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1964 Johnson 9.5 will not run at high speed

J

JustBass

New member
1964 Johnson 9.5 MQ10
The motor will not run at high speed/fast
Currently: (1) Motor starts fine (2) Idles fine (3) Both cylinder's compression checks fine (4) low and medium speeds run fine
Part upgrades: (1) New points (2) New Coils (3) New condensers (4) New carburetor kit (5) New spark plugs (6) Used proper tools for points and coil placement
Tiller Throttle: (1) Appears to be out of alignment (2) When rotating the throttle, it does not align with start in neutral (3) When rotating the throttle, it does not align with Fast

What am I missing? If it is the CAM adjustment or simply tiller throttle adjustment please do provide instructions on the proper alignment. Thanks in advance.
 
I have a 1966 9.5.

Questions:

Is this a new motor to you, or was it running properly before?

When you say "will not run at high speeds", specifically what does that mean? Dies? You turn the throttle but the RPM will not increase?

Can you increase the RPM with the throttle when in neutral? Yes, no, a little?

CMOS
 
If the engine is bogging... that is, it wants to die out when the throttle is increased, the most common cause is that the high speed jet is clogged somewhat... located way in back of the drain screw. Carefully clean it with a piece of single strand steel wire.
 
Hello CMOS

Thanks for you response.

Is this a new motor to you, or was it running properly before? Running properly about two years ago. It has been sitting in my garage.
When you say "will not run at high speeds", specifically what does that mean? Dies? It runs fine, does not die...it runs steady (idle and slow speed). You turn the throttle but the RPM will not increase? Correct. I can turn it to full throttle and it does not increase rpm.
Can you increase the RPM with the throttle when in neutral? Yes, no, a little? Yes; a little. It appears to go to the same rpm in neutral and in gear (forward). I had it on the lake yesterday and it ran fine at that rpm; but, it would not run at the high rpm on full throttle.
 
Hello Joereeves

Thanks for your response. It is not bogging or skipping. :eek: It runs steady; it just will not run at a high rpm. I did a carb rebuild, included jet cleanings.
 
Pull plug wires off one at a time.----------How does the motor respond to that test ?----Was compression test done ?
 
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Hello Racerone,

I tried that as well. My initial thought was running on one cylinder or a bad cylinder. Checked out fine, compression on both cylinders fine. I did find the bottom spark plug would not fully tighten; so no torque on the bottom spark plug. Both spark plugs burning fine. Replaced cylinder head, able to torque bottom plug ...thought the problem was resolved. The behavior did not change.
 
What was the compression psi reading on both cylinders?

The spark (with the spark plugs removed) on that model should jump a .1/4" air gap with a strong blue lightning like flame... a real SNAP! Does it?

You keep describing the problem as the engine will no run at high speed... I assume this means that as you increase the throttle, the engine dies out and stops running?

If you mean something else, explain what the engine is doing in detail. Possibly that you are able to turn the throttle handle to full throttle but the engine continues to run at a low rpm... something of that nature?
 
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Yes; I increase to full throttle and the rpm does not increase. The motor does not die out or stop running. It runs at low speed; I increase the throttle and the rpm does not increase. It runs with no increase in rpm.
 
racerone said:
Does the carburetor throttle butterfly go fully open at full throttle.-------And have you checked the reed valves ??
Click to expand...

No; it appears to stop about 1/2 throttle or a bit more. It stops; but, I can continue to turn throttle to full. I have not checked the reed valves.
 
So you have a throttle linkage problem. The throttle butterfly must open full in order to obtain full rpms... something you'll need to check visually.
 
joereeves said:
So you have a throttle linkage problem. The throttle butterfly must open full in order to obtain full rpms... something you'll need to check visually.
Click to expand...
I made adjustments; butterfly is opening fully. Barrow test seems ok. Taking out tomorrow. I will post results. I am extremely appreciative of everyone's input.
 
That motor is prone to under the cover exhaust leaks which may cause exhaust to be drawn in instead of pure air. Try running it with the cover off to see if that may be the problem.
 
Outstanding!!! Went out today and ran like a charm. Thanks to everyone for the transfer of knowledge. The throttle linkage adjustment fixed the issue. I ran with cover on an off. I received the same performance. Again... thanks to all.
 
Great news! These are fantastic motors.

I can't begin to tell you how reliable my 1966 9.5 is. I KNOW without a doubt that she will start weather the temperature id 95 or 35 - 2 pulls and she roars to life. I just love this motor.


CMOS
 
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