Gas In Oil

[Southern Comfort]

I have gas in my oil on my Kohler CH730 engine

 

[Sprinklerman]

Stuck float in carb is one possibility

 

[bigdeano]

I see that engine is listed as having a mechanical fuel pump. If the diaphragm has a hole in it it will pump the crankcase full of gas unless they've provided a vent hole or something to prevent it. Had it happen on a car once.

 

[CobyRupert]

How much gas in the oil?
Am I correct in my thinking that many gas engines get some blow by, but rely on the engine coming up to temperature to evaporate the gas out of the oil?
Thus a motor that is repeatedly run for only short periods of time and never comes up to temp can end up with gas in the oil?

 

[tjkubota93]

How much gas in the oil?
Am I correct in my thinking that many gas engines get some blow by, but rely on the engine coming up to temperature to evaporate the gas out of the oil?
Thus a motor that is repeatedly run for only short periods of time and never comes up to temp can end up with gas in the oil?

Kinda. It is helpful to run an engine at operating temperature for a while instead of just start and stop alot. The blow by has a lot of other things in it including gasoline or diesel fuel (should not be much raw fuel). Running at operating temp does help to get all the blow by crud and condensation out.

 

[TractorGuy]

Look on the bottom of the float bowl to see if it has a solenoid on it. Some small engines are fitted with a fuel shutoff solenoid on the main jet to prevent it from siphoning into the cylinder when the engine is turned off. Had that fail on a B&S engine and kept filling the crankcase full of gas. New carb was as cheap as replacing the solenoid. Also had to change oil twice.

 

[banjodunn]

I see that engine is listed as having a mechanical fuel pump. If the diaphragm has a hole in it it will pump the crankcase full of gas unless they've provided a vent hole or something to prevent it. Had it happen on a car once.

X2 It is not common but it does happen, fuel pumps are mounted on the rocker cover and if leaking will leak into the oil

Jon

 

[Dave M7040]

See the shop manual at the link below.
On page 22 the two possible fuel pumps are described.
In my experience the most common one is the vacuum pulse style.
If something is wrong internally with this pump the vacuum can suck gas into the engine.
http://www.mcelroy.com/documents/tr...H670_CH680_CH730_CH740_CH750_REVISED+1_12.pdf
The pulse style pump is $40 from amazon.
Amazon.com: Fuel Pump for Briggs & Stratton 491922,808656, Honda 16700-Z0J-003,Kawasaki 49040-7001,Kohler 24 393 04S,24393 16S, John Deere Lg808656 M138498 M145667: Automotive
Dave M7040

 

[Southern Comfort]

Thanks for all the replies. Definitely helps. I figured it had to be either fuel pump or carb. Going to give the engine a bath all full of oil. If it is the fuel pump could I replace it with an electric one that would eliminate the fuel pump in the future. I worry that with an electric pump I should have constant pressure of gas at my fuel bowl on the carb. Do you think I need a return for my fuel to the gas tank? Thanks everyone for the replies

 

[Dave M7040]

southern
Electric pumps deliver far too great a pressure to be controlled by the needle and seat in the float bowl.
Have you determined if you have the vacuum pulse pump or not?
There is nothing to be gained by an electric pump.
The proper Kohler pump will give years of trouble free service.
There is no point in re engineering the factory design and a lot of risk
Your experiences are unusual.
Dave M7040

 

[bigdeano]

Electric pumps made for carburetors only put out a few psi, like 3 to 5, should work fine. Kind of a tossup which kind to use.

 

[Dave M7040]

Electric pumps made for carburetors only put out a few psi, like 3 to 5, should work fine. Kind of a tossup which kind to use.

