QuestionQUESTION: I have an 11 year old Craftsman 14.5 HP IC Gold OHV Lawn Tractor with a B&S single cylinder engine (Model 287707, Type 1255-E1). It starts fine, but after about a minute of running (whether or not the choke is on) the carburetor floods with a very oily gas, which then shoots out of the air intake.
It was burning oil last season, but we didn’t notice any other problems. I removed the float bowl and cleaned it, the float and the needle. I also checked to make sure the float floated (it did). I didn’t take anything else apart, but it wasn’t very dirty in there. I also replaced the fuel filter, while I was at it, and was going to change the oil (it’s currently low too), but didn’t want to change it until this was solved. The spark plug is working and in decent condition; it did not have any oil on it when I checked, just normal looking carbon deposits.
Maybe I need to take the carburetor off and check the jets (or can I take out the jets without removing the carb)? It doesn’t flood when it is not running, but maybe that is because of the solenoid. I haven’t tried leaving it on (but not running) to see if it floods. My question is this: is there some other reason that this is happening, and why is it so oily? Also, what should I do next? Any help would be appreciated. Thanks.
ANSWER: When was the last major tune-up to include a valve adjustment and carburetor re-build? If the valves have never been checked I would start with that and also clean the valve breather. A bad valve breather will cause the crankcase to not hold vacuum which could allow a little oil to get by.
Have you ever checked the vavle clearance or cleaned the valve breather?
Eric
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QUESTION: It hasn't been tuned up in the last 5-6 years, but I've kept the oil changed and spark plug has remained in good condition. I'll clean the valve breather and check the valves (I haven't done this myself before). If the crankcase wasn't holding a vacuum, could that cause the fuel to build up in the carburetor and gush out of the air inlet? Also, I noticed on the schematics that there is a carburetor shield ( http://bsintek.basco.com/BriggsDocumentDisplay/default.aspx?filename=Z6hrsJVJ1Da - page 5, part 996) that covers the breather tube hole. I don't think my engine has ever had this (and I've never had any problems until now) and I was just wandering if that was only for some models, and what your best guess is to its purpose. In fact I pretty sure there isn't even a screw hole to be able to put one in, but if I have to order parts and it is best to have one, I'll order it too. Thanks, for your help and I'll let you know how it goes.
AnswerIf gas is gushing out of the carburetor it is usually casued by a leaking carburetor inlet needle seat or bad float. Briggs floats are pretty reliable but the inlet needles require frequent replacement depending on the quality of fuel in your area. Looking at the part diargram for the carbs available for your engine the intlet needle has a rubber, actually viton, tip that is suppose to seal and prevent gas from gushing out the carb. Sometimes a piece of dirt or even a small water dropplet can cause the needle to leak. In either case I would remove, dis-assemlbe and clean the carb with compressed air from an air compressor; blow air through all the carb passages to make sure they are clean. I would replace the inlet needle and float bowl gasket at a minimum. We also drain the fuel tank and clean by blowing compressed air through the entire fuel system to make sure there is no debris or water anywhere.
The shield should be in place but I have seen some of the screw holes strip and folks just leave them off. Usually does not hurt much but you may notice a little oil on the inside of the air filter.
Make sure you check the dipstick o-ring and dipstick tube gasket. Years ago Briggs had some issues with the o-rings leaking which cause a loss of crankcase vacuum and some engine consumed a little oil. Have not heard or seen any recent issues but I would still inspect them.
After cleaning the valve breather it should rattle when you shake it...you are hearing the check valve inside when you shake it.
How much oil is on the air filter?
Eric
