl. Now because these carbs are used on lots of different bikes, some with two-stroke engines, two outwardly identical carbs can be set up very differently, one would make the engine run very nicely, the other wouldn't work at all well.

Fortunately some folks on here are running with VM32s, if you search the forum archives someone will have posted this information - hang on, it's here. Just be careful NOT to follow the recommendations for a Mikuni TM32, this is a different type of carburetor from the VM32.

https://forum.classicmotorworks.com/index.php?topic=16053.0;all

As for getting the carb to fit the head without fouling the head steady brackets, try a spacer cut from 1/4" Tufnol to move the carb mounting rubber out a bit instead of butchering the brackets. The mounting holes are 60mm centers, 6mm bore, the hole in the middle will need to match the bore of the carb you're using.

A.

[Bess_GT]

Thanks Adrian II. I think it'll take a bit time for me with the carb to understand the tuning set up described in the link. Yeh, the inside diameter is around 32mm. Correct me if I'm wrong, higher the cylinder capacity higher the spigot diameter and jet sizes right?
I made a bracket from a nearby sheet metal store(attached pic) which suited well (but not sure it affects the engineering, but i think the whole frame was not designed for this engine because there is a small bit that help in extending the head stay screw, it shouldn't be there it seems)
Remaining work: 1. a button that need to be welded/moulded to the end of the carb throttle cable(i think the RE carb cable comes with this button, but this cable is japan made(wriiten) and don't want to waste it)
2. A cable free play nut at the accelerator end as there isn't a free play other than carb top pipe screw.
3.I'm thinking of attaching a rounded steel sheet  to connect air filter box to carb. Couldn't find similar rubber hose with length and also i think steel supports the carburetor too(as it is only holding on to the rubber flange)

[Bess_GT]

Update:
1. Cable button moulded with bronze(i thought it would be lead..but the guy used bronze i guess)
2. Maybe first try without freeplay nuts.
3. Made an iron pipe(welded)..but it will rub against the carb while running and it will ruin the carb(thought of attaching a rubber sheet inside but the welding done was so sharp that I couldn't modify the diameter).
 I will check the company store for 500 carb air pipe..i heard it's longer in length.
After that will attach a plate like head stay for carb stay..

I'm still not sure about the ECU circuit..because removing the fuel injection and fuel pump cable will result in ECU malfunction lamp right? (btb the instrument cluster has no light..had checked fuses and all.)

[gizzo]

I'm still not sure about the ECU circuit..because removing the fuel injection and fuel pump cable will result in ECU malfunction lamp right? (btb the instrument cluster has no light..had checked fuses and all.)

That seems to be the case with the commercially available carb conversion. It appears that the normal thing to do is just ignore the light?
Keep going and keep us updated. .

[Bess_GT]

Hi...
After fitting the carburetor with the above changes, the motorcycle didn't start. After few kickstarts and starter motor ignition, the fuel began to overflow from carb..not sure why and as it was without fuel tap the job went pretty nasty. I thought it was because the fuel jet may have clogged as there isn't any fuel filter with the above changes.
With the help of lathe work, attached fuel tap to the fuel pump unit plate. But not sure why the motor cycle failed to start, there were good sparks in the plug. Maybe the fuel didn't get to the cylinder head, or too much fuel(the plug was wet when opened to check spark).

[Adrian II]

A tiny piece of dirt can get lodged between the carb float needle and its seat and hold the valve open so that the fuel floods out of the carb. I have had this happen with a VM32.

The commerically available carb kits for the CGT 535 replace the fuel pump assembly with a plain adapter plate for the petcock, as the fuel is only gravity fed for the carb.

A.

[Bess_GT]

Hi Team,
Was able to start the motorcycle without the air pipe ☺️ 
Two things noticed:
1. I see petrol droplet at the bottom of carb..its not a leak, but that drop is still there. Is it an issue with carb? I haven't paid the guy who gave it to me as he said to check if it's working(he told it was new when someone gave it to him). So i need to make sure the carb is okay.
2. The exhaust smoke is thick black. Is it because its running rich?

[ace.cafe]

Hi Team,
Was able to start the motorcycle without the air pipe ☺️ 
Two things noticed:
1. I see petrol droplet at the bottom of carb..its not a leak, but that drop is still there. Is it an issue with carb? I haven't paid the guy who gave it to me as he said to check if it's working(he told it was new when someone gave it to him). So i need to make sure the carb is okay.
2. The exhaust smoke is thick black. Is it because its running rich?

