Tecumseh OHM90 9hp - Gas in the oil

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ztrain727

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Hey Everyone,

(disclaimer: my mechanic knowledge is very limited - please excuse any stupid remarks or questions)

Pretext:
I've got a home assembled kart with a a Tecumseh OHM90 9hp. The engine always ran great until this past winter. It was a cold day - about 20 f - so I reversed the cover over the carburetor as the manual says to do so the engine would suck in warm air. Anyway, assuming I had taken proper precautions, I fired up the engine. It was running pretty rough and almost stalled a few times but figured it just needed to warm up. I hopped in, drove about 100 feet, and suddenly the started to die and a huge cloud of white smoke poured out of the exhaust. Moments later it died completely and would not restart. I figured I had blown and engine and gave up on it.

Some months later, in the spring, I decided to try to start the engine again. To my surprise, it started, but ran very rough, producing excess black-gray smoke, and seemed like it might stall if I gave it too much gas.

Problem:
I soon realized upon checking the oil levels that the oil (SAE 30) smelled strongly of gas. I drained the oil (which came out completely black) and replaced it with fresh SAE30, because I had heard gas can leak past the pistons into the oil during cold weather operation. I started up the engine and it continued to run rough and produce excess dark gray smoke. I checked the oil again and it again smelled like gas.

From my limited knowledge and research, I've read that either the float seat/needle is sticking or my rings are blown. If the rings are blown, I'm in trouble, but if the needle is sticking it's a much less severe problem.

Summary:
Engine died, produced a big cloud of white smoke while running it with SAE30 in >20 f weather.
Engine now starts, but gas is getting into oil. The oil is black, as is the spark plug head. The spark plug smells like gas when I take it out.

Any help would be appreciated!
 

Blazkowiez

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This problem is really common on Honda engines when they sit and the carb does get clogged. Flush your oil a few separate times and rebuild your carb.

Steps: Rebuild carb, Change oil, run 5 min, change oil, run 5 min, check to see if oil is still very liquid from the gas or overflowing, may need to be changed 3-4 times. If it still runs poorly after these steps check your rings.
 

ztrain727

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OK, great. Thanks a lot for the advice. I've had a feeling the carb has needed a rebuild for a while, so it couldn't hurt.

Would you recommend buying a rebuild kit or should I just by some compressed air/carb cleaner?
 

Blazkowiez

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Rebuild kit and carb cleaner :) The reasoning here is that your problem is caused by bad gaskets more notably a needle/seat which is not doing its job.
 

ztrain727

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Ok thanks for the help - I'll go buy those things.

I don't believe the OHM90 comes with a fuel tap, but I wouldn't know where to find it and can't scrape up a manual online. I've heard that installing one might be another easy solution, however, if the gas is getting in every time I shut off the engine.
 

ztrain727

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Hey everyone -

So I know it's been a while but I got the carburetor off today and opened it up, and to my surprise it looks really clean. There's almost no gunk in the bowl, the float looked like new (both components were plastic to my surprise). It seemed to move up and down freely. I'm a bit confused as to the role of the needle and how I get it off to examine its condition. Can I just put a bit of water/carb cleaner in the bowl and see if the float floats? haha

I guess I need to keep browsing the net for a suitable rebuild kit... I think this is what I need: http://www.ecrater.com/p/7607617/632551-632709-oem-tecumseh-inlet-needle-seat

Thanks a lot for all the help - I really appreciate it
 

Blazkowiez

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The needle is typically removed using compressed air in the main gas inlet, it will shoot out like a bb so face the end of the needleseat compartment away from you to avoid damage to yourself. You can check the float by shaking it near your ear, if you hear nothing its good, if you hear liquid get a new one. The seat regulates gas flow and when it fails it can allow gas to flow into the main block and that is where you gained gas with the oil.
 

ztrain727

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The needle is typically removed using compressed air in the main gas inlet, it will shoot out like a bb so face the end of the needleseat compartment away from you to avoid damage to yourself. You can check the float by shaking it near your ear, if you hear nothing its good, if you hear liquid get a new one. The seat regulates gas flow and when it fails it can allow gas to flow into the main block and that is where you gained gas with the oil.
Ok thanks. I shook the float as soon as I got the carb out and it didn't sound like there was anything in it. I suppose I could fill the bowl with water, close all the holes, and let it sit overnight to see if water gets in.

I also sprayed the hell out of the whole carb with carb cleaner and it looks quite clean to me.
Should easily lift out once pin is removed that supports float.
As for the needle, it seems pretty clean and loose, but I cant get the pin off that holds the float. It's held between two little plastic nobs and I'm worried about breaking them.

Here's a photo:
A close-up of the needle/float pin


Thanks so much guys! I'm sorry for all the confusion and appreciate the continued help.
 

ztrain727

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Haha well I guess that makes sense doesn't it...

So I got the float/pin off and everything looked really clean. The seat under the pin does look a little worn, but not bad at all.

I tested the seal first with gently compressed air. Then I assembled the float, etc. and filled the bowl with gas. When the bowl was full, and the float was floating, no gas leaked out and when I pushed down on the bowl it of course leaked out.

I also submerged just the float in water for a while and shook it. It sounded dry.

I got a fuel tap too, so I'll install it as close to the carb as possible. Then a few oil changes and I'll see if gas is still getting in the oil.

Thanks again for all the help
 

ztrain727

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Thanks for the tips - I'll take better care of the engine from now on.

I reassembled the carb, installed a tap, and filled it up with sae30, though I have a lot of trouble reading the dipstick, so I just put in a bit less than a quart.

Engine runs - runs well, in fact - no black/grey/brown smoke except with choke open.

Problem is, I must have accidentally messed with the governor or hooked up the throttle cable incorrectly because the thing would take off when idling if it weren't up on a crate. It seems like there are about 10 places you can adjust the idle speed with all the different holes and connections between the throttle cable and carb. Is one easiest to start with?

I can push the throttle all the way back, but the kart won't even idle. If I let it go just a little though, it roars. :toetap05:
 
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