70 hp force outboards 91,93

[bandgdavis2000@yahoo.com]

I have twin 70hp force outboards.The 93 is actually a mercury-force. However, most parts are interchangable. After 3 stators in 94-95 the 93 runs great. My problem is with the 91.After 10+ years of no problems I,m having power loss. Both motors run off the same fuel tank. I decarbon once a year (50 hr). And I flush every trip.<br />Compression 120-130<br />Factory recommended champion plugs. (Heavy boat)<br />WOT 5400 5600 rpm<br />87 octane with Penzoil <br />It all started last season. The motor started to loose power and shut off but restarted. Found it wasn't firing on one of the cylinders. We replaced the switchbox and trigger. It ran better however after about an hour of running at 4200 RPMs it would start to loose power but seemed to run fine about 3500 RPMs. Checked fuel system , new fuel pump and it ran a bit better. At the end of this season it started the same problems again. As soon as we see the problem you can slow it down to about 3500 RPMs and the motor runs fine. The boat is too large to trailer to a mechanic and it is difficult to troubleshoot because the motor seems to run fine for the first half hour or so. We are always underway in open water when the problem reappears making it difficult to troubleshoot. I've done the obvious things, checked the choke, wire connections, fuel system and talked to the local mechanics. Does anyone have any ideas?

 

[steelespike]

Re: 70 hp force outboards 91,93

Bart, Have you tried choking the motor a little when it fades or try squeezing the primer bulb?<br />The clue may be in the time span.Possibly as the fuel gets lower in the tank that motor cant draw it out.Maybe try toping it up at that time and<br />see what the reaction is.<br /> Ive heard that the pulse port for the fuel pump<br /> can become restricted.<br /> Have you tried a known good portable tank?<br /> Some would say that by running 2 Forces you<br />have at least doubled your troubles.<br /> And probably tripled over 2 J/E/M motors.<br /> At any rate Good luck.

 

[bandgdavis2000@yahoo.com]

Re: 70 hp force outboards 91,93

Hello and thanks,<br /> Yes Have eliminated the choke. Been there done that. Also have run on seperate tank. The other motor makes no effect on the motor in question either (changing throttle speed). Reading the past entries here at this site I even put in a electric fuel pump. It may have helped a wee bit.<br />I also bought a new fuel pump. Maybe It's a weird eletrical problem. thanks spike

 

[hondon]

Re: 70 hp force outboards 91,93

A quicky is to take it out at night and run it with the cover off and look for any ignition arcing.

 

[OBJ]

Re: 70 hp force outboards 91,93

Bart...Ran across a similar problem couple years ago. Drove me batty for a while. Tried everything and then some. Finally I started checking carb bowls and in the last one I checked, there were three, I found a piece of core plug. Very small but big enough. What was happening was that the piece of core plug would get up against the high speed jet and partially block the flow of fuel to the carb. The rig ran well in smooth water but when it would hit wakes or rough water, the core piece would start moving around in the bowl and finally get caught against the high speed jet. Course this would slow the engine revs down. The bowls maybe something to check.<br /><br />Jim

 

[bandgdavis2000@yahoo.com]

Re: 70 hp force outboards 91,93

Thanks you guys for giving me something to think about. I could swap carbs again since I have twins. I did this at first and found the trigger problem. However the stators are different I couldn't swap those. As for running at night I dunno it takes up to a hour to go T/U sometimes.<br />I gave up the night crossings before I reached 30.<br />Tankers freightors Tug and crap. Thanks bart

 

[Hooty]

Re: 70 hp force outboards 91,93

What OutboardJim said has a lot of merit. Before swapping carbs though, take a spray bottle of premix and when you start loosing the engine, give the carbs a shot of fuel. If it's a carb plugging up, when you hit that carb with the spray, it should pick back up.<br /><br />g'luck & c/6<br /><br />Hooty

 

[bandgdavis2000@yahoo.com]

Re: 70 hp force outboards 91,93

Hey everybody thanks for the great input. That's a wonderful idea to shoot some pre-mix in there Hooty.