[8ball]

Spring out, fully compressed.

 

[CaTacL1sm]

Spring out, fully compressed.

thanks

 

[TrialsRider]

I'm having an idiot moment...

When filling the forks with oil, do you measure the oil level with the fork extended and the spring in, or the fork compressed and the spring out?

The clymer does not specify

Convention is full compressed, spring out, after you pump it several times and wait for the oil level to stabilize.
The important thing is that there is still some air space on full compression so that your forks don't hydraulic.

oops, ha ha, 8ball already said that yesterday at least we came up with the same answer

 

[CaTacL1sm]

I've assembled most of the parts I'll need for this winters rear disc conversion.

I'm going to use the rear hub and disc off of a KZ750b (twin cylinder). I've also got a caliper/carrier/master cylinder of a 750b as well, but am debating on using the grimeca caliper I have as it looks like it's smaller/lighter than the 750 one. (of course I have stock looking calipers in the front and kind of want a stock look caliper in the back to match)

This should be a pretty straightforward upgrade, I just need to get spokes to lace up to the 18" rim I have (unless it would be worth going to a 19" rim?) as well as wheel bearings, sprockets, chain, M/C rebuild kit, lines, and other misc stuff.

Here's a rough look at the size differences between the grimeca caliper and the KZ750 one (grimeca is on top).

I'll probably bring the bike over to my machinists shop so we can more easily make a bolt on bracket for both the M/C and new axle spacers.

 

[CaTacL1sm]

Did a pull on the dyno today to get some air fuel readings.
Idle is lean
Off idle to 1/2 throttle is super rich
1/2 throttle to WOT is good (around 12.5:1 AFR)

I'm going to order the next two larger (leaner) needles as well as the next two richer slow jet sizes and we'll go again.

Annoyingly, even though I have about 1/2" of clearance between the tire and inner swingarm, it rubs at WOT. I didn't know the tire would expand that much.

 

[CaTacL1sm]

Ok, so since I'm not sure if my previous post here will ever show back up, I'll provide another update.

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:

 

[brad black]

that is surprising growth. it was running to 105 mph at the top of the runs? that's not that high.

 

[CaTacL1sm]

that is surprising growth. it was running to 105 mph at the top of the runs? that's not that high.

We were also varying the resistance/braking of the dyno during the pulls to simulate loads/wind resistance. We didn't have the cables handy to log the bikes RPMs this morning

Also, that's a 3rd gear pull, not a normal 4th gear one

 

[brad black]

maybe next time get a bright light in there and video the tyre during the run.

 

[brad black]

if you go to a smaller main air jet (if those carbs have them?) you might be able to go to a smaller main and flatten out that air/fuel so it's not got a rich sag in the middle.

 

[CaTacL1sm]

maybe next time get a bright light in there and video the tyre during the run.

I stood and watched it one run as the tires circumference visibly increased at higher RPMs. It was wild.

The normal slow jet that these are equipped with are size "60". If I go up to those it should richer up idle enough and I can compensate with the additional fuel the circuit pushes across the rev range with going slightly leaner on the needle clip

 

[XB33BSA]

thats awesome you are getting it dyno tuned !
just sayin' but i would add a link or 2 to the chain it looks like you have enough axle slot to do so

 

[CaTacL1sm]

thats awesome you are getting it dyno tuned !
just sayin' but i would add a link or 2 to the chain it looks like you have enough axle slot to do so

Agreed. I'll do that this winter when I upgrade the rear to a disc brake

 

[CaTacL1sm]

So here's a question:

I'm using the rear caliper, disc, and master cylinder off of a 1977 KZ750b (the twin cylinder). It shares the same brake setup as most of the 70s KZ1000s. This master cylinder is a 5/8" one and let me tell you, they're not the most common ones to find in newer condition and there's no japanese aftermarket 5/8" rear master cylinders that I've been able to find.

A lot of the japanse aftermarket manufacturers like PMC (found on webike) make all sorts of rear brake upgrades for the Z1/KZ900/KZ1000. All of their upgraded rear master cylinders are 1/2" ones.

What is the down side to using a 1/2" master on a caliper designed for 5/8"?

Like I said, I can rebuild the 5/8" MC I have, but would not mind the flexibility of having a MC with a remote reservoir.

 

[irk_miller]

A smaller bore is going to make them more touchy. Some of the late 70s early 80s 1100's and 1000s may have had 5/8" bore. I know the GPZ's had 14mm bores, as did the Suzuki GS's and the larger displacement Honda's of that time.

 

[CaTacL1sm]

So 5/8" is about 15.8mm and 1/2" is 12.7mm.

A 14mm master would be a good compromise, but why would a common Japanese market upgrade for those KZs downsize that much?

 

[8ball]

Given an equal lever ratio and caliper piston size, a smaller mc bore actually applies more force to the calipers. See below diagram:

The block on top top represents the force applied at the lever. The cylinders represent the master cylinders. The first one has a 1sq. In. Cross section, the one on the right has a larger bore that gives it a 2 sq. In. cross section. The arrows represent the pressure exerted in the line. The smaller mc will have more travel because it won’t move as much fluid for a given lever pull distance, but it will have more “feel”. The larger mc will feel more wooden at the lever, but will have a shorter throw.

 

[CaTacL1sm]

So the regular MC won't fit:

Not nearly enough room. I may have to just go for the fancy japanese 1/2" one and see how it feels with the stock caliper... maybe upgrade the caliper too.

https://japan.webike.net/products/1523073.html

you can see how small it is compared to stock. That combined with a better brake line mounting point and a remote reservoir, I think it's my best bet.


Also, I fitted the replica giuliari seat:

(and compared to the corbin)

I need to do some trim underneath the back between the seat and the ducktail, but other than that I think I like it. it's a lot softer than the corbin.

 

[Cyorg]

The fancy Japanese one looks like the same one they use on 08 to 16 Yamaha R6 and if my failing memory serves me right, they are 1/2". The intake port is opposite the mounting flanges just like that one, so makes for a really easy fit in limited space. The plastic fitting on the intake port is round and held in with a circlip, so you can carefully remove it, clean it up and then you can swivel it around to whatever direction you want. Some come with the brake switch if that helps simplify things. Can be had for cheap and kits are plentiful.

Ps. Somewhere I have a picture of the frame on a Kawasaki endurance racer that would probably cause your toes to curl up and your eyes to roll back into the back of your head.

 

[CaTacL1sm]

good tip.

I have a grimeca dual piston caliper that I think would work perfectly with a 1/2" MC.

I should be able to make that better caliper work with the same amount of effort that it would take to make the KZ750 caliper work, I'll just need to make a carrier for it in addition to the axle spacers.