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Been a while since I've been on here after a few years away from bikes. So, bought a couple of race bikes the other day for me and my son to race. His fires up and runs well but mine refuses to fire. I've swapped over his CDI (standard, mines programmable), his carbs (appear to be same as mine, maybe jetted differently, and it still won't run. His runs with my parts on though. The only thing I haven't done is replaced the plugs for new. I'm hoping it's this that's the issue as after that im stumped. I've checked compression on mine and all are 100 to 150 psi. Mine has a quickshifter on which I've unplugged to rule that out. Still no dice. Any thoughts?

As an after thought I'll swap his coils for mine to rule out those plus the HT leads.

If your coils and plugs from non runners work on the working bike, but give you nothing when you put them back ontonyour nonrunner, check your pulsar/timing coil...I've known bikes where its been disconnected from the loom by accident.

Cheers for the reply. Where's the wire for that?

When sat on the bike, it comes out of the bottom right side of the bike, the cover in front of the clutch cover, 2 wires in a sleeve. It will route up sort of where the fuel pump is, goes into the loom and then joins onto the cdi on the smaller plug.

It's what tells the cdi that the engine has made a revolution, and thus controls the base timingnof the bike. If that signal is not there you will never get sparks

Ah, cheers for that. The plugs do spark though so maybe not that. Ordered some new plugs so will try those next weekend when I'm back.

Got both bikes running with new plugs. One of them is only running 3 cylinders though. Did a compression test the other week and it's 150, 100 100 150. Any thoughts?

stevezx7r wrote: ↑

Sun Feb 20, 2022 8:19 am

Got both bikes running with new plugs. One of them is only running 3 cylinders though. Did a compression test the other week and it's 150, 100 100 150. Any thoughts?

do another compression test and compare the results

Yeah 100 psi is too low/very bottom of acceptable minimum level.

And a 50psi spread from cylinder to cylinder is not good either for your crank.

Suggest retrying with a dry engine, then add oil to the bores and see if that increases compression. Do you have access to a leak down tester?

Cheers for the replies guys. I'm away with work all week so can't personally do anything with ATM although my dad is having a look. So far it looks like the carbs float hights on my bike are out and possibly the float rubbers on the stop may be worn. I've asked him to swap the carbs over from the running bike to see if it runs. If it does, it's the carbs at fault. If it doesn't it's got to be the engine. We only have a compression tester (rubber bung type, so not that accurate).

So, my dad has put the working bikes carbs on my bike and still not firing on 1 and 2. He's done a compression test (screw in to plug hole type) and they're 135, 145, 145, 145. So down a bit on c1 but nothing extreme. He's going to put the working bikes coils on and try that. If that doesn't solve the problem I don't know what it can be.