1991 Yamaha Moto4 - 250 - Starting help

[Spudhut001]

Hello all.  Happy to be on this site.   The information is priceless.  Quick background on me, I have built hot rod cars from 1920's to 70's for many years. 

I currently have a 1991 Yamaha Moto4 250 2wd quad.   The bike is in great shape.   I bought it from an older guy who used it around his farm until it decided to stop running.   He figured it was an electronic issue since it was a "crank no start" situation.   He replaced the original CDI with a cheap Chinese unit and a stator with a cheap amazon part.   What was happening, as you started it, with the spark plug grounded, it would spark on the the push of the starter button - then no spark as it turned over - then spark when the button was released.   When I got the bike, he did give me the oem cdi and stator.

Fast forwarding, I picked up a manual.  I started to check all the electronic specs.

~The original stator, falls in spec per the troubleshooting methods as described by Yamaha.   I swapped out the china stator for the original.   

~The china cdi box was removed and i put the original cdi back in.   What I discovered was the original cdi did not give off any spark.  I picked up another original 'good used' cdi as I dont know if it is possible to test.

~new DK coil pack, spark plug and spark plug cover and swapped it in. ( I tested spark plug cover, the manual says it should be 10 ohms but the plug cover is showing 5 ohms.  Not sure if this is vital issue)

Now I am getting spark consistently out of the plug, grounded to head/fins. 

I have 2 china carbs.  One that came on the bike and a 2nd new in box.  Fuel is flowing from the tank to carb.

When I try to start, the bike just turns over.  Fuel appears to be flowing from the carb (clear yellow fuel line), notably when I put my hand over the carb, I get fuel on my hand from the vacuum.  Every now and again, it does burp or 'fire' a few quick cylinder cycles (like "3-4 fires in cylinder"  (boom, boom, boom)).  It burps back through the carb more than it does to try to start.  I tried starting fluid, it does pop, but nothing consistent to want to run or even go vroom!.

I have checked the timing and it "appears" to be spot on.   I even check to make sure piston is all the way up on the firing cycle.  Without over thinking this, I did notice as the flywheel is at TDC, the cam gear was off a little to the right, not completely straight up and down to timing mark as per the manual.  With all that I have done, I feel like the timing chain off, and timing is the main issue (replace timing chain), am I wrong?

I have adjusted the rockers per cold values in manual.  I did a compression check and with the throttle closed, im getting 114 psi roughly.   I did see some posts saying that the throttle should be open to get the correct value, Ill perform this and update my post.

Unfortunately, its still not starting/running.  

I'm at a loss and about to replace the timing chain.   I dont think it is a mechanical issue, but I need some fresh perspective....

Any help is greatly appreciated.

[pikachu78]

i'm helping my dad work on this honda cr250 that has the same problem (the guy gave us two cdi boxes (i'm not too sure what is wrong) the kickstart pedal kicks back extremely violently // we are getting a 3rd cdi stator box from the guy (i will update you this Monday coming up and i will ask him more on the details so i can explain myself better!

 

[CalebM]

It could be something with the stator, I have a Suzuki Lt250ef and it was having spark issues and I replaced the pickup coil which signals when spark should happen and it solved the problem, do you have a timing light?  If you don't get one of those and check to see if the spark is happening at the right time it could be something wrong there.  Stators ussually can be adjusted because the bolts have some play to them so you can adjust spark timing, maybe it got knocked out of adjustment and it isn't sparking at the right time.