Author Topic: Continental.GT 535 converting to Mikuni Carburetor  (Read 6198 times)

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Bess_GT

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Reply #15 on: December 08, 2019, 02:30:32 pm
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

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Reply #16 on: December 08, 2019, 03:39:49 pm
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.


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Bess_GT

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Reply #17 on: December 09, 2019, 11:47:08 pm
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

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Reply #18 on: December 10, 2019, 04:15:04 am
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.
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Jako

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jez

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Reply #20 on: December 21, 2019, 12:19:37 am
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

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Reply #21 on: December 21, 2019, 09:35:22 pm
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

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Reply #22 on: December 22, 2019, 01:37:37 pm
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.
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jez

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Reply #23 on: December 27, 2019, 05:31:31 pm
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

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Reply #24 on: January 11, 2020, 06:00:07 pm
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,
« Last Edit: January 11, 2020, 06:57:44 pm by jez »


Bess_GT

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Reply #25 on: January 12, 2020, 02:34:57 pm
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)
« Last Edit: January 13, 2020, 02:52:32 am by Bess_GT »


ace.cafe

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Bess_GT

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Reply #27 on: January 13, 2020, 06:15:29 pm
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

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Reply #28 on: January 13, 2020, 07:18:18 pm
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".
« Last Edit: January 13, 2020, 07:32:50 pm by jez »


ace.cafe

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Reply #29 on: January 13, 2020, 08:39:33 pm
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.
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