QuestionHiya, a bit of a conundrum.. I have serviced this machine over the last 25 years, but this year it is giving me an ulcer.
I serviced engine: new breaker set, new diaphragm, carb/tank cleaned, de-coke, new oil etc.
On dismantling the carb, the "pulsa-jet" spring and washer were the tank side of the diaphragm (I think 15-year old grandson had been having a dabble!).
On reassembly, the machine started up fine and ran reasonably well at 3/4 - full revs (for a 30-year old machine at least), but started to run very rich when at lower revs.. Adjusting the mixture screw fully in still would not stop it 8-stroking, but the engine would starve when opening up the throttle again..
I had a much more recent primer type carb/tank assy which I tried - it too ran rich (maybe fluke that the diaphragm on that is duff I guess, but they usually run rich on high revs if that is the case).
There is a fair amount of wear on the top crank bearing, which caused a high tolerance on the breaker gap. I thought maybe the 8-stroking was in fact caused by the breaker gap increasing/decreasing at lower revs causing a miss, which made the engine sound rich. I replaced the coil with a solid state unit - but no improvement...
I'm at a loss to know what to do next.. Any ideas?
AnswerMany of the older carbs warp and leak fuel where they shouldn't. We sometimes remove the fuel tubes and "true" the carb base with a micro-flat stone.
Briggs also has a kit with a roll pin and a teflon washer that you can install. There was a service bulletin on this repair years ago.
Check to see that the carb and tank are not warped.
Let me know what you find.
Eric
