89 Force 85 HP Falls Flat after 30 Seconds

[ima.riverrat]

Hello Fellow Boaters,

Well I finally got my boat in today after tinkering with several motors. The current one on the 17' fish/ski is a '89 Force 85hp.
Runs fine in the drive way in a barrel... Fires right up, first rotation she gets going. Even after sitting for several days she will fire right up without pumping primmer bulb. Here is the problem, dropped her in the water hole shot good, ran to top end good, ran for about 30 sec the sputter... sputter... choke... choke... I backed off on throttle, and slow down for less than a minute and hit it again, she takes off for about 30 sec then same thing, sputter... sputter... back off and try again, same thing. Half throttle OK Idle OK. WOT not OK. Brought her to the dock and tied off... Now the Motor has good compression, good spark, ohm test coils, ok, New water is pump working just fine...I have a feeling it could be the fuel pump? I hope its not electrical, Please Help!

One other Question, I swapped this motor onto this boat now my tach doesn't work??

Thanks, Rich

Livin' in a Van Down by the River!

 

[scottmm73]

Re: 89 Force 85 HP Falls Flat after 30 Seconds

Sounds like the fuel pump diaphragm may be shot. The shot diaphragm can't keep up with the amount of fuel required to run at WOT. You retard the throttle and the motor requires less fuel, carb bowls are able to fill up again then you go WOT, the motor empties the bowls starts to sputter and choke. Take it out again run WOT, when it sputters and chokes, squeeze the fuel primer bulb. Is it soft, does the motor stop sputtering and choking? If so, confirmed bad diaphragm.

 

[foodfisher]

Re: 89 Force 85 HP Falls Flat after 30 Seconds

X2^^

 

[Frank Acampora]

Re: 89 Force 85 HP Falls Flat after 30 Seconds

Or, a partial clog in the quick-connect fittings if you have them, or partial clogging of the fuel inlet screen at the fuel pump. You need to diagnose why the engine is running out of fuel. It could be multiple causes.

 

[ferdly1]

Re: 89 Force 85 HP Falls Flat after 30 Seconds

I had a weird problem similar to yours. Crank up take off then boat would die. Bulb would go flat pump it up go a little further. Changed fuel line with new bulb mainly because it was so old. No luck. Rebuilt fuel pump. Still no luck . So I took some clear plastic tubing and hooked from fuel inlet to fuel pump. Then I hooked from pump to carburetor. I wanted to see what was happening. Cranked it up hauled butt and engine died. I noticed fuel going to pump was full of air. Since I had put in new line and bulb, I pulled the quick disconnect connection off the fuel tank. Low and behold some insect had built a coccoon inside there. No idea what kind of insect. Always thought all insects would die when exposed to gas. That fixed my problem. Oh yea, I even had put fresh fuel in tank to eliminate that as a problem. The plastic line I bought at tractor supply and it was compatable with gasoline however I did hook the old line back up afterwards.

 

[ima.riverrat]

Re: 89 Force 85 HP Falls Flat after 30 Seconds

foodfisher what does x2 mean?

 

[foodfisher]

Re: 89 Force 85 HP Falls Flat after 30 Seconds

X2= I agree, ditto, etc. ^^ points to previous poster.

 

[ima.riverrat]

Re: 89 Force 85 HP Falls Flat after 30 Seconds

Sounds like the fuel pump diaphragm may be shot. The shot diaphragm can't keep up with the amount of fuel required to run at WOT. You retard the throttle and the motor requires less fuel, carb bowls are able to fill up again then you go WOT, the motor empties the bowls starts to sputter and choke. Take it out again run WOT, when it sputters and chokes, squeeze the fuel primer bulb. Is it soft, does the motor stop sputtering and choking? If so, confirmed bad diaphragm.

OK...Replaced the diaphram/fuel pump, same thing... Actually now when it cuts out at WOT its more of a immediate drop!

 

[jerryjerry05]

Re: 89 Force 85 HP Falls Flat after 30 Seconds

Pump ok? Then the hose or squeezie maybe the quick disconects?
Compression test? #2 cylinder runs the pump.
The gasket in place behind the pump.
The pickup in the tank?
Floats sticking?The needle/seat stuck?

 

[scottmm73]

Re: 89 Force 85 HP Falls Flat after 30 Seconds

OK...Replaced the diaphram/fuel pump, same thing... Actually now when it cuts out at WOT its more of a immediate drop!

Did you confirm that it was the diaphragm? (i.e. squeeze the bulb at WOT) If so, as Jerry says.

 

[ima.riverrat]

Re: 89 Force 85 HP Falls Flat after 30 Seconds

OK... The fuel line (Mercury) actually separated inside!! So the inside of the line looked like a clogged artery! I have NEVER seen that!

Compression on all 3 at 120, New fuel pump diaphragm, new plugs, coils good, new fuel line and primer bulb. Now the after 30 seconds falling flat problem is gone! Now it appears to starve after 2 min at WOT, then bog down when I back off on throttle to an idle its ok then I can hole shot again. there seems to be a slight miss? When I WOT from a stop as it builds she has a miss, or like a "pop" you can here as it ramps up, and it also there during WOT, about every three seconds.

 

[scottmm73]

Re: 89 Force 85 HP Falls Flat after 30 Seconds

Carb sync and timing? Beginning of forum post by Frank A.