Kz650 '76 Historic Race Bike

considering that you havent done major work other than the bore kit, these are nice numbers!

trouble is that after the initial big gains, it will become harder to makes more +10% steps......

with the stock porting i am afraid that the higher lift will just make the engine more peaky for little top end gain. my 0.02$ of course...

We had a race meeting last weekend, the bike went well and I learnt some lessons! I took 2 seconds off my best lap time over the course of the weekend, doing the relaxed=smooth=fast method. Seems the biggest issue with my bike is the big nut on the seat
In this video, taken at our local country track, I was following another rider, a young girl on an LC Yamaha, who is a smooth rider. I made no attempt to pass her, as she is racing in another class and I didn't need too, just following a smooth rider I got a personal best and new lap record for my class. The best thing is I know I have a long way to go and improve my times every meeting.
Here's a video of that race, enjoy my learning process

congrats, 2 secs off is cool, thing is that next 2 secs will be much harder
from my 10 yrs racing i can confirm: you go into the track all charged and raging, youll go slower, go relaxed and youll go faster.
it's a sort of meditation...

The bike looks great and thanks for sharing your modifications and progress as you go

DISCLAIMER:I likely have no idea what I'm talking about. Please keep in mind how much you have paid for my comments.

In looking at the A/F graph, I wonder if the bigger problem is the needle? At the low end of the rpm I believe the mixture is largely controlled by the pilot circuit. Around 3000 rpm the mixture goes a bit leaner. Isn't this about the time that the carbs are transitioning to the needle? If so, this suggests that the needle is a bit too large at the top.
At around 5500, as the mixture goes suddenly rich. Is that the transition from the needle to the jet? If so, doesn't that suggest that the taper of the needle at the small end is too severe? When fully on the main jet, the mixture levels out only slightly richer than at low rpm.
In my jacked up brain, I am thinking that a needle that smooths out the graph would be the first step, then the task would be to get pilot and main jes that move the whole line to a fatter place.

ymmv

Thankyou for your excellent (free) analysis!
I am not a mechanic, nor any kind of expert, and just work this stuff out as I go. I'll have a think about what you said, buy some different needles and have a play. For the most part on the track I am in higher revs, but from time to time, coming on power out of a corner, I'm in a slightly flat zone mid revs. That's probably it...
Cheers
Paul...

Looks like you are having fun, and that is where it all starts out. The clock is your best friend to help lower lap times.

I thought I'd update this, as its been a while We've just finished another season and the kwakka is still going strong. It turns out that winning championships is about reliability more than anything. Not finishing a race, or crashing out of a day, can take a whole season to recover from, thankfully that only happened once this year.
The changes for 2018 were initially a set of Takasago rims, a 2.5" and 3.5" running a 100/18 and a 130/18. I went with 18 inch rims as I could get Conti Race Attack II CR tyres, which incidentally are excellent on track, and stuck with 18" as I didn't want to mess with the bikes handling too much. In hindsight that may have been a mistake, as if I'd gone 17"s I could run slicks and wets. My times improved as soon as I put the new wheels on, a big difference. At the beginning of the year I did some frame bracing, its not possible to prove whether it made a difference or not, but I think it did. Next came a set of Ikon shocks, which are a budget item but again an improvement over the cheap chinese shock (which lasted 2 years and are still going), and a Delkevic 4 into 1 which sounds great with no baffle . Lastly, near the end of the season, I put the bike on a diet. Chopped off the following! Seat 3.65kg (7lbs), a piece of frame 1.6kg (3lbs), a brake disc and caliper 4kgs (8lbs) and lots of little bits. I had to make a new seat, which only added 1kg (2lbs). Last meeting of the year set a PB and a lap record for my small local country track, so very happy with it. Lastly the oil cooler. We measured the crankcase at 125 degrees C after a race, she did not want to idle and I think she was getting too hot. Fitted the oil cooler we had on the shelf, and now she idles after the race, and feels much cooler. The actual cooler was 80 degrees C aftera 15 minute race on a hot day, so all good.
Next year crossing the country in January to race at Phillip Island, the Island Classic. I'll be racing against the unlimiteds, and will probably come last, but will have a crack at it

I'll be damn Just went through this again from start to finish on thus or fri and was wondering how things were going....... bike is looking so nice.... nice improvments and good job on the lap record...... Do you have the part number of the rear rim you picked up (always thought about a larger light weight rim but to cheap) I just looked up the website and can't seem to find the info .... also did you happen to record the weight diff between it and the stock medal rim ?

From your posted video above to your most recent video on youtube, it sounds like you are winding it up more, and riding better and smoother than before. Nice!!!


Have you tested other drive sprocket options?

Does you club let you race the longer part of that track?
historicracing.asn.au/our-racetracks/

Keep us updated on your progress.

KZB2 - Sorry, no part numbers or weights for the different wheels. The whole bike weighs in now at 175kg wet, from 219 factory, so it all adds up!

CoreyClough - At the moment 16/45 sprockets at the Collie short track, and I'll try stock 16/42 at the Island, for the higher speeds. I'm doing a 520 chain conversion, which means having 520 rear aluminium rear sprockets made, AUD$160 each. (Front steel for the conversion to 520 is a JTF565-16). The longer part of the track is still not open, but we hope will be next year. We're told here are 11000 tyres need bolting together for the barriers!