150 doesn't like to go slow

[Lil' Johnson]

Hey people, I have a 1985 Johnson 150 on my 19'4' deep vee center console. It has a 19 pitch prop. My problem is that my motor does not like to idle or even go slow at trolling speeds. It runs very well at cruise or WOT but if it idles for more than a few minutes, it will die and then it is a pain in the *** to get underway again. I can always get it started ok but when I put it in gear, it bogs and dies. When it does manage to get going it bogs pretty hard and then it catches and takes off. According to my tach(which I am not sure is accurate or not, but I think it is) the motor is idling at about 600 RPM. I have pulled the plugs right as I am having these problems and they are always pretty wet and black. I don't think I have ever pulled them and saw a nice tan color. (I am an auto mechanic by trade, but I am not sure what the plugs should look like with the oil mix in the fuel) I was thinking maybe raising the idle will help but I am not sure how to adjust it. I also thought maybe the idle mixture on the carbs was too fat but IDK where those adjustments are either. It looks like I adjust the idle on the throttle linkage. Any suggestions? I like to ask here before I go screwing with things that I should leave alone. Also my boat only shows to be turning about 5000 rpm and it used to show 5200. It goes about 42ish WOT. Is this an acceptable WOT RPM range? I am definitely happy with the boats performance other than the low speed issues. Motor has new stator, plugs, 1 power pack, and carbs have been cleaned checked and rechecked. any help guys?

 

[jtexas]

Re: 150 doesn't like to go slow

Fixed jets on the carbs, no mixture adjustments. You are correct theres an idle adjustment screw on the linkage.

I would have guessed float valves misadjusted or worn out, not closing off completely, flooding the motor. Did you install new kits when you cleaned the carbs?

If you been working on the carbs, have you gone through the link & sync process? You'd need a manual for the step-by-step.

After idling the plugs will be a little oily, but the insulator should turn that nice golden brown.

 

[emdsapmgr]

Re: 150 doesn't like to go slow

The idle is set on that engine by adjusting the idle timing, not by adjusting anything on the carbs. The idle adjustment screw is on the spark advance lever. Your engine may have the idle set too low. The engine should idle smoothly between 650-750 rpm, set when in gear at idle with the boat floating at normal level in the lake. It's not unusual for the plugs to be black and appear wet when the engine was just idling. You will get a light tan plug color if you do a 5000 rpm throttle cut off into neutral. Your engine should be running in the upper end of the "normal" rpm range, or 5500 rpm, (or slightly higher-5700.) See where your rpms are when you get things sorted out-but it is likely you need to go down a pitch on the prop.