The leak could be an issue with the float system. Check that out.

Black sooty smoke is typically rich. It could be jetting, or it could be a float problem.

[Jako]

Some tuning tips
 https://www.mikunioz.com/tuning-tips-and-manual-downloads/?v=6cc98ba2045f

[jez]

I'm sorry but you haven't a hope in hell of getting that carb to work properly. Mikuni round slide carbs have a bewildering  amount of options in the needles. Single taper double tape, different points at which the tapers start, different taper steepnesses, different lengths of needle. For instance the Suzuki SP370 has a needle that is just for that model, nothing else is correct and one can't buy it as it's a redundant Suzuki part. You also need a bunch of jets for the main jet, the needle jet and the idle jet; and have the correct cutaway on the slide. On top of that some round slide cabs are set up for two stroke, and you have to get the float height right.
Next you have to have a rudimentary understanding of how to alter the jetting and how to tune a carb, which you don't, and neither do most of the forum members that have contributed to this topic, or they would have warned you. It can take days just changing jets and trying again and again and again.
 Your only chance is to contact Allens Performance with your carb codes and ask them if they have knowledge of [and are willing to tell you] what combination of internal parts will work, and buy the jets etc from them. But I would imagine only Hitchcock know as they have done the set up work for their carb kit
 There's a sound reason the Bullet Whisperer uses Amal carbs. They are a fair bit easier to set up, being more influenced by the slide cutaway than Mikunis, and have far far far fewer needle options.
 'Fools rush in where Angels fear to tread' I'm afraid.

[jez]

Stolen from the Hitchcocks forum for your delectation
 'I have a friend with a 2005 Bullet. It has a 34mm Mikuni, free flow muffler, 535 alloy barrel and high compression piston. It runs very well and the carby set up is as follows: Main 190, pilot 42.5, slide 2.5, needle jet 159Q2, needle 6DH2 and clip in middle slot. The plug always looks rich to me but he is happy with it. My Mikuni is as follows: Main 200, pilot 25, slide 3, needle jet Q6, needle 6DP17 and clip in second leanest slot. I only have the standard exhaust with the cat?? thingo removed from the engine pipe (muffler end). The bike revs out better and has more top speed but still feels a bit lumpy down low and I use more fuel than I did. It could no doubt be better tuned but there are so many combinations of jets etc. I think a dyno and endless time would be needed and I'm not getting any younger. Not sure if any of this helps but at least I can sympathize with you. My carby has been on and off so many times I only have to say, "Carby off" and next thing it's on the bench by itself..'
and this
'Friends say they are brilliant carbs, but a swine to get set up correctly in the first place!! So, so true.'

[ace.cafe]

Stolen from the Hitchcocks forum for your delectation
 'I have a friend with a 2005 Bullet. It has a 34mm Mikuni, free flow muffler, 535 alloy barrel and high compression piston. It runs very well and the carby set up is as follows: Main 190, pilot 42.5, slide 2.5, needle jet 159Q2, needle 6DH2 and clip in middle slot. The plug always looks rich to me but he is happy with it. My Mikuni is as follows: Main 200, pilot 25, slide 3, needle jet Q6, needle 6DP17 and clip in second leanest slot. I only have the standard exhaust with the cat?? thingo removed from the engine pipe (muffler end). The bike revs out better and has more top speed but still feels a bit lumpy down low and I use more fuel than I did. It could no doubt be better tuned but there are so many combinations of jets etc. I think a dyno and endless time would be needed and I'm not getting any younger. Not sure if any of this helps but at least I can sympathize with you. My carby has been on and off so many times I only have to say, "Carby off" and next thing it's on the bench by itself..'
and this
'Friends say they are brilliant carbs, but a swine to get set up correctly in the first place!! So, so true.'

If you once get familiar with them, it's not so bad. Actually, they originally licensed the VM design from Amal, and are basically a Concentric with more adjustability.

[jez]

If you have and understand the needle codes  and if you actually understand how to tune a slide carb  I would agree. But that basic level of understanding is drying up as the generation brought up with slide carbs thins out. Outside of professionals I see very very little understanding in the forums. Folks don't  have a clue. One sees endless ignoramuses trying to solve carb issues just by changing the main jet.  I know just enough to just about get by.

