I'm just breaking in my new .72 Saito 4 stroke. Sometimes it backfires and the prop nut and the stop nut both loosen up. I try to tighten them as tight as I can while trying to keep the spinner backplate aligned with the prop ( BTW, it would be nice if APC would work with spinner manufacturers to fit a spinner to their props).

Anyone else have this problem? Any suggestions on how to keep the nut from loosening?

Thanks,
Dan

Dan most of the time a 4-stroke backfires it's to lean. On break in for the first few tanks it should be so rich
it will die without the glow starter on the plug. If you don't have a tach get one. That engine should run
6,000 or less for the first 2 tanks. Then less than 8,000 for the next two. I would not run it more than
8,000 for the first 7-8 tanks of fuel. Also , what prop are you using. You should be running an APC 13*6.
let us know what you figure out. later daveo

I've just started breaking my new 72 in and it started and ran great, I have it super rich as well, Be sure you are not hydrolocking the engine with too much fuel in it, they're real tight when new. I actually loosened up the glow plug slightly on the first run up to relieve some of the compression. Take your time breaking it in, they last a lot longer that way.

Absolutely Bird...

Saito specifies no more than 4,000 rpm for the first 40 minutes of operation. Gonna have to be mighty rich to do that.

All the extra fuel/oil is unburned, and has the benefit ofproviding a surplus of oil and carrying away excess heat created by new as-yet-unmated parts working themselves together.

Also...lay off the prop for the break in. If 13-6 is the anticipated flying prop....back off to a 12-6 for break in.

Good Luck! Enjoy the engine!

'Nite