GS750L wants to run, but....

[a_man0311]

So I've inherited a GS850 L from a friend and am attempting to revive it. Hasn't been touched in 13 years. I first just tried spraying some starter fluid into the airbox and jumping it. Figured if the engine was hosed I wouldn't bother spending huge time and $$ rebuilding it right? Anyway it seemed to run OK. Next I removed and cleaned the carbs - did a minimum effort job, just spraying out all the jets etc with carb cleaner and blowing everything out with air. Float bowls work, everything seems OK. So I can start the bike, it runs for about 5-10 seconds, then dies. I've reached a few thousand RPM and if I get high enough I get oil spraying out of the breather tube from the cam assembly. I'm talking like a 1/2 cup of oil. Oil sight gauege looks like it's completely full. Question is this - If the sight gauge is so full is the engine simply developing too much oil pressure? Or is the blowoff a symptom of a much larger problem? I'm trying to figure out mainly if the engine is in acceptable condition. If I can prove that I'll do a professional rebuild on the carbs...
Any advice is appreciated.

 

[tkent02]

Sounds like the crankcase got overfilled, probably with gasoline from a faulty petcock.
It should only be just up to the sightglass when the bike is on the centerstand.

 

[a_man0311]

thanks!

thanks!

OK So I'll drain the oil and replace. Just out of curiosity why would a malfunctioning petcock send fuel into the oil? Does it leak past the cyl walls or something?

 

[lucabond]

The petcock works off vacuum that comes from a port on a carb so if the petcock is bad fuel will flow down the vacuum line past an open valve and into the crankcase.
The starting and dieing could be due to old cracked o-rings that seal the intake boots on the engine side of the carbs to the head. Good luck

 

[Steve]

OK So I'll drain the oil and replace. Just out of curiosity why would a malfunctioning petcock send fuel into the oil? Does it leak past the cyl walls or something?

I see you are new, so I will suggest using the search function on the forum. TONS of posts on just that subject, but yes, a malfunctioning petcock can dump fuel right down into the oil.

If it is the vacuum diaphragm (the part that turns the petcock ON when you start the engine) that is leaking, it will allow gas to go straight into the intake tube for #2 cylinder. If the intake valve happens to be open, the gas will simply flow into the cylinder then go down past the rings and end up in the oil.

If it also possible that the piston/o-ring assembly that turns the gas OFF could be leaking. If that is the case, gas will follow its normal route to the float bowl. If the float valves also happen to be bad, the carbs can overfill. Since these carbs have no overflow vent, the excess gas goes through the carb, into the engine. Either way, it needs to be fixed.

Also, I hope you did not have your vehicle running that you used to jump the bike. If you did, you might also have electrical problems now, too.

I'm glad you realize that your little "spray and blow" job on the carbs is NOT a proper cleaning. The best thing you can do for your bike is a proper carb refurbishment by dipping the carbs (a full day each) and putting them back together with a new set of o-rings from cycleorings.com. While you are waiting for your carbs in 'the dip', adjust your valves and clean your electrical connections.

One last thing, get rid of the starter fluid. It's too easy to do a LOT of damage to the bike if you use it wrong.

.

 

[a_man0311]

Thanks!!!

Thanks!!!

I see you are new, so I will suggest using the search function on the forum. TONS of posts on just that subject, but yes, a malfunctioning petcock can dump fuel right down into the oil.

If it is the vacuum diaphragm (the part that turns the petcock ON when you start the engine) that is leaking, it will allow gas to go straight into the intake tube for #2 cylinder. If the intake valve happens to be open, the gas will simply flow into the cylinder then go down past the rings and end up in the oil.

If it also possible that the piston/o-ring assembly that turns the gas OFF could be leaking. If that is the case, gas will follow its normal route to the float bowl. If the float valves also happen to be bad, the carbs can overfill. Since these carbs have no overflow vent, the excess gas goes through the carb, into the engine. Either way, it needs to be fixed.

Also, I hope you did not have your vehicle running that you used to jump the bike. If you did, you might also have electrical problems now, too.

I'm glad you realize that your little "spray and blow" job on the carbs is NOT a proper cleaning. The best thing you can do for your bike is a proper carb refurbishment by dipping the carbs (a full day each) and putting them back together with a new set of o-rings from cycleorings.com. While you are waiting for your carbs in 'the dip', adjust your valves and clean your electrical connections.

One last thing, get rid of the starter fluid. It's too easy to do a LOT of damage to the bike if you use it wrong.

.

Thanks for all the info guys. This is a great help! Petcock makes sense. I noted the vacuum line when removing and replacing the carbs/tank and was wondering whether the petcock was properly operating. I know that the connection boots between the cyls and carbs are old and they are probably cracked. I'm trying to determine if there are any massive transmission/engine problems before dumping a few hundred bucks into the bike. Looks like the bottom line is the carbs need a dip, the petcock needs a rebuild and the carb to cyl boots need to be replaced - along with an oil change!

Steve - thanks for the advice on the starer fluid. I won't use it again - also I made sure to jump with the truck off and the negatives frame grounded. Learned that lesson long ago