Question-------------------------
Followup To
Question -
I recently had to install a new ignition on my 1999 Lawnboy SilverPro lawnmower. The mower ran fine for a short time after that but recently it has started to backfire a lot. Was there something that I could have changed/affected when I changed out the ignition module ? As a side note, the throttle has changed somewhat also in that it needs to be almost totally closed for the engine to run smoothly.
Thanks,
Jim
Answer -
Hi Jim,
When changing the ignition, the timing may have gotten changed. The only other common cause of backfiring is a leaking valve. (If your engine is a 4 stroke.) The throttle position is probably due to the bigger problem.
Do a compression test and think about or visually check the new ignition module for something that might have changed the timing.
Let me know how you make out.
Michael
Thanks for getting back to me Michael. The engine is a two stroke. I haven't been able to find any information on timing the engine. Any tips would be appreciated. One additional thing I did at the begining of the mowing season was clean the exhaust port. Could that have done any thing (I ask only because you nmentioned a leaking valve.
AnswerHi Jim,
Since a 2 stroke would have no conventional valves we need to look elsewhere. Cleaning the exhaust port shouldn't have caused a problem as long as the port wasn't damaged. Some ignition coils have slots that allow adjustment from side to side which is how the timing is set. A degree wheel, mounted on the crankshaft, is used to co-ordinate the coil with the piston. If your coil has no slots and can only be installed in one position then the timing is probably okay. If the backfiring is from the exhaust, there may be some damage to the cylinder or piston allowing leaking in that area. If it is from the intake, check for the presence of a faulty reed valve between the carb and engine.
Keep me posted on your progress.
Michael
