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Loses spark when hot

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fry177

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"I have an 18' 1988 celebr

"I have an 18' 1988 celebrity runabout with a 4.3 merc. the problem is I can run for a couple hours then when I shut it off, it won't start back up. this is the 4th time it is in the shop for the problem. and they say it is spark. the carb has been rebuilt, the coil replaced and shift interupter switch. if I wait 45 minutes/1 hour or so it will fire right back up. my mechanic is left scratching his head. what do you think?"
 
"maybe that is the problem...

"maybe that is the problem... the mechanic. Take it to another mechanic. Don't allow the guy to throw parts at it (on your tab) and hope the problem gets fixed.

If it is not getting spark during the fault condition, there is a specific process for diagnosing. Work back upstream from the plugs checking for spark on the secondary ignition. Is the coil getting signal? Do you have fresh cap/rotor?

Frankly, it sounds as though the engine mixture is a little rich and the plugs are loading up upon hot start. (try starting with throttle wide open but be prepared to pull back quick). Idle mixture is adjustable, btw.

That or you may have a vapor lock/fuel boil issue (in which case you can try running with the doghouse off to disipate heat and see if that solves)

my thoughts."
 
"well, It all started with me

"well, It all started with me thinking it was flooding, therfore the carb was rebuilt. he has a spark tester (whatever that is) and is trying to track it down. I have tried opening up the throttle and no responce. But by the time I get a tow, load, get it home, she will then fire up with a little work. The boat has new plugs and cap. Still stumped"
 
Is it electronic/breakerless d

Is it electronic/breakerless ditributor?
 
"I am pretty sure it is electr

"I am pretty sure it is electronic but not 100%.

also, I currently have the doghouse off so thats not it. I am just trying to get my boat back for this weekend."
 
"excluding the ignition wires

"excluding the ignition wires on the cap, how many wires coming from the distributor? If it has electronic ignition there will be more then two. If it has old school points/condensor, there should be only two wires."
 
"If it is not electronic and h

"If it is not electronic and has points and condenser, it could be a bad condenser."
 
"here is my thoughts on what i

"here is my thoughts on what is happening, obviously it only happens when it is hot, which leads me to think something is heating up and failing. first thing you need to do is get it to happen again (have another boat around to tow you in if need be)or (get it to happen on the trailer with muffs on) once you have the problem start checking everything out, start with spark,then fuel, and so on.. there is only so many things that can keep a motor from starting. if you have spark, fuel, air, and timing there's only compression left. then you need to check the compression in all cylinders when it happens. without knowing exactly what it is doing when it doesn't start for all we know it could be vapor locking.. what ever you do (unless you just have very very deep pockets) don't just start throwing money at it and hope it goes away.."
 
"If it is a Thunderbolt Igniti

"If it is a Thunderbolt Ignition, check the optic sensor under the rotor in the distributor. If it is rusted, replace it. Check ALL engine ground connections for clean and tightness. Any ignition component that has double nutted studs holding a wire connector, remove the top nut and wire and tighten the bottom nut. When the part heats up the lower nut moves and loosens the connection. Coil first."
 
The distributer is electronic.

The distributer is electronic. I guess after the motor gets warm when you shut it off and wait ten minutes it loses spark for some reason. If I wait 45 minutes then it comes back and fires right up. very intermittent. I will check to see if it is a thunderbolt. thanks
 
Coils can act like that when t

Coils can act like that when they are defective.
 
"The ignition is thunderbolt.

"The ignition is thunderbolt. the shop had the boat for 3 weeks and finally said they got it. they cleaned every connection and ground and the symptoms went away, but no garrantee. they only charged me $160, so I am not too upset since they did have a lot of time in it and that included a coil I requested. I have not had a chance to try it yet but hopefully this week. if it does not work you will probably hear me yelling.
thanks

John"
 
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