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.