Mtd Yard machine Tecumseh formula 12 ohv 125 only backfiring

[wilsonjay1981]

I am trying to get the old mower running but when i crank it over i get backfire out exhaust and carb. Has good spark but wont even start with starting fluid. Valve lash has been set at top dead center to .004 I'm lost at what else to do any help would be great.

 

[mechanic mark]

First check oil level, then check spark plugs, air filter & fuel filter for replacement, always use Tecumseh OEM parts. Make sure gas is fresh not stale or cheapest grade. Post all numbers from engine data plate, thanks.

need model & serial numbers from under seat, how does air filter look?

Tecumseh Service Manuals either rebuild carburetor with kit or purchase new carburetor. Locate your engine & carburetor in manuals.

"K&T Parts House Lawn Mower Parts and Chain Saw & Trimmer Parts"

http://www.tecumsehpower.com/CustomerService/BSI.pdf

 

[wilsonjay1981]

tecumseh formula 12 ohv 125 203038B. The oil level is good the spark plug, fuel filter and fuel lines are new. It also seems to be blowing fuel out carb.

 

[bertsmobile1]

Pul, the flywheel off the mower and check the fly wheel key.
Sounds very much like a sheared key which will affect the timing of the spark but not the strength of the spark.
It is all in the manual in the previously posted link

 

[wilsonjay1981]

Thanks for all the help!! I pulled the flywheel and the key was fine. I then pulled the head to see if a valve was sticking and sure enough the exhaust valve had a big gap on one side. I thought it was bent but with a little more investigating noticed the sleeve that the valve seats in had popped up on one side. Not sure why that happened but got it back down flat and good to go now. Again thanks for all the help guys.....