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CR29 jetting and decel backfire 10 Nov 2018 10:57 #793656

  • Move0ver
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A little bit of thread necromancy, but I've got some relevant updates for running CR29s on the (at least my ) Z1.

I've had the bike on the dyno a few times in the past week, dialing in my AFRs.
After the first run I saw that idle was super lean and then went off the charts rich just after throttle. AFR got better at 3/4 to WOT.

That told me two things, that I needed larger idle jets (what kerker/SUDCO call slow jets) and a larger diameter (leaner) needle.
Run 1 was with 52 slow, 112 main, YY8 needle 3 clips from the top.

Run 2 was with 55 slow, 112 main, YY9 needle 3 clips from the top.

On run 2, the idle was still lean, but not as bad as before.
I'm going to probably jump up to size 60 slow jets (which is what the carbs normally come with when you buy them new). That combined with the air screw adjustments should fix the leanness at idle.
Run 2 with the new needle showed marked improvement in the AFR at 1/4 to 3/4 throttle. We went from an AFR of 9ish/1 to around 11.2/1 (with the end goal of being 13.1fuel/1air).

***The snag is that with the aftermarket rim and larger tire, combined with the box swingarm I have about 1/2" of clearance. At high RPMs, the tire expands enough to rub on the swingarm cross brace (in the video you can see a puff of black)

I'm going to fix the clearance when I upgrade the rear to disc brake and then we'll do Run 3 in the spring.

Run three will probably be the following: 60 slow, 112 main, YY9 needle 2 clips from the top.

Here's the HP chart and AFR chart from the dynojet:
70hp at around 8k RPM... that's with significant rubbing of the rear tire, so hopefully it's a little more after I fix it.



Here's a quick video of one of the intermediary runs (not the spray of rubber near the end of the pull)




Finally, pictures of the rubbing and existing clearance:







Hopefully this information is helpful. I'll update it again in the spring once I get back on the dyno.

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