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1988 Mercury 25hp stalling at idle

Crowens

New member
I have a 1988 mercury 25 hp 2 stroke that is stalling at idle rpms. When I first start the motor it will idle fine. When I throttle it up, it runs fine at high rpms but when I try to go back into idle it starts to bog down and makes a "knocking" noise. I can shut it down and let it sit for a while and come back and the motor will crank up and idle fine until the throttle is increase and the problem returns. Any help would be great. Thanks.
 
Have you rebuilt the carb/s and if so did you set the float/s correctly? Check the mixture, smell the exhaust when bogging down, does it smell rich or nothing?
 
Then it's probably getting too much fuel. Replace the fuel pump diaphragm as maintenance and see what happens.
 
Everything racerone said and i will add do a compression test. If you rebuild the carb make sure you get the complete gasket set including the primer diaphragm. The primer is the main culprit for flooding in those motors. Make sure you check the ball and spring assembly, the ball can get pushed into the spring and cause it to flood.
 
Update on the motor: did a complete carb rebuilt and clean out. Motor is still acting up, will start fine and idle fine but starts to run rough upon acceleration and will no longer go back into idle after that. Checked timing on both cylinders and I am getting fire to both cylinders when I should. Did a compression test and it was 150 psi in one and 130 psi in the other. Would this uneven compression be the cause of the motor running rough at higher rpms and bogging down?
 
I doubt your compression is that high. Do you have service manual? Is this a tiller model? Did you service the primer assembly including ball and spring? What is your low speed screw set at? Initial adjustment should be 1.5 turns out from lightly seated . That will get you started and find the after warm. Get a manual for the link and sync.
 
I doubt your compression is that high. Do you have service manual? Is this a tiller model? Did you service the primer assembly including ball and spring? What is your low speed screw set at? Initial adjustment should be 1.5 turns out from lightly seated . That will get you started and find the after warm. Get a manual for the link and sync.

I do not have a service manual and it is a tiller model. I’ve adjusted the only screw on the carb I’ve found and it will idle initially until it throttles up and starts to run rough.
 
Does anyone know the timing linkage specs or the timing specs for this model motor? Don't have the serial number with me but it is a 1988 mercury 25 hp 2 stroke.
 
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