johnson 9.5 won't run properly at high speed

emoe850 · Apr 28, 2010

Hello,

I have a 1965 9.5 Johnson Seahorse short shaft motor (MQ11?)

The problem is it does not run properly in the high speed circuit of the carburetor.

From idle up to where it engages the throttle on the cam there is good engine response.

Once in to the high speed circuit the engine can?t get enough air (too much fuel).

I have tried to run at full throttle and after a while stop and look at the plugs and they are soaking wet with fuel.

If I pinch off the fuel feed line and run the fuel out of the carburetor, there is a spot where the Air fuel mix is good and the motor takes off like a bear.

I have checked the carb float, shutoff, mainjet (.048 dia) seem to be good.

The propeller seems to be the correct size, infact it is worn and is smaller in diameter?.71/2 or so.

I have replaced the points and condensers, good spark, starts fine.

Over the winter I used some seafoam and got a lot of black goo out of the engine.

Rick. · Apr 28, 2010

Re: johnson 9.5 won't run properly at high speed

I would suggest you try to do a high speed run with the cowl off. It could be you have an exhaust leak into the cowl that is causing the engine to get insufficient fresh air. I had some difficulty with mine at high speed and it turned out to be incorrectly adjusted/dirty points. Best of luck. Rick.

ultra353 · Apr 28, 2010

Re: johnson 9.5 won't run properly at high speed

According to my `71 service manual the high speed jet should be .048", sounds like you have too big of a main jet, thats why its flooding out at full throttle.

emoe850 · Apr 28, 2010

Re: johnson 9.5 won't run properly at high speed

Rick, what wasn't adjusted right? I have tried with the cowl off and you are right it does run better than with it on....but still not like it should.

emoe850 · Apr 28, 2010

Re: johnson 9.5 won't run properly at high speed

Ultra, you are right it is .048

ultra353 · Apr 28, 2010

Re: johnson 9.5 won't run properly at high speed

I thought you stated you had a .056'' jet, my mistake. Check you float level, needle and seat not sealing, tear in your fuel pump- letting fuel get in the motor.

Rick. · Apr 28, 2010

Re: johnson 9.5 won't run properly at high speed

I found I had one set of points not adjusted correctly (should be dead on .020) and I cleaned them at the same time. It made a world of difference to the performance. If you find yours runs better without the cowl you probably have an exhaust leak getting into your air stream. Did you try it without the cowl on the lake or in a barrel? 9.5's are notorious for running poorly in a barrel due to the engine sitting so low and sucking up exhaust fumes. I have had luck putting a fan beside mine so the exhaust is blown clear but on the lake the exhaust will not be a problem unless you have a leak into the cowling. Hope that makes sense. Rick.

emoe850 · Apr 28, 2010

Re: johnson 9.5 won't run properly at high speed

Ultra, thanks I will check the seat again

emoe850 · Apr 28, 2010

Re: johnson 9.5 won't run properly at high speed

Rick, Yes I run it on open water, it still is running to rich. Ultra suggests looking at the float seat. The confusing part to me is that it runs exceptionaly well when the gas is shut off and the carb is run out of gas...for that breif moment when the air fuel mix is just right the motor runs strong.

Rick. · Apr 28, 2010

Re: johnson 9.5 won't run properly at high speed

I'm hoping ezeke will jump in here. He's forgotten more about 9.5's than many of us will ever know. But in the mean time.... have you done a linc and sinc? and when your at WOT check to see your throttle plate is fully open. Let me know what you find out. Rick.

emoe850 · Apr 29, 2010

Re: johnson 9.5 won't run properly at high speed

are you talking about the cam and the carburetor syncronization? I have set it up to the book. I've thought about delayong the carb from opening to try and help get more spark advance and less fuel

Rick. · Apr 29, 2010

Re: johnson 9.5 won't run properly at high speed

Yes that is what I meant. The carb. float shuts gas supply to the carb. off. A rich mix (as I understand it) would not be caused by that seat. The amount of gas your carb. actually uses is determined by the carb. settings not the fuel pump. I know you said you've cleaned the carb. but you might have to try it again. Did you check to see if your throttle plate fully opens at full throttle? Rick.

emoe850 · May 3, 2010

Re: johnson 9.5 won't run properly at high speed

Thank you all,

It was the point timing that was the problem. once I set the points to break at the correct time the motor runs like it should.

Thanks again

Rick. · May 3, 2010

Re: johnson 9.5 won't run properly at high speed

Glad to hear your back on the water. I know with my 9.5 the point gap has proven to be far more critical than other motors if seen. It will run with them incorrect but it lacks horse power if they aren't spot on. Rick.

johnson 9.5 won't run properly at high speed

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