[jez]

I have a Hitchcocks kit Amal in mine. It carburates perfectly. I have no reason to suppose the Mikuni kit is not as good. It is likely to last longer as the Concentric isn't the most durable of carbs,

[Bess_GT]

Hi Team...Happy new year..sorry got bit busy in-between.
@jez thanks for the input..one thing is for sure..it takes a lot of time to tune this as that to match the engine and i'm not getting any younger.. family members started asking why i'm investing time on this as on most weekends  i'm behind the motorcycle...but the thing is that i do like it.

The updates:
1. Yesterday I rode the motorcycle(with carb) all the way to an old mechanic who deals with carb tuning(but he only has ideas with old motorcycles and no clue about ECU or electrical systems)...and the motorcycle is there now..
The carb needle is at the lowest slot.
Present issues:
1. The exhaust smoke is thick black..the mecahnic's suggestion is that it might be burning oil..not sure why as on EFI it doesn't even have smoke..just white little smoke if looked keenly.

2.The exhaust pipe bend(where the catalytic converter sits..i believe) is red hot like a furnace after revving hard for a few mins. Attached pic (red_hot_pipe).  There was a cover-plate on top of it(removed), so i believe it gets hot but i don't think getting hot this much is normal.

3. The motorcycle stalls at idle after a minute. Pilot jet not working? But i had ensured the jet is clean on each installation.
Fact: Around 1.5L fuel gone with the wind on 2.5 km run(without air pipe). Should we be talking about jets or needle slots?

Limitations:  Its not possible to get different types of mikuni jets here in India, and i don't think there is online sale also. May be I'll be in Japan after this month(an onsite work) and may be I could buy the carb jets from there(still not sure if this model jets are available)

[ace.cafe]

Time to start learning what you are doing.
PDF download for Mikuni Tuning Manual.

https://www.google.com/url?sa=t&source=web&rct=j&url=http://www.mikuni.com/pdf/vmmanual.pdf&ved=2ahUKEwjPkprN0f7mAhXLY98KHTutAnwQFjAAegQIBRAC&usg=AOvVaw2cacd6NH74DJud4i2WKejr

[Bess_GT]

Thanks ace.cafe, that manual is exactly for this model.

On a retrospective note, I think all issues boils down to one thing..the engine might be running too rich..the unburned fuel might get accumulated at the catalytic converter and it gets burned there...which answers the thick black smoke and the 1.5L/2km gone with the wind fuel economy...

Maybe its time to dabble with fuel jets..

[jez]

I very much doubt I'd try and do what you are attempting and I can get parts in Britain. You can't know what sizes to start with before you even begin fine tuning. I'd give it up before your wife deserts you citing  "that bloody motorcycle".

[ace.cafe]

Thanks ace.cafe, that manual is exactly for this model.

On a retrospective note, I think all issues boils down to one thing..the engine might be running too rich..the unburned fuel might get accumulated at the catalytic converter and it gets burned there...which answers the thick black smoke and the 1.5L/2km gone with the wind fuel economy...

Maybe its time to dabble with fuel jets..

It would be strongly advised to get that "catalytic converter" contraption off your bike, and put on a real exhaust silencer, such as "sports silencer" or something that will let the engine breathe.
If you are going to go thru all this tuning work, you may as well do it with a better breathing system, instead of having to re-tune later when you pull off that piece of junk that the factory calls a silencer.

Any parts you might need for the carburetor are readily available on EBay, no matter where in the world you live. They deliver.

[JVS]

Bess_GT

Once you confirm that the carb is a VM32 or equivalent, you need to contact Hitchcocks to see what jets they supply with their carb kit for the Conti 535. They will most likely tell you this even though you haven't purchased a kit from them. Contact them at info@hitchcocksmotorcycles.com

They reply promptly.

For the 500cc UCEs, they supply a VM32 and have jetting supplied for a freer-flowing configuration (exhaust + air filter) around sea-level. Their 500cc Mikuni kit comes with the following jets:

25 Pilot jet,
Q6 Needle Jet,
6DP17 needle,
185 Main jet,
Needle clip in 3rd position (middle),
Slide cut-away 3,
Float height 23-24mm.

You need to at least start around those jets if you're at sea-level. Secondly, you need to ensure that your idle air-screw mixture setting is correct. This is done after the bike is warm. If this is not set properly, your bike will run like crap, no matter if your other jetting is relatively correct.

