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Old October 21st, 2020, 12:57 AM   #1
punishum808
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Keihin CR Carbs

Tried searching only found one thread here that was more asking if they should get it.
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I got the factory CVs running great with vel stacks and a 3rd stage jet kit. Super snappy and had it a tad on the fat side.
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The factory mains on the CRs are 118 and these carbs are 31s compared to the factory CVs that are 28s and factory mains are 98. I ran 114 on the CVs with the jet kit and stacks. It said that the 118s on the CRs are supposed to be for a stock motor, which I have and a pipe, which I have also, a full exhaust with a small can which almost a straight pipe. It was running extremely fat with the 118s and would not even fire.
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Has anyone else had similar problems with the factory CR jetting? Thinking of going to 114, 112 or even 110s and have the needle set at #3 to start. Any input from guys who have had this same scenario would be greatly appreciated. Mahalo
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File Type: jpg Ninja 250 CV Carbs3.jpg (86.1 KB, 3 views)
File Type: jpg CRS 1.jpg (78.9 KB, 1 views)

Last futzed with by punishum808; October 21st, 2020 at 01:10 PM.
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Old October 21st, 2020, 09:42 AM   #2
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Quote:
Originally Posted by punishum808 View Post
Has anyone else had similar problems with the factory CR jetting? Thinking of going to 114, 112 or even 110s and have the needle set at #3 to start. Any input from guys who have had this same scenario would be greatly appreciated. Mahalo
Bottom-line with power-generation is number of oxygen-molecules you can injest per intake-stroke. Then petrol is metered to match that oxygen-supply.

With pre-gens, it's extremely difficult to improve on engine's VE, it's so well-optimised from factory with max-power close to redline. There's minor restriction on intake, and you get a tiny gain with full-exhaust (unlike new-gen). Factory 28mm carb is way larger than tiny 15mm intake-ports, so you can increase carb-size all you want, but most-restrictive part is still inside head. Only way to make any major increase in airflow through engine is with boring and bigger pistons, installing larger valves, head-porting and cams.

So with not really improving air-flow any, adding massive carbs and humongous jetting will only result in super rich mixtures. Try going smaller-than-stock for power-increase since factory mixtures are already too-rich from factory. No factory engineer is gonna be crazy enough to set up bike with optimum max-power 13.5:1 AFR. That's just way, way too much liability. Out of factory, bikes are always super-rich in 10-11:1 range. Reports of upsizing jets and gaining power are due to people who've got dirty carbs and too lazy to fully clean them. Of course replacing any clogged jets in dirty carbs will result in improvement, but only back up to factory levels.

BTW - good read is Dan Gurney's moment-canceling engine patent. Too bad he died before getting it mass-produced. Particularly notice intake tract design, very innovative, intuitive and simple. Makes me smack my head thinking, "why hasn't anyone done this before?"
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Old October 21st, 2020, 12:03 PM   #3
punishum808
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Quote:
Originally Posted by DannoXYZ View Post
Bottom-line with power-generation is number of oxygen-molecules you can injest per intake-stroke. Then petrol is metered to match that oxygen-supply.

With pre-gens, it's extremely difficult to improve on engine's VE, it's so well-optimised from factory with max-power close to redline. There's minor restriction on intake, and you get a tiny gain with full-exhaust (unlike new-gen). Factory 28mm carb is way larger than tiny 15mm intake-ports, so you can increase carb-size all you want, but most-restrictive part is still inside head. Only way to make any major increase in airflow through engine is with boring and bigger pistons, installing larger valves, head-porting and cams.

So with not really improving air-flow any, adding massive carbs and humongous jetting will only result in super rich mixtures. Try going smaller-than-stock for power-increase since factory mixtures are already too-rich from factory. No factory engineer is gonna be crazy enough to set up bike with optimum max-power 13.5:1 AFR. That's just way, way too much liability. Out of factory, bikes are always super-rich in 10-11:1 range. Reports of upsizing jets and gaining power are due to people who've got dirty carbs and too lazy to fully clean them. Of course replacing any clogged jets in dirty carbs will result in improvement, but only back up to factory levels.

BTW - good read is Dan Gurney's moment-canceling engine patent. Too bad he died before getting it mass-produced. Particularly notice intake tract design, very innovative, intuitive and simple. Makes me smack my head thinking, "why hasn't anyone done this before?"
That is NOT what I asked. It was about CR carbs and the jetting that comes from the factory. I was seeking baselines for jetting the CRs.

As for dirty carbs I have turned the clicky thingy a few times so I do have very little experience with vehicles. But here are a few of the present projects to which I have built myself.

