2 cylinders when cold

[Danno]

My GSX1100 fires up on 2 cylinders when cold.Once it has warmed up, it lets out a couple of massive backfires when the other 2 start to come online.
Once warm, it runs sweetly.I have fitted new spark plugs but with no effect.
As you sit on the bike, it is the 2 left hand cylinders that are the issue.
Any ideas most appreciated !

 

[JTGS850GL]

The way I figure, in general, it takes 4 things to fire a cylinder:

1: Compression
2: Ignition
3: fuel
4: Air

Since the two offending cylinders are adjacent I would rule out ignition for now.

An air blockage would most likely not only affect only 2 cylinders and probably wouldn't be affected by temperature either.

That just leaves fuel and compression. I have seen marginal compression cause cylinders to not fire when cold and come back once the engine heats up, so a basic compression check would be in order.

Fuel is most likely the culprit. Could be an issue with the enrichment circuit running lean or even gas pooling from a leaking petcock that needs to be burnt off. If you leave the bike on the side stand, the gas could pool on the left side and cause a flooding condition on initial startup. Just my thoughts. Others with more direct experience will most likely chime in.

 

[tkent02]

What have you done to the carburetors so far?

 

[Big T]

Which 2 cylinders don't start up?

If they're on the same coil, that may point to the issue

But, it sounds like clogged pilot jets

 

[Danno]

Thank you for the advice.
The carbs have k&n type filters and have probably never been jetted to suit.
The affected cylinders are run by 2 separate coils, so I assume that rules them out.
Pilot jets sound like a likely culprit.
I'll give them a blow out.

 

[JTGS850GL]

Don't waste your time doing a "blow out". Take them down and do a proper rebuild or you'll be revisiting them again.

Here's the rebuild tutorial to help you along:

http://www.mtsac.edu/~cliff/storage/gs/Mikuni_BS-CV_Carburetor_Rebuild_Tutorial.pdf

Follow it step by step and you'll be in good shape.

 

[tkent02]

It sounds more like the choke feed passage in the float bowls is clogged. Did you dip the float bowls?

 

[Danno]

That tutorial is just what I need thank you.
Not sure what is meant by "dipping the float bowls" but I have done nothing yet.
Beer seems to have taken priority for the moment !

 

[Scout]

That tutorial is just what I need thank you.
Not sure what is meant by "dipping the float bowls" but I have done nothing yet.
Beer seems to have taken priority for the moment !

TKENT02 "It sounds more like the choke feed passage in the float bowls is clogged. Did you dip the float bowls?"



Do what he advised. Their are passages in the bowls that are probably gummed up. Sounds like everything else is running correct when warm so lucky you, you may not need a full teardown of the carbs. Take those bowls off and dip them

 

[cowboyup3371]

Please go read this about cleaning your carburetors:

http://www.mtsac.edu/~cliff/storage/gs/Mikuni_BS-CV_Carburetor_Rebuild_Tutorial.pdf

 

[850 Combat]

It sounds more like the choke feed passage in the float bowls is clogged. Did you dip the float bowls?

Yes, it does.

 

[tkent02]

Let me guess, this bike sat a long time sitting on the side stand?

 

[Johno]

All good advice. I would also check the valve adjustment as well. Good luck!

 

[Danno]

Thank you all for the advice.
Yep, it has been on it's side stand for a while.
Looks like i have some cleaning to do this weekend !