idle adjustment on 1989 70 hp carbs...no adjustemnt!

[bob johnson]

so the early 89 70 hp J-E carbs didn't have an idle mxture screw adjustment....I see they didn't have them in 88 or 87 as well....how do you adjust the idle MIXTURE...my motor doesn't have a great idle and I just cranked the large screw in almost all the way to get the motor to idle about 900 in the water........but Im thinking the mixture is what needs to be adjusted........I have the manual , but I cant find it ! ...as of right now....so ill ask here

 

[oldboat1]

What large screw? Think you must mean the bottom plug (h.s. jet is behind it.) That plug has to be tight/closed. I think the idle jet is open at the top (no plug). In any case, only thing you can do is thoroughly clean the jets. You can replace them (idle jet, for example) with a different size. The throttle idle setting will boost or reduce rpms, though. If the carb is clean and the motor is otherwise in good shape, you should get about 700 in the water, warm and in gear.

Because OMC went to an adjustment needle after/during the '89 model year, probably fair to assume there were some earlier idling issues.

 

[flyingscott]

The only way to adjust the idle mix is by replacing the idle orifices. I have a 1986 model very similiar to yours never got it to idle better than 850 in gear. Those motors do not have smooth idle idles very common with them. The adjustable carbs do not help as much as you think they will. By the time you get the idle smooth the motor won't accelerate any more because it is to lean. I have a 1992 model I am rebuilding that has decompression holes in the cylinder to help smooth out the idle. I personally never liked the adjustable carbs on the 3/cylinder motors. My 1986 model after the rebuild had to be rejetted I went from 33 to 36 orifices. Could not tell the difference on the idle at all. Mine used to rattle things in my boat it idled so bad.

 

[flyingscott]

What large screw? Think you must mean the bottom plug (h.s. jet is behind it.) That plug has to be tight/closed. I think the idle jet is open at the top (no plug). In any case, only thing you can do is thoroughly clean the jets. You can replace them (idle jet, for example) with a different size. The throttle idle setting will boost or reduce rpms, though. If the carb is clean and the motor is otherwise in good shape, you should get about 700 in the water, warm and in gear.

Because OMC went to an adjustment needle after/during the '89 model year, probably fair to assume there were some earlier idling issues.

He means the large screw on the side of the motor for the idle adjustment. Not realistic thinking that motor will idle at 700 rpms.

 

[oldboat1]

Good info. Thanks! Have to have limited expectations for it, I guess.

 

[bob johnson]

it was idleing probably about 750 or so id guess, based on the fact that after I turned the screw in to push off the stop it went up to about 900..in the water in gear......but the motor shook a lot and it LOOKED like it might stall, even though it never did. i m guessing that little jet on top in the center of the face of thje carb is the "idle jet"....but it doesnt seem to be in the fuel supply chain!!!!!!!!....if anything its just an air feed..... thats why i didnt think it was the idle ":jet". Even though the motor didnt die....when it seemed for sure it would.....im concerned that once it gets colder... IT WILL DIE at idle.....is there a down side to me screwing in that overall idle screw in to raise the rpms to about 900????thanks

 

[racerone]

Any other testing done ??----And does the tell tale hose come off the side of the block or the top ??-----Compression test first.---Flywheel key checked ?------In good condition they will idle nicely.------

 

[bob johnson]

i did the water hose retrofit.... the compression was great.... dont know about the flywheel key...is that a recurring problem? i was going to start another thread on the WOT issue i experienced...

 

[bob johnson]

so thats the nature of the beast....its good to hear that im experiencing the same thing that most of you are for that year motor.....and it does make sense that there was an "UPGRADE " to the carbs put in place mid year in 1989... for this motor because of apparent issues.... so ill just live with the rough idle...it wasnt the big issue i have with the motor, but i figured it would be the easiest to fix, so i brought it up first....next will be the WOT issues...another thread

 

[racerone]

Checked for cylinder sleeve out of position ?

 

[bob johnson]

Checked for cylinder sleeve out of position ?

no....would not have thought to look for that.... i was looking for the simple exterior setting adjustments!!!!!!!!!...frankly...if the cylinder sleeves go out of position enough to be a regular issue...Id look at just getting rid of the motor!

 

[racerone]

Cylinder sleeves out of position is NOT a common problem.----With the right tool ( camera on probe ) it is easy to check.