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Garden Tractors Discussion Forum

8 Hp. Tecumseh snowking backfires

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49 Studie

12-27-2010 18:53:19
66.103.165.129



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8 hp.tecumseh runs rough,pops and backfires at high idle,runs fair under load,cleaned carb and fuel system several times.Any advice?Float setting wrong?Checked for intake leaks,comprssion okay.Thanks for any advice.




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jdemaris

12-28-2010 13:45:36
67.142.130.38



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 Re: 8 Hp. Tecumseh snowking backfires in reply to 49 Studie, 12-27-2010 18:53:19  
Weak spark, retarded ignition timing, and a lean mixture can all give those symptoms. Since the engine is fairly simple, it usually make sense to pull the carb apart, yank the flywheel off, and pull the head, i.e. check everything.

With the carb, the fuel seat can fall out (very common). Nothing holds it in but a tight fit. Also the main jet-adjuster tends to get full for crud. Just remove it with a 7/16" wrench and eye-ball it. Jiggle the float and make sure it's empty aslo.

Tecumseh (R.E. Pehlon) aftermarket condensors are often crap. So, it's imperitive to check the condensor (for short, for capacitance, and for holding a charge). Make sure no wires were left hanging out and got cut by the flwheel (also common). After setting the point gap, check when timing is taking place and adjust the stator plate if needed.

You mentioned the possbility of a valve sticking. Yes, it's possible and also very easy to check. Sticking exhaust valves are more common with Kohlers, burnt ex-valves more common in Tecumsehs, and loose exhaust seats in Briggs. Just pop the head off and look at the valve face - and check how tight it is. Taking a head off and on is a ten minute job and a new head gasket is rarely needed.

When we used to take in these things for repair, diagnosis of one particular problem was rarely worth the bother. That mainly because the engines are so simple, you can pull apart and check all the systems pretty quick.

A sticking exhaust valve will not sound the same as when an engine has weak spark, late spark, and/or a lean mixture - but the difference can be a subtle one.

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B-maniac

12-28-2010 07:34:49
207.241.137.116



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 Re: 8 Hp. Tecumseh snowking backfires in reply to 49 Studie, 12-27-2010 18:53:19  
what others said and also... A lot of these engines had two small square magnets epoxyed to the inside of the flywheel which when passed by the coil made the power for the spark. These have a tendancy to rust loose and move around. Don't know if this would change timing because the points still release the spark energy but it would cause problems. Most older engines had the magnet made right into the flywheel but not these. More than likely bad plug or lean mixture.

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49 Studie

12-28-2010 06:57:27
66.103.165.70



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 Re: 8 Hp. Tecumseh snowking backfires in reply to 49 Studie, 12-27-2010 18:53:19  
Thanks for the input,it is a older engine with brass float and adjustable jets,mostly seems to run lean at high idle,will run better when first started.Any possibility of a valve warping as it warms up?Thanks again.



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joe csuti

12-28-2010 13:33:40
70.111.203.15



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 Re: 8 Hp. Tecumseh snowking backfires in reply to 49 Studie, 12-28-2010 06:57:27  
Might also try re-torqueing head bolts or replaceing head gasket,same may start to leak when eng gets hot.If valve warped it would be a problem at all speeds,if eng getting tired & burning oil a more probable cause of problem would be carbon on valve stems causeing valves to stick at low speed,worn valve guides,carbon buildup on valve seat or low compression when eng gets hot due to worn cyl/rings.

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joe csuti

12-28-2010 02:17:58
70.111.203.15



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 Re: 8 Hp. Tecumseh snowking backfires in reply to 49 Studie, 12-27-2010 18:53:19  
If eng has a fixed hi speed jet,the most common cause of problem would be dirt/varnish in main jet & low speed/idle passages of carb body,these carbs normally run lean,the slighest restriction in passages will cause fuel mixture to go lean,also if you haven't done so already,install a new spark plug,you may just have a plug going bad.Other possible cause's,carbon on valve stems causeing valves to stick,carbon buildup on valve face/valve seat,problem in ign module,flywheel key bent,changeing ign timing.

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t.r.k.

12-27-2010 19:37:12
205.188.116.79



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 Re: 8 Hp. Tecumseh snowking backfires in reply to 49 Studie, 12-27-2010 18:53:19  
Check valve adjustment. Intake may not be closing completely before spark.



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