Am I getting vapor lock?

[montejw360]

I'm on kicker heading back to the marina again. It runs for about a half hour then stalls and won't start. It's running on old fuel, but I would think if that's the problem I wouldn't make it out of the marina. I've done this three times now. I replaced all filters thinking that was the problem but it didn't help. Thanks

 

[dubs283]

Re: Am I getting vapor lock?

and what motor is this??

make/model/serial number/year??

 

[montejw360]

Re: Am I getting vapor lock?

and what motor is this??

make/model/serial number/year??

My bad. 1980 mercruiser 470

 

[dubs283]

Re: Am I getting vapor lock?

i would start by replacing the old/bad fuel first - its a known possible culprit

when was the last FULL tune-up??

have you checked the fuel tank/pick-up for debris?? anti-siphon valve/tank vent??

have you checked for spark when it dies?? fuel at the carb??

 

[montejw360]

Re: Am I getting vapor lock?

i would start by replacing the old/bad fuel first - its a known possible culprit

yeah, i know, but i haven't. 35 gallons of the old plus 15 fresh i put on top of it. anyway, i've had it out 3 times now, the first time on the old fuel, the 2nd time was on a 12 gallon portable tank of fresh fuel, it ran the same.

when was the last FULL tune-up??

who knows. probably 2 years ago from what i know about the history of the boat.

have you checked the fuel tank/pick-up for debris?? anti-siphon valve/tank vent??

haven't checked the fuel pickup, but it's done the same thing on a new portable tank. i've replaced all the fuel hoses, took the anti-siphon valve off and checked it, it seems to work. the engine will run for at least 1/2 hour before quitting.

have you checked for spark when it dies?? fuel at the carb??

no, didn't think about checking for spark. it will start, but it's really hard to keep running and won't get above 2000 rpm and has no power. talked with a marine mech tonight he says it might be a bad coil, going out as it heats up. i'm going to put a coil on it and plumb the fuel directly to the main motor again.

before today the kicker was plumbed to the main tank fuel line through a T fitting, no selector valve. last night i added a Racor fuel filter water separator and plumbed the main tank (same old fuel) directly to the main motor through the new filter. the kicker i plumbed directly to the portable tank.

as far as checking for fuel at the carb when it died, i didn't check. didn't feel like removing fuel hoses while out on the water.

hope this makes sense. the main thing to me is the merc 470 will run for 1/2 to 3/4 hour and die. it's done it on the main tank as i bought the boat, on a 12 gallon portable tank of fresh fuel, and on the main tank with the kicker removed from the fuel system and a new filter/water separator and new fuel hoses installed.

i can install a new coil and replumb the portable tank to the merc again and try tomorrow evening.

 

[dubs283]

Re: Am I getting vapor lock?

don't just replace the coil, check the ENTIRE ignition system, points, cap ,rotor, plugs, wires, all wiring, look for loose/corroded connections, etc...

to check for fuel at the carb simply remove the flame arrestor and move the throttle to full wot and see if the accel pump is squirting fuel into the throats

 

[montejw360]

Re: Am I getting vapor lock?

don't just replace the coil, check the ENTIRE ignition system, points, cap ,rotor, plugs, wires, all wiring, look for loose/corroded connections, etc...

i want to install electronic ignition. tonight all i can do is the coil from an auto parts store. have to work tomorrow, so can't get the rest of the parts to change points, cond, cap, etc. would probably do electronic before spending the time/money on the old tech.

to check for fuel at the carb simply remove the flame arrestor and move the throttle to full wot and see if the accel pump is squirting fuel into the throats

good point, hadn't thought of that. i did check to see if the choke was open, but i was back at the marina by then and it was open. i doubt it was the choke anyway.

thanks for the help.

 

[Doernuth]

Re: Am I getting vapor lock?

This may sound really stupid but did you check the oil? If it is low, or the wrong weight that engine (I believe) has an oil pressure kill switch on it. As it heats up and the viscosity goes down the switch may be killing the engine. Or the switch itself may be bad and effected by the heat.

Following that check the choke and maybe strip/rebuild the carb. Assuming your fuel supply to the carb is sufficient that is.

 

[ziggy]

Re: Am I getting vapor lock?

would probably do electronic before spending the time/money on the old tech.

food for thought. and if that isn't the problem, and you miss install the new electronic ign. you'll have two problems and not know it... imho. best to put it back to oem first. have it running tip top, then if ya wanna do the conversion. go for it. if it don't work after the conversion, you'll know it is the conversion that's causing the problem.

fwiw, i still run points type ign. it worked fine in '75, works fine now too. it's the igns system that was designed by the oem to work well with my particular engine.