quits after idleing

handball

Petty Officer 2nd Class
Joined
Dec 13, 2002
Messages
161
1990 4 h.p. johnson starts easily with a choke, runs great at high speed. when left to idle in nuetral it slowly slows down after a minute or so and then quits. Also will only stay running if put in gear at very high idle speed.Installed new plugs with no change. Also there is a knob for choke that rotates left and right , I assume this is the low speed adjustment.<br />Bill
 

Kev

Seaman
Joined
May 15, 2005
Messages
61
Re: quits after idleing

The motor dying at low speeds and only shifting without dying at higher speeds sounds like it's either leaning out (wrong carb setting) or has a dirty carb. (You are running 50:1 gas:eek:il mix, right?) First, try adjusting your carburetor. Hopefully this fixes your problem. The slow speed needle valve is that Rich-Lean knob you see. (instructions below) Second, try cleaning your carb thoroughly (soak it 24 hours, blow out all passages with compressed air, remove metal plug to clean out idle passages and replace with new plug) and rebuilding it with an OEM carb kit. <br /><br />Thank Joe Reeves for these awesome instructions!<br /><br />(Carburetor Adjustment)<br />(J. Reeves)<br /><br />Initial settings are: Slow speed = seat gently, then open 1-1/2 turns.<br /><br />NOTE: For engines that DO NOT have a shift selection, obviously there is no NEUTRAL position. Simply lower the rpms to the lowest setting to obtain the low speed needle valve adjustment.<br /><br />(Low Speed) Slow the engine down to where it just stays running. Shift into neutral. Again in segments of 1/8 turns, start to turn the top needle valve in. Wait a few seconds for the engine to respond. As you turn the valve in, the rpms will increase. Lower the rpms again to where the engine will just stay running. Eventually you'll hit the point where the engine wants to die out or it will spit back. Again, at that point, back out the valve 1/4 turn. Within that 1/4 turn, you'll find the smoothest slow speed setting.<br /><br />When you have finished the above adjustments, you will have no reason to move them again unless the carburetor fouls/gums up from sitting, in which case you would be required to remove, clean, and rebuild the carburetor anyway.<br /><br />Good luck and report back with your results! An OEM service manual for your motor will be a great help with maintenance and adjustments.<br /><br />Kev
 

handball

Petty Officer 2nd Class
Joined
Dec 13, 2002
Messages
161
Re: quits after idleing

Thanks Kev,<br />I totally agree with you that it sounds like the mixture is leaning out and thats the reason it quits. I do own a johnson service manual but it covers a number of engines some but its not real good for detail.<br />I have bought a carb rebuild kit but have not done the job yet.<br />The only knob the engine has for carb. adjustment is also the choke knob, so every time you start the engine using the choke you disturb the carb adjustment. I would like to give the guy that came up with that idea my 2 cents.<br />Thanks again Kev.<br /><br />BILL
 

Kev

Seaman
Joined
May 15, 2005
Messages
61
Re: quits after idleing

Wow Bill, that's an interesting choke design. Didn't realize. I should have looked it up. Sorry 'bout that. Can you find the optimal low speed carb setting and re-center the knob? That way if you change it to start the motor you can easily return the knob to it's "running" setting? On my 9.9 you can easily recenter the knob so if you want to run richer for cold starting you can turn the knob, then it's easy to go back to the center position and know you have your normal slow speed carb setting again.<br /><br />Let us know how the carb rebuild goes too!<br /><br />Good luck!<br />Kev
 
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