Don’t really know, size vise they should be exactly the same.
But I think it doesn’t matter which one you choose because the idle jet is also a factor
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CD1 seems to flow a lot more fuel that B100. Not sure if it’s the diameter, holes or because it’s shorter. I have both, I’ll take some pictures side by side when I have them handy. Personally, I use it only when I want the jet on top of it to be 70 or higher, below that I use B series. But I know people that go a different route as well
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…no issues with hijacking I think jetting is still a relevant topic…at the end, excluding the other trivial things, it’s the only thing that can cost you a lot of money if you seize an engine that way. Most of the settings we shared here are very close in approach and end result (except one that I’m curious about, few posts above). Hope it will help people from going absurdly lean and then keep seizing, spending a lot and hating the platform for it, when the issue is very simple
This is the current KZ restricted (KZ4) rules here in NZ. Basically a safe tune provided in the regs so no worrying about jetting during the race day. Jets required as posted with option of 150 or 155 main. This was on a 10C. Only called a restricted class as it has fixed jetting and a mandatory axle. No other changes.
Thanks! It’s fascinating, I’ve seen a similar jetting before, using a U12 needle, but that was for a track with short straights only. I guess the safety margins are wider than I thought if you run that in varying weather conditions through the year with no problems
What is the essential tools to have when doing a bottom end rebuild? I know the basics since I’m doing the top end in my 10c myself.
I currently own a press and a crank disassembly tool.
And how to remove the bearing inner rings off the bearings on the crank?
Super excited for your documentation on the full rebuild.
I will post a breakdown in a little, but for the bottom I’m still debating…meaning the only hangup to full DIY are the tools…in addition to press and crank disassembly tool (say $1,000 combined) you need to add the assembly/alignment tool ($500 to $800) and the crank truing bench ($300 to $1,000+ depending on how fancy you want to go) and the tool to press the bearing race ($100) and a good lead hammer ($50). All that to save $50 to $100 of crank service, so it takes about 30 crank rebuilds to just break-even on tools which is not a realistic scenario for most people
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Don’t forget about properly torquing the transmission shift fork tension adjusters after reassembly. Don’t want to get that wrong.
Me, I’m happy to know & admit my limits. I’ll just outsource bottom end rebuild work to the experts. Top ends are far more straightforward.
Oufff that seems way to much, I’ll stick to my trusty bottom end builder then 
He charges 250$ roughly for a bottom end overhaul including parts
Exactly…usually I do the entire job myself except for the crank. I bring the crank only to a shop to do that (around $50, including pressing out the roller bearing inner race and installing the new one, but I know others charge more). Then I take the crank back and re-check it myself (paranoid) prior to installation and make any adjustment to zero it out perfectly, if needed. At that point the crank is ready to go…this way I save most of the equipment cost
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That seems pretty reasonable! I will talk to my guy about only bring the crank to him. Im able to do the rest of the job myself to save some $$
I got a CD1 with a recent parts order, and give it a closer look vs the B100. Pretty large differences between the two, as you can see in the photos below. I’d estimate the CD1 passage diameter to be around 1.4mm. I don’t have anything precise to measure, but a 1.2mm throttle cable can pass through while still having a small gap. The emulsion holes are also larger and all at the same height on the CD1.
CD1 on the left, B100 on the right:
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Thanks for posting it! A new meaning to “a lot more”, it’s a riverbed!
I have few working theories I learned over time on this subject, it’s probably the least documented part of jetting, maybe worth a discussion on the jetting thread!
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This thread is GOLD for us shifter folk! Thank you all!
at Sonoma raceway they run an exhaust restricted version of the ROK 125 shifter that seems like such a no brainer, they all make essentially identical power and entire group is nose/tail down the straight, the restricted exhaust makes them very very tolerable to a newb doing the jetting, they get 8+ hours on a piston and the motors last a long long time, and they are not down on power much vs the uncorked ones, the lap time differences between the restricted ROKs and the unrestricted is farrrr smaller than you might guess and looks like way more fun and dramatically more reliable, and the lower power is not quite as hard on tires or the body for older guys out to have fun. Then Sonoma still runs unrestricted ROK for the big guns who want to run that. Restricted ROK at sonoma had great turnout last year and looks like a blast. Admittedly the powerband is a bit weird because the torque curve is so flat from the exhaust restrictor but it really prevents you from reving them that high which makes the bottom ends last a long time. Karting really needs some turned down shifter class for mere mortals on the weekends, I still don’t see why restricted ROK like Sonoma does has not caught on more widely.
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this is an awesome thread by the way!!!
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While the restricted deal isn’t a bad idea for beginner shifter folks, or older drivers the Rok is very reliable in unrestricted version. I’ve easily run 8hrs on an engine and at 14k that’s hardly buzzing an engine. More likely to buzz the engine on downshifting too aggressively. Restricted engines on a Tag frame with no front brakes like 80’s always were would be interesting. Less cost and different driving experience.
Watch this space - Musgrave Racing Co is working on a solution for a long-life, modest-power adult shifter.
The long-life alternative for shifters is running an SSE 175 on a suitable fuel (100 RON or more). I got 54 hours out of a bottom end and 41 on a piston using Marathon gas for the first half on the east coast and various racing gasolines in California. It is not an easy engine to drive but it sure is fun!
(Ricky - edit was to distinguish the new MRC solution from the 175)
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The what? 175? Never heard of her… 
Expensive boat anchor for most, but more power to you. I love my Rok, and it’s fun when I have it in KZ form too.
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Just what we need is more engine programs. 
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