Author Topic: Continental.GT 535 converting to Mikuni Carburetor  (Read 10542 times)

0 Members and 1 Guest are viewing this topic.

JVS

  • Grand Gearhead
  • *****
  • Posts: 1,507
  • Karma: 0
  • I love chicken
Reply #30 on: January 14, 2020, 10:06:42 am
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:

Quote from: ace.cafe
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.
« Last Edit: January 14, 2020, 10:18:33 am by JVS »
Sons continuing wars, our fathers were enemies



Bess_GT

  • Neophyte
  • *
  • Posts: 20
  • Karma: 0
  • As above, so below...As within, so without...
Reply #31 on: February 16, 2020, 12:00:39 pm
@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

  • Grand Gearhead
  • *****
  • Posts: 3,224
  • Karma: 0
Reply #32 on: February 16, 2020, 01:50:15 pm
@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.
2011 Royal Enfield B5 500, 2018 16.6 kWh Zero S, 2016 BMW R1200RS, 2009 BMW F650GS, 2020 KTM Duke 390, 2002 Yamaha FZ1


jez

  • Neophyte
  • *
  • Posts: 31
  • Karma: 0
Reply #33 on: February 16, 2020, 06:25:00 pm
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

  • Grand Gearhead
  • *****
  • Posts: 2,471
  • Karma: 0
  • Live slow, die whenever
Reply #34 on: February 16, 2020, 09:13:18 pm
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?
simon from south Australia
Continental GT
Pantah
Monster
DR250
DRZ400SM


JVS

  • Grand Gearhead
  • *****
  • Posts: 1,507
  • Karma: 0
  • I love chicken
Reply #35 on: February 17, 2020, 10:50:07 am
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).
« Last Edit: February 17, 2020, 11:02:51 am by JVS »
Sons continuing wars, our fathers were enemies



ace.cafe

  • Grand Gearhead
  • *****
  • Posts: 13,762
  • Karma: 0
  • World leaders in performance/racing Bullets
Reply #36 on: February 17, 2020, 01:13:30 pm
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.
Home of the Fireball 535 !


Bess_GT

  • Neophyte
  • *
  • Posts: 20
  • Karma: 0
  • As above, so below...As within, so without...
Reply #37 on: March 08, 2020, 09:53:35 am
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

  • Grand Gearhead
  • *****
  • Posts: 13,762
  • Karma: 0
  • World leaders in performance/racing Bullets
Reply #38 on: March 08, 2020, 02:00:49 pm
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.
« Last Edit: March 08, 2020, 02:07:11 pm by ace.cafe »
Home of the Fireball 535 !


Bess_GT

  • Neophyte
  • *
  • Posts: 20
  • Karma: 0
  • As above, so below...As within, so without...
Reply #39 on: March 08, 2020, 03:25:16 pm
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

  • Grand Gearhead
  • *****
  • Posts: 13,762
  • Karma: 0
  • World leaders in performance/racing Bullets
Reply #40 on: March 08, 2020, 09:12:05 pm
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.
Home of the Fireball 535 !


Adrian II

  • Grand Gearhead
  • *****
  • Posts: 1,977
  • Karma: 0
  • Sharing my ignorance with anyone who needs it
Reply #41 on: March 08, 2020, 09:52:49 pm
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.
Grumpy Brit still seeking 500 AVL Bullet perfection! Will let you know if I get anywhere near...


jez

  • Neophyte
  • *
  • Posts: 31
  • Karma: 0
Reply #42 on: March 09, 2020, 02:09:24 am
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

  • Neophyte
  • *
  • Posts: 20
  • Karma: 0
  • As above, so below...As within, so without...
Reply #43 on: March 09, 2020, 04:13:43 pm
@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

  • Neophyte
  • *
  • Posts: 31
  • Karma: 0
Reply #44 on: March 10, 2020, 12:30:19 pm
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.