Re: 90hp force 1990 sluggish???
Ok! First, you have a black flywheel so put a small amount of white paint on the marks to make them more visible.
Next, while stopped, set the engine in neutral. Move the low speed stop screw to about the middle of its length. This is the screw on the bottom of the tower that bears against the block when at idle. Do not re-lock the nut yet
Check the throttle advance cam. If it has two closely spaced marks, the throttle roller should be between them. If it has one line on it, the throttle roller should be on the line. If it is not, disconnect the link connecting it to the tower and adjust the length of the link so the roller is on the line. The throttle roller is on an eccentric screw. Loosen the nut slightly and turn the roller to the point where it just touches the cam. Re-tighten the nut.
Remove the air box from the carbs. Push the throttle to full open and while holding open the chokes, look into the carbs. See if the butterflies are equally open and horizontal. see below. A very slight bit off horiz. will not matter but they should be substantially level. If not, you must re-adjust the carb link to make them level. Now come back into neutral. If you have re-adjusted the carb link, then you must adjust the stop screw until the cam is lined up correctly with the roller. Lightly lock the idle stop screw.
Next, using a water muff, start the engine, warm it up and bring back to neutral. Check timing. If it is not 0 deg plus or minus 2, turn off the engine and reset the screw up close to the flywheel. ---Do this with the engine running and you are a candidate for the 9 finger club!----
Now take it to the water. With the engine warmed up and in forward gear, the rpm should be about 700. If not, adjust the idle stop screw. With someone to help you, take the boat out and check timing at WOT. It should be 30 deg. If not, adjust it then go back down and adjust the idle stop screw. These engines used to be timed at 32 but in the 80s for a variety of reasons, Chrysler decided to reduce timing to 30. 32 won't hurt but anything more makes the engine lose power and become a candidate for melted pistons.
If you have done steps correctly, the screw up by the flywheel should be somewhere between 1/2 and 3/8 inch between the two plastic ends. The black plastic end on the trigger lever (aluminum lever under the flywheel ) should be in the outer hole if the trigger lever has two holes and it and the adjusting screw should be on the control side of the engine.
Top cylinder is #1 and timing is taken off it. If the carbs are not opening equally, remove the cam link from the tower, move the cam out of the way, and adjust the carb link bar with the carbs all shut. this will equalize them. re-attach the cam link.
Do not attempt to diconnnect the cam link at the cam; you run the risk of bending the cam.
Carbs should be initally set with the low speed needles at 1 1/4 turns open from lightly seated. with the engine warmed up and at idle, turn each needle in 1/8 turn at a time and let the engine respond. RPM will increas with each adjustment then drop off. Note this point. Now adjust the opposite way. The engine will break up and attempt to die rich. note this point. Set all three needles midway between the two points. However, under no circumstances go leaner than 3/4 turn out. Go out on the water and quickly open the throttle fully. If the engine goes lean and almost dies then recovers and accelerates, it is too lean. open the needles 1/8 turn at a time until smooth acceleration it acheived. If the engine stumbles and bumbles then clears itself and picks up it is too rich. adjust low speed needles. Again DO NOT SET LEANER THAN 3/4TURN. To do so invites melted pistons. Explanation: The low speed circuit on these carbs is always drawing fuel because it is always exposed to manifold vacuum. The high speed jet ie sized to compensate for this at WOT. so if you set the low speed needles too lean, at WOT the engine will have detonation. It happens very quickly and by the time you hear it, it is too late.
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