IH10020

Member
Redone a k-301, valves, new piston
rings & rod. It occasionally
backfires through the exhaust at
midrange. Have set points from 16 to
20 doesn't make much difference.
Thanks in advance.
 
Backfire through exhaust is usually an indication you are getting unburnt fuel through the cylinder and its exploding in the hot muffler. Or else the exhaust valve is staying open.

When you re-did the valves how did the exhaust valve seat look? I had a tractor once that was doing that and the valve seat eroded at one place.

I am guessing you de carboned the head when you did the overhaul.

One other thing you may wish to try: Run a new wire from the coil to the points. I had one that ran really funky and that fixed it. I am thinking the wire was shorting through the metal mounting clips, causing the coil to fire at odd times.

Another thing is to try a different known-to-be-good condenser on it.
 
My Gravely was doing the same thing only it was maybe once few hours & would sometimes be hard starting. Found exhaust valve had carbon build up on stem near top of valve.Simple fix remove valve & clean.
 
NO need to ever muck around with a dirty, potentially oily feeler gauge that can cause premature point failure... when the factory service manual details how to set the timing/point gap.

Once you do that, we can move on to other potential causes of your backfire, which are covered in the linked manual, as well.
OFFICIAL service info
 
What kind of machine is this on? Any safety switches? Any loose connections, shorting wires, defective kill switch, any way it is intermittently loosing spark?

That is a common cause of exhaust backfire, loose and regain spark and unburned fuel ignites in the muffler.
 
Lapped the valves cleaned all carbon from head,thinking it is external in the wireing or maybe condenser,havent had time to work on it.unit is on a 127 cc with danco r-2000 loader.🚜
 

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