Bike has fresh stator, new volt reg, new battery. When cranking via Elec start, spark is weak then gets NONEXISTENT. Use the recoil and spark is good. Bypass starter system with direct power to starter and no spark. WTF ??? Anyone with similar or ideas ??

 

I've had this on Hondas and never cured it. Owners get used to "bliping" the starter button, one of those sparks will catch. Some say it is dirt on the trigger coil in the alternator.

 

Sounds just like what has happened on a lot of Polaris 500s.Would recoil start,but not electric start. Pick up coil or flywheel magnetic tab dirty or distance too far. Don't know if this helps,but what one member found out on his atv. no spark to plug when using electric starter - Page 3 - ATVConnection.com ATV Enthusiast Community

 

OK, I'm going to pull the Stator cover off. Move rotor mag to pulse coil. If need be, I'm going to SLOT the pick up mounts to get it maybe .004" from the magnet and see what happens.

Will post results

 

Don't know if Yamaha shows the pulse coil (pick up) gap to flywheel distance or not,but as a reference, Polaris shows between .016 -.040 as the gap clearance. .004 may be a tad too close? Kinda brings back ancient memories of setting point gaps before cdi ignition came out.

 

I had a weak spark on my 500 where it would start with pull rope but not electric.
Turned out the tigger /Pulse coil's magnetic face had metal filing and dirt stuck to it. I cleaned it up and it was all fine.

 

Moved pulse coil to the point of contact an back ever so slightly. Marginal if any change.
Being I do see a spark, but not as strong as with the recoil, the amount I'm getting should still be enough IMO to start it. Being its a PAIN IN THE A#$$ to pull, I'm focusing on elsewhere. Spark, compression , fuel.. Valves set and carb cleaned.. Now to pull the pipe and see if some "critters" made a home inside, or left a cache of nuts/seeds which will stop the combustion process.. Will post back results

 

Pulse coil could possibly be weak. You said it had a "fresh" stator,but did you replace the pulse coil with it? Stator new or used? If you had the resistance specs on the pulse coil along with the stator specs,it would possibly help to narrow down the problem.This where a good service manual comes in.

 

pulse coil included with Yamaha stator. NEW components..

 

another yamaha yfb 250 start problem is also the neutral switch, located directly behind the shifter, pointing down. if that wire is dirty, frayed, it makes the neutral light flicker and they wont turn over or barely turn over, but you can pull start the quad or even jump the solenoid and it will fire.