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Tractor Talk Discussion Forum

Onan 18hp B48M-GA018 engine

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fletcher

06-07-2005 22:04:26




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Hello, I have a Case/Ingersoll garden tractor with a 18 hp Onan engine. The engine is hesitating/misfireing during idle and open throttle operations. This condition is noticeable from near start-up and get worse under longer operating periods. At first it would take 20 to 30 minutes for the misfireing to start, followed by back fireing. I have replaced the ignition coil with two different used coils but still have the same problem. The engine has 544 hrs on it with the original points and condenser installed. I replaced the plugs last fall when I was having this problem but I am not sure if I set the plug gap. I think maybe I can rule out an ingition coil problem. That leaves a condenser, points, or plug gap problem! If anyone has an more insight or comments on this problem, I would like to get your thoughts! Thanks, Dan

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Giles

01-16-2006 16:09:41




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 Re: Onan 18hp B48M-GA018 engine in reply to fletcher, 06-07-2005 22:04:26  
I had a simular problem with a different Tecumseh engine. The vales were to tight I set them at .010 because I had no book. Most of the stuff I've worked on is ususally between .008 and .012 If they get tighter after warm up it will get worse.
Giles



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chris sweetland

06-10-2005 19:29:55




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 Re: Onan 18hp B48M-GA018 engine in reply to fletcher, 06-07-2005 22:04:26  
had the same problem on mt bolens 1886 i put on a ground strap and it runs very well nowmake sure you have a good ground to the engine they sometimes sit on rubber mounts... hard to get a ground through them



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Big Bo

06-08-2005 09:06:36




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 Re: Onan 18hp B48M-GA018 engine in reply to fletcher, 06-07-2005 22:04:26  
I had a JD 316 with a Kholer engine that did the exact same thing. JD dealer did a valve job on it and ended the problem. I"d try the electrical route first, though. Could save you a bunch of money.



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old

06-08-2005 08:11:09




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 Re: Onan 18hp B48M-GA018 engine in reply to fletcher, 06-07-2005 22:04:26  
I'd replace the points and condenser and see what happens, cheap fix and it never hurts to replace them every once in a while any how. You could also have a problem with the carb or even if it has one the fuel pump.



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hlc

06-08-2005 04:07:37




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 Re: Onan 18hp B48M-GA018 engine in reply to fletcher, 06-07-2005 22:04:26  
I had a car once that did this and it had a bad condenser. I have see spark plugs do this. Also suspect would be a bad intake valve. This could cause gas to be sucked into the cylinder at the wrong time when the valve should be closed.



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