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1995? Johnson 40HP run/miss/run/miss at Mid-RPM

J

JeffYo

New member
Just bought skiff with above. Starts and runs fine at idle and low RPM. On acceleration it won't go past about 2000rpm and "skips beats". I'm new to two-cycles! See attached and listen closely if you can. Any help appreciated! Thanks.

Jeff

Sorry - couldn't get attachment uploaded. Will try later. Still hoping for some info!
 
You say it doesn't go past 2000 rpm and skips beats... what does that mean?... Ignition breaks up, stays running, but is misfiring, stalls out and dies, what? Sometimes it's difficult but try to define exactly what the engine is or is not doing.

Info we need..... Compression psi reading of all cylinders..... With s/plugs removed, the spark should jump a 7/16" gap with a strong blue lightning like flame, a real SNAP! Does it?
 

If I did this correctly, here's the motor mis-behaving. Yes, I know I'll need to test spark/compression. Very soon! Thanks!
 
joereeves said:
You say it doesn't go past 2000 rpm and skips beats... what does that mean?... Ignition breaks up, stays running, but is misfiring, stalls out and dies, what? Sometimes it's difficult but try to define exactly what the engine is or is not doing.

Info we need..... Compression psi reading of all cylinders..... With s/plugs removed, the spark should jump a 7/16" gap with a strong blue lightning like flame, a real SNAP! Does it?
Click to expand...

Ok finally did compression/spark test. 140/150 bottom/top. Def good spark. Dumped 1 gal fuel out of tank into clear container and it’s nice and clean no water. Now what next? Carbs? Fuel pumps? Timing? Oh and it revs up nicely in neutral at rest.
 
You state "Def good spark"... By that, I'm assuming that the spark jumps a 7/16" air gap on all cylinders with a strong blue lightning like flame... a real SNAP! ?

That video sounds like (to me) both cylinders cutting in & out via 1 second intervals. A fuel problem wouldn't cut the engine off/on that quickly so I'm leaning more towards ignition.

Disconnect the black/yellow wire (kill circuit) from the powerpack that leads to the ignition switch... or from the ignition switch itself to see if that has any effect.

Also.... the timer base under the flywheel that rotates as the throttle is increased.... Check all its wires as possibly, at some point in rotating, one or more may have frayed and is shorting out to the block/crankcase or experiencing a make/break situation.
 
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joereeves said:
You state "Def good spark"... By that, I'm assuming that the spark jumps a 7/16" air gap on all cylinders with a strong blue lightning like flame... a real SNAP! ?

That video sounds like (to me) both cylinders cutting in & out via 1 second intervals. A fuel problem wouldn't cut the engine off/on that quickly so I'm leaning more towards ignition.

Disconnect the black/yellow wire (kill circuit) from the powerpack that leads to the ignition switch... or from the ignition switch itself to see if that has any effect.

Also.... the timer base under the flywheel that rotates as the throttle is increased.... Check all its wires as possibly, at some point in rotating, one or more may have frayed and is shorting out to the block/crankcase or experiencing a make/break situation.
Click to expand...

I'm using the OTC 6589 spark tester, and the sparks are regular, blue, and seemingly "strong". Somebody did run a separate kill circuit to a push/pull switch other than the standard ignition switch. I'll investigate that and flywheel wiring. Thanks again.
 
So still no answer to the ----Does spark jump a gap of 7/16" , yes or no ?-----Folks do not understand how important it is to state clear facts ----But that is just my opinion.
 
Trigger wires, I am leaning with Mr. Reeves. Is the boat from an area that gets really cold while the motor is being used? Like Minnesota? I get more problems, it seems, with wiring, than normal.....especially when motors are used in May and Oct/Nov.
 
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