Force 1991 120hp low speed problems

[afd2131]

Having a problem with a 1991 Force 120 HP. The engine seems to run great at higher speeds, however when you throttle down for say a no wake area, the engine begins to run very rough, with an almost knocking sound coming from it. The engine will begin to drop off until it almost stalls out. This is a newer problem, no adjustments have been made recently. We did have a problem with water in the fuel last year, so thinking maybe its causing this problem since fuel isn't being used as much at lower speeds. Any ideas or thoughts?

 

[foodfisher]

Fouled plugs, idle speed screw vibrated loose, clogged fuel recirculating system. Smoking more?

 

[jerryjerry05]

The idle/air screw needs to be set?
Try setting at 1 and 1/8th turn out for initial adjustment.
Then adjust in the water while warm.
Check for water(again)?
Add a water/ fuel sep. system.

 

[afd2131]

I saw that system, and Im 99.9% sure an outboard such as mine does not have a water/fuel seperator system, is it possible to install one on an older outboard like that?

 

[Frank Acampora]

First change or clean the plugs! Because of the type ignition system, fouled plugs will fire at higher RPM yet misfire at low RPM. ANY time a Force engine has trouble starting or running at low speed, the first step should be to clean or replace the plugs.

 

[jerryjerry05]

Yes you can install the water/fuel sep.

 

[Jeffromxer]

I just worked through a very similar problem with my force 75. Would run good with higher rpms but wouldn't idle or run decent at low rpm. It turned out to be a broken reed on 1 of the cylinders. If you are seeing excessive smoke when starting or when revving in neutral I would pull the reeds to inspect them. A broken reed will allow excessive fuel into the cylinders and you may even have fuel dripping from the throats of the carbs.

 

[Jiggz]

"A broken reed will allow excessive fuel into the cylinders and you may even have fuel dripping from the throats of the carbs."

Although this may seem to be an accurate symptom for a broken reed the fact is broken reed does not allow more fuel to get into the cylinder. Instead, the fuel accumulates in the crankshaft because not all of it is not pushed into the cylinder but instead blown back out the intake manifold and adapter and some out the carb throats. The heavier smoke results because a cylinder with broken reed will not scavenge exhaust properly nor will it allow the proper amount of fresh fuel-air mix in hence results in misfires. At high speed, it seems the misfiring goes away, but more likely it is masked.

As for the OP, the best course of action is to find out which cylinder is not firing or misfiring. From there, find out if it is electrical, fuel or mechanically related. You can just use the plug wire pull (quick to prevent damage to CDM) while monitoring engine speed. This should tell you which cylinder is misfiring or not firing.