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I installed a new Onan brand on my 1980 4. BFA series

I installed a new Onan...
I installed a new Onan brand carburetor on my 1980 4. BFA series generator. I had the RV electric aux fuel pump on to get fuel to the engine and generator. I left the aux pump for a few minutes while I checked the gas lines for leaks. The air cleaner duct was not installed. I started the generator and it ran OK with some black smoke but with smooth operation after I adjusted the choke a bit. After about 3 minutes oil shot out of the oil breather line and I shut down the generator. I checked the oil dipstick and the oil pan was over filled and oil and apparently gas flowed out. I called Cummins and they suggested a cracked block but I am unsure how this would cause that much gas to get into the oil. Any ideas?
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Answered in 1 hour by:
9/22/2017
Curtis B.
Curtis B., Technician
Category: Small Engine
Satisfied Customers: 31,896
Experience: have worked on and around most engine models for 35 yrs./Polaris ATV expert
Verified

Welcome to JUST ANSWER small engines, let me try to help you !! I don't know it all, but maybe together we can get you a satisfactory answer!

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Where is the vent line? Before the carburetor in the intake? Was this in place? If not, the oil had to already been thinned and over full before you installed the new carburetor. Why was old carburetor removed. All you have is gas in the oil from the carburetor needle valve not seating, letting gas flow into the crankcase vent line.

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Customer reply replied 11 months ago
The vent is the flexible rubber hose that is hooked up to the air cleaner intake duct just prior to the carburetor intake. It sucks fumes out of the crank case. It was blowing oil like a volcano. The old carburetor was old and in need of a rebuild so I just replaced with a new unit. I didn't check the oil before starting the generator with the new carb so maybe it is an old carb issue. To hopefully confirm the fuel leak I will:
1. Drain all the oil and leave the drain line open,
2. Turn on the RV electric boost pump.
3. Look for fuel leak in the oil pan by checking for fuel flow out of the oil drain line.
4. If no fuel is flowing then I will close the oil drain line and let the electric boost pump run for a few minutes.
5. Open oil drain line and look for fuel leak in the oil pan by checking for fuel flow out of the oil drain line.
6. If no fuel is found then I will refill the oil.
7. Run the generator with the electric boost pump off.
8. Check oil level for signs or fuel intrusion.
9. Run the generator with the electric fuel boost pump on.
10. Check the oil level for signs of fuel intrusion.
I'll let you know what I find.

OK> I think you will find the gas was already in crankcase, I have never seen this as a block problem!

Curtis B.
Curtis B., Technician
Category: Small Engine
Satisfied Customers: 31,896
Experience: have worked on and around most engine models for 35 yrs./Polaris ATV expert
Verified
Curtis B. and 87 other Small Engine Specialists are ready to help you
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Customer reply replied 11 months ago
I
1. Drained all the oil and left the drain line open,
2. Turned on the RV electric boost pump.
3. Looked for fuel leak in the oil pan by checking for fuel flow out of the oil drain line.
No fuel was present, must a problem with the old carb, maybe that is why is wasn't running too good!
Thanks,
Bye

Thank you!

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