(Backfire Out Of Exhaust (At Idle) Question

[boodaddy]

Hey Guys,

Just got my rebuilt engine put back together, and mounted. Started right up, but at low RPM or idle it tends to backfire a lot out of the exhaust. At higher RPM it sounds fine, and every so often a little backfire. What could be the issue?

The carb was rebuilt with a kit, and triple checked timing marks before putting the engine back together. I used a air gun for the flywheel wheel, so I believe that's all good and tight. I used a business card to gap the Magneto, so I think that is good. Plug is new. Gap is .003 for the intake, and .005 for the exhaust.

I'm not sure if the mixture screw is off or not. I started 1 1/2 turns out if I turn it counterclockwise the engine will speed up, and slow down clockwise.

Here is the Youtube link to the video I took of it running in case it helps. (Apologize for it being a little shaky.) Briggs & Stratton Rough Idle & Backfire - YouTube

Appreciate any help and advice.

 

[DaveTN]

On mixture screws, I turn counter-clockwise to enrichen it until it starts to bog down and blow black smoke. Then I slowly turn it clockwise until it picks up highest rpm. Then leave it. Sounds like it's running lean and not getting enough gas. The exhaust backfire could be from a sticking valve.