adjusting idle and low speed adjustment

brothere

Cadet
Joined
Aug 9, 2004
Messages
14
Hi, I have a 15 HP Johnson...(1985) that has an idle adjustment and a low speed adjustment...Idle seems to be fine but I would like to know if anyone knows of a good starting point with these adjustments and how do I know if I should lean it or turn it the other way? (forgot what its called LOL)...low speed adjustment mean trolling speed? thanks a bunch!!! all of you have been a great help so far!!!
 

rickdb1boat

Supreme Mariner
Joined
Jan 23, 2002
Messages
11,195
Re: adjusting idle and low speed adjustment

Turn the low speed needle in until lightly seated. Then turn it out 1.5 turns for starters. Then in gear on the water, adjust it in 1/8 increments in or out, until the smoothest idle is obtained. Not sure of you idle speed, but I would guess around 650-700 RPM's in gear at idle speed... Some folks turn the low speed out from the 1.5 setting until the motor stumbles and the turn it back in in small increments until it smooths out... This wil give you a slightly richer mixture than above..
 

rwise

Captain
Joined
Jul 5, 2001
Messages
3,205
Re: adjusting idle and low speed adjustment

brothere<br />Quote from Joe Reeves<br />The proper adjustment procedure follows:<br /><br />(Carburetor Adjustments - Two Adjustable N/Vs) <br />(J. Reeves)<br /><br />Initial settings are: Bottom high speed = seat gently, then open 1 turn out. Top slow speed = seat gently, then open 1-1/2 turns. <br /><br />Setting the high and low needle valves properly: <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 />(High Speed) Start engine (it will run pretty rough), shift into forward gear, take up to full throttle. In segments of 1/8 turn, waiting for the engine to respond between turns, start turning in the bottom high speed needle valve. You'll reach a point whereas the engine will either start to die out or spit back (sounds like a mild backfire). At that point, back out the needle valve 1/4 turn. Within that 1/4 turn, you'll find the smoothest setting. <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 />--------------------<br />Joe (30+ Years With OMC)<br />end quote
 

chimo

Cadet
Joined
Jun 5, 2003
Messages
26
Re: adjusting idle and low speed adjustment

Is this the adjustment screw you are talking about?<br />Thanks!<br />
Carb.jpg
 

rwise

Captain
Joined
Jul 5, 2001
Messages
3,205
Re: adjusting idle and low speed adjustment

if it has just a low speed adjustment start at 1.5 turns out. that could be the low speed fuel mix, but,,, "bump" maybe someone will see it that knows
 

Bass2ply

Cadet
Joined
Jul 30, 2004
Messages
12
Re: adjusting idle and low speed adjustment

Low and high speed adjustments are made at the front of the carb, not where pictured above.
 

rdav13

Seaman Apprentice
Joined
Jul 6, 2004
Messages
44
Re: adjusting idle and low speed adjustment

sure looks like an adjustment screw to me.
 

chimo

Cadet
Joined
Jun 5, 2003
Messages
26
Re: adjusting idle and low speed adjustment

I was told since this post that it was the air/fuel mixture adjustment screw. I do not see any other adjusting screws on the carb.
 
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