Topic: Keihin CR Carbs....

[MRieck]

 Who here has used them (either the 29's or 31's). I'd be interested in swapping the good and bad points as well as common problems. I'll start first by saying Sudco is friggin useless. Their first response to 99% of problems is "that's the first time I've heard of that". If I had a dime for every time I've heard that from them as well as other suppliers.Christ  I don't think the old Sudco receptionist knew they sold carbs.

[Sam Green Racing]

Was telling Sean just that last week.

[caferacer550]

I too was wondering if anyone could share opinons on these carbs.
Easy to install and tune?
Are they worth the money?

[MRieck]

I too was wondering if anyone could share opinons on these carbs.
Easy to install and tune?
Are they worth the money?

I do have lots of experience AND opinions on CR's. One opinion is a accelerator pump would not be a bad idea as long as it had good adjustablilty like the Mikuni RS series. The Keihin FCR accelerator pump has poor adjustability. They (the carbs alone) are worth 4 or 5 on top with port work.

[caferacer550]

Are they considered to be strictly race carbs.
Or can they be used for a daily rider?

[scondon]

Who here has used them (either the 29's or 31's). I'd be interested in swapping the good and bad points as well as common problems.

I'll have some input in just a couple more months

   Mike, I'm sending you some mail this Friday. You should expect it next week. 

[Sam Green Racing]

Are they considered to be strictly race carbs.
Or can they be used for a daily rider?

I should think you could use them on the road as Mike does, not sure about availability of filters though.

We have been useing them for 3 years now and not had to touch them, then again one dosn't clock up a lot of miles drag racing.

Sam

[MRieck]

Are they considered to be strictly race carbs.
Or can they be used for a daily rider?

I should think you could use them on the road as Mike does, not sure about availability of filters though.

We have been useing them for 3 years now and not had to touch them, then again one dosn't clock up a lot of miles drag racing.

Sam

Sam is correct....I have used them for years (29's and 31's) on the road.

[78CB750F1]

I am running 29mm Keihin CRs on my CB750 with stock motor and the performance is great - for daily use, I would recommend running the individual K&N filters rather than the velocity stacks that come with the CRs.

[MRieck]

   On the sets that I have used, I usually modify the stock idle screw for a remote idle screw (usually mounted to the air box mountng flange) . The stock idle screw is on top of the carbs and hard to get to when installed.
 
 Daniel

  Like this..........

[dusterdude]

how does one go about fashioning such an item like that?

[caferacer550]

Where is the best place to by a set of CR's for my 550?
Or are they all selling for the same price? (M3, Sudco)

Does anyone know if there any other after market carb options for the 550 besides the CR's?

Thanks.

[MRieck]

how does one go about fashioning such an item like that?

Mark, I made that from an old ZX10 part. The ZX10 bolt at the end didn't fit so I cut it off, drilled into the top off an Allen head bolt and soldered in the cable. I put some shrink wrap on it prior to soldering and shrunk it aroung the head of the Allen and the end of the cable. I wouldn't be surprised if the remote adjuster from a set of Keihin FCR's would work. You could just order it from Sudco then.

[MRieck]

Where is the best place to by a set of CR's for my 550?
Or are they all selling for the same price? (M3, Sudco)

Does anyone know if there any other after market carb options for the 550 besides the CR's?

Thanks.

Sudco supplies all the Mikuni and Keihin carbs in the USA. Everyone has to get them from Sudco. Sudco doesn't list 26mm carbs for the 550 BUT they do for the 400F. I'd guess the spacing is the same but I'm not sure. If they will work I'd just order them from Sudco unless someone is giving a discount. There really isn't that much mark up though

[Jerry Rxman Griffin aka MuthaF'er]

I think what Mike said about the mark up is correct. I had a dealer friend request a new catalogue and check on pricing for a set of 31mm. He told me his cost was almost $600.   

[dusterdude]

how does one go about fashioning such an item like that?

Mark, I made that from an old ZX10 part. The ZX10 bolt at the end didn't fit so I cut it off, drilled into the top off an Allen head bolt and soldered in the cable. I put some shrink wrap on it prior to soldering and shrunk it aroung the head of the Allen and the end of the cable. I wouldn't be surprised if the remote adjuster from a set of Keihin FCR's would work. You could just order it from Sudco then.

cool,you`re a smart mutha.

