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Discussion Forum

Poor running 18 Hp Onan B 48M

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George

10-30-2002 14:15:53




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My well used garden tractor with an 18 Horse Onan B 48 M 2 cylinder engine is running poorly. It starts good but surges, back fires and loses power. It's worse when it is warm. Thinking it was a fuel problem I overhauled the Carb, and changed the fuel filter and gas lines, & set the valves. Still no good. What now? Change the points? Reset the valves? Any Ideas? George




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randy a

11-20-2002 10:58:11




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 Re: Poor running 18 Hp Onan B 48M in reply to George, 10-30-2002 14:15:53  
had one do what you are saying once and it turned out to be a camshaft press in bearing (their thin)that had worked out.the motor would still run but with the bearing gone it screwed up the valve opening and closing.put a compression tester oneach cyl and see what u get.



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Randy Roberson

11-03-2002 19:27:43




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 Re: Poor running 18 Hp Onan B 48M in reply to George, 10-30-2002 14:15:53  
I agree with checking the valves, but also check the camshaft gears; sounds likt they may have started to strip.
Best Regards,
Randy



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Robert in W. Mi

11-01-2002 18:46:38




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 Re: Poor running 18 Hp Onan B 48M in reply to George, 10-30-2002 14:15:53  
When mine did that, it was ready for a valve job. Those Onans seem to run too hot, and then have valve problems. Hope yours is better than the few i've been around. Hope you find the problem, Robert



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