1996 Force 75HP Fuel Problem

[drobertsobx]

Hi,
I have a 1996 Force 75HP. I got back from a trip a week ago and the motor quit while I was flushing the system on the hose. If I pumped the bulb it would start again but then fail. I took the hood off and watched the see thru filter and could see it was not being pumped full so I ordered the diaphragm kit and installed this morning. When priming the bulb pumps up hard and fills the filter with gas. On the initial start all seemed fine it idles for about 3 minutes and I was about to declare it fixed but then it pumped dry again. So I pulled the pump again and double checked all parts installed correctly and all was good. I tried again all seemed fine even taking it up to 2500 the filter remained full and all seemed good then it quit. This time the filter was full of fuel so I pumped the bulb and the filter emptied immediately and it became apparent the bowl was empty so I dropped the bowl to check for dirt or a frozen float valve. There was no apparent problem the float seemed to function correctly as I lifted it up and down while pumping with the bulb. So I replaced the bowl and primed and drained a couple times to verify the float wasn't sticking and started again... This time I pulled the feed line from the filter to confirm that fuel was being pumped... and it had good pressure and fuel flow for about 3 secs then the hose went dry. I connected back to the filter and it seemed to begin pumping again but for the idle run it was the same thing... seems to work great for about 3 minutes then stops pumping. I am out of ideas as to what to check or do next.
any ideas or suggestions would be appreciated.

--Don

 

[TwoFish]

Re: 1996 Force 75HP Fuel Problem

A couple of things to look for.

Air leaking into the fuel system. Check all fuel lines for cracks and check the connections are tight. Eliminate any unnecessary joins in fuel line. Replace fuel line with E10 resistant marine grade hose if in any doubt.

The check valves in the primer bulb can swell and stick causing a blockage in the fuel line. Replace.

Debris in the fuel tank blocking the intake tube.

Low engine rpm at idle causing insufficient crankcase pressure to work the fuel pump.

 

[foodfisher]

Re: 1996 Force 75HP Fuel Problem

Obstructed fuel tank vent?

 

[drobertsobx]

Re: 1996 Force 75HP Fuel Problem

Thanks for the replies
More info and check results:
I pulled the inboard tank and cleaned thoroughly this spring and installed a new vent and fill lines.
The main connector line that feeds the pump had crusted with varnish in the past from being stored wrong. I found chips of varnish in the inlet diaphragm section of the pump during inspection. I ordered that line and the pump kit at the same time.
When I primed the system I could hear the check valves in the ball and a I just did a blow back test to confirm they are working correctly.
I also just hooked up a brand new portable tank system with all new lines (3/8) and bulb with the same result... so I don't think air infiltration is the major factor.

The line from the tank to the filter is 5/16 black 3 ply. The line from the water sep/filter to the female connection fitting are new e-10 but look to be 3/8 and again the barb connectors look to be 5/16 (the ends of the hose look really stretched over the fittings)
It idles at 1300 to 1500 +-50 connected to the water hose.

The more I am looking at the fuel lines on the motor to and from the pump... It looks like the system was designed for 5/16 line but the hoses appear to be a mix of 3/8 and 5/16 (they look to have been replaced quite a while ago with the 3/8 they do not match the other lines in appearance or size).

The main line in is 5/16 (factory replacement I installed)
Output line from pump to carb starts 3/8 from pump to the filter top (old black 2 ply) then goes to 5/16 from the filter bottom to the carb (looks to be original black 2 ply).
The crank pressure lines appear to have 5/16 barb fittings with 3/8 line stretched onto them (old black 2 ply).

Could it be a pressure issue from all the different line sizes?
I am thinking of purchasing 10' of SHIELDS SILVERADO 3000 OUTBOARD FUEL LINE 5/16 and replacing all the old black 3/8 and the newer gray e-10 3/8 lines so everything is the same size from the filter to the carbs???
It does seem to do better with higher rpm's (above 2k) or I may just be tired

 

[Frank Acampora]

Re: 1996 Force 75HP Fuel Problem

Remove the quick-connect fitting at the engine (and tank if one is there). It probably has junk behind the check ball. You can TRY depressing the ball while pumping the bulb but it probably will not clean it. Clean the fitting through the barb end and also the ball end. I believe you can remove the ball O ring and the check ball and spring will come out the front.

Bypass the water separator to test if it is clogged.

Different sized fuel lines will not cause problems and 5/16 is plenty for that engine. 3/8 is just a bit extra insurance.

 

[roscoe]

Re: 1996 Force 75HP Fuel Problem

sounds like an air leak somewhere.

At the bulb, or after the fuel pump.

I know, you think it would be leaking fuel if it was after the fuel pump, but I have seen it more than once.

 

[foodfisher]

Re: 1996 Force 75HP Fuel Problem

Doubt the line sizes had any effect. Maybe the ages,ethanol collapse. Try a portable tank, borrowed/spare, and bypass the the inboard tank.

 

[drobertsobx]

Re: 1996 Force 75HP Fuel Problem

Thanks for the replies...
I misspoke last night (long day) the smaller lines are 1/4 inside dia. over the 5/16 fittings found it printed on the hose wall.
I just pulled off all lines and inspected for cracks and cut to eliminate as much air leak as possible at the connectors. Just need to wait till 9 am so I can test again...

 

[jerryjerry05]

Re: 1996 Force 75HP Fuel Problem

You say you changed the diaphram.
Did you install the gasket behind the pump right?
Inline connectors?Replace.
Compression ok?Low comp will not operate the pump.Hope it's not the comp.J

 

[drobertsobx]

Re: 1996 Force 75HP Fuel Problem

Both gaskets and both rubbers in proper order. When I pulled the line from the top of the filter it sprayed gas under considerable pressure while it was running then continued to spray in pulses till it went dry.

 

[drobertsobx]

Re: 1996 Force 75HP Fuel Problem

Keeping my fingers crossed... I cut all the hose ends then re-attached and synched with cable clamps and it idled fine!!! I tested from 900 rpm to 2500 running a couple minutes on each change and could visibly see the fuel level moving in the filter as the float came on and off...
The plugs seem to be fouling now (Ile speed has dropped from 1380-1560 to 1100-1250).

Another question... idle air adjustment.
I gently seated the screw... then turned out 1 full turn and started the motor (has been hard starting since the fuel issue started).
Then screwed in until rpm gain (was approx 1/2 turn) then went back to 1 turn and backed out about 1/4 and it started stumbling... So I set it to split the diff at about 7/8 turn out from seat. is this close to what it should be?

 

[surfsalterpath]

..... idle air adjustment? or idle mixture screw??
1996 FORCE 75hp here & stumbled on this thread b/c it would hold idle under 1700rpms. After much trial/error adjustments sucked it up and tried 3 new REED BLOCK ( valve) ASSEMBLY & clean/rebuild carb. THAT fixed the no idle issue! BUT still trying to fix 3/4 hard & sometimes losing hard prime ball. Thoughts? Been missing Frank's inputs!!!