1987 johnson 120 hp

[RONSMLR]

have to set timing to 20 atdc to get anywhere idle rpm still 1200 rpm motor acts like it has a horrific air leak into manifold (all work done with muffs ) motor stalls when introduced to water at proper depth to correct back pressure

 

[Joe Reeves]

Re: 1987 johnson 120 hp

The timing must be set to factory specifications (whatever that is) unless you want to melt a piston.<br /><br />What is the compression on each cylinder? With the spark plugs removed, does the spark jump a 7/16" gap on all cylinders with a strong blue lightning like flame?<br /><br />If you've had the flywheel off and did not torque it to factory specifications (145 foot pounds), the flywheel key has no doubt sheared and threw the engine out of time. If this is the casae, clean the flywheel and crankshaft tapers before attempting to install a new key.<br /><br />The key should be installed with the straight edge vertical with the engine (straight up and down), not slanted with the crankshaft taper.

 

[AUGIDAWG]

Re: 1987 johnson 120 hp

Never try to tune or adjust things on the muffs.<br /><br />Try setting the idle timing to zero degrees, top dead center, and run it in the water. Warm the engine up to normal operating temperature. If it idles too fast, retard it (ATDC). If it won't idle, advance it (BTDC). <br />Get it ideling well, and let Joe Reeves know what the timing at idle ended up to be.<br />Everything may be ok at the lake, not in the driveway on muffs. That's my personal experience.

 

[Dhadley]

Re: 1987 johnson 120 hp

Have the carbs been off?

 

[RONSMLR]

Re: 1987 johnson 120 hp

yes carbs have been cleaned appeared ok except idle air jet is 16 & intermediate jet is 43,,what info i have says idle air should be 41 & intermediate should be 50 waiting for service manual for proper settings & jet sizes thanks( believe carb "o" rings seated properly but will check when it quits raining also finding some loose motion in arm connected to throttle shaft seems to allow 1 throttle to open b4 the other by 2 to 3 degrees

 

[rodbolt]

Re: 1987 johnson 120 hp

Hello <br /> you say it acts like an air leak? usually any airleaks will cause a lean sneeze or cough and a lack of idle speed just before the piston melts. some of the 120 140 loopers as they wear wont idle very well on a flusher. my poor old 120 idles about 1800 on the flusher but will troll for hours at 650 rpm in the water turns up to 5500 pusing an old thunderbird tri-hull about 33 mph. I have seen a few other motors do the same. good luck and keep posting<br /> oh another thought on the airleak. I have seen a few lean backfires actually blow out the intake to crankcase gasket and 2 that blew the gasket out from the reed block to intake

 

[93bronco]

Re: 1987 johnson 120 hp

actually for the 1987 120<br />its<br />#16 idle air<br />#42 intermediate starboard<br />#45 intermediate port<br />#59d high speed<br />-<br />the #41 & #50 are for 1988 and up to 1991.