1996 115hp V4 loses rpms

[Alitak]

I'm experiencing something similiar to Kenai 52's problem with his 40hp but with my 96 115hp.

Engine started to lose RPM when at top end and problem would get worse until even at low end would bog down and die. Bulb was losing prime and so replaced fuel pump, fuels lines, checked filter...no luck. Cleaned jets in carbs and put some new plugs in...bam! ran perfect...for about 40-50 miles...then same problem at top end (4600 rpm), engine would bog down but could get her back up by pumping the bulb..but once again problem got worse. Any ideas?.. Bad ignition, oil injection, coil, plug wires?

Thanks, Matt

[Ken]

Matt,
I would check all connections from the fuel tank to the fuel filter - sounds like your motor is having trouble getting fuel from the tank.
If your tank is equipped with an anti-siphon valve, it could be sticking and not allowing enough fuel to flow. Also, make sure your tank is venting properly.
Don't think your problem is bad ignition since you can pump bulb and the motor responds. Next time it starts to lose power after running at high rpm, don't pump the bulb - shut motor off and remove the hood - check fuel filter bowl - if it is not full, then fuel starvation is from there on back to the tank. If the bowl is full, then problem is from there to the carbs.
Good luck,
Ken K

[Alitak]

Thanks Ken, I will use that method to isolate the problem on one side of the filter or the other. Now I need to get the problem to return. Prior to talking to you I put new plugs in and the engine returned to normal. Previously it took about 30-40 miles (cruise speed) for the problem to return. Why would it take that long for the problem to remanifest??? Is the fuel starvation fouling the plugs or would the plugs be fouling (oil-injection problem?) and then causing fuel starvation??? As you suggested I check the external fuel delivery sources. The tank is a well ventilated 50 gal Aluminum tank without an antisiphon valve. I replaced the fuel line from the tank to the racor filter and from the filter to the engine too. I also put a new racor filter on; the filter housing is old but doesn't appear to be leaking anywhere.

Will respond back when I try the isolation test.

Greatly appreciate your response,

Matt

[Alitak]

Well, I wasn't able to reproduce the fuel starvation that I was previously getting, so I wasn't able to isolate the problem. I replaced the hose coming out of the external fuel filter and fittings...that could have been the problem. Now its just cold starting and I have to use starting fluid to get it going in the morning...Arrrgggh. This engine has always been the mystery machine, however its lasted quite some time so I can't complain too much.

Ken, thanks again for your troubleshooting advice, I don't think I've given anymore info to troubleshoot. Our Salmon season is winding down and won't have to use the big skiff til next year.

[Ken]

Matt,
Man, I envy you being able to catch salmon and halibut - I see it on tv, and say to myself "some day".
On the cold starting of that 115 - make sure the choke butterfly valve is closing fully when engaged. If that valve is not completely closed, then the 115 is hard to start - I know, because my brand new 2000 C115 was hard to start for several months until I figured out what was wrong.
Pull the air breather and look directly down the barrels of the carbs and pull the manual choke. Make sure the valve closes fully - if not, then adjust linkage. Now check the remote choke switch on the console to see if choke solenoid is doing its job - if not, adjust linkage so that valve is closing fully.
Good luck,
Ken K