1973 135hp johnson idle issue

[rob 135]

do these motors run rich at slow speed and idle. Hard to get engine at smooth slow speed or loads up while idling . not anything to bad , plugs burning well .Carbs clean and synced.

 

[racerone]

What does a compression test show ?

 

[rob 135]

all good ,fresh rebuild last year . Has always done it even before rebuild. I changed plugs from surface gap to regular ones and that made big difference in low end

 

[emdsapmgr]

The crossflow carbs do tend to overfuel at idle. Just pull a plug out after idling. It will be black and wet. The later crossflows were designed with a recirculation system on the intake manifold. Purpose was to drain excess fuel built up behind the reed boxes and improve idling. Not designed for your early model. Make sure the idle is set to 650-700 when floating in the lake and in forward gear. Your model has very high compression heads. I am sure that you enjoy the holeshot, but the high compression probably adversely affects idling.

 

[Roj115]

I agree with emdsapmgr, from what I've head the '73 heads are the highest compression that they made on those motors and I've also heard the 135s from that era never idled as well as the 115s. Maybe some 135 owners could comment on that.

I have had a '74 115 Johnson since it was new and it idles pretty well but it doesn't run at such high compression and it's a 115. You may be able to tweak some settings to get your engine to idle a little better but it just may be the case that you'll never get the engine to idle very smoothly just because it's a '73 AND it's a 135.

 

[rob 135]

Does have fuel buildup in air snorkel. Does that drain that goes back to engine work very well.You do need a good battery and starter to turn over.