66 johnson 40hp reving high in neutral

[timbo471]

I just got my first boat, a 1966 Shell Lake. It has a 40 hp Johnson, the motor rev's very high in neutral.
The needle valve (rich/lean) adjustment has been tried.
The cable adjustment has been tried.
The only way we have been able to get the motor to idle down in neutral, is to move the choke setting between automatic and on.

Any idea what could be causing this, or how to repair it?

Tim

 

[wilde1j]

Re: 66 johnson 40hp reving high in neutral

I just got my first boat, a 1966 Shell Lake. It has a 40 hp Johnson, the motor rev's very high in neutral.
The needle valve (rich/lean) adjustment has been tried.
The cable adjustment has been tried.
The only way we have been able to get the motor to idle down in neutral, is to move the choke setting between automatic and on.

Any idea what could be causing this, or how to repair it?

Tim

Keep revving it high in neutral and you won't have a motor to worry about and doing that tells you zero about the motor's health.

 

[timbo471]

Re: 66 johnson 40hp reving high in neutral

Right, that is why I want to know what is causing it to rev high in neutral. So I can fix the problem. The only way I have been able to get it to not rev high in neutral is adjusting the choke setting between automatic and on.

I know that is not the best way to fix the problem. I really do not want to run the boat like that either.

 

[bktheking]

Re: 66 johnson 40hp reving high in neutral

What model motor is it? I'll try to explain what I think is happening.
On my neighbours 64 the side of the carb there is a round plate with screws holding the plate in place with the word "lean" written on it. If you loosen the screws and rotate the plate it have an effect on where that choke plate sits when it's set to automatic. It sounds as if the plate isn't opening up fully when the choke is NOT activated. I hope this makes sense, maybe F_R can explain better, I just know that I had to make adjustments to this part of the carb to get my buddies motor to idle properly (needles aside).

 

[bktheking]

Re: 66 johnson 40hp reving high in neutral

I just read the procedure on how to set it , I have an excerpt from the manual in PDF form I can email you if you'd like, PM me your email addy and I will send it to you.

 

[timbo471]

Re: 66 johnson 40hp reving high in neutral

It is model rk-28B

I would appreciate any help you can give me.

 

[F_R]

Re: 66 johnson 40hp reving high in neutral

If it takes off and revs out of control, the vacuum cut-out switch is not working. It is there for exactly that reason.

It is a characteristic of the Big Twin motors to run wild if you rev it up beyond a fast idle--and when it starts to run wild, it won't slow down by itself. That is why they put the vacuum cut-out switch on it. It senses the high vacuum in the intake manifold during a runaway condition and shorts out one cylinder till it slows down.

Way too many of those switches have been deep-sixed by people that don't have a clue what it is there for. Also, the vacuum cut-out switch won't work if the starter safety switch is missing or shot.

 

[bktheking]

Re: 66 johnson 40hp reving high in neutral

What about linkage, is it synchronized properly?

 

[timbo471]

Re: 66 johnson 40hp reving high in neutral

I believe the linkage is adjusted properly.

I will check into the vacuum cutout switch when I next get time to work on the motor.

Do you think the vacuum cutout switch could be the problem?

Reguardless if the vacuum cutout switch the causing the problem. I will still be fixing it. My intentions are to fix the motor and all its working parts to run exactly how they were suppose to.

I am a firm believer in fix it right the first time.

Oh if you do not think the vacuum cutout is the cause of the problem, what else should I be looking for that might need repairing?

 

[F_R]

Re: 66 johnson 40hp reving high in neutral

What does it take to initiate the high revving? Will it start up and idle as long as you don't advance the throttle control? If not, then you have a control or linkage problem.

However, suppose you have it running at idle, and then advance the throttle a bit, and that causes it to take off uncontrollably. That is the vacuum cut-out switch not working.

 

[timbo471]

Re: 66 johnson 40hp reving high in neutral

Just starting it up it will want to rev, if I do not do something to stop it.