You can have a look at the following videos on how to adjust the idle air screw or follow the instructions in the VM tuning manual as posted by ace.cafe, (section 5.3 on page 10 of the manual).

https://www.youtube.com/watch?v=67Nb3DI-B3s
https://www.youtube.com/watch?v=q5pFOBSkMX0

Or follow these steps as highlighted by ace.cafe in other posts:

The usual procedure is(before you start the engine) to turn the air-bleed screw in until it stops all the way in.
Don't jam it. Just turn it in until it stops.
Then turn it out 1.5 turns, as a basic starting point.
Then, start the engine,and set a somewhat fast idle with the big-headed idle speed screw.
From your basic starting point of the little air-bleed screw at 1.5 turns out, the entire range of turning available on that screw is only 1.5 turns in or out.
You can turn it in or out from your starting point of 1.5 turns out, untll you can find your highest idle speed that the air-bleed screw can give you.
When the bike is warmed-up.
Then after you find that spot, use the big-headed idle speed screw to lower the idle to a steady reliable idle speed.
That should do it.

The hiccup off idle was probably nearly eliminated by cleaning the pilot jet and pilot circuit orifices, and getting it fairly closely tuned in with the air-bleed.
The air bleed adjustment can make or break your idle and low-speed running with just 1/8-turn of the screw. It is pretty sensitive.
So, once you find the highest idle with the air bleed screw, you only want to fine-tune it very little in the direction that might help out your hiccup. And you don't know which direction until you try it. Although, my guess would be that turning it in very slightly would be the direction in your case, IF you need to do anything after you get it set properly at highest idle when warm.

Remember not to unscrew the air bleed screw more than 3 turns. If you're close to 3 turns out, you might need one smaller pilot jet size (e.g. 22.5).

This should get you very close.

[Bess_GT]

@JVS
Below is the reply from Adrian@Hitchcock who was kind enough to share the information and replied promptly.( Actually the thing is that i did contact Hitchcock earlier a year ago for getting the quote for their carb conversion kit, but it was above my budget when converting pound to inr)
""The Mikuni carburettor conversion kits we sell are jetted with the following;
185 Main jet
25 Pilot jet
2.5 Slide
Q8 Needle jet
Standard float height of 24mm
These settings are intended for use with a free flowing conical air filter, using a different filter may require different settings.
The needle position will vary as will some of the above settings as fuel quality varies considerably around the world, I would treat these settings as a starting point then fine tune according to how well the bike goes.""

The carb which i'm having
Main jet: 147.5
Pilot jet: 50

I was trying to find the 25 pilot jet online and offline but with no luck. Found this jet in dimecity website https://www.dimecitycycles.com, but they havn't yet replied regarding the quote with international shipping.
I believe the stalling at idle is because of this 50 pilot jet, excess fuel...

@ace.cafe sure, i will remove the stock air filter and exhaust, luckily those parts are available, k&n free flow filter and red rooster exhaust.

[Richard230]

@JVS
Below is the reply from Adrian@Hitchcock who was kind enough to share the information and replied promptly.( Actually the thing is that i did contact Hitchcock earlier a year ago for getting the quote for their carb conversion kit, but it was above my budget when converting pound to inr)
""The Mikuni carburettor conversion kits we sell are jetted with the following;
185 Main jet
25 Pilot jet
2.5 Slide
Q8 Needle jet
Standard float height of 24mm
These settings are intended for use with a free flowing conical air filter, using a different filter may require different settings.
The needle position will vary as will some of the above settings as fuel quality varies considerably around the world, I would treat these settings as a starting point then fine tune according to how well the bike goes.""

The carb which i'm having
Main jet: 147.5
Pilot jet: 50

I was trying to find the 25 pilot jet online and offline but with no luck. Found this jet in dimecity website https://www.dimecitycycles.com, but they havn't yet replied regarding the quote with international shipping.
I believe the stalling at idle is because of this 50 pilot jet, excess fuel...

@ace.cafe sure, i will remove the stock air filter and exhaust, luckily those parts are available, k&n free flow filter and red rooster exhaust.

25 and 50 pilot jets ring a bell with me. My 1978 Yamaha SR500 came from the factory with a 25 pilot jet in its carburetor and would barely run on part throttle. It would pop and wheeze like a two stroke. I replaced it with a 50 pilot jet and it ran fine after that.

