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spark plug misses????

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jpl

12-30-2006 16:16:38




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806 gas eng, misses on one cylinder but if you put the plug wire close to plug instead of on it, it fires ok.( when the spark jumps it then fires ok.)havent taken comp test yet.




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Brownie450

01-01-2007 07:18:10




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 Re: spark plug misses???? in reply to jpl, 12-30-2006 16:16:38  
Try gapping the plug .005 wider than specs call for.



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John T

12-30-2006 20:05:50




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 Re: spark plug misses???? in reply to jpl, 12-30-2006 16:16:38  
jpl, I agree with OLD n the other gents, sounds like you have a plug thats partly fouled out, try a new one bet that will cure it for a while at least.

When a plug develops a foul it has a build up of gas n oil n carbon etc on the insulator (porcelain/ceramic) which can partly conduct electricity so the plug never fires cuz that conductive current path bleeds off the coils stored energy n voltage BEFORE the voltage rises high enough as it normally does and arcs current across the open plug gap. In the normal situation the voltage across the plugs gap (since no conductive fouling material exists) ramps up until its high enough to cause a sudden current arc across the gap HOWEVER if the insulator is full of gas n oil n carbon etc as the voltage starts to ramp up the current slowly bleeds off the energy and it gets expended and the voltage never rises high enough to arc current. BUTTTTT TT when you introduce that extra wide gap like pulling the plug wire off the plug that fouling short is out of the circuit (cant bleed off the energy) so the voltage rises high enough and then POWWWWW WWW it can suddenly arc current across the gap n she fires yayyyyy yyyyy yy

NOWWWWW W theres no free lunch (you cant create or destroy energy only change its form) and when you do things like create extra wider artificial gaps in coil n plug wires what youre doing is making the coil work harder and have to rise to higher voltage n produce n waste more heat then normal. True an otherwise fouled plug can then fire buttttt t at the expense of a hotter and harder worked coil and less energy expended across the plugs gap to better ignite the fuel cuz youre wasting stored coil energy in the form of heat (less efficient coil operation).

Try hotter plugs like Old said buttttt tt if it keeps happening it could well be a broken ring or bad valve and/or low compression on that cylinder causing less efficient n complete combustion leaving more of the unspent fuel n residue on the plugs insulator n fouling it out

Ol John T and all in Indiana

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FarmallMick

12-30-2006 19:40:04




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 Re: spark plug misses???? in reply to jpl, 12-30-2006 16:16:38  
Guys,

Could there be a similar condition w/ the coil on my H? Earlier this year I noticed it was harder to start. While checking for spark @ coil it started right up. Put wire in coil & it wouldn't start. Pull wire out of coil & hold close, great spark & fired right up. I've been running this way w/out any problems ever since. Is my coil bad & if so why does it still run?

Mick



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old

12-30-2006 19:13:41




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 Re: spark plug misses???? in reply to jpl, 12-30-2006 16:16:38  
Simply saying the plug is fouled for some reason and doing hwta you do makes it jump a spark that it can't other wise because your holding it that way makes it build up more votlage. I would replace your plugs with the next type hotter or maybe 2 or 3 sizes hotter



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Randy as in Randy-IA

12-30-2006 18:47:50




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 Re: spark plug misses???? in reply to jpl, 12-30-2006 16:16:38  
What James say's is true . John T. I think is a electrical engineer and might be able to explain it better . Something about the way electricity works causes it to increase voltage or amperage or something to jump a gap . ...Randy



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Randy as in Randy-IA

12-30-2006 20:03:45




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 Re: spark plug misses???? in reply to Randy as in Randy-IA, 12-30-2006 18:47:50  
To see if it's a wire or a plug just switch the plug wires . If the miss follows the plug wire location there ya go ! If the miss stays in the same cylinder it's the plug . Good luck ! ...Randy



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GA Dave

12-30-2006 17:42:00




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 Re: spark plug misses???? in reply to jpl, 12-30-2006 16:16:38  
A guy gave me a single front tire BF Avery about 30-35 years ago he wanted out of his field. Muffler rusted away, exhaust manifold gaskets gone and engine locked down . I forgot what I used to get the engine loosened up but after getting it running it smoked like a tar kettle fouling the plugs. I cut every spark plug wire and inserted a shirt button where it would jump a gap. Took the exhaust manifold off and applied JB Weld. I used it nearly ten years for minor bush hogging and driveway scraping. It might still be running today had my son not forgot the number one rule. Check the oil, the gas will take care of itself. David.

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James Williams

12-30-2006 16:38:26




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 Re: spark plug misses???? in reply to jpl, 12-30-2006 16:16:38  
jpl,Change that plug,pulling the wire off and holding it a little away from the plug caueses it to fire hotter



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