Onan bgm 5500 blowing gas through air intake

[Cheepjeep80]

Hi,

I have a new to me 98 Bounder. It has a onan bgm 5500 generator installed. It was hunting really bad when running and would eventually cut off. I replaced the carb, fuel filters, oil filter, oil, plugs, regulator, and circuit board. After completing all this, I couldn't get it to start, it would crank over fine, had good spark and was getting fuel. I unbolted the air filter and it's housing from the carb and manually opened the choke a couple of times. After doing this it started. The generator ran great for about two hours and I turned it off. I didn't put the the air filter housing back on while it was running, because the filter was very oily and dirty. Today when I tried starting it it did the same thing, it would crank over fine but wouldn't start. I followed the same procedure as before, but the carb started spitting gas back out through what looked like a hole in the base of the carb where the air filter bolts up. At this point I'm at a loss. Any help will be greatly appreciated. Sorry for the long post!!

Matt

[bigskymt]

The oily air filter combined with back pressure through the carb may indicate blow-by from a cylinder and through the breather. A poor seal on an intake valve is another possibility but that usually results in "popping" through the carb on compression strokes. I'd run a compression check first.

[rgreen45]

Inspect the gasket you used to mount the carb. Onan carbs come with a pack of several gaskets that all will bolt up. Some however, are shaped slightly different and can interfere with the operation of the choke and/or throttle plate.

[frankdamp]

Another possibility is that an exhaust valve pushrod has broken or slipped out of place. I had this problem on one of our Renaults a few years ago. The sysptom was rough running and great gouts of fuel vapor coming out of the air intake.

The cylinder fires, but the exhaust valve doesn't open, so when the inlet valve opens on the next stroke, what should have gone down the exhaust pipe blows out of the air intake.

[Cheepjeep80]

Thanks for all the advice!! I'm getting my compression tester today and should hopefully have some answers.

Thx!
Matt

[She and I]

Originally Posted by Cheepjeep80

Thanks for all the advice!! I'm getting my compression tester today and should hopefully have some answers.

Thx!
Matt

I wouldn't think the problem is compression if it ran good for 2+ hours,and the way you got it started was by moving the choke butterfly...sounds like the choke stuck..and the second time you tried to start it same thing happened... the choke stuck... and then it was flooded.. thats why it ran gas out ...hold the choke open before that happens....clean and lube linkages...retry..
Richard

[Cheepjeep80]

So it turns out that it was a combination of a fuel pump putting out too much fuel and a bad from stock carb. Replaced both and it's running great. Thanks guys!

Matt