Keihin CR33 settings.

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laverdakeith

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Hi, been lurking and reading posts here whilst slowly working away on the rebuild of my 1972 Combat roadster. Among the many modifications I'm making along the way I have a couple of Keihin CR Special 33mm carbs to fit. I have had great success previously with these replacing Dellorto's on various Laverdas.
I have searched the forums and although I can see others have used these carbs I cannot find any specific set up data. In particular I am looking for needle type and slide cutaway, main and pilot jet settings. Any pointers would be greatly apreciated.

Many thanks.

Keith
 
Jim Schmidt knows as does anyone that has purchased 33mm CRS carburetors from JS Motorsports.

Below are some numbers I found, but caveat emptor. Not all motors are alike and these settings could melt holes in the top of your pistons for all I know. I have 35mm FCRs on a vertically oriented engine, so can't verify. Somebody must have some good starting point settings for a 750 with a 2S cam in it.

120 mains
40 starter jet
YY8 YY7 needles clip 2nd position from the bottom
68 pilots
230 air jet
3.0 slide
Idle screw 1 turn out from closed. Could be talking about the idle mixture screw
Float height 14mm
 
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Well, apparently all the tuners that hang out here are too busy polishing their muffler bearings. ;)

My memory is poop, but I think those are early 33mm CRS tuning numbers Jim posted a long time ago. Some of those specs may have changed but might be a good starting point.
 
Schwany said:
Well, apparently all the tuners that hang out here are too busy polishing their muffler bearings. ;)

My memory is poop, but I think those are early 33mm CRS tuning numbers Jim posted a long time ago. Some of those specs may have changed but might be a good starting point.
Click to expand...
Thanks Schwany, I'll give those settings a go and report back whenever I get the bike finished. I did ask Jim but got no reply. I can work it out myself I have access to a dyno and I have done a lot of carb set up work over the years. Just need a basic point in the right direction specifically on needle choice as mid range fueling is controlled entirely by the needle in a CR, the needle jet is a fixed size. With Keihin needles costing over twenty quid a pop and being a canny Scott I wanted do do as little experimentation as possible. :)

Keith.
 
Got a pair of those from Jim for my project, but at a financial pause (TTI and Alton wanted first.) at the moment, but any info' on them I'm interested.
 
laverdakeith said:
Thanks Schwany, I'll give those settings a go and report back whenever I get the bike finished. I did ask Jim but got no reply. I can work it out myself I have access to a dyno and I have done a lot of carb set up work over the years. Just need a basic point in the right direction specifically on needle choice as mid range fueling is controlled entirely by the needle in a CR, the needle jet is a fixed size. With Keihin needles costing over twenty quid a pop and being a canny Scott I wanted do do as little experimentation as possible. :)

Keith.
Click to expand...
Carburetor tuning does have the potential to be tedious and in the case of Keihin, expensive. One thing that would be helpful when tuning carburetion for an old butt dyno tuner like myself is to have an abandoned air strip.

Almost on topic notes: The only Sudco Keihin CRS kit I am aware of with the right intake manifold spacing for a Norton head is the 016-3234 SRX600 kit. I have no clue what jetting those come with. My guess is you could start a Norton with that kit and make it idle. Not sure how well it would run off idle though. If building your own set, I think you'll have some interesting work ahead of you. Hopefully those jet and needle numbers are close.
 
Schwany said:
... I think those are early 33mm CRS tuning numbers Jim posted a long time ago. Some of those specs may have changed but might be a good starting point.
Click to expand...



JS current CRS 33 settings are:

130 mains

YY7 needles with clip 2nd from bottom (yy6 for richer jetting just above idle). Note that needles are only different at cylindrical section which only effects mixture just above idle.

68 pilots (idle jets)

230 air jets (main air jet) - effects mixture at ¾+ throttle (bigger number is leaner)

3.0 throttle slides (standard for all)

slide gap opening approx .020” at bottom

idles screws 1+ turn

#40 starter jets (smaller number idles faster when choke is on)
 
jseng1 said:
JS current CRS 33 settings are:

130 mains

YY7 needles with clip 2nd from bottom (yy6 for richer jetting just above idle). Note that needles are only different at cylindrical section which only effects mixture just above idle.

68 pilots (idle jets)

230 air jets (main air jet) - effects mixture at ¾+ throttle (bigger number is leaner)

3.0 throttle slides (standard for all)

slide gap opening approx .020” at bottom

idles screws 1+ turn

#40 starter jets (smaller number idles faster when choke is on)
Click to expand...

Many thanks for the reply, and the pm, Jim, much easier than starting from scratch. I will post up how it all goes when its all going.

Keith
 
Without derailing this thread too much Keith, do you have any experience of those carbs on a 750 SF Laverda? Any dyno numbers?
For those not aware, Keith is being a bit coy about his experience, he is the No.1 Laverda guy in the UK ;).
Looking forward to updates on this bike!
 
wavey_davey said:
Without derailing this thread too much Keith, do you have any experience of those carbs on a 750 SF Laverda? Any dyno numbers?
For those not aware, Keith is being a bit coy about his experience, he is the No.1 Laverda guy in the UK ;).
Looking forward to updates on this bike!
Click to expand...
Stop it, you'll make me blush ;) I've fitted several sets of CR Specials to Laverda triples and twins, I run my own daily rider 3c on 33mm CR carbs. Pictured is an instal of 37mm CR Specials on an 880cc 270degree converted SFC I built a couple of years ago, this made a couple of pennies over 80bhp at the rear wheel. Beautifully made carburetors that function very well, my 3c does 50 miles per gallon and goes like a cut cat, so I'm looking forward to seeing what they do for a Norton. Hopefully this year...
 

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They work so well on a Norton. Perfect idle. Smooth linear power delivery. Plus max top end flow with the smooth bore. But you're going to have a problem with too much return spring pressure. I had to make some important modifications to the carbs and the twist grip to solve that problem.
 
laverdakeith said:
Stop it, you'll make me blush ;) I've fitted several sets of CR Specials to Laverda triples and twins, I run my own daily rider 3c on 33mm CR carbs. Pictured is an instal of 37mm CR Specials on an 880cc 270degree converted SFC I built a couple of years ago, this made a couple of pennies over 80bhp at the rear wheel. Beautifully made carburetors that function very well, my 3c does 50 miles per gallon and goes like a cut cat, so I'm looking forward to seeing what they do for a Norton. Hopefully this year...
Click to expand...
where did you get the carbs from please?
 
Mine are 35mm, but in case helpful I'm pasting in an excerpt from a prior post of mine:

----------

The current settings are the result of a lot of experimentation over an extended period of time. Took quite a while, but these work great for me. Power, mileage, and plug appearance are all very, very good.

The FCRs are awesome carbs!

140 main jets (came with 152s)

Needle clip in #2 slot (from top; there are seven slots; the needle clips came in #5 slot I believe)

Stock pilot jets

Slow air screw out two turns (were originally out one turn)
 
For the CRS Keihin carbs on Nortons you can also use YY6 needles. I've been doing this lately and it richens the mix just off idle to eliminate hesitation when you dump on the throttle. Above 1/4 throttle the rest of the needle taper is exactly the same with all needle #s. I still use 2nd notch from the bottom but some go to 3rd notch from bottom. Nortons still run clean with YY6 needles.

Using a #40 starter jet in the carb bowl gives you a richer choke and it may not idle when choked. A #35 starter jet will probably give a faster idle when choked.
 
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