78 Everude 70hp cutting out at full throttle

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davidpa

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Sep 17, 2012
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Hello my 70hp cuts out at full throttle after about 5 min of operation,but when throttle is brought back to 3/4 the surge or cut out goes away? I have resealed the crankcase,replace seals,and gaskets,could i have an ignition problem?
 
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Daviet

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Re: 78 Everude 70hp cutting out at full throttle

The way you describe the problem, it sounds more like a fuel problem.
Have you tried pumping the primer bulb when it misses, maybe you have a weak fuel pump.
Have you checked the high speed orifices in the carbs, maybe one of them is plugged or restricted or plugged.
You can use a timing light to check each plug wire when it acts up and see if you are loosing spark on a cylinder.
 
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davidpa

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Re: 78 Everude 70hp cutting out at full throttle

Daviet said:
The way you describe the problem, it sounds more like a fuel problem.
Have you tried pumping the primer bulb when it misses, maybe you have a weak fuel pump.
Have you checked the high speed orifices in the carbs, maybe one of them is plugged or restricted or plugged.
You can use a timing light to check each plug wire when it acts up and see if you are loosing spark on a cylinder.
Click to expand...

have replaced fuel pump and lines,and primer bulb,and pumping the primer does not help,seems to be heat related as it runs fine for the first 5 min or so and if i idle the engine for a few minutes the return to full throttle it will run for 2-3 min the starts to surge again?
 
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Daviet

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8,958
Re: 78 Everude 70hp cutting out at full throttle

Could be either, it takes a few minutes to burn the fuel out of a carb, when you slow it down the carb fills back up and runs until you get low on fuel in a carb.
You can eliminate the ignition by checking the spark with an inductive timing light, just check each plug wire when it is acting up. If you have steady flashes on each plug wire, you most likely have a fuel problem.
You could also remove the air silencer and carb cover and check the high speed orifices without removing the carbs. If you do have a plugged or restricted orifice it would be best to remove the carbs and clean them properly.
 
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davidpa

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Re: 78 Everude 70hp cutting out at full throttle

Thanks for the info I will check both!
 
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Daviet

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Re: 78 Everude 70hp cutting out at full throttle

Let us know what you find.
 
fireman57

fireman57

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Aug 24, 2004
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Re: 78 Everude 70hp cutting out at full throttle

Do you have an overheat alarm that is hooked up and working. The reason I ask this is because I have the same engine you do and experienced the same problem. Changed out electronics and everything but it turned out that the alarm was not working. I unhooked the tan wire to test and viola, the problem was solved. But a new horn on it and it is fine. It never was overheating but somehow it shorted and told the engine that it was so it would cut out the top cylinder. It's worth a try.
 
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davidpa

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Re: 78 Everude 70hp cutting out at full throttle

fireman57 said:
Do you have an overheat alarm that is hooked up and working. The reason I ask this is because I have the same engine you do and experienced the same problem. Changed out electronics and everything but it turned out that the alarm was not working. I unhooked the tan wire to test and viola, the problem was solved. But a new horn on it and it is fine. It never was overheating but somehow it shorted and told the engine that it was so it would cut out the top cylinder. It's worth a try.
Click to expand...

I checked and the alarm is functioning! I unhooked the sensor and grounded the wire and the horn does work? I will try running the the sensor unhooked also Thanks for you input!
 
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