Elec. problem on 40hp, 1979 Merc.

kerby7

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Serial # 5253426 2 cly. Motor starts and runs good for about 15 minutes and then dies . Will restart in about 20 minutes after it has cooled down. Installed new stator and switch box. Helped some, runs longer, but still dies. Help please !
 

JUSTINTIME

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Re: Elec. problem on 40hp, 1979 Merc.

u need to check fuel lines/vent lines
clean carbs
check fuel for water also
 

WillyBWright

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Re: Elec. problem on 40hp, 1979 Merc.

How's your water pump? How's your gearlube? Are you putting oil in your gas?
 

kerby7

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Re: Elec. problem on 40hp, 1979 Merc.

I don't "think" its a fuel problem. Water pump and gearelube are fine. Doesn't sound like its getting and spark when its warmed up but I'm not sure.
 

davebad22

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Re: Elec. problem on 40hp, 1979 Merc.

Could it be overheating? You said it runs for 15 min. and then dies. Are you running it on open water or hooked up to a hose?
 

kerby7

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Re: Elec. problem on 40hp, 1979 Merc.

Both. Does the same thing in open water as it does hooked up to hose. Getting good stream of water from impeller. Could it still be overheating with the water pump working properly ?
 

TriadSteeler

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Re: Elec. problem on 40hp, 1979 Merc.

If you have absolutely ruled out a fuel issue, including vapor lock, It may be possible that the one of the coils (or another plastic module in the ignition train) has a crack in the plastic casing and after it heats up, the crack widens, flexes, and breaks the connection. (I had this happen in a car years ago with a hairline crack in the dist. cap.)
 

georgiaboy

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Re: Elec. problem on 40hp, 1979 Merc.

run it with the cover off. I had a problem like that and it was a small hole in the tube feeding water to the pee hole. It would drip down over spark plugs and finally ground out the ignition.
 

Laddies

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Re: Elec. problem on 40hp, 1979 Merc.

You need to see if the engine is losing spark or not, I think it probable is, If it is electric start the rectifier could be the problem (don't just change things it don't work ck them) disconnect the 2 yellow wires a the rectifier tape and run the engine, if it don't act up then change the rectifier, if it does ck the trigger wires (brn to white for continuity) if the are open change the trigger. Either part will cause the problem you are experincing
 

kerby7

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Re: Elec. problem on 40hp, 1979 Merc.

Laddies said:
You need to see if the engine is losing spark or not, I think it probable is, If it is electric start the rectifier could be the problem (don't just change things it don't work ck them) disconnect the 2 yellow wires a the rectifier tape and run the engine, if it don't act up then change the rectifier, if it does ck the trigger wires (brn to white for continuity) if the are open change the trigger. Either part will cause the problem you are experincing
 

kerby7

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Re: Elec. problem on 40hp, 1979 Merc.

Thanks Admiral, It was the trigger.

P.S. I wasn't just slapping parts on without cause. The wiring on the stator was shot. I got a NEW one on Ebay for $100. A friend had a new switch box he let me have for $50 , and I spliced all the wiring on the internal wiring harness with new. I tell ya, this thing has so many bright and shiney new wires I may just use it with the cover off for awhile. lol
 
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