GS1000 only running on 2 cylinders.

[steve murdoch]

It is a '78 GS1000 with only 24,000kms and it will only run on cylinders 2 and 4.
The bike sat for 7 or 8 years occasionally being turned over with an ounce of oil down the plug holes.

In the past month i have completely disassembled the carbs twice, dipped the first time, ultrasonic the second time.
New o-rings installed. I am confident they are clean.
Valves clearances were all tight and with help from Ray and the Shim Club they were all brought into spec.
A compression check showed a low 90 for all 4 cylinders. 89-90-90-92 The consistency is nice but the low number is a concern
Dyna ignition installed decades ago.

I have gas in all the carbs, spark in all 4 new plugs and only 2 and 4 will run. 1 and 3 remain cold.
Can't see it being coil related.

Any ideas as to where i can check next.

[azr]

Is fuel getting to #1 & 3? have you tried swapping around the plug leads from the cylinders that are firing to the ones that aren't? are the cams set properly? I've had a few bikes through the shed with this issue to find out someone previous was into the cams and didn't put them back in properly. Just some ideas.

[huntb]

Are you just testing this at idle? Your carbs could be way out of sync.

[jeff.saunders]

You probably have the plug wires mixed up.

You have 2 coils. The plug wires from one go to 1 & 4, and from the other 2 & 3.

The easiest way to check is pull the spark plugs out of the engine, put into the plug caps and lay them on the cylinder head. With a wrench on the end of the crank and the ignition turned on, turn the crank until you see #4 plug fire. At that point the #1 & #4 cylinders should be at top dead center.

Don't leave the ignition on for long - you can burn out a coil.

[wymple]

I would second guess your compression test to begin with. I'd bet it's ok. My money is on either a faulty coil, or incorrect firing order. I just replaced a coil this summer that failed to fire only on #3 at idle, but ran well off idle. I couldn't believe it was a coil problem, but it was.

[steve murdoch]

Thanks for the input, gents.
This thing still has me puzzled.
Fuel is getting to all the carbs and they were bench synched after cleaning. The cams have never been touched since new.
The proper plug leads are going to the proper cylinder. There is a strong, fat spark at each plug.
Having half a coil go bad from both coils is hard to believe but i will swap them out and try it again.

After a small amount of oil was added to the cylinders overnite the compression test raised to a consistent 100 across.

[azr]

Well 100 is definitely enough to flash up a cylinder. I'll be interested in the results of swapping the plug leads. This is odd to say the least. If it winds up that you need coils I've got a shed full.

[steve murdoch]

I tested 4 coils, primary and secondary and they all tested fine.
The problem remains.
Any other thoughts?

[azr]

Well you only need 3 things to have a cylinder fire up. Gas, electricity, and air. It can only be one of those. Very odd. What do the plugs on 1&3 look like after trying to start? wet with fuel? I know you tested the coils but did you swap the leads from the cylinders that are firing to the ones that aren't? As long as you did a pretty good bench synch it 'should' fire up, have you thrown a vacuum gauge on it though while you're trying to start just to make sure?

[steve murdoch]

Swapping coils, wires and plugs has not solved the problem so the carbs are off again.
Third time is the charm, right?

[KARLM]

gs 1000 carb issuse

similar problem with my gs1000 it fires on 3 cylinders had carbs cleaned new main and pilot jets, carbs balanced still only runs on 3 new plugs coils + caps still on 3 im really stuck as to what to try next the stock filter has been replaced with s&b (k&ns) rap a rag around the end one and it starts to jump to 4 so tells me its a vacuume problem help

[steve murdoch]

It can be annoying when people do not follow-up on their threads when a solution is discovered. Myself included.
The carbs were being contaminated by the auxiliary tank i was using. The rubber hose off the tank was disintegrating on the inside and i found black bits on the third cleaning.
To complete the embarrassment, I had forgot to plug the vacuum hose running off #3.

[alke46]

Oops, but at least you discovered the problem. That has to be worth something.

[jdvorchak]

Best thing is he found the solution and then reported back! Thank you.

[520eek]

Thanks for the follow up on what you found....makes for good closure!