Hi Rich, I have the same problem except it backfires on stopping when the ignition cut out works. I think this maybe because it revs up when going through the start position. Did you ever find out what the issue was?
It's normal on most Powertorque Victas to rev higher again as you go through the start position before stopping it. That's to help it start easier in the start position.
I have had the problem of the motor backfiring as you shut it down. It turned out to be the decompression valve. After replacing it with a used one the problem went away.
Ahh, if only victa had kept producing the thumblatch catcher series, they would be in better shape today!
Thanks for that info. My decompression valve tested ok but it did seem slow in operation. Might be worth a try to try a different one as see if there is a difference.
Just to add to your discussion, other things which reduce the idle are the following:
1. Reduce air leak after the venturi (manifold and crankcase o'rings and crankcase oil seal) 2. Non functioning governor or vacuum control (connection between rear of carby and bottom of the engine) 3. Poppet valve setting (the highest step is the lowest idle or change with later model black poppet valve) 4. Adding cam brass spacers. 5. Changing the return spring with a softer one (less gram e.g. 150gm. The stiffer the higher the revs) 6. Changing the jet with lower flow rate in ml/min (mainly the two rings)
A simple way to find out if you have an air leak is to spray some Nulon SYB around the place. If all of a sudden the rev's drop when you spray in a specific location, you know that there's an air leak there
Remember to try to diagnose before replacing, saves money and grief
