25hp still giving me fits

Nighthawk

Seaman Apprentice
Joined
Mar 24, 2007
Messages
41
When I bought this motor 2 months ago it would idle but would not accelerate. I have cleaned and rebuilt the carb , changed the plugs , replaced the fuel line and tank, all to no avail. I then took the advice I received here and did the link and sync procedure. That didnt seem to help either. When I took the boat to the lake after the link and sync I adjusted the spark advance until I got the motor to accelerate but now there is way too much advance. The motor will start and idle fine and when given throttle slowly and smoothly it will accelerate up to a point then it wants to bog down again , but before it bogs it seems to be running at severely high rpms ,I cant check the rpms because the boat doesnt have a tach . From being an auto / aircraft mechanic though , it seems I have added too much advance but when I retard the timing the motor runs even worse. I am running the correct prop according to Mercury .
Anyone have any input / ideas ? They will be greatly appreciated.
 

redjmp

Chief Petty Officer
Joined
Mar 16, 2005
Messages
536
Re: 25hp still giving me fits

Its the same procedure for all 2 strokes.
First you have to check the compression and make sure you have all cylinders within 10% worst case and at least 100 lbs. More is better like 125.
Then you have to check for good spark under load. An easy way is to clean then check the plugs after running at high revs for 10 minutes. Are they hot?
Do they have sooty deposits starting to form or are they clean with gas?
Then comes the fuel. Make sure you soak carbs overnight and use compressed air to blow out all the passages.
Finally, it comes down to link and sync. Do NOT over advance spark as this will melt your pistons quickly!
If all checks out and boat won't accelerate, then back out your idle needles 1/4 turn at a time until it does.
 

Nighthawk

Seaman Apprentice
Joined
Mar 24, 2007
Messages
41
Re: 25hp still giving me fits

Compression is 128 on both cylinders , spark plugs are clean and wet with fuel/oil mixture, carbs have been soaked and rebuilt , new fuel line , new gas tank , link and sync performed following seloc manual .
 

j_martin

Admiral
Joined
Sep 22, 2006
Messages
7,474
Re: 25hp still giving me fits

When you did the link n sync did you do the dial indicator/depth gauge thing? If you didn't the rest of the timing is invalid.

It sounds like either your fuel pump is messed up, a hose is pinched preventing fuel flow, or your timing is far off, like the flywheel is bolted together wrong.

Is this a modern motor, or are we talking points?

hope it helps
John
 

Nighthawk

Seaman Apprentice
Joined
Mar 24, 2007
Messages
41
Re: 25hp still giving me fits

this is a 1987 motor. I checked the timing with a light as described in the " how to " listed under the FAQ's . The fuel pump is integrated into the carb and all diaphrams were replaced when the carb was rebuilt. I have all but eliminated a fuel problem .The complete fuel system from tank to motor is new , squeezing the primer bulb doesnt help nor does using the enrichment circuit .The tank vent is open and working as well. When I bought the motor the seller told me it would not build any speed .
I would really like to get this resolved. The motor has good compression at 128 per cylinder and runs great at low speed but my seloc manual is vague at best when it comes to timing and sync procedures.
 
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