Force 120 starves for fuel above 3000-4000 rpm's

[taxpop]

Force 120 ELPT, 1997, ID OE275799. We have this on a 24' pontoon boat. It starts fine and idles ok. Will go to 3000-4000 rpms and run fine. If you give more throttle, it hesitates, chokes back and goes to slow speed. Then it will surge a little and hesitate again. I usually pull back to idle speed, give it a moment, then go back to 3000-4000 where it runs fine.

I put a new primer pump on. It never gets hard when I squeeze it up but you can see fuel flowing through the clear glass filter and it starts right up. Not sure if it is going flat when the hesitation occurs. Never tried to squeeze it while trying to run at full throttle.

The fuel lines are about 2 years old and don't show any cracks or fuel leaking anywhere. They appear tight.

There was some leakage from the front of the float bowls when motor was trimmed up. I put in new float bowl gaskets and there is no leakage when motor is running while trimmed all the way down in water. Still have slight leakage when trimmed up. Have read in this forum that this leakage is normal so guess that's not the problem.

Have been considering rebuilding fuel pump but not sure if that's the right thing. Would prefer to save the money and do it myself but am close to calling the boat mechanic. Problem is , what to do? When the grandkids are in the tube hollaring "faster, faster", I like to oblige. Very disappointing when we can't get over 3000 rpm. Will greatly appreciate any advice!! Thanks!

 

[Jiggz]

Re: Force 120 starves for fuel above 3000-4000 rpm's

There are a few reasons for fuel starvation at high speed. Improperly vented fuel tank, improperly working fuel pump, improperly set carb floats or maybe it is not even fuel related but rather improperly synch throttle valves with the throttle control (at full throttle verify the throttle valves are at horizontal, no more no less). You can replace a fuel diaphragm really very easily. No mechanic is required for such maintenance. Just make sure you take pics of the stuff while disassembling to make sure you can put it back properly. For venting fuel tanks the best way to find out is use an external plastic tanks and see if this will mitigate the speed problem.

 

[jerryjerry05]

Re: Force 120 starves for fuel above 3000-4000 rpm's

First a compression and a spark test???
Profile? Location? You might be close to someone who can help.

The pump is an easy thing to check.Easy to disasemble.
If the ball never gets hard then the pump or the ball is suspect.
The balls can be bad from the box.
An inline connector can suck air and look great doing it!!
I routenly cut them out.
Install a water/fuel seperating filter someplace between the tank and the squeezie.
Make sure the vent lines are clear and not twisted!!

 

[taxpop]

Re: Force 120 starves for fuel above 3000-4000 rpm's

Jiggz and jerryjerry05, thanks for good tips. I'm starting on them now.

 

[taxpop]

Re: Force 120 starves for fuel above 3000-4000 rpm's

Problem solved. Tightened three loose connections at fuel pump and both carburetors. Put on new primer bulb. Squeezed fuel into motor until it overflowed from carburetor with motor tilted up halfway. Bulb was hard for first time in memory.

Took it out and motor ran better but then hesitated again above 4000 rpms, which was higher than before. When this happened the brand new primer bulb was flat. I swapped the fuel line over to my spare tank while still running. Then it ran faster and better than in two years. No hesitation. Apparently at higher rpms the male fuel connector on the external tank would not allow any fuel flow. I think the three air leaks had been hurting performance because it ran about 600 rpms faster than I've ever seen before. I'm off now to buy a new connector or fuel pickup. Thank you both for your advice. Could not have found this alone. Many thanks to all the iboats contributors for their understanding of how outboards work. Think I'm going to be my own mechanic where ever possible with iboats's help.

 

[Jiggz]

Re: Force 120 starves for fuel above 3000-4000 rpm's

Pops, just a word of caution. With external tanks there is a vent screw that needs to be opened when the tank is in use. If this is close, the primer bulb will deflate and so does the plastic external tank. Just making sure you are barking on the right three. Lol.

 

[emoney]

Re: Force 120 starves for fuel above 3000-4000 rpm's

My last boat I found out what Jigg was talking about the hard way. My vent screw had tightened itself on a WOT run. As soon as I entered the channel, she died. I could start it up, idle but as soon as I "punched it", bog down and die. Only about a mile offshore, but it was getting dark and the tide was running out. To end they story, I took the cap off to look in the tank to prove to myself I had fuel, and for some reason checked the vent screw. Y'up....problem solved.