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1996 40HP - Clean #1 Plug

F

FormulaGust

New member
Hi All,
I have an issue with my 40HP 4 cylinder 2 stroke Merc. I had an issue where the motor seemed to be missing a bit. I decided to swap the plugs and it was still happening. When I pulled the new plugs back out, the plug for cylinder 1 looked like it just came out of the box. I checked compression and it was about 120 across all cylinders. I checked for spark and there is plenty of that as well. What would cause this?
 
Try another plug in cylinder #1-----Plenty of spark ?----Does the spark jump a gap of 3/8" ( 1 cm ) or more on the top plug lead ?-----Perhaps an issue with the plug leads.----Perhaps look into an issue with reed valves if spark is OK.-------Love to help you here but , you need to put hands on and check your motor out.
 
That usually means it's being gas washed or water is getting in from the left side exhaust plates.

A bad plug will be gas washed, but the loss of ignition IN RUN will do that as well.

Jeff
 
Racerone - I initially tried new plugs, have swapped plugs, etc. Spark will easily jump 3/8" gap. Reed valves are tough to check on this motor because they are buried in the motor on the crank. I have hands on, thanks
Fastjeff - the plug itself is definitely good. I have swapped it with other cylinders that are firing and it fires fine in the other cylinder. I don't think it is losing ignition because when I put a timing light on the lead it is being triggered. If I pull the exhaust, is there anything specific to look for on the plate? I am very familiar and experienced with 4-stroke motors (rebuilding etc) but do not have a ton of experience with 2-strokes.
 
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