85hp yamaha problem

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yftcaptdan

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Joined
Oct 27, 2010
Messages
8
I've got an 85hp yamaha and have just redone a lot of the electrical(new relays and new pulser coil). I'm getting a shudder like a spun hub on the prop when I try to give it gas to try and plane off. It will move forward at a low rpm ok. I just put a new prop so i know its not the hub. Sometimes it will plane off fine and run great. When it does do the shudder it also will not rev in neutral. It goes into a safe mode of sorts and will rev a little then kind of sputtter like its dropped a cylinder. Will a bad neutral safety switch do this or is it a pad plug or is it a bad cylinder? I checked compression and the top cylinder is a little off from the others. Thanks for any input.
 
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jeffersondodson561

Ensign
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Oct 28, 2010
Messages
923
Re: 85hp yamaha problem

What's a little? The neutral safety switch is located in the remote control and if it was bad the motor would not even turn over. What year is it, model number?
 
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yftcaptdan

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Joined
Oct 27, 2010
Messages
8
Re: 85hp yamaha problem

I figured it out. I had a mechanic clean the pistons and cylinders (mistake, i was too busy to do myself) and the dummy put the wrong spark plugs in. He put ones rated for 150hp and up. I changed them to the right ones and now the motor runs great with no shuddering or rev problems.
 
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rodbolt

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Sep 1, 2003
Messages
20,066
Re: 85hp yamaha problem

same plug
either b8 or br8, either can be used in the c85.
 
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yftcaptdan

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Joined
Oct 27, 2010
Messages
8
Re: 85hp yamaha problem

I put b8hs10 ngx's in. there was br9hs10 ngk r in from the mechanic :mad: I noticed the washer is different and even the threads look a tiny different. I was concerned that I'd overtighten the new ones and strip the head. :eek:
 
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rodbolt

Supreme Mariner
Joined
Sep 1, 2003
Messages
20,066
Re: 85hp yamaha problem

same threads, thats not a problem just the 9 is slightly colder than the 8.
 
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