1996 Mercury 2 stroke/ 4 cyl C40ELPTO max WOT only 3000 rpm in Drive?

Montepete

Recruit
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Jun 25, 2013
Messages
4
Hello there, new user , first posting. I have a Mercury 4 cylinder/ 2 stroke 40HP 'C40ELPTO' (serial# 0G313349) that runs to maximum RPM fine when in neutral but only 3000 rpm when in drive (on a 22ft pontoon). The first outing this year the engine ran fine, second outing is when I noticed the problem. What I have done so far:

changed all four spark plugs (upper two were 'as new' , lower two had signs of carbon deposits)
replaced fuel line and primer bulb between tank (fixed 20 gallon) and engine
treated gas with 16 oz seafoam
used seperate fuel tank with fresh fuel
swapped fuel filter and fuel pump with spare parts (donor engine)
checked plug wire resistances (all very close to each other)
120 PSI cranking compression (throttle closed) all four cylinders
removed, checked and cleaned both carbs
checked choke solenoid for sticking (clamped supply line from carb bowl and disconnected wiring)

the only thing I did between first and second usage was add 2 stroke oil?? Again, runs to full engine speed ONLY when not in drive, in drive just reaches 3000 rpm?

Thanks!

Pete.
 

mgjtkt

Seaman
Joined
Apr 19, 2010
Messages
59
Re: 1996 Mercury 2 stroke/ 4 cyl C40ELPTO max WOT only 3000 rpm in Drive?

Bottom carb, the nut that holds the bowl on is the main jet. There are holes around the side of the jet that will allow trash to get in. Look at it under a magnifier and push small pieces of stranded copper wire thru the jet. You may not have to take the carb off. That's what I found with similar symptoms. Hope that works.
 

Montepete

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Joined
Jun 25, 2013
Messages
4
Re: 1996 Mercury 2 stroke/ 4 cyl C40ELPTO max WOT only 3000 rpm in Drive?

Carbs were fully inpsected and cleaned, I noticed the upper two spark plugs were wet but clean, unlike the lower two which showed miore signs of operation. Should I check for spark strength and the coils/ trigger, I did not detect any ignition ' missing' , I do not have a service manual for the correct specs.
 

Montepete

Recruit
Joined
Jun 25, 2013
Messages
4
Re: 1996 Mercury 2 stroke/ 4 cyl C40ELPTO max WOT only 3000 rpm in Drive?

Update - I checked the spark plugs, only the bottom two are firing, I swapped ignition coils over, problem stayed, I think I need to replace the ignition trigger assembly? - any other ideas appreciated!!

Pete.
 

Montepete

Recruit
Joined
Jun 25, 2013
Messages
4
Re: 1996 Mercury 2 stroke/ 4 cyl C40ELPTO max WOT only 3000 rpm in Drive?

Anyone know where I can find a wiring diagram, I've been told to swap signal wires from stator to see if issue moves, if no,t probably the switch box has failed..
 
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