1988 100hp mercury spark plugs

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scotty8882003

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Does anyone know the spark plug number for this motor? The one that are in are flat and don’t look like a traditional spark plug. When I look it up it’s giving me the traditional style . Was hoping someone might be able to get me a number
 
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brodmann

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My Google search says NGK BP8H-N, which is a "standart" lookin plug. Those plugs that are flat were used a lot in outboards also. I've never tried them. What's wrong with the motor?
 
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scotty8882003

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brodmann said:
My Google search says NGK BP8H-N, which is a "standart" lookin plug. Those plugs that are flat were used a lot in outboards also. I've never tried them. What's wrong with the motor?
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Well It wouldn’t start so I took the bottom plug out and it started on three cylinders and gas was coming that cylinder hole. So I tested the e for her valve and it being was coming out at first and then went back and tested it again and then it wa ls flowing fuel. Still cooks t get it to start after with all four plugs in so I swapped the #4 plug for #3 plug and it’s been running great ever since. Think I might have had and obstruction and a foiled plug. Just want to make sure I’m getting the correct plugs. I noticed it called for a traditional plug and not the flat ones. So not sure which way I should go
 
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brodmann

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I can't understand most of this, but sounds like plugs would be a good place to start.
 
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Chris1956

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The Crowleymarine site lists 4 spark plugs Champ L76V which is a surface gap plug, NGK BUZHW (NLA), also surface gap, NGK BP8HN-10 and NGK BPZ8HN (NLA) likely conventional plugs.

So it looks like you have a choice of the Champion surface gap plug or an NGK Traditional plug. The L76V plug was used on many, many motors in the 70s and 80s. I run a surface gap plug in my '93 V6.
 
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racerone

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You are aware that this motor only runs on the top 2 cylinders at idle??----Bottom 2 carburetors start adding fuel to #3 and #4 once engine is at 1800 RPM.
 
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Dave1027

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The factory recommended spark plug for that motor is NGK BUHW which is a flat gapless style. At one point Mercury was recommending changing to a regular gapped automotive type plug. I tried them and found the engine did not have the same holeshot and went back to the BUHW's. Maybe the gapped plugs work better for trolling?
 
flyingscott

flyingscott

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You have a fuel issue. There should be no fuel in the bottom 2 cylinders for starting. The was a service bulletin for those motors. So the ones you gap should work fine. A spark plug should not cause hole shot issues.
 
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scotty8882003

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flyingscott said:
You have a fuel issue. There should be no fuel in the bottom 2 cylinders for starting. The was a service bulletin for those motors. So the ones you gap should work fine. A spark plug should not cause hole shot issues.
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Would the enricher valve cause the fuel to be in the bottom cylinder like that ?
 
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scotty8882003

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flyingscott said:
You have a fuel issue. There should be no fuel in the bottom 2 cylinders for starting. The was a service bulletin for those motors. So the ones you gap should work fine. A spark plug should not cause hole shot issues.
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I did swap out the bottom plug with the #3. And maybe the enricher valve was stuck or something stuck in it because it didn’t shoot any gas through it at first and then I finally got it to . Once did that and swapped the plugs out it’s been running fine. Just wondering if the enricher valve would cause the fuel to be in the bottom cylinder like that
 
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Chris1956

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A lot of 2 cycle motors use the crankcase pulses to drive the fuel pump. If the fuel pump diaphragm leaks, raw fuel gets into the crankcase, and eventually thru the cylinder out the exhaust port.
 
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Dave1027

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flyingscott said:
You have a fuel issue. There should be no fuel in the bottom 2 cylinders for starting. The was a service bulletin for those motors. So the ones you gap should work fine. A spark plug should not cause hole shot issues.
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I would agree there should be no difference in holeshot but there was. The gapped ones just did not hit as hard. No doubt about it. Not sure why.

Also, the enrichner sends gas to all four cylinders for starting on this motor.
 
flyingscott

flyingscott

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Dave1027 said:
I would agree there should be no difference in holeshot but there was. The gapped ones just did not hit as hard. No doubt about it. Not sure why.

Also, the enrichner sends gas to all four cylinders for starting on this motor.
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No it doesnt. There are accelerator pumps on the bottom 2 carbs that can leak.
 
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