[Bobby05]

My gs750 has had some idling problems ever since I put a set of Murray’s carbs but the man who sells says it’s not the problem it’s the bike. I believe him a little bit.

cylinder #2 so the left middle one, it’s exhaust header tube is not heating up like the other three

I ran a compression test on all four and they were all good and all have spark

I just want some ideas on what to look for

 

[woodsman]

Are you getting fuel to that carb?

 

[TrialsRider]

... this is the one running 2 carbs if I recall correct
Need more detail on 'some idle problems' and what is all good, compression test gives numbers and they are rarely all identical on a poor running 4 cylinder, the numbers if only down a little bit would have me adjusting and inspecting the valves on that one. Problem only on one cylinder narrowed it down a lot

 

[Bobby05]

Are you getting fuel to that carb?

... this is the one running 2 carbs if I recall correct
Need more detail on 'some idle problems' and what is all good, compression test gives numbers and they are rarely all identical on a poor running 4 cylinder, the numbers if only down a little bit would have me adjusting and inspecting the valves on that one. Problem only on one cylinder narrowed it down a lot

For the first question- yes as far as I know of

for the second question- yes the two carb one. So when the choke is turned off to the left carb ( the one controlling 1 and 2 ) the bike starts to stutter and then shut off. For compression test cylinder #1 was at 112.8 psi #2 was at 113.1 #3 was at 112.9 #4 was at 113.2

 

[TrialsRider]

How about switching around or outright replacing the ignition wire set and plug cap on the lazy cylinder

 

[Bobby05]

How about switching around or outright replacing the ignition wire set and plug cap on the lazy cylinder

Already did that one and didn’t change nothing

 

[TrialsRider]

Curious, given the compression, everything bad should be happening in pairs save the electrics to that cylinder, this is a tough one without hands on. Does it smell of raw fuel in either the exhaust or crankcase breather after it stalls out?

 

[Bobby05]

Curious, given the compression, everything bad should be happening in pairs save the electrics to that cylinder, this is a tough one without hands on. Does it smell of raw fuel in either the exhaust or crankcase breather after it stalls out?

Well it does back fire a little bit and you kind of have to slow rev it up or it’ll stall out. I can’t say I haven’t smelled it bad I can’t say that I have either so idk on that one

 

[TrialsRider]

Well it does back fire a little bit and you kind of have to slow rev it up or it’ll stall out. I can’t say I haven’t smelled it bad I can’t say that I have either so idk on that one

The backfire might be the raw fuel from that cylinder and then you wouldn't smell fuel if it is running a 4 into one or collector or balanced exhaust header. If it heats up the #2 header half way, that still suggests an ignition issue still being the only thing that doesn't run in pairs and you can swap things significantly including the coils

 

[Bobby05]

The backfire might be the raw fuel from that cylinder and then you wouldn't smell fuel if it is running a 4 into one or collector or balanced exhaust header. If it heats up the #2 header half way, that still suggests an ignition issue still being the only thing that doesn't run in pairs and you can swap things significantly including the coils

Yeah i might try swapping the coils when I get the time

but would it be worth my time and money for it to get looked at

 

[TrialsRider]

So much trouble-shooting you can do, you either do it or you pay somebody to do it, I'd be doing the trouble-shooting or just replacing the coil and ignition set on that pair with new, everything right to and including the plugs. The ignition parts are not outrageous cost as a mechanics labour bill would be.

Manual says you can service everything right down to removing the pistons with your engine still in the frame

 

[Bobby05]

So much trouble-shooting you can do, you either do it or you pay somebody to do it, I'd be doing the trouble-shooting or just replacing the coil and ignition set on that pair with new, everything right to and including the plugs. The ignition parts are not outrageous cost as a mechanics labour bill would be.

Manual says you can service everything right down to removing the pistons with your engine still in the frame

That is very true I’m going to look into it more and see what I can do

 

[CaTacL1sm]

So on my 79 GS750, I solved all of my starting and running problems by balancing the carbs and adjusting the valves.

 

[Bobby05]

So on my 79 GS750, I solved all of my starting and running problems by balancing the carbs and adjusting the valves.

I have a different set of carbs than the originals but should I really try adjusting the valves if it basically has the same compression as the other cylinders

 

[Classic250]

Have you pulled #2 sparkplug to see if it is wet? If it is, then fueling probably isn't the problem. As stated by others, I would be exploring the ignition system.

 

[Bobby05]

Have you pulled #2 sparkplug to see if it is wet? If it is, then fueling probably isn't the problem. As stated by others, I would be exploring the ignition system.

I have and it was basically dry, and the whole ignition system work to my knowledge but I can give it another once over I guess

 

[CaTacL1sm]

I have a different set of carbs than the originals but should I really try adjusting the valves if it basically has the same compression as the other cylinders

Are you confident the new set has been balanced? It's absolutely worth checking.

 

[TrialsRider]

I have a different set of carbs than the originals but should I really try adjusting the valves if it basically has the same compression as the other cylinders

Once you rule out everything else that is unique to #2 cylinder and can't make the problem go to a different cylinder, yes, setting valve clearances and looking for problems on #2 valves would be prudent, compression test is just a diagnostic.

 

[Bobby05]

Are you confident the new set has been balanced? It's absolutely worth checking.

the new carbs came pre-balanced to the bike and i was told not to change them at

Once you rule out everything else that is unique to #2 cylinder and can't make the problem go to a different cylinder, yes, setting valve clearances and looking for problems on #2 valves would be prudent, compression test is just a diagnostic.

I'm going to try and switching the carbs around since I can but i'm going to take the valve covers off and check the lobes on the cam and also do a set of new gaskets for the whole bike since there's a tiny external oil leak which may be a copart in cylinder #2's problem

 

[TrialsRider]

Good logic your carbs came bench synchronized, if the manifolds came with a spigot you could use a vacuum gauge to confirm the balance. External oil leak (clean oil) or black mung leaking out of the exhaust system? - first issue is serious and the second is not so bad.

Lobes on your cam will look perfect unless it was seriously starved for oil, cam is hardened steel, it's the valve seats that gets mushed out and make it need a valve adjustment.

Do you have access to fibre optic viewing equipment? Visual inspection is very handy for finding problems.
... 'full set of gaskets' some you will need more frequently then others, the most critical being the ones that seal in engine combustion pressure.

valve guides - it's critical that you don't have leakage past valve stems. Not good if your valves are wobbling around when they go up and down.