QuestionRiding mower: MTD (from Montgomery Ward 1997) 42" Model TMO-30000A
Engine: Briggs and Stratton Model 422700 18HP
Problem: From a cold start with choke full out and throttle
full on, engine starts and runs smoothly. After 15 seconds
as the engine begins to sputter, we push the choke in all
the way and the engine then runs normally, except that it
revs up and down constantly every 3 seconds or so. Looking
under the cover, we can see the idler arm constantly adjusting
one direction, then the other. If we reach in and hold that
arm still, the engine runs smoothly and constant. The previous
owner (who is the original owner as well) said that the
engine did that from day one. What could be causing that?
We checked the fuel line and fuel filter and it looks clean,
though never has been replaced. We never opened the engine
carbureter area nor adjusted the idle screws or anything like that.
The battery is good. Of course the amp meter shows the battery
charging at 5amp at max rev and a little less at minimum rev.
We just replaced the solenoid which went bad, and had the
ignition switch checked - both are good. The revving up and
down though is not related to that.
We are in the upper midwest. The oil is drained annually and
the battery is pulled and kept indoors during the winter.
AnswerHi Jim
We come across this problem here in the south too. Here are some things to try. Check your gas cap to see if it is venting properly. Also a good complete cleaning of the carb, use a higher grade of gasoline. Also if this is an overhead valve engine, make sure your valve clearances are in spec. Hope this helps.
