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Author Topic:   1991 Johnson 40-HP: Idle Speed Adjustment
JL8Jeff posted 06-19-2005 11:52 AM ET (US)   Profile for JL8Jeff   Send Email to JL8Jeff  
I noticed that the idle on my Johnson 40 seems a little lowm and it wants to stall when you put it in gear. I took a look, and there is nothing in the owner's manual about adjusting the idle. I can see that the throttle linkage is not quite making contact with the cam--I guess that's what it's called--that controls the throttle blades to both carbs. Is it just a matter of adjusting the throttle cable until this cam touches the roller to increase the idle speed or is there an adjustment on the carb itselfm like adjusting air screws or something? Thanks,
jimh posted 06-19-2005 03:23 PM ET (US)     Profile for jimh  Send Email to jimh     
A two-stroke motor's idle speed is also affected by the ignition timing. You may want to check that this is also within specification.
whalerskiff posted 06-19-2005 10:38 PM ET (US)     Profile for whalerskiff    
There is a Idle Stop Screw Located on the LEFT SIDE as facing engine from front. What it actually does is advance or retard the timing before the throttle cam comes into contact with the throttle roller. Idle adjustment is always done in forward gear,with the propeller fully loaded in the water. Never do this adjustment using ear muffs. The engine needs to have some exhaust backpressure to be accurate and the only way is to have the lower unit in the water,in gear. Best thing to do is refer to an actual OMC Manual for this procedure. It will also detail the throttle sync,and the cam contact position. Hope this helps,but it is too hard to convey the actual instructions here.
JL8Jeff posted 06-20-2005 04:22 PM ET (US)     Profile for JL8Jeff  Send Email to JL8Jeff     
Thanks for the responses. I made a typo though, it's a 1999 Johnson 40 hp. And yesterday I was getting ready to go out with it and had the engine running on the fast idle for about a minute to warm up and then dropped it back down to normal idle for a minute. Just as I grabbed the dock line to untie, the engine sputtered and stalled out in a cloud of blue smoke. It restarted once and stalled out immediately. I couldn't get it restarted after that. I changed the plugs and I could see quite a bit of oil coming out of the carbs when I tilted the motor up. It still wouldn't restart. It seems like the oil injection suddenly got overly rich and flooded it. I'm not sure if I'll have time today to check it out, but does this sound like an oil injection problem? I never had the chance to touch anything regarding the low idle so I know it wasn't anything I did.
jimh posted 06-21-2005 12:51 AM ET (US)     Profile for jimh  Send Email to jimh     
Check your gas line primer bulb. If you don't have a good prime on the gasoline line you could get a bad mix of oil, gasoline, and air. Also check the oil primer bulb.

The oil line usually has a clear section under the cowling to show good oil flow and prime.

I find that if my engine stalls at idle speed it is often due to poor priming of the gasoline line.

More information about the VRO2 system is available in the Reference area:

VRO STORY—The Myth of the Mixer
by Bill Grannis

jimh posted 06-21-2005 12:56 AM ET (US)     Profile for jimh  Send Email to jimh     
Some advice on starting and warm up: read the owner's manual. Your engine has a fast start system which will automatically adjust the engine idle speed based on the temperature. If you are manually moving the throttle to fast idle, you probably are not following the recommend starting procedure.

If you follow the recommended procedure and let the engine handle the starting conditions it will:

--adjust engine timing for better starting
--add extra fuel at start up
--run at fast idle until warm

and it will do all of this automatically. If you fiddle with the throttle yourself, you lose all this stuff.

I find that I can typically start my engine from a cold start on the first crank, and it will run until warm without stalling or re-starting, if the fuel line is properly primed and I follow the owner manual's procedure.

JL8Jeff posted 06-21-2005 08:45 AM ET (US)     Profile for JL8Jeff  Send Email to JL8Jeff     
From what I remember reading in the owner's manual you are supposed to set the fast idle lever when starting it. I'll give it a try without using the fast idle lever. The previous owner said he used to flood it out all the time and he went by the manual for starting it. Does anybody know of any really good books for these motors(1999 Johnson 40 ELP)? I'm one of those people who can't just use something, I need to know how it really functions so I can tell if it's running properly.
jimh posted 06-21-2005 08:59 AM ET (US)     Profile for jimh  Send Email to jimh     
I have the OMC shop manual for my OMC engine. It has hundreds of pages and photographs. It has detailed procedures for disassembly and repair. Your OMC dealer sells them.
JL8Jeff posted 06-21-2005 09:03 AM ET (US)     Profile for JL8Jeff  Send Email to JL8Jeff     
That was a good article on the VRO. I thought of a quick question while sitting here at work. How much fuel should there be in the fuel filter? I remember looking at it thinking it almost looked empty. Then I could see that there was maybe a 1/2" of fuel in the bottom of the filter(since it sits verticle). The boat has the fuel tank and oil tanke mounted under the center console(15' boat) and I'm wondering if there is an issue with the fuel line or primer bulb. Thanks for the tips.
TexasWhaler posted 06-21-2005 12:51 PM ET (US)     Profile for TexasWhaler  Send Email to TexasWhaler     

Take a looksy at something else on your 40. On the side of each carb, there is a small screw (for a flathead) to adjust what I think is the needle valve for each carb. I had a 1989 Evinrude 40 that was the EXACT motor as yours - even the same as the 2005 Johnson 40s.
It had a problem that sounds exactly like what your experiencing, and tweaking with those little screws fixed the idling problem. Adjusting these had no effect on speeds above idle.
Make sure to adjust these while the engine is running in idle.

What you can do is start with the top carb first. Adjust the screw clockwise a couple of turns and listen, then counter-clockwise a couple of turns and listen. If the top carb is the offending client, you'll hear the idle get noticebly better by the adjustments made to it.
Keep track of the number of turns in either direction you make.
If the idle does not get any better, return the top carbs screw to its original position and repeat these steps for the bottom carb.

This may not be the problem, but it's easy to check and it's free!

JL8Jeff posted 06-21-2005 11:15 PM ET (US)     Profile for JL8Jeff  Send Email to JL8Jeff     
Well, I only had a minute today to take a quick look at things and I noticed that the fuel tank under the console has a 3/8" fuel line going to the primer bulb and then a 1/4" fuel line going from the bulb all the way back to the engine. The tank is under the center console. Also, the 1/4" line has started to harden pretty bad so I think I will replace all of it to eliminate the possibility of air getting into the fuel lines.

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