# 8 HP Tecumseh HM80-1556585 surges/backfires



## tdennis (May 25, 2009)

I bought a used Craftsman rear-tine roto-tiller last winter. I cranked it and ran it several times before I bought it. The owner had put a new carb and gas line on it. It crank and ran fine until a nice day when I tried to till the garden. The engine started to surge and at times back fired. I have been in the hospital a couple of times and have not had time to try it again until today. I cranked it the AM and it ran fine at idle and full speed. I started to till the garden and it starts to surge and at time backfires. It just kept doing it.

I quit tilling and brought to garage. Checked for leaking gasket around carb, everything tight, new air filter on engine. The governor linkage is free and seems to work as it should. I also loosened the gas tank cap, no change. I figured crankshaft key must be slipped so I pulled the flywheel and not a problem there. It has Solid state ignition so I assume that is probably the problem but at $50 and no return one electrical parts I am a little un-easy replacing that unless others think that might be the culprit.

Before I possibly throw away $50 for an ignition mod anyone have a thought on what it might be causing the problem. 
Thanks
Dennis


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## LowRider (Dec 23, 2008)

Gas? even if you used gas with fuel stabilizer in it from last year the gas can still go bad from being in a garage.


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## tdennis (May 25, 2009)

I can not remember for sure. It may have gas in it from my generator which had stabilizer in it. I will drain it and try fresh gas but I have used that gas in my lawn mowers (14 HP Koller and 3.5 HP Briggs) without those problems.
Dennis


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## tdennis (May 25, 2009)

I bought a new ignition module/coil and replaced the old one. I also drained the gas tank and filled with fresh gas. The engine still surges and back fires! The carb was replaced the end of last year (problem started a few weeks later). I pulled the bowl off the carb and it was full of gas and runs freely until you hold up on the float and close the needle and seat. I don't know what to try next. 

The engine has plenty of compression and this is just a wild thought could it be sticking valves? If so what should I try?
Dennis


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## LowRider (Dec 23, 2008)

i had this problem several days ago. carb was fine, i replaced the air filter, gas filter. it wouldn't hit a lick. adjusted the valves and it worked fine. give that a go and see what happens. if you valves are out of adjustment that can cause backfire, the surging may be the governor. but adjust the valves first and see if that works, also replace the gasket around the valve cover with a new one.


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## light mechanic (Jul 18, 2008)

Lowrider, is it the model that has points and condesnor, if it would be sounds like they are in need of changine them, when the coil is bad it will let the machine run some what good but at higher speeds it will start to spit and spudder makeing one think that it is in carb, hope that might help, Light Mechanic


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## LowRider (Dec 23, 2008)

to behonest i'm just giving out basic troubleshooting. i have no way to look up the model


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## Lawnmowertech (Nov 12, 2008)

normally the popping sound the backfiring normally = carb issues too much fuel or not enough or water in fuel 
it also can mean a ignition timeing issue if it has pts its possible the pts are firing way to early or to late one creating a backfire situation 



get me the model and spec # i can supply you with a link to parts list 

calvin


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## tdennis (May 25, 2009)

It is an 8 HP Tecumseh number HM80-1556585 It is not overhead valves and it had the capacitor discharge ignition which I replaced. Also replaced the crankshaft key. I thought maybe it was a sticking valve and mixed some 2 cycle oil with gas, no change so I drained that gas and put in fresh but added a little Marvel Oil. Still surges and after a little back fires through the muffler!
Dennis


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