Symptoms of need for new/rebuilt petcock?

[Guest]

If my petcock required a rebuild or replacement, then what symptoms would it exhibit?

Thanks!

[JTGS850GL]

Depends on how it has failed. If the vacuum diaphragm is leaking then it could be pulling in gas from the vacuum line into carb #2 flooding cylinder #2 with gas. If the valve is leaking then it would be like the petcock is in the prime position and could flood any cylinder that has a leaking float valve ultimately flooding that cylinder with gas. It could also leak enough gas to wash down the cylinder when the engine is off and dump gas into the oil.

Bottom line is it puts gas where it doesn't need to be.

Why are you asking? Do you have some unusual running or starting problems?

[MidWestCoast442]

Thanks.

Asking because use I can't figure out the source of why my bike is running so horribly. Replaced the RR (should've probably been done, regardless) and the problem hasn't improved.

Here is what happens: the bike starts without issue, idles fine, and revs appropriately. Then, shortly after it has been running, the motor surges and pops/backfires and is altogether unrideable. Twisting the throttle yields a very very lazy rev which plenty of popping.

[azr]

Could be a fuel starvation issue, 'possibly'. Is your tank so low that the petcock needs to be on the "reserve" position instead of "on"? Is a fuel line kinked? do you have an inline fuel filter that isn't working? is the filter on your petcock plugged. It's pretty simple to verify that your petcock is working properly.

[mikerophone]

You should do a plug chop, but at the very minimum, pull your plugs and see if any of them are black and wet with gas after it gets warmed up and starts running bad.

When was the last time you went through the carbs? Checked for leaks at the boots or airbox?

[Grimly]

Thanks.

Asking because use I can't figure out the source of why my bike is running so horribly. Replaced the RR (should've probably been done, regardless) and the problem hasn't improved.

Here is what happens: the bike starts without issue, idles fine, and revs appropriately. Then, shortly after it has been running, the motor surges and pops/backfires and is altogether unrideable. Twisting the throttle yields a very very lazy rev which plenty of popping.

If it were me, I'd be looking at the coils and HT leads first. Not saying that's what it is, but a dying coil does exactly that kind of thing when it gets hot.

[eil]

Clean the carbs (no, really clean them), seal the airbox, replace the carb boots, and then troubleshoot further from there.

[Call Me Ahab]

If my petcock required a rebuild or replacement, then what symptoms would it exhibit?

Thanks!

Doesn't sound indicative of a bad petcock - as others have mentioned, start with the carbs themselves, clean them thoroughly, break them all apart, dip or boil them, and reassemble them.
Verify float levels, ensure that your float needles are not sticking, clean all jets as thoroughly as possible.

Next, verify that all 4 carbs are synchronized correctly. This could very well be your issue, as it was with me a while back.
While you are cleaning the carbs, consider the intake o-rings on the engine itself - have they been replaced? do you see deposits around the boots where they meet the engine? You could have an air-intake leak right here. Seriously consider replacing them with a viton o-ring if not already done.

After the carbs, go through your airbox as well, clean or replace your filter. Seal both side panels of the box with some EDPM (EPDM?) rubber weatherstripping that resists oil and gas. Ensure that your oil-breather line is connected. Ensure that the vacuum line that connects your petcock to the #2 carb is connected, not cracked or split, and not leaking.

Take a good look at the spark plugs, the wires, and the connections to the coils. Your issue doesn't sound electric, but it could very well be something hidden. Are the plugs in good / serviceable condition? Set gaps to .032; are the wires split / burned? Are the spade or bullet connections to the coils themselves in good condition? Corroded? Burnt?

Finally, but definitely not least - how fresh is your fuel? Are you certain this problem is not the result of bad gas or water in the carbs?

One thing to consider - how does it run on prime? The only thing that could fail w/ the petcock, as mentioned already, is the diaphragm inside that opens / closes to allow fuel to bypass the piston - if this is torn, it would cause #2 to be over-saturated w/ fuel, as well as potentially starving 1,3,4.

Did you adjust your idle-air mixture screws? Improper settings here could cause all sorts of strange problems.

[OldVet66]

If it ran well before and hasn't sat too long, it could very well be the carburetor boots failing if they haven't been replaced. Sounds like a vacuum leak when the bike starts to warm up causing it to run real lean. Start there and continue with the carburetors if it doesn't cure it. When were the valves adjusted last?