Wow, you sound really knowledgeable, what is VE?
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Old October 21st, 2020, 04:46 PM   #4
Dave Wolfe
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Ive recently got a set of cr special 33s on my bike. The main jet doesnt seem to influence off idle as far as I can tell.
These carbs only need a tiny crack of the choke.
To get mine to rev thru the mid range I had to move the needle clip down one position.
118 mj should be in the ballpark with no air filter. Im at 122 mj with no filter but have 300 ccs and 33mm cr carbs. All ive done for the idle mixture is turn the air screws. Of course im a racebike so I dont care much about low or mid range tuning.
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Old October 21st, 2020, 05:23 PM   #5
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Quote:
Originally Posted by punishum808 View Post
That is NOT what I asked. It was about CR carbs and the jetting that comes from the factory. I was seeking baselines for jetting the CRs.

As for dirty carbs I have turned the clicky thingy a few times so I do have very little experience with vehicles. But here are a few of the present projects to which I have built myself.

Wow, you sound really knowledgeable, what is VE?
Sorry I got mixed up about factory vs. your CR carbs. Best to use wideband and datalog actual AFR. Then go from there. You can do it by feel, but it takes a lot longer and you end up leaving lots of power on table. With wideband, dyno and programmable EFI, I can extract max-power out of engine in about 5-10 dyno pulls, 30-45 minutes. Last 3-4 runs typically eeks out just +1-2% more.

VE = volumetric-efficiency. It's where intake & exhaust tract size, length and shape along with valve-size, lift and timing all coincides for maximum-flow. Due to helmholz-resonance of engine and timing of pressure-waves bouncing back and forth, engine has maximum efficiency in getting most air into cylinders only in certain range of RPMs. Above and below this, it takes in less air per intake-stroke.

When max-VE occurs, cylinders suck in most air per intake-stroke and generates maximum BMEP - Brake Mean Effective Pressure in cylinder. This generates most PSI pushing down on piston and gives most torque. On Ninjette, this occurs around 8-9k RPM (see dyno chart below).

Factory bike slows down acceleration after torque-peak. On race engines, you want to tune to move this torque-peak into higher-RPMs. Calculated max-HP is then also increased which really helps trap-speeds. Main benefit is allowing bike to stay in lower-gears all way to redline for maximum thrust at contact patch.




Nice ride! and awesome photo!!!
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Old October 25th, 2020, 12:14 AM   #6
punishum808
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Quote:
Originally Posted by Dave Wolfe View Post
Ive recently got a set of cr special 33s on my bike. The main jet doesnt seem to influence off idle as far as I can tell.
These carbs only need a tiny crack of the choke.
To get mine to rev thru the mid range I had to move the needle clip down one position.
118 mj should be in the ballpark with no air filter. Im at 122 mj with no filter but have 300 ccs and 33mm cr carbs. All ive done for the idle mixture is turn the air screws. Of course im a racebike so I dont care much about low or mid range tuning.
Thanks Dave, yeah, I went to a guy at a local shop and he was telling me its the pilots, I went back and checked and the pilots were plugged. This is turning out to be now just a road race bike too, so much for using it as our pit bike already. Will test again next week as it has been raining like cats and dogs every day and I have the Ninja covered outside to have more room to work on it. The dragbike is taking up all the room in the garage at the moment. Mahalo Dave
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Old October 25th, 2020, 12:20 AM   #7
punishum808
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Quote:
Originally Posted by DannoXYZ View Post

VE = volumetric-efficiency.
Thanks Danno, sorry I was being facetious, sorry but thank you. I need to hit you up on wiring.The photo was where the new racetrack on Oahu is to be built. It was also taken by the guy spearheading this whole Circuit Hawaii project.

I am eliminating the left hand controls, when I unplug all that side it will not allow the bike to turn on. What can I jump in that side of the harness to be able to get the bike to turn on and run while eliminating all that for a pure racing bike only. I also DM'd you also. Mahalo

Thanks
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Old October 25th, 2020, 02:02 AM   #8
punishum808
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Dave or Danno, there is a siphon tube and in the bowl is a jet, what is it? Thanks
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Old October 25th, 2020, 06:10 AM   #9
Dave Wolfe
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The jet is the starter jet. Im not too sure about the tube.

Get a copy of the manual here:
https://classiccycles.org/2167.html
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Old October 25th, 2020, 07:27 AM   #10
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Sent you DM on bypassing clutch switch. Personally I would go with safer option of requiring bike to be in neutral to start.
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Old October 25th, 2020, 10:29 AM   #11
punishum808
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Mahalo guys, appreciate the info
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