Don Terrill’s Speed-Talk

Hello everyone, i need expert opinions and suggestions regarding my motorcycle for drag racing 250meters. the last time it runs very good about 10 seconds but suddenly after an overhaul and intake valve leak fixed it runs 12 seconds on 250meters. it has good rpm and i can hear it outputs higher rpm but reaches the finish line longer. We thought it was the clutch slipping because all the gears got used up half way down the track but bike lacks speed. So we changed the clutch plates and springs but still bike eta is 12 seconds. really need your help guys. im thinking maybe it wants ignition timing retard? I will post videos on the 10 second run and 12 second run so you can have a have a good idea on the difference on how it runs. Thanks a lot guys.

10 second run
https://www.dropbox.com/s/zvd6l4e5ide5u ... 2.mp4?dl=0

12 second run
https://www.dropbox.com/s/zvd6l4e5ide5u ... 2.mp4?dl=0

IF you didn't change anything and can't find a mechanical issue or fuel issue it should not need a timing change.
That's unlikely to pick that 2 seconds back up anyway.
It's likely electrical. Almost always is when all else remains the same.

Is it possible the cdi has issues? I know cdi will either work or not and thats it.

The 250 meters?
Is this on a track with timing clocks?
How did 250 meters come about?
800 feet is an odd length even for the drag racing world.

Edit. oops. Just looked at the video.
Sorry, You cannot use this street/butt dyno method to determine ET.
Everyone that ever tries gets wildly variable results.

But we can clearly see and feel the bike slowed down. We used a stopwatch and it is about 2 seconds difference on the time. getting frustrated already. Many parts have been swapped but still problem exist. We cannot get our 9 sec run again

So, you have now lost 3 seconds as opposed to your original 2?
This thing used to be quicker as time passes?

Yes sir it has lost 3 seconds. I was wrong its 3 seconds not 2. problem mostly on the higher gears. Its not pulling like it used to be. Is my flywheel too light?

Problem started after an engine overhaul where we fixed something dragging on the trasmission. Now rear wheel turns smoothly, also there is slight intake valve leak where we did fix also. Then its time for testing and bike slowed down significantly. we loss about 3 seconds. Doesnt seem to make sense 'cause its supposed to be faster because now there is no valve leak and rear wheel turns much more freely. I can post more videos if that should help.

Any chance you missed a tooth on the cam timing putting it back together? Also, if you haven't checked the ignition timing with a light, now is a good time for that as well.

James, we double checked the cam gear timing and it was correct. this bike uses a cdi so i guess timing wont change coz it electronically controlled?

How is the cdi triggered, any chance of a problem with a crank sensor? Just trying to think of ways the same pile of parts could give such different results .

James,
Thanks for the reply. Its using a magnet pickup coil trigger. bike starts easy and runs without cutting out. If the ignition pickup coil has problem it wouldnt even start right?

Seem the bike is "laboring" at high rpm. There is something holding it back. Too much ignition advance? it reaches high rpm but very slow acceleration.

Have a look at the throttle linkage?