Merc 165 missing at speed

[MolsonCanadian]

Hey folks.

Boat is a 1977 Doral 19' with the Merc 165 L6 (Chev 250) with the Pre-alpha MCI Drive.

Owned the boat 5 years or so, first three seasons had no problems, rebuild the carb mid third season. Boat then sat in storage for last two seasons, didn't have time to use it.

Pulled it out this year, cleaned it up, etc. It fired right up, went for a few rides, everything worked great, no problems.

A Couple weeks ago we went out, approx 30-40 mins into the ride, the boat while on plane cruising at 3000 RPM, it would cut out, then run, then cut, eventually dying (in about a span of 60-90 seconds).

Restart, and boat idles fine, get back on plane, and 30 secs later it would start it again.

I discovered I had a battery issue, the wingnut got lose and heated the battery. Came home, replaced battery, and used proper nuts.

While it was out of the water I had the gimbal bearing changed, new bellows, new impeller, new gaskets. Also did plugs, wires, cap & rotor, points and condenser. Points and timing set, idled like brand new.

replashed the boat last night. idled out of the launch with a bigass grin on my face. Got up to temp, out into the bay and opened it up to cruise. After 20 mins it started cutting out again, same issue. Would cut out and/or stall at anything above idle.

Carb MAY be a little gummy from sitting. And its a mechanical fuel pump, which, in my limited knowledge, either works, or doesn't. They usually don't get "weak" like an electric pump can.

Any ideers?

 

[ziggy]

Re: Merc 165 missing at speed

while i'm not the pro here. seems like you've approached everything on the elec. side. so next i'd move to the fuel side. starting with the fuel filter...

after it dies. ya might undo the fuel cap make sure the fuel tank is getting air. if it goes woosh, sucking air in fast, that could indicate a problem with venting.
there's also a fuel system test up in the adults only section. pretty in depth discussion for testing your fuel system.

for general knowledge. i'd also run a compression test so ya have a base idea where that's at for future reference.

 

[MolsonCanadian]

Re: Merc 165 missing at speed

Hey Ziggy, fuel filter is brand new. No sign of debris or water. As far as I know the fuel tank is venting fine, no wooshing. I'll look into that fuel system testing. thank you.

 

[Howard Sterndrive]

Re: Merc 165 missing at speed

wingnut got lose and heated the battery.

heated the battery? never seen a battery heat up with a bad connection...unless you mean it melted the lead post...seen that

I would put a voltmeter between coil + and batt neg and get someone to drive while I observed voltage at the coil.

I think you have a bad connection somewhere (low V to coil), or an alternator regulator issue that is cooking the coil, or a ballast resistor issue cooking the coil.

caould also look down the carb throat while on plane to see what the fuel is doing

 

[MolsonCanadian]

Re: Merc 165 missing at speed

heated the battery? never seen a battery heat up with a bad connection...unless you mean it melted the lead post...seen that

I would put a voltmeter between coil + and batt neg and get someone to drive while I observed voltage at the coil.

I think you have a bad connection somewhere (low V to coil), or an alternator regulator issue that is cooking the coil, or a ballast resistor issue cooking the coil.

caould also look down the carb throat while on plane to see what the fuel is doing

Yes, you're right, it melted the lead post. Poor articulation on my part.

I looked down the carb at plane, fuel seems to be flowing fine through both venturi's. It may be sputtering a bit when its missing, but its hard to tell.

I'll check coil voltages as soon as I can.

 

[ziggy]

Re: Merc 165 missing at speed

ya could try running on a remote fuel tank. if it fixes it, the problem lies prior to the fuel pump. or if it don't the problem is not prior to the fuel pump.

 

[MolsonCanadian]

Re: Merc 165 missing at speed

Good call. I guess I could use a fuel can with a small chunk of line attached to the filter/pump.

 

[MolsonCanadian]

Re: Merc 165 missing at speed

I'm going the route of suspected water in fuel. The new filter was dirty and appeared to have some water in it. I drained the tank, cleaned the carb and I'm changing the filter tonight and adding a fuel/water separator. I hope that helps.

 

[Kainon]

Re: Merc 165 missing at speed

could be water in the fuel, a fuel/water sep will help but best to drain the tank, at least pour some in a glass jar and let it sit for a little while, you'll see air bubbles ( water ) sitting on the bottom.

also I'd think about if you've got a cracked manifold, search the posts here for "Reverse Flow Cooling" Kit in reference to the Inline 6. I had a NEW Manifold crack because of it.. when the manifold is cracked, warms up and with the engine at speed can suck in a little water and cause a miss..

