# Onan gas problem



## mowerboy24 (Nov 30, 2012)

My Onan b48m on my sears suburban I think. its drinking way to much gas I think it's either a small gas tank or its sucking too much gas in but it's running fine plz help me find a way to fix this problem. Zach


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## jhngardner367 (Apr 5, 2011)

Welcome to the forum, Zach!
There are a couple of things that can cause this. the air filter could be dirty/wet. The choke could be out of adjustment. The float could be set too high.
Do you have any problems getting it started,or does it run rough? Any black smoke,while running ?
Also,the carb could be out of adjustment.


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## mowerboy24 (Nov 30, 2012)

jhngardner367 said:


> Welcome to the forum, Zach!
> There are a couple of things that can cause this. the air filter could be dirty/wet. The choke could be out of adjustment. The float could be set too high.
> Do you have any problems getting it started,or does it run rough? Any black smoke,while running ?
> Also,the carb could be out of adjustment.


I can't tell if it smokes because of the blow by but it is dark smoke I use it for pulling other lawnmowers around I own a lawnmower salvage


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## wjjones (May 28, 2010)

Welcome to the Forum!..Zach..


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## dangeroustoys56 (Jul 26, 2010)

Well, if its a twin cylender ( any for that matter) - reguardless what is done to them, theyre pretty thirsty motors. I own a few twin cylenders and they use quite a bit of gas.

Alot of single cylender machines seem to use gas as well - actually years ago i tried an experiement ( my friend and i were testing it out) with my '82 dynamark 11HP single briggs - tried tweeking the carb, adjusting choke, tune ups, new magneto - any and everything to tweek more fuel economy out of them. We didnt see any serious improvement, just a little .

As mentioned, it could probably use a good tune up- new plug, carb cleaning/adjustment , new air filter - if it has points they can either be adjusted or replaced - id almost say the little blow by might be fouling the plugs a bit - maybe changing to a hotter plug would help.


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## mowerboy24 (Nov 30, 2012)

dangeroustoys56 said:


> Well, if its a twin cylender ( any for that matter) - reguardless what is done to them, theyre pretty thirsty motors. I own a few twin cylenders and they use quite a bit of gas.
> 
> Alot of single cylender machines seem to use gas as well - actually years ago i tried an experiement ( my friend and i were testing it out) with my '82 dynamark 11HP single briggs - tried tweeking the carb, adjusting choke, tune ups, new magneto - any and everything to tweek more fuel economy out of them. We didnt see any serious improvement, just a little .
> 
> As mentioned, it could probably use a good tune up- new plug, carb cleaning/adjustment , new air filter - if it has points they can either be adjusted or replaced - id almost say the little blow by might be fouling the plugs a bit - maybe changing to a hotter plug would help.


Is the blow by supposed to blow a little oil I think it could get down in the carb making it smoke do u think


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## dangeroustoys56 (Jul 26, 2010)

I had a couple tractors that oil would literally pour from the bottom of the carb - those turned out to be faulty breathers - a breather lets out crankcase pressure , its not to let oil circulate back thru the motor - sort of like a car's PCV setup from the valve covers to the carb/intake.

If any sort of oil is going into the carb - then id check the breather assembly.

Another case of blow by could be worn/sticky rings on the pistons - could do a compression test to check for worn rings. If it looks like it could be a sticky ring , as a initial fix that might work is to soak the combustion chamber with PB blaster overnite, the best part about PB is itll burn easily and fire right up.

If it is bad rings that that doesnt work- then its time for a new set of rings.


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## Rattosh51 (Sep 10, 2008)

If you're Onan's smokin', it's probably ring time.


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## country Gent (Jul 22, 2010)

Sounds like a Onan that has been run hard and put away wet. If you have that kind of blow by, your wasting your time trying to get better fuel mileage. Find a better one in your boneyard.


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## Mickey (Aug 14, 2010)

mowerboy24 said:


> My Onan b48m on my sears suburban I think. its drinking way to much gas I think it's either a small gas tank or its sucking too much gas in but it's running fine plz help me find a way to fix this problem. Zach


For the sake of this discussion, it could help if you could give us some indication of how much is too much. Even something as simple as, I used to do this chore using X amount of gas. Now same chore is taking X+ amount of gas.

Since you say it is running fine, I think it is something other than a dirty air filter or carb adjmt. I could be all wet but that's my take.


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## mowerboy24 (Nov 30, 2012)

Is a set of rings for that Onan pricey and also it smokes dark color smoke like the choke is pulled slightly but do you think I should run it and spray a bunch of carb cleaner wile its running to clean that out because I don't want to risk messing around with removing the carb and getting it out of adjustment just one square carb I have with the fuel pump (discontinued) but the carb alone goes for $590


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## TRACTOR MAN (Dec 30, 2012)

Should have a adjustment screw to change how much gas runs in the carberator not too sure but if it runs fine idk


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## mowerboy24 (Nov 30, 2012)

Where should this screw be located at


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## wjjones (May 28, 2010)

mowerboy24 said:


> Is a set of rings for that Onan pricey and also it smokes dark color smoke like the choke is pulled slightly but do you think I should run it and spray a bunch of carb cleaner wile its running to clean that out because I don't want to risk messing around with removing the carb and getting it out of adjustment just one square carb I have with the fuel pump (discontinued) but the carb alone goes for $590




Believe it, or not I just started putting sea foam in mine I cant post the results yet because I havent run it much but they say its ok to use in power equipment. I plan to put it to the test though to see how it turns out. If it cleans the mower engine carb out like it did my truck then it will be good.


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## wjjones (May 28, 2010)

mowerboy24 said:


> Where should this screw be located at




Some of those screws on certain engines are plugged off where you cant adjust them.


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## dangeroustoys56 (Jul 26, 2010)

Ive never been a fan of additives, until the quality of gas has gotten worse - i regularly run marvels mystery oil and sta bil in my stuff. Ive noticed if the gas stays in the carb over long periods, itll draw condensation in and start to corrode the float bowl. One tractor ran fine, i pulled the carb for general cleaning and was loaded with crud.

If the carb has never been off, it might be due for some cleaning.

Sea foam is good for storage, keeps things from sticking - like at end of year storage- altho ive herd theyre a bear to start in the spring.


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