backfires

I installed a header, dyno cam, and 18lbs springs. It idles perfect but one you give it throttle it hesitates and backfires. And if you give it throttle and hold it, it has uneven rpm and like its restricted. I DONT HAVE INTAKE OR BIGGER JET. AND STOCK FLYWHEEL. .....HELP

This mower is going on its third season but it's only been used for triming so she's seen light duty. Yesterday it was running fine and then just stopped, we didn't hit anything, the blades are good, had fule.... I had a chancen to look at it today, hears what I know: -good spark -getting...

I just finished rigging up a throttle mechanism for my new Tecumseh LH358XA-34 (HM100) engine. I'm pretty sure this engine was designed to go in a generator or something else that is meant to run wide open all the time because it didn't come with a throttle lever or anyway to connect a remote...

After rebuilding the engine because the piston rod broke, I just can't get this 3.5 HP tecumseh to run correctly. I even just bought a brand new carb for it. I got it to idle great. I can even give it about half throttle and it's ok. But as soon as I open it up all the way, it starts...

Running one hour and the next doesn't, im thinking the valve lash is off? any Ideas? Thanks