1977 merc 700, wont launch

[adam89k]

I have a current thread for loss of power I was told to adjust the idle screw so it ran a bit rich but it doesn't seem to have changed. I also adjusted the idle in fwd the way the manual said to.

Boat thundercraft wildcat II 16 feet. Motor and boat are a combo pck since new. I'm the second owner and have never had a problem till last year.
Boat goes crazy once it planes, lots of power but it will not pull a skier out of the water anymore not sure why. Throtle seems like it's either on or of no happy medium.(very sensitive)

Fuel 50:1, Cap vent is full open, plugs are new, comp check is perfect, cylinders have been looked at and are good, carbs have been done.

Any Ideas.

Previous thks to responders.

* I'm also mixing 23lts of fuel with 500ml of oil because of the age of the motor.
( the exact mixture is 23lts fuel and 460ml oil could this cause the problem?)
This boat has been in the family since new it has never had problems pulling skiers out in the past. boat is only 900 lbs. what speed should I get out of it?

 

[CharlieB]

Re: 1977 merc 700, wont launch

Adjusting the idle mixture LEAN is the WRONG way to go, with a possibility of burning a piston.

2 strokes do not have an accelerator pump to richen the mixture for accelerating the motor. Idle mixtures MUST BE set slightly fat to compensate for this.

Most manuals clearly state that idle mixture should be adjust running, in FORWARD gear, adjust mixture very slowly to the best/highest idle speed.

Once set then the engine should pull strong and steady when the throttle is opened fully. If any hesitation of throttle bog then fatten each idle mixture screw just the width of the screw slot and test again, repeat if needed but it should take but once or twice til it runs great.

This is all assuming that your compression is acceptable, ignition system is hot, fuel pump is good, carbs are clean, and you have no other problems other than you have messed with your carbs such that they need attention. Once adjusted they should run fine for years.