Stihl 066 magnum help.

arboristdean1130

arboristdean1130

Location
Fort Covington, New York
So I bought a stihl 066 of eBay last year. It ran fine then but then sounded like bearing going in it. So I tore it apart. Cylinder was in good shape but piston had a few marks on it...The rattling sound was extremely worn clutch springs.
So I then replace the clutch, oiler, new meteor piston and cylinder. Put it back together. It started up fine good compression. But then the carb was dumping fuel and saw was back firing. So I bought a new carb.. just started it today and no more fuel being dumped but still backfires but not as bad. So when I rev it high throttle it cuts out but doesn't die. It idles awesome. I do notice gas cap leaks can hear the leak. Could that be doing it or another leak somewhere else?
 
Couple things you may check,
Fuel tank vent may be bad if you hear leaking through cap
Also usually backfiring is an ignition timing issue so check flywheel key.
I'm assuming you changed the plug.
I would recommend doing a vacuum / pressure test and figure out why old piston was marked up.
 
Had a 361 doing something similar with the back firing and but idle fine. Turns out the porcelain and electrode inside the plug was broken off wire was holding it inside the plug body. A few chips marked up the piston a bit and had some transfer but it cleaned up good .... +1 on the pressure / vac test before you get to thinking its all fixed and stuffs

Jesse
 
arboristdean1130 said:
Thanks for the feedback will check everything. . Where is a good place to get vacuum/pressure test kit from. I have found alot of high priced ones.
Click to expand...
I got my vacuum tester at Napa but it doesn't do pressure. Reasonably priced. I use my air blower and soapy water to pressure test but I am very careful not to blow anything up.
 
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