[jez]

Change all the jets to the Hitchcocks settings, not just the idle.
Changing to a leaner idle will lean out the carb at all settings
Buy from here
http://www.allensperformance.co.uk/

[gizzo]

Don't forget to go back and check the float valve for leaking and the float height per ace's advice.  I can't imaging 1.5 litres even being able to flow through the jets in 2.5km ride. 
Sounds to me like the float bowl overfilled and flowing into the engine.
Does the vm carb have a fuel bowl overflow to prevent that?

[JVS]

You definitely need to change to those jets mentioned by Hitchcocks as a first step. The 50 pilot is crazy big. On the other hand, the 147.5 main jet is inadequate.

And do confirm the float height / valve operation as gizzo mentioned. The float height should be 24mm.

Another option / place to buy jets from is an Australian seller - 'MikuniOz'. I've been buying mine from here. The needle jet can be a bit expensive, but the Q8 makes sense for the UCE 535 after my experience with various needle jets on the 500 UCE. The slide can also be expensive. But these are worth buying if you want to have a decent running machine.

Pilot jet: https://www.mikunioz.com/shop/vm22210-pilot-jet/?v=6cc98ba2045f
Main jet: https://www.mikunioz.com/shop/4042-main-jet-large-hex/?v=6cc98ba2045f
Needle jet: https://www.mikunioz.com/shop/mikuni-159-series-needle-jet/?v=6cc98ba2045f
Slide cutaway: https://www.mikunioz.com/shop/vm34110-slide-suits-most-vm30-32-34-carbs-with-lh-idle-screw/?v=6cc98ba2045f
Jet needle: https://www.mikunioz.com/shop/jet-needles-6-series/?v=6cc98ba2045f (You need to get a 6DP17 needle)

Despite the correct/relatively correct pilot jet (e.g. 25), you need to ensure you set the idle mixture properly with the air mixture screw. Any discrepancy in this setting can cause it to run rich as well, or lean if you go in the other direction.

The 50 pilot is overkill. With 3 turns out, it will be very rich. Even with a 30 pilot, depending on your elevation, this will be quite rich on the UCE (based on a much more free-flowing exhaust/filter system as compared to stock).

[ace.cafe]

Most times when buying Mikuni carbs off the internet, they are jetted like that. I think it might be for some 2-stroke engine.
Anyway, the Hitchcock jet recommendations look fairly good for a starting point.

[Bess_GT]

Dear JVS, ace.cafe, gizzo,

I tried the pilot jet 12.8 which comes as stock in 500 UCE carb and it suited correctly in Mikuni and the idle and running seems fine with the same main jet and Q4 needle jet.
The exhaust didn't have that red-hot furnace looks after high rpm revs and it seems the fuel consumption is also fine. Next week I'll update the details after somewhat long ride(hope it runs good).
 
I tried checking out the MikuniOZ cart with the parts, and the pilot jet alone costs me around 1K INR with the shipping charge and I think I will invest on a brand new Mikuni Carb with the recommended settings later rather than buying/investing on new parts for my old carb.

 

[ace.cafe]

You should be aware that the UCE 500 carb is a CV carb, so that 12.5 jet you bought is not the correct jet for your carb.
Hence, if you order your new carb with that jet specification, it will not work right.

I don't have time to read the entire thread again, so please say what your elevation above sea level is. If you plan to buy a slide carb like the Mikuni you have now, you will have to jet for your elevation and temperature.

BTW, 1000 INR is dirt cheap for a carburetor jet. They cost twice that much in the US, and we don't even think twice about buying a variety of them for fine tuning our jetting.
It is important to not let the cost get in the way of proper jetting.
Also, you will need different jets for summer and winter, and also if you ride high up in the mountains or down by the ocean.

[Bess_GT]

Hi ace.cafe,
Thanks. The elevation is 11m above sea level amd tempeeature is 30-40deg celsius.(native of alleppey in kerala)
I mean i'll invest in the hitchcock recommended setting new carb later.
Is it true that one need to change the jets from sea level to topstation? coz i have seen bullet UCE 500 carb riders going on trip to topstations and havent heard them switching their jets.

[ace.cafe]

It is needed to switch jets for high elevations if the engine was jetted for low elevations.

Depending on elevation change, the rider might simply opt to run rich until the engine just stops running. Or, it is somewhat common for Bullet riders to remove a screw in the inlet manifold, and make an air leak to get it running leaner.

However, the BS29 carb on the regular UCE 500 is a CV carb which self-compensates for elevation changes.

