20 Most Recent kawasaki Fh641v 21hp 21 Hp Riding Lawn Mower Engine () - Page 9 Questions & Answers

IS IT GAS OR ELECT?MAKE SURE PROPER FUEL OIL MIXS IS CORRECT//CHANGE OR CLEAN SPRK PLUG WITH SMALL WIRE BRUSH,CAREFULL NOT TO PUSH TOO HARD DOWN CAUSEING SPRK PLUG GAP TO CLOSE!!IF ELECT CHECK ELECT CORD MIGHT HAVE BURNED OUT WIRES INSIDE PLUG,OR SWICH MIGHT HAVE WORN OFF INSIDE CONNECTION..

Bit late to help the owner of this question and yes it could be a carbie issue but also check the idle speed. If it has dropped out of calibration and is idling too low it will start then stop. Try starting with some throttle, keep it running if you can until it warms up then let the throttle go back to idle. If it stops check to see if opening the idle screw solves it.

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If the unit runs normally after it starts it is probably a defective coil that isnt changing timing relative to crank speed. It is running advanced even at slow speeds and that is the backfire. You could also have a slightly bent flywheel key. This is what sets the primary timing so it is always a good idea to check it when you have the engine cover off!

Might be Coil Breaking down under heat. Not sure best way to diagnose other the cross your fingers and buy a new coil. Sounds like you did everything you could do Fuel -wise.

We had issues in the UK with issues like this, they would blacken and soot up the plugs and start to run on on cylinder, there was an internally vented carb rather than the externally vented carb to cure this.

Well yes and yes. It is engine oil but it is synthetic. That is what many smaller hydro units use.