Backfiring

fayjim2

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Dec 31, 2010
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Hello 1972 Fiberform 165 hp 6cyl inline GM This thing starts so good, idles so good runs under low / medium/ high power setings so good. Butttttttttt when you go from idle to gently engaging forward or reverse it will backfire thru the carb. Maybe once or rapid 3/4 times then stall or transition into your desired settings. I,m no boat person just a helicopter wrench. This thing does so much right I just don,t know where to look. It set for 4 years, but once again it started right up. I,ve run at least 20 gallons of fuel thru it . Ran a can of Gumout thru it and a can of Heet also . Help a poor guy out. Thanks Jim Athol Idaho. (EDIT) THANKS
 
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fayjim2

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Dec 31, 2010
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Re: Backfiring

I guess no one has encountered a backfire from a 6 bangin GM Oh well
 

Don S

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Re: Backfiring

You don't want to gently put it in gear, that allows the shift dogs in the drive to ratchet (Not good). You need to briskly put it in gear, not hesitate or go slow. Then you get a single clunk as it engages.
If it's stalling going into gear, you need a new lower shift cable to cure that problem. I would guess when you are gently engaging into gear the shift interrupt system is causing the backfire.
 

fayjim2

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Dec 31, 2010
Messages
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Re: Backfiring

What exactly is a shift interrupt system and what does it do?? Why would that cause a backfire? Like I said I,m no boater but trying to learn. Where might this be located?/ How can a cable cause a stal?/ Confused Helicopter Mechanic Thanks Jim
 
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Re: Backfiring

What exactly is a shift interrupt system and what does it do?? Why would that cause a backfire? Like I said I,m no boater but trying to learn. Where might this be located?/ How can a cable cause a stal?/ Confused Helicopter Mechanic Thanks Jim

Many Mercruiser drives can not be shifted out of gear without some help. They use the shift interruptor, which basically stalls out the engine for a split second which makes shifting the outdrive effortless. Here is how it works:

HOW TO: How the Shift Interrupt system works
http://forums.iboats.com/showthread.php?p=1930449#post1930449
 
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