85 Force Runs well for awhile

[heco]

I did a search to see if this question had been asked but-<br />I have an 1986 85 HP Force. To get it to start I have to have the vent screw closed down and the bulb hard. (It takes 4 minutes of cranking to get it to start with the vent open. Close the vent screw, pump the bulb, and it starts in 5 seconds). It's like it needs the pressure in the tank to start, but it wont run that way. After starting I have to get to the back of the boat to loosen the vent screw so it wont die. Motor Idles fine. Run around the lake 10-15 minutes then slow down. Idles poorly for 2 -3 minutes then stalls and wont start again , like its flooded. Vent screw still wide open. The vent screw is marked "Drain".<br /><br />We used to have a 25HP Evenrude attached to this same tank (same connector) and never loosened the vent screw. Never had a running or idle problem. Could the bigger motor need a different fuel connection? Could changing out gas tanks help with new connection. We had a reputable mechanic tune it up. Compression = 135. Runs fine for him but he didn't take it out.<br />Sum it up: It seems like it gets too much gas with the drain screw open, and not enough when it's closed based on the varying fuel demands of running fast or at idle. A few other posts had problems with an "antisyphon" valve or a too strong valve spring.<br /><br />Agitated. Thanks for any suggestions.<br />Paul

 

[The Marine Doctor]

Re: 85 Force Runs well for awhile

Check the fuel pump for a torn diaphram, and check the carbs to see if one might have a bad needle and seat.<br /><br />TMD

 

[heco]

Re: 85 Force Runs well for awhile

Thanks Doc. <br /><br />Should have mentioned I know squat about motors. Guess I figured that would be self evident from my question. I'll take it in.

 

[The Marine Doctor]

Re: 85 Force Runs well for awhile

Nah...there is no need to take it in.<br /><br />This is all simple stuff that you can do yourself.<br /><br />TMD

 

[seldont]

Re: 85 Force Runs well for awhile

Follow your fuel line up to the side of the engine and you will see a housing the fuel line attaches to and another line up to the carbs. Under this housing is your fuel pump diaphragm. Probably this just needs replaced. Even if is is not the only problem it probably has not been replaced in a long time and could use it anyway. I agree with TMD and it does sound like the same problem I had when my old 100 horse Chrysler refused to run for any length of time after starting. My 85 horse Merc did the same as well. Easy to do.

 

[backdraft]

Re: 85 Force Runs well for awhile

Heco, could be the fuel pump as others say, but first I would try another tank with a good fuel line. Use a genuine OMC or Merc squeeze bulb. Sounds like the bulb is defective with a good chance of a tired fuel pump. The older OMC fuel tanks had an automatic vent on most of them. That drain as you are calling it, is it a screw on the black fuel connection or is it actually a threaded knob on top of the gas fill cap? nevjb

 

[heco]

Re: 85 Force Runs well for awhile

Nevjb,<br /><br />There's a (black)unit on the top of the tank with the male adapter on it (about 1.5 inched square)- the fuel guage is incorporated into the same unit. There are 4 screws (one in each corner) holding the unit to the tank. One of them is marked "Drain" and has an arrow pointing to it. When I loosen it pressure releases from the tank and sometimes gas comes out and runs down the side of the tank.The female end on the gas line has two receptical holes and a silver clip. I just push until it clicks. I thought one of those was the vent, but guess not.<br /><br />Thanks for all your great suggestions. Everyone is a great help<br /><br />Paul

 

[heco]

Re: 85 Force Runs well for awhile

Nvjb<br /><br />It's not a threaded knob on top of the gas fill cap

 

[backdraft]

Re: 85 Force Runs well for awhile

Heco, that is an old tank that has been adapted . The screw that says drain is to totally drain the tank by turning it upside down. Buy a new tank , plastic is alright and put a new OMC hose. This is probably the problem you are pursueing. nevjb

 

[heco]

Re: 85 Force Runs well for awhile

Thanks - that would be great if thats it. I'll get a new tank and line. I followed the line up as suggested and found that some of the fuel line connections (at the pump and between the carbs)weren't that great and some gas was leaking. Perhaps some air was getting in also. I'll let you know how it goes.<br /><br />Paul

 

[heco]

Re: 85 Force Runs well for awhile

P.S. Not to push my luck with the advice but to get to that fuel pump diaphram do I just take off the cap (marked FILTER) or do I undo the bolts holding the pump onto the block and it's under there?<br /><br />I know I need a manual, and will get one - just thought someone would know off hand. <br /><br />New tank and hoses go in right after work.<br /><br />Thanks

 

[The Marine Doctor]

Re: 85 Force Runs well for awhile

You will have to disassemble the pump.<br /><br />TMD

 

[backdraft]

Re: 85 Force Runs well for awhile

heco, fuel leaking out is air leaking in when running. Combine that with a tired pump, and she will not run properly especially at high speed. The fuel pump is easy to take apart. Remove the outer plastic piece , then the plate wherethe diaphram is located. Place new rubber dia. on ,put back the plate and the {usually }black cover after cleaning the screen. Finger tight only on that outer cap. Otherwise it cracks. nevjb