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Following on from the brief interlude in the "introducing myself" thread....
In a nutshell, I acquired a YFM250 Moto 4 (1991) for cheap recently with the previous owner citing "no spark, needs a new magneto coil and I don't have time to fix it"... anyway I am dubious that the magneto/generator is the issue and thinking more along the line of ignition coil as after a clean up of the magneto I was able to get a rather decent voltage reading off the magneto with pull start and resistence readings seem to check out that the magneto is all ok (all 3 x phases = 1.2 ohms and no run to ground)
None the less I ordered a new Ignition coil and Magneto/generator coil and am waiting for them to arrive.
In the mean time I cleaned up the current Magneto, popped in a new battery and sparkplug, checked out all the wiring harness, all seemed good except I came across the "neutral switch" wire was broken.
After wiring up a new neutral switch wire, the neutral light now comes on (small win) and the starter relay (attached to rectifier) now clicks. If I hit the starter switch on handle bar the starter motor spins and if I pull the cord starter I get a spark on pull....YAY!! I'll try and attach a video below if possible.
So onto the starter motor. Starter solenoid seems to work A-ok, even if it looks crappy and starter motor spins as it should when I hit the start switch....but here is my issue.
When the starter motor runs it turns Cog #1 and Cog #2 (see photo below)....but the chain in the back of the starter which I assume is the timing chain, does not move and there is no apparent movement of the piston in the cylinder.
If I turn it by hand (per photo) or with the pull starter however the chain moves and the engine turns. However cog #2 rotates but not fluidly with the "Crank" (part I turn by hand) for the lack of a better word to use if that makes sense?
Is there a grub screw or similar on Cog #2 that fixes it to the center shaft to make it all turn when the starter motor is run? Could there be a part missing? Previous owner had the starter apart so could be possible?
The outer/front part seems to be on a key-way so not sure how to remove this easily to check how Cog #2 is attached.
What am I missing here?
So my latest find is a Moto 4 250. Looked in good shape, started right up but would backfire and die upon acceleration but you
could get it to go if you were good with the throttle. I figured it was the carb. was a brand new Chinese carb, he didn't have original.
I took it apart and cleaned it, only thing I found was some debris in main jet and the main adjustment on bottom was at 41 turns. Cleaned
it out and set at 2 turns, re installed. Starts up, runs better actually drove it but seems really sluggish, once I hit 3rd gear could barely pull
it. Rechecked everything, even ordered a new carb as I had this problem with another atv but still same problem. Now I pull it apart and
decided to check compression, I show only 85 psi. I checked valve adjustment (after aligning up cam gear to mark on case). to make sure not too tight still right at 85 psi.
I assume I need to pull the head and look at the valves, Any ideas I am missing something? motor does not smoke but is super sluggish.
The specs I find are off the downloaded manual of a 94 but figure should be the same. It states compression standard is 128 and Minimum is 114 and Max is 142
Any other Ideas before I tear it down? Thanks in advance Az
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