76 merc 850 thunderbolt (idle problem)

hydrohuman

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May 21, 2006
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I just bought this motor from a friend for my cheetah. all he said it needed was the internal wiring harness so I replaced the harness. It starts and sounds good. The only problem so for is the idle runs at about 1200 rpm I tried to adjust to around 850 or so but below 1000 rpm it stumbles and try's to die. My question is do the carbs need adjustment or do they need to be rebuilt? any help would be appreciated because the manual I have is not real helpful. Thanks
 

tashasdaddy

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Re: 76 merc 850 thunderbolt (idle problem)

need more info. how long has this engine sat before you got it? has it ever had a decarb? find as much service history as you can, seeing it was a friend you got it from. search 'awakening a sleeping outboard' in e the engine faq section. welcome to i boats, i also am a disabled vet. i run a '71 1350, and a '55 15hp rude. post back what you can find out, you'll get better answers.
 

hydrohuman

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Re: 76 merc 850 thunderbolt (idle problem)

Thanks tashasdaddy I'll get ahold of him this weekend and post back.
 

hydrohuman

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Re: 76 merc 850 thunderbolt (idle problem)

update- found out its never had carbs rebuilt, It ran good last year also I took it to the local lake for a test run and it had problems idleing I put in gear. I had to feather the throttle to get it going. but after the rpm's came up it ran Ok until I tried to give it full throttle and it wanted to bog so to me it sounds like it needs carbs rebuilt. Any opinion would helpful to see if I'm going in the right direction. I've cleaned the fuel filter and there are no leaks from the carbs. Thanks
 

tashasdaddy

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Re: 76 merc 850 thunderbolt (idle problem)

sound like a carb rebuild and decarbing the engine with seafoam is in order. search carb rebuild and seafoam also decarb. good luck, it's all been said in previous post.
 

Chris1956

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Mar 25, 2004
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Re: 76 merc 850 thunderbolt (idle problem)

Hydrohuman, It is likely your carbs are the problem. Also, someone likely turned up the idle speed, so it wouldn't stall with these dirty carbs. After the carb cleaning, you chould check the timing and synchronization of the motor as well.
 

hydrohuman

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May 21, 2006
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Re: 76 merc 850 thunderbolt (idle problem)

Thanks Guys. Time to start ordering parts.
 

GA Paramedic

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May 30, 2006
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Re: 76 merc 850 thunderbolt (idle problem)

When you start looking for timing and sync... look for the post by clams. He's the man for that kind of stuff!
 

Clams Canino

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Jan 10, 2004
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2,179
Re: 76 merc 850 thunderbolt (idle problem)

Originally posted by hydrohuman:<br /> I just bought this motor from a friend for my cheetah. all he said it needed was the internal wiring harness so I replaced the harness. It starts and sounds good. The only problem so for is the idle runs at about 1200 rpm I tried to adjust to around 850 or so but below 1000 rpm it stumbles and try's to die. My question is do the carbs need adjustment or do they need to be rebuilt? any help would be appreciated because the manual I have is not real helpful. Thanks
IF you can get the idle-needles on all three carbs to work properly, THEN the carbs do not have to come apart. See my timing and sync post too.<br /><br />-W
 
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