[sparty]

   On the sets that I have used, I usually modify the stock idle screw for a remote idle screw (usually mounted to the air box mountng flange) . The stock idle screw is on top of the carbs and hard to get to when installed.
 
 Daniel

  Like this..........

Mike,
Can you, when you find the time, send me a list of parts that I would need to make a remote idle screw for my CR carbs and some detailed instructions on how to do it?

Thanks,
Sparty

[aptech77]

I'm running 31MM CVR on my 400F. Easy to work on, No problems, BAD ASS!!!!   

[Hockers Choppers]

anyone running the mikuni smooth bore carbs? can find them on ebay all the time but can't find any cr's and don't have $700 to spend. need them for a 750 with cam, porting and 836.

[heffay]

ok... trying not to sound like a moron... is my terminology correct?

CR: constant ratio
CV: constant velocity

?

[crazypj]

First time I saw the insides of them I thought 'hey, AMALS done modern' As long as you dont go too big they make excellent street carbs. They flow much better than standard round slide so you use a smaller size which gives better carburation everywhere.
I put a set on a CB 350 a while back,(modified from a Z 900 rack) must be good as I haven't seen the guy since (you know he would be back to complain if it wasn't right)
The Mikuni's are very similar( they were originally AMAL made under license) and Sudco seems to have a lot more experience with them (and parts seem to be easier to get)
BTW, if you need odd sized taps and dies,(5x0.5mm for example) Victor Machinery Exchange in New York is the best place I've found in all the US and was a lot cheaper than getting stuff from Europe, (particularly the way the dollar has tanked recently)
PJ

[crazypj]

ok... trying not to sound like a moron... is my terminology correct?

CR: constant ratio
CV: constant velocity

?

NOPE, CV is vacuum operated, you can put huge carbs on and engine only takes what it wants. CR have a block inside the slide (which is either linkage or direct cable operated, although I don't think thy were originally designed for direct cable operation, I make new tops and slide mods). the slide walls are very thin so don't disrupt airflow. It looks like an inverted tube with a cap on one end where linkage ( or cable) connects
Heres a picture of a Mikuni smooth bore, through the carb bore. the slide rides in the narrow slot
PJ

[Geeto67]

ok... trying not to sound like a moron... is my terminology correct?

CR: constant ratio
CV: constant velocity

?

NOPE, CV is vacuum operated, you can put huge carbs on and engine only takes what it wants. CR have a block inside the slide (which is either linkage or direct cable operated, although I don't think thy were originally designed for direct cable operation, I make new tops and slide mods). the slide walls are very thin so don't disrupt airflow. It looks like an inverted tube with a cap on one end where linkage ( or cable) connects
Heres a picture of a Mikuni smooth bore, through the carb bore. the slide rides in the narrow slot
PJ

CV does stand for "constant velocity". They are vacuum operated carbs where by the draw of engine vacuum lifts the slide instead of a cable, and the engine takes what it needs. They are called constant velocity because the carbs work by balancing vacuum of the engine (below the slide) and the the vacuum above the slide.  (right on the description, wrong on the name crazypj):

"When you twist the throttle, this lifts the slide and immediately increases the size of the carburetor opening letting in more air/fuel mix and increasing the speed of the motor.  On CV carburetors, the throttle cable actuates a butterfly valve and, as the throttle is opened, the air pressure difference between the sealed chamber above the vacuum slide and inside the carburetor venturi forces the slide (located in front of the butterfly valve) up and down.  The downside to the CV carb is a lack of immediate throttle response. Twisting the throttle gives relatively leisurely acceleration compared to a conventional carburetor. One of the advantages is that the carburetor adapts nicely to altitude changes and good gas mileage ."

http://www3.telus.net/dougsimpson/CVcarb.html

This place seems to list both SOHC and DOHC cb750 CR carbs. I've NEVER dealt with them so cavet emptor:

http://www.cyclewareables.com/pages/keihin_cr_parts/keihin_cr_four_cylinder.htm


I always thought the CR was just a carb series or model number (like mukuni VM) - I too would like to know if it stands for constant ratio?

[Hockers Choppers]

I think CR stands for competition racing.

[aptech77]

You are right on with the your info....except....."The downside to the CV carb is a lack of immediate throttle response. Twisting the throttle gives relatively leisurely acceleration compared to a conventional carburetor"....Not so true....there are ways to take care of this and the operation of CV carb is MORE responsive and smoother run with a more balanced flow. My launches like you were on the shuttle.