1977 85 hp Johnson

R

Raffus

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Mar 25, 2011
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Runs great for about 10 min then starts to miss then finally shuts down completely. Primer bulb is hard and your can put your hand on motor so it's not a fuel or overheating problem. I've put close to 60 hours on it this spring with no problem. I did change the rectifier and still no change. Any suggestions.
 
BonairII

BonairII

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2,727
Re: 1977 85 hp Johnson

Check compression then spark.

My guess is that a coil(s) or PP is malfunctioning when they get warm.

Your probably going to need a DVA adapter to test PP, stator etc

What made you think that the rectifier was the culprit?
 
R

Raffus

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Mar 25, 2011
Messages
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Re: 1977 85 hp Johnson

I had a extra one so I thought I would try it before buying a power pack
 
BonairII

BonairII

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Re: 1977 85 hp Johnson

You may have more than 1 cyl misfiring(or not firing at all). Check with an adjustable spark tester...and/or drop test each cyl.
 
R

Raffus

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Re: 1977 85 hp Johnson

I know how to use a adjustable spark tester but I do not know what drop test means. Thank you for your help
 
J

JDusza

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Apr 21, 2009
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963
Re: 1977 85 hp Johnson

I believe the drop test is when you pull the ignition wire from a cylinder to observe any changes in engine performance or rpm.
If the ignition is pulled, and the cylinder "drops out", a noticeable change in performance indicates the cylinder is running.
If you "drop" a cylinder and nothing changes, then the cylinder is suspect bad, it's not noticeably helping.
I believe...
J
 
BonairII

BonairII

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Re: 1977 85 hp Johnson

Yup. The motor should stumble each time that a plug wire is disconnected. An adjustable spark tester is a better choice of tests though, cause you will be able to see the "quality" of the spark.

The V-4s can run pretty smoothly on just 2 cyls. It's when you ask the motor for power or rpm that you realize something is wrong.

The fact that the OP's motor actually "shuts down" leads me to believe that he has a major ignition component(PP, stator, trigger) going bad.

The key is to actually diagnose what is wrong, rather than throwing new parts at the motor "hoping" that it will fix the problem.
 
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emdsapmgr

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Dec 9, 2005
Messages
11,551
Re: 1977 85 hp Johnson

When you first prime the fuel hose bulb at the start of the day, it should get hard. After the engine has run for a while, the fuel primer bulb should not be hard. As fuel runs through it, it will soften up-but not collapse on itself. That's normal. If it is truly hard as you state, it is possible you have a problem with the ball valves in the hose bulb.
 
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