So, it depends on the type of carb involved, and how the rider may want to deal with it.
That Mikuni VM that you showed in the photo is a slide type carb that needs jetting changes for elevation. The BS29 does not because it is a CV type carb.

[Adrian II]

I understand the UCE 500s actually have 33mm CV carbs, the 350s have 29mm. Having said that, the Electra-X/AVL Classic/A500 Machismo were only fitted with 29mm CV carbs. I think we lost out!

A.

[jez]

If you  run the engine for any length of time without safe baseline jet settings and don't understand how to check for various throttle openings you could easily seize the engine. One or two people have kindly gone to great deal of trouble to furnish you with the correct specs and advice, but by now they must be wondering why they bothered.

[Bess_GT]

@jez thanks for the caution. But please understand that because of this thread someone newbie like me will find it easier on this conversion..which is the very purpose of forums i believe.

The sole purpose of me getting this carb conversion was because after the motorcycle was kept to sit for years , the injection pump motor got failed and i lost faith on this electronic item after a second hand motor too got failed(may be that was not genuine). So i had this thing hit my mind about a mechanical part and here I am asking for carb functions.

If the carb needs jet changes on elevation variation and like jez mentioned about engine siezing, i think buying a new fuel pump motor for 14k will solve all problem..may be thats why company switched to fuel pump motor/efi despite its electronic malfunctioning at times.

[jez]

Carbs will work happily over a wide range of elevations without any alteration. When all bikes were carbed manufacturers didn't supply different jetting for different parts of Europe. Competition models, that's different. Having said that you are a great deal safer just replacing the pump.

[Jako]

With 3 fuel pump failures  I'd bet there's nothing wrong with any of them. More likely to be a faulty  relay or wire .

[Bess_GT]

Hi Jako,
Nope, the first pump motor rotorgot stuck due to years old fuel clogged the motor, and after opening the motor and cleaning and sealing the pressure got changed, but it worked but the acceleration was like riding a horse due to pressure/vaccuum prob after sealing. The 2nd motor was not for this model just got it second hand in black market.

I'm going for a ride tomorrow with the current carb setup.

[Jako]

If you decide to refit EFI  a cheaper pump option and direct fit  https://www.ebay.com.au/itm/153747026576

[Bess_GT]

Thanks Jako, i could'nt find this model pump delivery to my location. There are similar cheap ones like below
https://www.amazon.in/dp/B084BXYZSB/ref=cm_sw_r_cp_apa_i_zPpBEbXGWY0NF
But not sure if anyone had tried and tested this on C.GT.

I took the motorcycle for a short ride today, and i'm happy with the current carb set up. Throttle response is good.  I understand that it is not at par with the recommended tuning and performance but i'm happy with current set up and i would like to continue with this as long as it goes.

One doubt: i'm afraid if the tyre will break as the motorcycle was in storage condition for 3-4 years. Is there any method i could check the tyre condition. No visible cracks or any similar marks outside.

[jez]

Well don't open the throttle all the way or you'll seize the engine.

[Bess_GT]

May i know how the engine seize with open throttle? Engine seize happens due to oil starvation right? How does the current set up affect oil circulation?

[ace.cafe]

Engines often seize from heat.
Piston overheats from lean mixture, expands further than normal, and contacts the cylinder wall, scrubbing off any remaining oil film, and then locking up tight.

[Bess_GT]

Will checking the spark plug color help?
https://images.app.goo.gl/yFtVQJHjzfy8r6Ac9
At present the color of the plug is thick black as mentioned in the chart it comes in the oil fouled region. Is there any problem? Is it because oil is getting mixed with fuel..is this normal?

[Arizoni]

If the sparkplug shows a "wet", black coating, it is probably oil.  If it is a "dry" powdery black coating it indicates a fuel/air mixture that is too rich (or the spark plug heat range is too cold for the style of riding you do).

Back in the days of the carburetor, a rich condition could be the result of a lot of different things ranging from a leaky float to a change in altitude or a dirty air filter.

With the fuel injected engines of today a rich fuel condition is most likely caused by a dirty or oil fouled air filter although a failed oil temperature sensor could also be at fault.

