Topic: I swear I searched!! Gas in oil question

[karmasevo]

As the subject line says I did search but none of the parameters of prior posts fit my situation. So keeping it short and sweet here goes:

Bike is a 1974 CB750 punched to 836CC. 836 kit was done before I bought it and bike runs great. I have Gas in the oil and have changed the oil multiple times. Just changed oil last night. Rode about 25 miles and can already smell a faint whiff of Gasoline in the oil. The head gasket is most likely bad as the bike is now seeping a bit of oil out the top of the heads. My question is ( as I'm very new to these cb's) why do I have gas in the oil??

It's not from leaving the petcock on when the bike is parked so we can rule that out. Thank you so much for any help. I have learned a ton in the short time I have been a member here.

[Terry in Australia]

Don't rule out the "It's not from leaving the petcock on when the bike is parked" so quickly mate, you can have the petcock in the "off" position and it can still leak fuel into your carbs thru the two petcock mounting screws, if the washers aren't sealing properly. It's happened to me and several other members here.

Fuel fills your carbs, runs into your open inlet valves, runs down past your pistons, into your crankcases. Don't ride your bike until you get it fixed, as the gas will wash the oil away from your bearings, and you'll do lots of damage, and of course, it's potentially explosive........... Cheers, Terry. 

[Tews19]

Don't rule out the "It's not from leaving the petcock on when the bike is parked" so quickly mate, you can have the petcock in the "off" position and it can still leak fuel into your carbs thru the two petcock mounting screws, if the washers aren't sealing properly. It's happened to me and several other members here.

Fuel fills your carbs, runs into your open inlet valves, runs down past your pistons, into your crankcases. Don't ride your bike until you get it fixed, as the gas will wash the oil away from your bearings, and you'll do lots of damage, and of course, it's potentially explosive........... Cheers, Terry. 

Bearing go bad? How can one tell?

[david 750f]

Check the carb overflow tubes.. If they are pinched gas will run back into the engine. (Don't ask how I know)
+1 with what Terry said.

[dtmmil]

Any straight on side pics of the bike?  I am looking at the angles of the carbs, I have seen where the carbs sit at such an angle and the floats not being set to compensate and it will flow into the motor. Or could be bad needles and seats, bad or out of adjustment floats, etc. I never shut my fuel off on mine, if it leaks somewhere, something is wrong and needs to be fixed.

[Terry in Australia]

Check the carb overflow tubes.. If they are pinched gas will run back into the engine. (Don't ask how I know)
+1 with what Terry said.

That's a good point mate, I've had that on a couple of old CB750's as well. Cheers, Terry.

[karmasevo]

well I know the petcock doesn't leak as I have taken the tank off the bike and checked the petcock while syncing the carbs. I think it's time to take the carbs off and make sure all is right. Based on what you all are saying here. Will start on that tonight. Thanks