12hp Powerbuilt engine problem.

So I just got a new murray and it has a 12hp powerbuilt motor on it. It has been sitting for a year. Soooo I took the air filter off and sprayed a little carb cleaner in it. I also cleaned the spark plug and made sure there was spark. I zaped myself lol. I thought it might have a broken rod but I put a screw driver in the spark plug hole and felt the piston moving. To make a long story short it will not fire up... A flame shot out of my exhaust pipe and started the mower on fire.. lol I crapped my pants. So any ideas what the problem is?

does it have enough compression?

make sure the flywheel key is not torn in half. if it has spark, good compression and fuel then the only other thing is timing. if the keyway for the flywheel is broken then the spark wont spark at the right time and it wont run. not too hard to replace a keyway. good luck bud!

Compression sounded good when I had the spark plug out you could feel the air blowing out of it..

how about the cam or valves. there could be some carbon build up

id say they carb could use a cleanin if it was sittin that long

https://www.youtube.com/watch?v=VG-d6cbeQsM
https://www.youtube.com/watch?v=xI4wVKyQ5Ls



Still lost lol.. Any ideas?

perhaps a timing problem? Anyone know how to fix this?

If its a timing issue, take the flywheel off and check the keyway. If it aint the flywheel key than it might be the cam wasnt put in corectly. also take the head off and make sure both valves are actually moving! the stems might have snapped. If it aint any of theses suggestions then i think its time for a new motor lol

I know for a fact the 12.5 power builts are junk - ive had 3 tractors ( recieved that way) with snapped rods.

Youll want to put the plug in, turn it over and see if itll suck air in the muffler and exhaust thru the carb - then its a snapped flywheel key - itll be 180 degree's off.

need to check compresion with a gauge to see if it has enogh sounds to me it doesent turns over to easy and with flam out carb need to check fly wheel key and make shore intake valve is closing all the way where it sat for awhile it could be sticking

Long story but I just got a killer craftsman 20hp lt1000 with a 6speed from my buddies down the road. I told my other friend who does a lot of small engine work but who wanted me to give him a working offroader that he can have the murray as long as he fixed the problem and offroaded it with me. I want him to get in to offroading and he loves offroading to but he expects a free lawnmower that runs and moves perfect.. I was like um.... you got to put some time in to it yourself..

I took the carb off and noticed the valve on the inside is not moving very far. I think that you were right it is the intake valve..

Try spraying some PB blaster in the combustion chamber and also around the valves - and let it soak. i do that for the non running clunkers i drag home , also worked in freeing up a nearly seized motor as well.

If that doesnt work- then youre looking at cracking the block open....

How far should the intake valve be moving? Just to make sure we are on the same page the intake valve is the valve you see when you take off the carb? PB that is a great idea.. I will try.. thanks