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Two ???s regarding 2001 J25 3 cylinder

daselbee

Advanced Contributor
J25TEL3SIE. This is a three cyl 2001 Johnson looper with optical ignition.

First, compressions are: 1---90, 2---95, 3---80.
Does anyone know if this engine should have higher compression than this? It sure seems to turn over by hand way, way to easy.
I cannot feel any resistance as a piston comes up in the cyl...it just seems as if the plugs are out it is so easy to turn.

Second, I am having a fit with the ignition. The sensor under the flywheel is clean, the encoder ring is not broken, but I cannot retard the timing back down to 4 degrees ATDC (spec) for idle. It will not idle, slows down way to slow, and dies.
So, trying to do a link and sync is almost impossible...it only runs when timing is at about 6deg BTDC. Ten degree difference.

My question...can a bad sensor still provide good strong spark, but just way off...like ten degrees?

Carbs are spotless. Owner has a spare pack we will try tomorrow.

But this timing being way out......weird. Anyone with J25 3 cyl experience?
 
Is it running with the " mickey mouse " oil injection ??--------The pack looks after the timing based on engine temperature.----Thermostat installed and working properly. Sensor working properly ?---------Carburetors adjusted by the manual , not just by the normal 2 turns out ?-----------Experience,? I own a number of them for rebuilding.---Have factory manuals too which is a MUST !
 
Thanks Racer. I have a manual. Following it to the letter...even the part about "measuring" the idle mix adj screw head to body length for the initial adjustment. Says it should be out 0.39"...not turns out like normal....

Anyway, I will deliberately disable QS tomorrow, check temp sensor, etc....

What is the compression that you have measured in the past? Should it be up at 120 or so, or is the 90 range I am seeing correct?

No, the guy is running 50:1 premix. No oiling system installed.
 
Well, I guess I am going to assume that this is normal looper compression, and should be around 90-100 when it is a new, fresh motor.
But I don't think that compression is my problem. It must be ignition related, and I strongly suspect the timing sensor.

QS will be disabled this morning to double check. But if I cannot get it to even approach 4ATDC, it has to be pack or timing sensor related.
I will try his other pack this AM also.

Thanks for the help.
 
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