slow speed fixed jet??????? how to get lower speed idle set

Joined
Jul 22, 2012
Messages
6
1974 20 HP johnson rebuilt at dealer and brought home running perfect now two years of setting in my heated basement it will only stay running half throttle to full ... cleaned Carb and still the same why would there be a fixed jet on the slow speed.....ggggggrrrrrrrrrrnow how does one adjust the low speed.....? Any help is appreciated
 

ultra353

Petty Officer 1st Class
Joined
Jun 21, 2009
Messages
388
Re: slow speed fixed jet??????? how to get lower speed idle set

Sounds like your carb is still clogged since it ran fine when you put it away. How did you clean the carb? Make sure all gaskets are there and in good shape. Carb cleaner and compressed air threw all jets and passages ( removing the core plugs as well and will have to be replaced as once removed their ruined).
The low speed mixture is controlled by the taper of the needle it doesn`t have a physical jet like the high speed jet of the carb. Once carb is completely clean, turn the low speed mixture in (clockwise) until it lightly seats. Turn it 1 1/2 turns out and start motor. Let motor warm up, this should done on the water and in gear but to make sure it runs ok first try it at home in a barrel of water. Turn mixture knob in 1/8 turn and let motor respond for 10-15 secs, rpms should increase- lower rpms a bit with idle adj. Keep doing this proceedure until motor starts to cough or miss, turn mixture knob out about 1/4 turn +/- this should smooth out motor.
 
Joined
Jul 22, 2012
Messages
6
Re: slow speed fixed jet??????? how to get lower speed idle set

But there is no adjuster for slow speed at all just a bolt with gasket on outside of bowl and some kind of fixed jet or something on the inside of bowl... can't adjust slow speed at all.... there's a high speed adjuster needle. But no slow speed adjuster at all
 

Daviet

Fleet Admiral
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Sep 24, 2008
Messages
8,958
Re: slow speed fixed jet??????? how to get lower speed idle set

You have your jets mixed up. The high speed jet is in the bottom of the carb bowel behind the 7/16 drain screw. The low speed jet is the adjustable one towards the top of the carb, the needle valve is brass and sticks out towards the front of the engine.
What is your model number, I didn't see a 20hp listed in 1974.
 
Joined
Jul 22, 2012
Messages
6
Re: slow speed fixed jet??????? how to get lower speed idle set

20ba-74m made in Canada on my motor casing it says slow on bottom and I am 100% sure as I am looking at it now.... maybe an aftermarket. Carb in it? I can't find any info on this motor at all... it looks as if there had to be some kind of. Adjuster there before nothing now..... thanks for the help
 

monnewbie3

Petty Officer 3rd Class
Joined
Sep 12, 2011
Messages
90
Re: slow speed fixed jet??????? how to get lower speed idle set

I would open the carb up and rebuild it if it hasn't been already.
I think those old carbs used cork gaskets... Sometimes the "o" ring seal on the jets could be toast... If that's the case your low speed won't work.
But then again you can't find parts for it...no other info on the motor?
 
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