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Merc Model 40 4 hp

K

Ky Howard

Contributing Member
I am resurrecting a Model 40 4 hp . When I turn the throttle handle to wide open, the plastic arm that attaches to the butterfly only opens it about 25%. The timing advance mechanism seems to run out of travel and the arm that rides the throttle cam never reaches the highest part of the ramp, which would be WOT. That cannot be right correct?
 
Last edited:
Ky Howard said:
BTW, its a 1974 SN 3767948
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i just checked a 1973, 1980 and 1985 4 and 4.5's I have in stock and all have the same throttle linkage so yours should be the same. It appears that the throttle pick up is adjustable and the throttle lever is slotted to allow for this adjustment. The screw may be loose and the follower may have pushed away from the cam which may keep it from opening the throttle up all the way. I could send you pics of what the throttle "should" look like if that will help. I can check if there is anything in 1966-1974 Master Service Manual about this adjustment later today. Also these engines have no neutral rev limiter so in gear or neutral they will open wide open regardless.
 
"the throttle pick up is adjustable and the throttle lever is slotted to allow for this adjustment. The screw may be loose and the follower may have pushed away from the cam which may keep it from opening the throttle up all the way." I see the slot and the pick up is forward as far as possible. It shows in the bottom picture.
Re: Pictures 2.jpgThis one shows where the follower is when the tiller is at full throttle. Still a long way to get the butterfly fully open.
4.jpg This one shows how far the follower (black thing) is from the cam when I move it to wide open. You can see a little of the slot under the adjustment screw. The cam ramp has a little dip right at the end (WOT) but the follower never even goes close.
 
Something isn't right here (obviously) the cam is not in the correct position, remove the phase maker magneto plate, flip it over and see if there is another set of mounting holes for that cam. I looked at my engines and really can't see under there but the cam position is different and none of them have that notch at the end cam.
 
fitz73222 said:
Something isn't right here (obviously) the cam is not in the correct position, remove the phase maker magneto plate, flip it over and see if there is another set of mounting holes for that cam. I looked at my engines and really can't see under there but the cam position is different and none of them have that notch at the end cam.
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`Yes, that's kind of the conclusion I was approaching. I will take it apart and see if I can flip it. BTW, your info is well appreciated
 
As an addendum to my last reply, I bought this little motor "as is" knowingly. I've found some interesting facts that make me believe the owner may well have been in way over his head. That is: the plug wire was bad, the points were at .015 and a lawn mower plug was loosly in the plug thread. The carb was fairly clean though and it has 110 psi compression so I figured it was worth a little time to see if I can straighten it out. I love these simple little motors....
 
fitz73222 Found the problem. I'll include some picsinterferance.jpglg nut.jpgscrew.jpg The previous owner had changed a stud on the engine block under the point plate and connected it with a 1/4-20 nut that was bigger than the factory nuts. The crews that hold the piece that keeps the point plate from rising toward the flywheel interfered with that nut. Bring in Mr Grinder and problem is fixed. Thanks for your help. Now to the next project- replace the wires to the coil.
 
I wonder how many other motor owners on this forum or in the world are victims of the previous owner's repair efforts? I know I am!
 
I girl I know brought me an early 90's Evinrude 60 that was running horribly, when I popped the cowl I almost wanted to tell her to take it way, every adjustment screw was cranked in or out of sync, carbs leaking and you could tell someone had been inside them. What a mess. Managed to fix everything and get it running well. This little 4hp is a prime example. What's even more scary is that I see orange silicone sealer around the top bearing cap so the same "technician" has been inside this little guy.
 
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