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90 Johnson High Idle

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dballardmacon

New member
I have a 1990 90 hp johnson. Ir runs great to 5000 rpm. Bad idle.
I rebuild the carbs, replaced a broken vac hose below the bottom carb. New spark plugs. Idled better but still unacceptably rough. Compressions 135 all cylinders.

Drained the gas, and replaced with new mix gas.
Installed new power pak, coils and plug wires.
I unplugged the gray fast start wire on the power pak. Cranked and checked the WOT timing, it was at 16, specs call for 28 BTDC. I increased the timing to spec. Cranks and idles at 2000 rpm. Verified throttle plates fully closed. Ran the timing back and the idle decreased to 1500, but surges. Hoever, runs smooth on all cylinders, just fast at idle. I do not see any loose vacuum hoses.

What to look for to get the idle back to 900?
 
Timing on a motor like this is set at the factory and rarely goes out of adjustment.-----Does primer bulb go hard ?------All linkages in place?-----Is timer base rotating back to idle position ?----Orange wires to coils are orange / blue stripe on both upper coils ?----Flywheel key checked ?
 
racerone said:
Timing on a motor like this is set at the factory and rarely goes out of adjustment.-----Does primer bulb go hard ?------All linkages in place?-----Is timer base rotating back to idle position ?----Orange wires to coils are orange / blue stripe on both upper coils ?----Flywheel key checked ?
Click to expand...

Primer does not go hard, but the carbs do have plenty of fuel. I am wondering if I am getting an air leak in through there.
All else as you asked.
Flywheel key, no I have not pulled the flywheel. But, I did put a pencil in the #1 cyl an drotated the flywheel. The TDC does line up with the pointer.
I just cranked the engine and after a couple of minutes, it took off to 3000 rpm.
does the 1990 model have an optical sensor?
 
racerone said:
No optical sensor.-------Primer bulb has to go hard , if not you have a leak somewhere or a bad bulb.
Click to expand...
So I pulled the carbs and studied the engine for a while. Nothing was amiss. I had pulled the carbs for cleaning and decided to remove the bottom bowl cover. In the cleaning, I removed the 2 silver discs to verify the circuits were cleand and open. I put new discs in the asame manner I found. The discs are curved, concave or convex depending on how you look at it. I found that one disc had just dropped off and was laying in the bottom of the cover. This allowed that carb to an unrestricted flow of fuel. The surging was the carb coming off of the diel circuit to main jet with this fuel flow and high rpm. I can imagine other people who had the carbs cleaned or rebuilt having this issue if they have sudden high idle rpm and nothing other obvious in sight.
 
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