1982 Johnson 115 inconsistant idle

[jwjw7108]

Hello. I have a 1982 Johnson 115 with hyd. tilt/trim. I have a problem with inconsistant idle. This motor Idles rough on muffs at around 1000 rpm. Idle is at about 850/900 rpm on water in nuetral. And just in gear at 600 rpm. The problem is when throttled up just a tiny bit to maintain a higher side trolling speed(between about 3.5/4.5 mph on gps) the idle begins to increase then decrease back and forth. Increasing throttle speed to about 5 mph seems to cure this problem. I have tried trimming up and down in the water to see if it will eliminate the problem. It does'nt. I have new plugs, cean carbs. Carbs are sinked. Plugs are gapped at .030.(even though .040 according to the service manual, not the technical change the boat shops have seem to have much smoother idle results while on muffs). Compression is between 108 and 115, 1 thru 4 cylinders. It takes it a few more turns of the flywheel to fire up gapped at .030 but either way allways fires up. What the heck is goin on. Is this a normal condition for that rpm range? Any help or input on this would be greatly apreciated. Thank you to everyone who took the time to read my post!!

 

[Daviet]

Re: 1982 Johnson 115 inconsistant idle

I think your idle is a little low to start with. Shouldn't it be about 700-750 in the water in gear?

 

[jwjw7108]

Re: 1982 Johnson 115 inconsistant idle

Thank you for the reply. I agree with you. But as i am new to outboard motors, i take a lot of advice from local, more experienced and knowledgable outboard service techs but get inconsistant answers. The one that I believe has a much more broad range of motors of many diferent brands told me to go from 650 to 750. That being said, I decided to go with 650 only because it idles much better in that range once it is out of the water on muffs while flushing the cooling system. If I go much higer than that while adjusting on the water, It runs closer to 1300 on muffs. Idont think i am too comfortable running it that high on muff pressure for 5 minutes or so to clean out the system. What do you think? Thanks again for the reply Daviet!

 

[Daviet]

Re: 1982 Johnson 115 inconsistant idle

When running on a hose the idle will be faster because of lack of back pressure in the exhaust system. It will be OK to run the engine at a 1300-1500 rpm idle on the hose to flush it out.

 

[jwjw7108]

Re: 1982 Johnson 115 inconsistant idle

Ok. I will bump it up. Do you think that will stabilize the slow on rpms? And what is your opnion on the spark plug gap issue I am facing? The manual I have is a Johnson/Evinrude 1980 edition and I was told that the information was correct for maintenance on my 1982. My manual specifically states .040 gap. I hav not seen any technical change myself but am told by some of the other mechanics that the tech. change to .030 is legitimate. Why would they change the gap when it makes such an obvious idle difference towards the negative? Or has it been proven to make a positive change, and I am missing something else possibly in the timing system or something like that?

 

[Daviet]

Re: 1982 Johnson 115 inconsistant idle

If your idle is to low, sometimes the engine will surge at idle, set it properly under load and in the water and see what it does.
There are many opinions on the plug gap, I set them at .030, and don't worry about it. Sometimes they change the specs for unknown reasons.

 

[jwjw7108]

Re: 1982 Johnson 115 inconsistant idle

Ok. Thanks for the info. I will reset it.

 

[emdsapmgr]

Re: 1982 Johnson 115 inconsistant idle

Make sure both the upper and lower carb butterflys are absolutely closed at idle. (you may have to remove the airbox cover to confirm their position.) If one of the carb butterflys does not close fully, it can cause your idle problems, including hunting. You have not mentioned complete carb cleaning. If you get any dried fuel in the idle passages, it will idle poorly.