One cylinder not firing gsx1100 ES

[MSteenJ]

Hello everyone,

I hope one of you brainy folks can help me:
My Suzuki gsx1100 ES has been haunting me for some time...

I simply cannot get cylinder 1 to fire.

My bike has a carburetor bank of Mikuni BST36SS on it with a dynojet kit stage 3 in it, a freeflowing 4-1 exhaust and dual KN-filters.
It has 150 mains and the pilot mixture screw is 2.5 turns out.

It easily turns on, idles and revs fine BUT without cylinder 1. (exhaust manifold is cold) 

I have tried switching the two coils, and also the leads between 1&4 without any luck. 
Compression is at 120+-5 on a stone cold engine.
The carburetors has been ultrasonicly cleaned.
The valves has been adjusted.
The ignition timing has been adjusted.
The rubber boots are in good condition and without cracks or signs of wear.

I cannot figure out what the issue is.

Any guesses?

Best Regards
Morten
 

[Gixer1460]

Check basics and report back - is there a spark?, plug condition / use new plug, valve clearances etc. Did the problem move with coil / lead change? If not it strongly points to a carb problem - is there fuel? Don't assume - check!

[Dezza]

If it sparks and there's nothing obvious, borrow a known set of good carbs, those from an oil cooled bike or even an air-cooled Krapasaki are spaced the same so will work for diagnostics, then see if it runs on four.

[Rsk_141]

As 1460 says swap plugs and HT leads if the problem moves change offending item .

Happened to me twice last month,

First time took ages to diagnose going mental  changin carbs etc had spark but couldn't have  been strong enough it was the plug .

Second time fixed in 5 minutes .

Good Luck!

[Blubber]

Check the Igniter plus connectors via the manual 

[johnr]

youve tried swapping the plugs round?
i know it sounds daft, but when it was apart, you didnt stuff a rag down the inlet to keep dirt ouut then forget to remove it?

[Dezza]

I had the same problem. After eliminating carbs (as described above) I found it was a faulty CDI unit

[MSteenJ]

Thanks for the replies!!!

I know i have a spark, since switching the leads between 1&4 didnt solve the problem(cyl 1 still didnt fire).
Same thing when i swapped the coils...
The spark plugs are BRAND new, put them in yesterday.

I will try and find the original carbs, clean them up and try it out, hopefully it will be a carb related problem.

Thank you, ill keep you posted later today.
 

[bluedog59]

Given that you've checked that you're getting a spark, the valves are adjusted correctly and you have compression, I would suggest that you are not getting fuel into the cylinder to ignite. Is the plug wet when you take it out ? Are you actually getting any fuel into #1 float bowl ?

[Sheep]

44 minutes ago, bluedog59 said:

 Is the plug wet when you take it out ?

If this is the case it doesn't matter how new the plugs are,I have found from experience plugs do not like wet ends and have a few NGK's in a box to prove it after having issues with a sticky float needle..

[bluedog59]

Very true but what I'm trying to establish is, are we actually getting any fuel in there to ignite ? Even with a blocked pilot circuit you would normally get something out of #1 as the other 3 cylinders drag the revs up.

[Dezza]

It is not true that a single cylinder not firing cannot be caused by an ignition system fault, other than in the components unique to that cylinder (lead, cap, plug) as my bike ran on three with a faulty CDI. Don't ask me how this works though. But it won't harm in changing the plug again and checking the lead and cap. Also, check the connections to and from the CDI as they often corrode. Switching the carbs will reveal if it's a carb fault though.

[MSteenJ]

UPDATE:

I started the motorcycle today, and all four cylinders were running!!!

A lot of smoke though. Hmmm. 

Then suddently, cyl 1 stopped...

I then saw that carb 1 was leaking from the top and noticed the vacum hose was wet. I drained the fuel bowl of carb 1 and there was a lot more gas than the bowl alone could fit. I removed the spark plug and let the gas in the cylinder evaporate. When i felt like it was dry, i put the petcock on prime for just a sec or two and then shut it off completly. The engine then started on all four cylinders Until the bowl Ran dry of course!!! 

silly me, that i didnt even give the old petcock a thought throughout the engine rebuild...

oh well, off to buy a repair kit for it. Hopefully this is the Only culprit.
 

thanks again,

i will return once i have fixed it, maybe next weekend.

[bluedog59]

Sitting on the side stand, number 1 cylinder floods.

[Zenerdiode]

It sounds more like you have described the symptoms of a failed needle/float valve for carb #1. If the level is going much higher than what you’d expect in the bowl; the mixture is probably too rich for cyl #1 to fire. If the petcock has failed (which indeed it may have as well) when running it would have no effect, as it’s ‘on’ in any case.

So when the engine is not running and petcock in ‘Prime’, the bowls should fill to their fuel height and shut off. The petcock is really just there in case the needles weep a bit.

Have you checked the fuel level in all of the bowls?

Edited October 11, 2020 by Zenerdiode

[Captain Chaos]

What Diode says. ^^^

Float valve is leaking, fix that first and it will probably run ok.

[MSteenJ]

The float valve is in good condition with a good spring and without grooves. The float is also leveled.

I tried to suck through the vacuum hose to the petcock, and gas came through it. My thinking is that gas flow to the top of the carb 1 through the vacuum hose, flooding the came.

putting it on prime does not make any og the carburetors overflow, why i ruled the float valves out.

i will however check the float valves until the new petcock arrives.

[Captain Chaos]

also check the O-rings around the float valves.

[Captain Chaos]

39 minutes ago, MSteenJ said:

putting it on prime does not make any og the carburetors overflow

I probably missed that bit

[bluedog59]

Maybe also check your "float" has not become a "sunk".

[RGSX]

Address the simple solutions and eliminate them first.

Pull carb 1 disassemble and give it a good cleaning to eliminate plugged orifice as an issue.

If you had the carb apart before was it reassembled correctly.

My last carb mystery traced back to a leak in the diaphragm, before that I never noticed  a missing 2mm o-ring in an air-cut valve.

 

 

 

 

 

 

 

[MSteenJ]

I took the petcock apart, and sure enough the diaphragm was broken in the metal and the rubber had a leak.

off to get a repair kit and get it sorted.

[taxi]

Got the same problem but no 3 cylinder all exhaust pipes hot except no 3 plugs slightly sooty on all four plugs

[Gixer1460]

Is that a statement or a question? If the latter, all the diagnostics are as above!