One aspect to consider re your comment on electric pumps being ok for carbs is to consider the actual mechanism within the carb which has to deal with the pump pressure, the lawnmower float is much smaller than the automotive one and as a consequence there is less mechanical force holding the needle closed. My experience trying electrical pumps on small engines was a disaster plus they are more expensive than the proper pump.
Bigdean, have you actually used one on a small engine? If you did and it worked I would like to know more details. Make and model of pump and on which engine. Perhaps my experience is not broad enough if you had success.
Dave m7040

 

[bigdeano]

The only electric pump I have on a small engine is on a Honda CX500 motorcycle engine in my garden tractor. Don't remember the pump number. But do some figuring. If the hole the needle valve is closing is 1/8 dia, the area is .012 sq in. At 5 psi that's a force of 1 oz pushing the needle open. The float has a large mechanical advantage over the needle so it seems like it should easily close it.

What electric pump were you using? Maybe it put out more pressure.

I recently bought a 24 horse B&S for a project. When I get that far I'll give it a try. I bought an electric pump on ebay for $10 that works fine so far on my diesel gen for a lift pump.

 

[Walt 2002]

Look on the bottom of the float bowl to see if it has a solenoid on it. Some small engines are fitted with a fuel shutoff solenoid on the main jet to prevent it from siphoning into the cylinder when the engine is turned off. Had that fail on a B&S engine and kept filling the crankcase full of gas. New carb was as cheap as replacing the solenoid. Also had to change oil twice.

A surprisingly common misconception. That solenoid has absolutely no affect on whether or not fuel will entire the carb and eventually into the oil. It is NOT to "prevent gas from siphoning into cylinder when engine is turned off". It is only to help prevent "after fire" from lean burn EPA requirements when the engine is shut off.

Walt Conner

 

[old243]

I had fuel going through the carb, into the crank case. Brigg and Stratton. I put an in line shut off in the fuel line. When Im done using it I shut the tap off. This is an old toro rider, with a million miles on it. old243

 

[DJ54]

I didn't have the best of luck with an electric fuel pump on my Bobcat. And the only reason I put one on, is because the rental company that I bought it from had put one on, so was just replacing it. Being the only place to mount it, is in the engine compartment, the fuel pump got so hot, the little oscillating piston would seize up ,and quit pumping fuel after 20-30 minutes, depending on the temps. Let it cool for 30 minutes, and it was good to go.

After looking closer, I saw there was a engine driven fuel pump on it. Got one, replaced it, and never looked back, and that's been 8 years ago. No problems with it since.

 

[fidowanttobe]

I have an old Onan 2 banger in a garden tractor that had an engine driven fuel pump that had it's hands full trying to suck the fuel from under the seat all the way to the carb. Crappy design. Bought a used Onan inline electric fuel pump on Ebay, (trying to find a low pressure pump, not brand specific,) and it turned a frustrating PITA into a workhorse. Have no idea how it survived since 1972 with the mech pump and yes I did replace it once.

 

[bigdeano]

I like that electric pumps fill the carb bowl without cranking the engine. Makes them start a lot easier after they've been sitting a long time.

Pumps made for fuel injection put out way too much pressure for a carb. Make sure to get a low pressure pump that doesn't need a return line.

 

[hawkeye08]

Look on the bottom of the float bowl to see if it has a solenoid on it. Some small engines are fitted with a fuel shutoff solenoid on the main jet to prevent it from siphoning into the cylinder when the engine is turned off. Had that fail on a B&S engine and kept filling the crankcase full of gas. New carb was as cheap as replacing the solenoid. Also had to change oil twice.

Had my solenoid fail and dump some gas in crankcase, looked up parts and choose to purchase inline fuel shutoff instead for $3. I shut off the fuel when done mowing and turn it on when I get the mower out. Runs fine.

 

[banjodunn]

Had my solenoid fail and dump some gas in crankcase, looked up parts and choose to purchase inline fuel shutoff instead for $3. I shut off the fuel when done mowing and turn it on when I get the mower out. Runs fine.

G'day the cause of that is more than likely a leaky needle and seat this is why your inline tap stopeed it, the solenoid in the bottom of the carb just puts a plunger into the bottom of the main jet stopping the engine from running on when hot also helps prevent that shutdown backfire.

My better half has a chinese push mower with a honda copy engine and the needle and seat let go after about 18 months filling the sump full of fuel put an inline tap in ($5 from local mower shop) and haven't looked back since.

Jon