 

[MolsonCanadian]

Re: Merc 165 missing at speed

Thanks Kainon, I haven't suspected a cracked manifold, but stranger things have happened.

 

[Doernuth]

Re: Merc 165 missing at speed

I woudl agree with the water theory. When the boat sat was there gas in it? How much? Did you add stabilizer? Empty gas tanks will get condensation in them over time. That condensation does not go away and gets sucked out of the bottom of the tank.

Ethanol bonds to water and sinks out of the fuel also, same problem layer of water at bottom of tank.

Fuel water seperator may fix, keep an eye on it and change as needed. Much will depend on how much water is in the tank. If it is alot you may need to drain it and dry it to completely solve the problem.

 

[MolsonCanadian]

Re: Merc 165 missing at speed

Thanks Doernuth.

The boat sat for 2 years in storage. When stored the tank was full, and the fuel was stabilized. But after two years approx $30.00 worth, or half a tank had evaporated. I have no doubt condensation formed.

I have drained the tank the best I could, I will be refilling with higher octane fuel, some gas line antifreeze and carb cleaner to be sure. The filters will be replaced and a fuel/water separator installed. I also blew out the carb in case any water was sitting in the bowl.

 

[MolsonCanadian]

Re: Merc 165 missing at speed

I think I may be closer to figuring it out. My theory is the vent line from the tank is clogged.

After I installed the new sierra fuel/water sep I ran it on muffs to get up to temp, ran fine.

Took it out to the lake, idled out of the launch area, and opened it up, ran fine for 6-8 mins or so. Then it started dying out.

Took off the aircleaner, looked in the carb while the GF opened it up, fuel was a little sputtery.

After 5 more mins it stalled. No restart.

Removed fuel line from carb, turned engine over. no fuel.

Unscrewed fuel filter, heard a hiss as it released the vacuum. Turned it over again, lots of fuel out of the fuel line.

I had to do that twice to get the boat back to the launch. Tonight I'm going to try to get up in the bow and remove the vent line and check for blockages, or a stuck check valve.

 

[MolsonCanadian]

Re: Merc 165 missing at speed

I figured some of you may want to know the outcome of this.

I ended up rebuilding the carb as the accelerator pump rubbers fell apart due to drying out in storage.

Took it out again, ran much better, but after 30 mins it did it again. Fuel starvation.

Reset the float, cleaned all filters, etc. Ran pretty good. Took our trip up the Trent from Midland to Orillia, half way there it dies, wouldn't even idle anymore. Figured the old fuel pump konked out.

So we trailered to orillia, put a new pump in and went. Tested great, decided to do the return trip home (its a 4 hour boat ride) 20 mins in, it died again, same symptoms, fuel starvation.

SO we yank it out of the water again, and pull the tank out. Took every line off and checked. The armoured fuel line was fine, no soft spots and no collapsing. New vent line is fine. Pickup screen nice and clean.

Then we unscrewed the checkvalve. The ball was sticking!! Seems after it built up enough pressure, it wouldn't let any more fuel through. Tossed that out, put a new fitting on, and made the ride home with no problems.

All that for a $3.00 check valve.

 

[chriscraft87]

Re: Merc 165 missing at speed

I have a 87 Chris Craft that I just purchased a few weeks ago. Ive seem to be having the same problems; Just re-built the carb. replaced all the fuel lines from the tank to the pump and to the carb. also put a new vacumn line from the carb to the pump.
Ran good for the 1st 30 min then started starving for fuel.

Where is this "check Valve" at? That may be my problem too, im out of ideas of what to do, please help.. .
thanks,
Logan

 

[Eric 3.7LX Alpha 1]

Re: Merc 165 missing at speed

I have a 87 Chris Craft that I just purchased a few weeks ago. Ive seem to be having the same problems; Just re-built the carb. replaced all the fuel lines from the tank to the pump and to the carb. also put a new vacumn line from the carb to the pump.
Ran good for the 1st 30 min then started starving for fuel.

Where is this "check Valve" at? That may be my problem too, im out of ideas of what to do, please help.. .
thanks,
Logan

You should start a new thread with your problem, no one will see it here.

 

[MolsonCanadian]

Re: Merc 165 missing at speed

In my steel tank, the check valve was the barbed fitting that screwed into the pickup line.