misfire on high revs

[merc man]

ok
where do i start just came back from using my boat and my 40 hp 4 cly mercury has developed a misfire at high revs /under load it's not noticeable at low revs but when you open the throttle it misfires any one out there know wher to start ? many thanks all :blue:

 

[Bosunsmate]

Re: misfire on high revs

for stsarters check your plugs.
they might show water intrusion or something else

 

[Texasmark]

Re: misfire on high revs

I was always taught plugs at high rpms.

Mark

 

[merc man]

Re: misfire on high revs

new plugs cleaned carb new fuel still misfire on high revs what about coil packs ? any ideas anyone please

 

[Texasmark]

Re: misfire on high revs

Get a helper and a battery powered timing light like you used to use when you had the old auto ignitions with points and a coil. Get her out and when she starts messing up have your friend get the TL sensor near the plug wires, don't have to touch, just near. If you are dropping a CDI the light will quit firing. Easy and cheap and "dirty". Grin

HTH,
Mark

 

[merc man]

Re: misfire on high revs

Get a helper and a battery powered timing light like you used to use when you had the old auto ignitions with points and a coil. Get her out and when she starts messing up have your friend get the TL sensor near the plug wires, don't have to touch, just near. If you are dropping a CDI the light will quit firing. Easy and cheap and "dirty". Grin

HTH,
Mark

Thanks for your help but is there any way i can test the coils ? without cranking over