Engine knock reasons?

[fouchis]

Engine is knocking and losing power. Backfired a couple times when trying to start. Hard to start and will not stay running without babysitting. My suspicion is something with timing, but dunno for sure.

I continually do Air leak tests. Still good!!
Piston, rings and cylinder still look fabulous (just rebuilt 30hrs ago and was running beautifully until yesterday)
went through heat cycles and proper break in
totally forgot to make a video of the noise. It's a very hard knock though.

Helpful ideas appreciated?

Chris

 

[dirtysquared]

Take a look at your reeds first. Make sure they are still there and seating properly.

The other thing that causes backfires is a sheared woodruff key. That will throw the timing off as well.

 

[fouchis]

all of that is good.

Update: I assumed the worst when it was something so simple and unexpected. Main jet in carb was clogged with gunk!! You wouldn't believe the knock it was causing.