1975 Johnson 9.9 occassional speed fluctation @ WOT

[malverts]

I have a 1975 Johnson 9.9 in good shape. It starts right up, runs all day, great motor.

I recently had it out and was running it at wide open throttle and the power significantly cut back for a short amount of time (5 seconds or so) and then returned to normal.

I have replaced the fuel pump and it has not changed the problem.

I have noticed that one of the coils? perhaps is seems rusted and the "stacked" metal material has expanded due to rust.

How do I isolate the problem vs. throw parts at it?

thanks,

Mike

 

[reload]

Re: 1975 Johnson 9.9 occassional speed fluctation @ WOT

It could be dirt in the carb. I would not worry about the rust on the coils core. Was the power loss associated with a miss or did it just feel as if you throuttled back?

 

[lexkyboater]

Re: 1975 Johnson 9.9 occassional speed fluctation @ WOT

You might want to try verifying plug wires are good with an ohm meter. You can connect your meter at both ends, then wiggle to find any open connections, and while you're at it, resitance should be near 0. This can also cause weak spark. This was a problem on my recent diagnosis of my engine, and plug wires can cut in and out like that.

 

[malverts]

Re: 1975 Johnson 9.9 occassional speed fluctation @ WOT

It did not seem like it was missing/running on one cylinder, more like I had throttled back.

When I changed the fuel pump, the old pump had about 1/3 to 1/2" gastket and the new one did not. The directions said not to put the old gasket on but I did anyway. Any thoughts on this contributing?

thanks!

 

[reload]

Re: 1975 Johnson 9.9 occassional speed fluctation @ WOT

You are talking about the gasket between the bkock and the pump? There is a rather thick gasket there. Yes it needs one, did yours look bad? It compresses a ggod bit. May be you have an air leak.

 

[malverts]

Re: 1975 Johnson 9.9 occassional speed fluctation @ WOT

The directions for the new fuel pump said that the gasket was no longer needed.

I put it on anyway.

The problem is occasional, maybe 3 to 5 times per hour.