# Sears st12 tecumseh hh120 has me stumped



## Alm200 (Apr 5, 2013)

Hello all im new here and am impressed by the amount of knowledge shared here so i decided to sign up heres the deal i got a 70 something i think 74 sears st 12 with the cast iron 12hp tecumseh my problem is when i turn it over it will spit gas (when choke is on) and pop and backfire out the carb and puff smoke from exhaust valve timing is correct valves seat well and the seats look fantastic nice and shiny and smooth has good compression new carb air gap for ssi has been set fire is strong and bright blue flywheel key is not sheared i cant find any reason for this motor not to run the whole time iv had it i got it to start and run once then had to shut it off cause i had shroud loose and it started rubbing flywheel and havnt got it to start since it makes no sense valve timing is right ignition air gap is right flywheel key is good valves and seats are good piston has lil to no play cam is in good shape lifters look good i mean im a well seasoned mechanic and im stumped itsgot fuel fire and compression and wont run just spit and pop out of carb like i said it ran once intake valve has a lil to much clearance .010 just moves around and another thing when it did start the key switch knocked the fire out of me or if your turning it over and your holding key and touching motor it will knock the fire out of you but just figured a wire was touching somewhere but anyway can someone please tell me whats wrong with this thing lol thanks!!!


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## stickerpicker (Sep 16, 2003)

I tend to fix what I know is wrong first and sometimes other things just fall into place. So in your case we're pretty sure it shouldn't be knocking fire out of you so I'd probably solve that problem first even though it may seem a moot point.


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## Alm200 (Apr 5, 2013)

I agree i actually just solved that problem i had a stator wire bare touching the frame now no more shock but still no start


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## Mickey (Aug 14, 2010)

If memory serves me right, that engine has 2 pins sticking out of the flywheel that controls timing. The pin that passes under the ign module first should have a larger gap than the second pin. At slower speeds this first pin does nothing but as engine speed increases, the first pin triggers the timing. If the first pin is too close it will cause the timing to fire too early and possibly engine won't start.


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## Alm200 (Apr 5, 2013)

That may be the problem the first pin that passes is short and the second pin hat passes is long maybe they were put in wrong?


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## Alm200 (Apr 5, 2013)

But then again the first pin that passes is pretty short second is twice as long well almost


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## ftorleans1 (Jul 12, 2009)

I had a similar problem with my Tecumseh equipped 14/6. Sounds like too short of a gap with the first pin on the ignition. Mine was firing too late. Even with ignition points experiance, the solid state set-up can play with your mind if not careful.


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