[jez]

  Dorthy Parker's quip  "You can lead a horticulture but you can't make her think" is apposite. As has been painstakingly explained to you, slide carbs have several fuel circuits controlled by jets and needles etc that each control to a varying degree a particular part of the throttle opening. Folks have helpfully pointed towards texts for your delectation and understanding  [which you haven't taken on board]. Thus your engine can be rich at idle, lean just as you open the throttle and rich and lean all the way to a fully open throttle, or any combination thereof. In your case, as has been carefully pointed out, your carb's main jet is far smaller than advised, not a bit smaller, much much smaller. Thus when you open the throttle fully [and before you misunderstand further this has little to do with engine revs]  you will have a very weak mixture that will  in a short time overheat the piston.
 Peering at the plug is not going to help as you neither understand the basics nor how to do plug chops. It would tell ace.cafe a lot, and me a bit, but not you.
 I'm not really sure why I'm bothering as it's akin to explaining what colour is to someone who only sees in monochrome. However, as you yourself have said, this thread might come in handy for someone with the wit to benefit.

[chuychacon]

After 4 pages of helpful info , you should fix the EFI

[Bess_GT]

Dear JVS, ace.cafe, gizzo, Adrian II, Richard 230, Jaiko and Arizoni...
Thank you all for the information you have shared on this thread to help me, I can assure you that it was not futile..because I'm riding my GT with carb(even though the tuning is not at par with recommended settings..and I will surely optimize this when time and money allows)..and i think its time this thread can be closed as it will deviate from the subject...i wish you guys were somewhere near me...
@jez thanks for that sarcastic last minute advices..i would like you to re-read this post...not mine..yours..the advice that was worth was the last post about the open throttle that too you were wrong at some point..because at idle the current setting is not rich..it should be a little lean..if you are continuing to use this forum i have an advice..please don't give such/any replies as it will make the spirit low of the newbie...because there will be few who come by this road on this era of electric motors...asking for carb function..pls don't make their morale low...
I'm sorry to end the post like this...

[gizzo]

All the best,  @Bess_GT.

Good closing comments, BTW. It's easy to tear someone down without thinking about how it might affect that person.

[axman88]

  Dorthy Parker's quip  "You can lead a horticulture but you can't make her think" is apposite. It would tell ace.cafe a lot, and me a bit, but not you.
 I'm not really sure why I'm bothering as it's akin to explaining what colour is to someone who only sees in monochrome.

Seems a bit excessive.  You should consider yourself restricted to one wise crack, or one put-down per post.  Let's remember that by joining the forum, we've agreed that, "Our members ... are to be treated respectfully and with kindness. If you disagree with someone it must be done with the utmost discretion and respect."

https://forum.classicmotorworks.com/index.php?topic=12.0

From my limited experience here, it appears that indulging oneself in negative comments on other members, as you did, has led to several threads simply disappearing in the last month and a half, and that benefits nobody.

[motopike]

The other option here with the cylinder head plate is to place them both on the left side of the head mounting (sandwich the two plates together to maintain similar stifness), then theres no cutitng involved. This is what I did with my VM conversion

[Starpeve]

I'm sorry but you haven't a hope in hell of getting that carb to work properly. Mikuni round slide carbs have a bewildering  amount of options in the needles. Single taper double tape, different points at which the tapers start, different taper steepnesses, different lengths of needle. For instance the Suzuki SP370 has a needle that is just for that model, nothing else is correct and one can't buy it as it's a redundant Suzuki part. You also need a bunch of jets for the main jet, the needle jet and the idle jet; and have the correct cutaway on the slide. On top of that some round slide cabs are set up for two stroke, and you have to get the float height right.
Next you have to have a rudimentary understanding of how to alter the jetting and how to tune a carb, which you don't, and neither do most of the forum members that have contributed to this topic, or they would have warned you. It can take days just changing jets and trying again and again and again.
 Your only chance is to contact Allens Performance with your carb codes and ask them if they have knowledge of [and are willing to tell you] what combination of internal parts will work, and buy the jets etc from them. But I would imagine only Hitchcock know as they have done the set up work for their carb kit
 There's a sound reason the Bullet Whisperer uses Amal carbs. They are a fair bit easier to set up, being more influenced by the slide cutaway than Mikunis, and have far far far fewer needle options.
 'Fools rush in where Angels fear to tread' I'm afraid.

Christ you make fuel injection sound appealing!!
And that’s coming from somebody of the carby gen.!
I hate the f@&$$&g things!

[ace.cafe]

I have made hundreds of Mikuni carbs run perfectly, and show excellent results on the AFR test.
Plenty of positive results of jetting, especially TM32 flat slide are in the archives here.

[jez]

 "It just needs to be tuned by somebody who knows how." You said it Ace