1989 85 hp Force dies if throttled up slowly at 2100rpm

[JoeKop1]

I been fighting this problem for a couple of years. If I accelerate slowly, The engine will run good and then die at around 2100 rpm, If I go Full throttle, Most of the time it will take off with lots of power and run great above 2300 rpm. I replaced the charge coils, rebuilt the carburetors, Cleaned the fuel recovery system, substituted CDI's, Checked spark at idle, rebuilt the fuel pump, the trigger coils resistance is within tolerance, I even tried adding an electric fuel pump both inline with existing fuel pump and also feeding the carburetors directly in case it was a fuel delivery problem. It seems to get worse after the motor heats up after a while. This problem only shows up under load and not while using muffs. I'm 70 miles from nearest lake which makes troubleshooting a real pain. Also compression checked good. Would appreciate your thoughts on this
Joe

 

[lmuss53]

Float height maybe?

When you flog it it consumes the fuel in the bowl quickly and opens the needle before it can start to starve. When you try to give it the throttle slowly it consumes the fuel slowly and gets to a starvation point before the needle can open.???

I realize there is a point at which the needle opens and it should be the same place all the time. I'm thinking it could be right on the edge of being OK and needs to open just a tad sooner.

I am just thinking out loud here, but if it was mine I would flip the carbs over and bend the floats down a few degrees so the needles open a bit sooner.

It could also be a sticky needle that when the float falls quickly, opens, but when you ease the throttle on the float falls slowly, the needle hangs up and the motor starves for fuel. If you are going to pull the carbs, you might as well get the needles and seats and change them out.

 

[Jiggz]

Do a logical troubleshooting rather than trying to shoot in the dark. First, if you have not done it yet, install a clear fuel filter between the fuel pump outlet and the carbs inlet. At any given time and rpm this clear fuel filter should be at least half full. It empties, it means it is a fuel delivery problem upstream of the clear fuel filter, i.e. fuel pump, leaking fuel hose, clogged vent fuel tank, faulty check valves on primer bulb, etc.

It stays at least half full all the time, check the carbs' floats and make sure the inlet valve is not restricted. You can check this by removing the bowls on each carb. Get an extra length of fuel hose and connect it to the inlet fitting of the said carb. With float in full down position, with one hand slowly blow into the fuel hose and there should be no resistance. Slowly raise the float on the carb with the otherhand. Just slightly above horizontal position on the float, the needle valve should close and prevent you from blowing into it. Do this on the remaining carbs.

If problem persists, try running the motor without the top cover. If the problem goes away, you most likely have an exhaust leak inside the engine that is choking the engine. However, if problem persists, dismount each carb and do a visual check on the reeds.

 

[jerryjerry05]

I don't think the seats are replaceable.
​I believe they are pressed in.
​Most times they just need a good cleaning.

​There could be another problem: the tip of the needle could be rubber, it can deform and "lock" into place.
​Or the needle could be solid and the seat has an o-ring that deforms and blocks the flow.

​But from the description, the float needs adjustment??

The trigger leads can cause the problem too.
They are very tiny and can break under the shrink wrap and stop the motor.
Replace them all.