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Followup To
Question -
I'm a small engine tech at an ACE hardware here in Upper Michigan. I've been doing this kind of work for about 15 years and have come across a head scratcher involving a Briggs 18hp (422700 model series). It is in an older Gilson riding lawnmower that my customer uses with a blade in the winter. For some reason, it fouls the left cylinder plug repeatedly (side away from armature coil). The compression is equal at 110#, the spark is bright blue and hot with fresh plugs and it has the carb with a fixed jet (no antifire valve). I checked the valve clearances and found them to be within specs. I even pulled the heads to inspect the top of the cylinders, very little carbon buildup on either side. The only difference was the problem side's exhaust valve was covered with black sooty deposits while the other side's exhaust valve had a flaky white deposit. I'm just not sure where to go now, I've checked everything I can think of, any fresh ideas for me?
Thanks, Jim B
Answer -
We had a similar problem years ago and eventually ended up replacing the coil.
Before replacing the coil I would try another brand of spark plug. I'm not sure about you but we often find fouled Champion brand plugs in 4 cycle engines...2 cycles I can see but fouling in 4 cycles?
Anyhow, we found NGK or ND plugs are much more reliable and rarely foul. Granted they can be difficult to find but they are very reliable.
Have you checked the intake gaskets and valve breather. Kohler engines are bad about the breather sticking so we always check the vavle breather with weird problems like yours.
Please let me know if a different brand plug solves the problem.
Eric
FOLLOW UP QUESTION
Eric --
Thanks for the suggestions. I too have had alot of problems with Champion plugs over the years. I will try a set of NGK B2LM's when I put this all back together. One thing I forgot to mention under the symptoms -- the air filter keeps getting soaked with fuel. Breather problem you mentioned? Usually I look at the breather when I have oil on the filter. Could the stuck breather be blowing the fuel charge back up the intake?
I was doing some reading in a Briggs service manual (Twin Cyl MS-7000) under carbs. The last page it has a note about Model 401700 series operating under 40 degrees at light loads may experience plug fouling and crankcase oil dilution from gas. They recomend changing to updated (J19LM) plugs, but if it continues to install Intake Elbow Kit #394598. Ever hear of that one before? I've never had a chance to go to the Briggs school (cheap bosses) so I'm mostly a self taught small engine tech. I don't always get a chance to hear about the latest fixes. Thankfully they have this forum to help guys like me.
I have the next two days off, so I have time to research this some more. Thanks again, Jim B.
AnswerI do recall the intake elbow but have never installed one. I'd try different spark plug brands before changing the spark plug heat range.
The valve breather could cause the soaking filter but so could crankcase vacuum, which is controlled by the valve breather and rest of the crankcase gaskets.
Do you have access to a manometer or vacuum gauage?
Let me know.
Eric
