Gas blowing through carburetor and out of exahaust

[Cabinnut 1]

I am working on an 1996/97 Onan P220G engine that is on a portable saw mill (sorry, not on a wheel horse tractor!) and several different times  over the last several years I had gasoline blowing out of the carburetor and both exhaust pipes after starting it after a long sit time. Also, discovered gasoline had filled the oil pan each time. Cylinders also were flooded with gasoline. I rebuilt the carburetor already once and it happened twice after that. I, however, had times when the engine ran great with no fuel or carb issues.  At first I assumed it might have been because the engine sat idle for a while and the gas tank, which is above the engine on the mill head, was pressurizing and pushing gas through the engine somehow so I installed a fuel shut-off. That didn't do it...this last time I turned the engine off for about an hour and restarted it and the same gas blowing out of the exhaust crap happened! So, I assumed carb issue and bought a brand new Nikki carb for it. I installed the new carb the other day, took the cylinder heads off, cleaned them up, replaced gaskets and spark plugs also. Fired it up. Slow to warm up but seemed to run OK. I soon noticed one cylinder was smoking badly. Upon further inspection the exhaust pipe was puking gasoline! Ugh! I'm not a mechanic but do OK with DIY engine work...however, I am now beyond my knowledge base as to what is going on with this engine! Can anyone help me troubleshoot this? I'd hate to have to replace the engine, but maybe something bad is going on in there. Thanks in advance!

[SylvanLakeWH 27,589]

 

The engine / carb experts will be along shortly…

 

How about a pic of that saw mill?

[pacer 3,176]

Thats the perfect description of a carb problem -- (float sticking). While my Onan is a bit older than yours I can definitely feel your pain, I have had the same problem .... several! times! Apparently - based on the many other posts re this problem, the Onan carb is just --- well, finiky/picky!  On several occasions I worked on every thing I could think of only to not find a thing, and put it back together and do it all over again!!

 

I generally end up replacing the needle/seat and sometimes float and eventually will run OK (I've wasted a many quart of perfectly good oil draining the crankcase to get the gas saturated oil out) The fuel shut-off should stop that while sitting, but it wont help in running mode - or lack thereof!

 

Wish I could give you a "do this/that and it'll fix_ but alas I cant!

 

As mentioned its a pretty common prob and maybe one of the other guys will have better insight on the problem.....

 

And ..... yeah, wheres a pic of that sawmill????

 

 

 

 

 

 

 

 

 

 

 

 

[8ntruck 7,395]

I'll agree with @pacer - it sounds like a float issue.  Another possibility would be the fuel pump - if it has one - might have a bad diaphragm, allowing gas into the crankcase.

 

Most of us here are like 5 year olds.  We like pictures 'cause they are easier to read.  Plus, saw mills are always interesting.

 

I need to give you the required Wheel Horse solution to this problem:  buy a 14 hp or larger Wheel Horse tractor and use its PTO to drive your saw mill - lots of models in this range to choose from .

 

Good luck.

Edited April 19, 2022 by 8ntruck

[lynnmor 7,575]

Where did you install the fuel shut-off, was it between the carb and the fuel pump?

 

Is there a vacuum hose connected to the intake manifold and did someone connect it to the fuel line?

 

Are you running the stock fuel pump that is mounted on the blower housing?  Is it in good condition with a good hose on the rear of it connected to the engine block?

 

I'm trying to find a different route for excess gasoline since carb rebuilds and replacements failed.

[Ed Kennell 40,509]

13 hours ago, Cabinnut said:

, discovered gasoline had filled the oil pan each time.

The pulse fuel pump  may be leaking fuel back into the pan and blowing it past the rings flooding the cylinders. 

This is a disaster in progress.     Replace it with an electric pump for about $20.

 

 

Oh,  to the 

Edited April 19, 2022 by Ed Kennell

[lynnmor 7,575]

17 minutes ago, Ed Kennell said:

The pulse fuel pump  may be leaking fuel back into the pan and blowing it past the rings flooding the cylinders. 

This is a disaster in progress.     Replace it with an electric pump for about $20.

 

 

Just to be clear, the pulse hose connects to crankcase air using the pulses there.   I wonder if the fuel tank is higher than the fuel pump, that could explain the flooding during non use.  On a Wheel Horse, the fuel pump is higher than the tank.

[Ed Kennell 40,509]

13 hours ago, Cabinnut said:

the gas tank, which is above the engine on the mill hea

@lynnmor        This was in the first post Lynn.     That's why I susspected a leaking pump diaphram.

[gwest_ca-(File Mod) 11,251]

 

[roadapples 6,983]