Indy 500 Crankcase Full of Gas

Couldn’t start my 2000 Indy 500 today. Pulled the crankcase drain plugs and I’d say about 3 measuring cups of gas came equally out of each cylinder. If 1 carburetor’s needle and seat was leaking would it fill both sides of the crankcase like this? If not I’m having a hard time believing both carbs decided to leak.

Could the fuel pump pulse line fill both side with gas if it were leaking? Just trying to find a starting point for troubleshooting.

I’ll add that the machine has never done this. It happened after my daughter and her friends were putting around the yard last weekend when temps were in the 40’s. After about an hour they came to me and said it was “running funny”. Engine was very hot and I let it sit until today.

Could the warm temps and low rpm operation cause an excessively rich condition and unburned fuel to fill the crankcase? After I drained it and cleaned the plugs it runs fine.

If everything in your carbs is working right (and the jets are right) it won't make any difference what the temp is or the speed you drive it. It may be a little off on power at higher temps but it would never fill the crankcase with gas.

The seal system that Polaris uses on that crankshaft is not a positive seal so yes one leaking carb (or leaking impulse line) can fill both sides of the engine.

Probably a leaking needle & seat. The best way to test a needle & seat is with a small pump that has a gauge and puts about two pounds of pressure against the needle & seat. If you flip the carb upside down with the bowl installed while testing the amount of weight the floats put on the float arm is close to the buoyancy of the floats. Pump it up and watch the gauge yours should leak down fairly fast.

Mike-DRH said:

If everything in your carbs is working right (and the jets are right) it won't make any difference what the temp is or the speed you drive it. It may be a little off on power at higher temps but it would never fill the crankcase with gas.

The seal system that Polaris uses on that crankshaft is not a positive seal so yes one leaking carb (or leaking impulse line) can fill both sides of the engine.

Probably a leaking needle & seat. The best way to test a needle & seat is with a small pump that has a gauge and puts about two pounds of pressure against the needle & seat. If you flip the carb upside down with the bowl installed while testing the amount of weight the floats put on the float arm is close to the buoyancy of the floats. Pump it up and watch the gauge yours should leak down fairly fast.

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Thanks for clarifying, that gives me a better understanding.

I believe I can make something to pressure test. I think it’d be cheap insurance installing a new set of needle and seats and rebuild the fuel pump on a 20 year old sled. I’ll pick up the parts and pressure test.

Thanks

Don't buy cheap crap, buy genuine Mikuni Viton tip needle & seat.

I was just going to reply the needle and seats cause that but when I scrolled down saw Mike already responded.

Leaking needle and seat on left carb. The little black rubber tip was gone and a leftover chunk was causing it to leak by pretty good. Replaced both with Polaris parts. $50 a piece at the local dealer...ouch.

Funny how the pain of repair costs quickly fades when you’re back on the trail, though.

I’m glad you got it fixed!

For future ref. You can buy genuine Mikuni for about $20.00 each from many independent shops.