How to smooth out the idle of 150 Johnson carb'd ?

[bgreene]

After running fine at cruising rpm ( 4,200 + or - ) for miles, when I slow down to slow forward, or idle
in neutral ( 1,000 rpm or less ) the engine will run with a slight "cough " and tend to stall.

It starts right back up, and is in great shape otherwise - compression etc fine.

Is this a carbon build up thing, and anyone know of any treatments to avoid this ?
Fuel additive etc ?

Engine's a 94' Johnson Ocean Runner 150 hp carb'd .

[dmartin1953]

decarbon, change the plugs, have carbs rebuilt and run Ringfree

[Lone Ranger]

Had the same problem with my 1995 175 Oceanrunner,AFTER I had 2 Carbs replaced.Guy I had do it Re-adjusted the idle mixture screws[all carbs.] to 5 turns out causing a lean idle condition.I took them out to 6 to 6 1/2 turns out just as they were when I got it.Would idle all day without a hic-cup after I re-adjusted.

Those plastic carbs are JUNK!!If they go bad ,REPLACE them[as needed],You will Never find out what is wrong with it[carb/s][Mike]

[stevec717]

If you haven't done it this year - decarb, decarb, decarb. This fixes 90% of idle issues with Johnsons. First thing a dealer would do. I like to use thge OMC Engine Tune (about $10). It has the hose that goes right to the fitting on the Johnson. Follow instructions. We hadn't done ours in a couple years. Same issues you mentioned. We did it and there was a black patch about 5' in dia on the lawn where all the sh*t blew out. We did a second treatment, then ran her out under load (to clear out thoroughly) then changed to new plugs. Restored beautiful idle and no more roughness, stalling, "sneezing".

Good Luck

Steve

[bgreene]

Thanks for the suggestions. I really like the simple reliability of these Johnson carb'd engines.