Stalling after 30 minutes run time

[Golson Molson]

Hello all: Have an ongoing problem which is perplexing. 140 Mercruiser approx.1978 MCM 140 Serial #A344469 Not sure if anyone remembers last year when I bought this boat, but had to replace the head gasket as the previous owner overheated it. The following items were replaced during the rebuild: -new points - new rotor -new dist. Cap -new wires -new plugs The last time last year I had the boat out I thought I was running out of gas but made it back to the dock. Put some gas into it and stored it for the winter (properly). This year went out the first time ran for about 30 minutes started sputtering and then died, no restart. Brought it back thinking it was a gas issue, filled it up and started in the driveway on the muffs. Went out again, same thing. Sputter and no restart. The battery was weak so I replaced it. Tried again, same thing. Then a brainstorm.......coil. Installed new coil. The new coil says use with external resistor on but I have the purple/yellow resistor wire. Went out again today ran great for 30 minutes, started to sputter and quit. No restart. Undid the gas line to the carb and gas spurted out. Brought it back, was pissed of, ripped the floor out, pulled the float and the gas was fill to the top. Put back together, ran it on the muffs in the driveway for about 20 minutes and sputter and stall. No restart. Pulled the coil wire off the dist. Cap and good spark when grounded. I did after looking inspecting for leaks ect. Find a small 1 inch long cylinder lying under the engine which used to have 1 wire sticking out the top. It looks like at some it had a bracket on it to bolt somewhere which is broken. Don't know what this is. Also checked the fuel venting and no blockage. Anyone have any ideas what the issue could be? I'm now dumbfounded!

 

[glenn property of pam]

the one inch can with a wire sounds like a condenser. My guess would have been a overheated coil but as you have already replaced that I would go back and check the points setting at least.

 

[bspeth]

My thought was condenser,did you replace that as well when you did the points?

 

[Golson Molson]

Couldn't remember so I checked this morning and the condenser was replaced. The one I found is painted black.

 

[Golson Molson]

Update: found the location on the backside of the alternator. Book says it is a condenser. Could this be the problem?

 

[Golson Molson]

Found the fuel line cracked from the tank to the fuel pump. Cleaned the basket gas filter and replaced the anti siphon valve. No change.

Sprayed carb cleaner into the carb. Did find an intake leak when spraying the carb cleaner around the base of the gasket. The motor was hot and dropping RPMS. Will try again to see if it happens when cold.

 

[Golson Molson]

Rechecked gap on points, replaced carb gasket and checked timing. No change. Runs for a while and then dies.

 

[Golson Molson]

O.k. Weekend wrecked and wife is pissed off. Found line from tank cracked. Replaced and installed in- line water separator and drained several litres of fuel, Regapped the spark plugs. Checked as many grounds as I could find. Removed the grey wire to the tach, rechecked gap on points. There is nothing I haven't inspected, repaired or replaced. I bought new digital volt meter today with a digital read out and found that the volts at the coil on the positive side engine off is reading11.8v spikesto 12.25 unde higher RPM''s . All grounding was checked and charging voltage was 14.8v The engine continues to sputter and stall after 30 minutes. My last resort is to install a ballast resistor on the purple wire to try and drop the voltage at the coil.

 

[bouncefactor]

Any progress am having similar problem. If you figured it out please post what you did.

 

[Golson Molson]

Not yet. Gave up and sent the boat in to have the dwell and timing properly checked with better equipment. Both were off and the carb was then adjusted. Ran it for a while on muffs but still stalled out it but lasted longer and recovered much quicker. Need to get it out in the water for a run. Also would like to get most of the old gas out and try again with new.

 

[Golson Molson]

I am officially stumped:

Everything has been checked, rechecked, rebought and then checked again.

Just tried a new 12v internally ballasted coil with the same outcome. Runs well for 30 minutes and then sputters to a stop. I have mounted the two old coils on a block in the engine compartment and when it stalls out, I can switch the hot coil to a fresh coil and the boat fires right back up. Definitely not a gas issue, it is electrical. Also checked under the plate of the dist. to check to see if the arms were moving freely for spark advance and they work perfectly.

Does anyone out there have any ideas?

 

[coronatrophy]

I noticed you say the voltage to the coil is around 11v and 12.2 when running. This voltage seems low to me, it should be system voltage, 14+. Maybe after a while of running with the low voltage the coil doesn't like it. Try running a new wire or find out why that wire has low voltage (possible corrosion). It should be the same as your battery voltage with the engine off and system voltage with the engine running.

 

[thumpar]

I noticed you say the voltage to the coil is around 11v and 12.2 when running. This voltage seems low to me, it should be system voltage, 14+. Maybe after a while of running with the low voltage the coil doesn't like it. Try running a new wire or find out why that wire has low voltage (possible corrosion). It should be the same as your battery voltage with the engine off and system voltage with the engine running.

It is actually high. It should be around 7-9 volts to protect the ignition system.

 

[coronatrophy]

It is actually high. It should be around 7-9 volts to protect the ignition system.

Read post #11 Thanks

 

[Howard Sterndrive]

sounds like your coil is overheating and you figured out the supply side issues, but too much spark plug gap can also make the coil screaming hot, or improperly set dwell, or other issues in the secondary side of the system like crappy spark plug wires, bad condenser etc. Even a goofy tachometer can heat the coil.

 

[alldodge]

Thumper has the clue, and using a 12V internally ballasted coil is not going to stop it. IMO you have a points system which is designed to start on 12V and run on 7-9 volts. This is done to reduce the current to the coil and the points, which include the condenser (capacitor). There is some serious EMF going on here with a points system.

1st post -- Then a brainstorm.......coil. Installed new coil. The new coil says use with external resistor on but I have the purple/yellow resistor wire.

The purple/yellow is the by pass wire used to supply full voltage during starting.

post 4 -- Couldn't remember so I checked this morning and the condenser was replaced. The one I found is painted black

Condenser should not be painted, it needs to be grounded on the casing. If it is not grounded the EMF being feed back into the coil will heat it up big time if not burn it out. Will also burn the points out fast.

IMO, I would either get a non-internal resistor coil and a ballast resistor and install it so it runs through the resistor. Only use the purple/yellow during starting. Either that or rip it all out and install a Delco EST