CR33 / CR31 Carbs

CR33 / CR31 Carbs

Postby Dutchie » Thu Oct 18, 2018 3:34 am

Hi guys, we are two guys from the Netherlands and we've both e few CBX 1000 and we love them. Our CBX1000 bikes all runs perfectly but to get more power we recently bought 2 sets of Keihin CR 33 ‘s , or so we thought...
We had many problems installing the carb’s onto a test-engine, none of the carb’s were in line with the cylinders...so we had to reposition all carb’s. Unfortunately it was no plug and play! This was disappointment nr 1.
After some inquiries we found out that the carb’s were not the CR33 but CR31 series... This is engraved on the carb’s, disappointment nr 2.
After installing the set on one of our bikes it runs badly.
Now we've some questions for the CBX1000 experts in the USA, does it give problems to put 31 carbs on the CBX instead of 33's? Does someone has experience with the CR 31's on a CBX? Does someone have an example of the jettings on a CBX which drives perfectly?

Thanks CBX friends.
Henk and John.
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Re: CR33 / CR31 Carbs

Postby steve murdoch icoa #5322 » Thu Oct 18, 2018 7:43 am

Rick is using CR carbs on his race bike. I don't remember which size.
A long thread so maybe contact him directly.
viewtopic.php?f=6&t=10003
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Re: CR33 / CR31 Carbs

Postby Dutchie » Thu Oct 18, 2018 10:41 am

Thank you Steve
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Re: CR33 / CR31 Carbs

Postby Warwick Biggs » Sat Nov 30, 2019 7:27 pm

I have only just noticed this thread so my response is probably out of date but for anybody running CR carbs here are a few tips. The 31's are the correct size for your CBX. Keihin recommend them for smaller engines but they are talking 4 cylinder engines, not 6 cylinder so don't worry about the diameter. 31 is correct for 6 cylinder motors up to 1300 cc.

Main jets are 120's. I am currently running 118's in my race bike with YY7 needles. The CR's are very adjustable for main jet size, level of the main jet pick up aperture (you need a magnifyin glass to see this difference), needle height, taper, etc as well as slow jet size and even the velocity stacks and alloy mouths that screw in and fit to the rubbers are all replaceable with different diameters and lengths and its easy even for the experts to get a bit lost with the settings.

However, if the carbs are second hand they should be given a thorough clean with carb cleaner. They should be fully dis-assembled and the jets inspected under a magnifying glass/light. The slow jets in particular are very fine and easily blocked by fuel residue or 'varnish' left by evaporating fuel.

Do not overlook the choke mechanism. If the choke becomes gummed up it will not seal properly and you will have fuel bypassing the needle and seat by going up the emulsion tube and flooding the motor (even tho' the choke appears to be off). Clouds of black smoke and sooty plugs will result from blocked or sticky chokes.

CR's are not easy to fit being a solid bank of 6. I use a bit of rubber grease on the rubbers and to reduce the strain on the rubbers from the weight I run a couple of cable ties from the frame to support each end. CR's are also quite heavy on the throttle hand which is why Honda used vacuum assistance with their CV's. So careful attention needs to be given to cable routing and lubrication to reduce friction but they will still be heavy so do not be tempted to remove the return spring or the return 'push' cable unless you want the throttle sticking open when you open it up.

If you re-route the crankcase breather tube, the oil lines and the wiring loom it will give you more room for installation and then screw in the cable adjusters on the carbs all the way so you can slide them into the space between the motor and the rear engine hangars. It is a tight fit but carefully rotating them as you slide them in will help.

My advice to anybody contemplating fitting CR's to their road bike is, 'don't do it' unless you have access to expert assistance. SUDCO specify that the CR's are for race use only.

My photographic partner Quidnunc reckons there are 2 letters missing from the name of these carbs - 'AP' but they are designed for race use, not road use. For racing they are very popular because of their adjustability for tuning but you really need a good dyno to get the best from them. Roly Skate, Bill Brint at TIMS and James Fisher in the UK all use them on their race bikes but they do take a bit of work to set up and maintain.

It also occurs to me that you may need to consider whether to retain the diaphragm in the fuel line because the CR's will draw more fuel and also make sure your fuel petcock is flowing freely. I have installed a BMW RR quick release in my fuel line because the tap may leak and without the diaphragm, fuel can leak into the cylinders. The result could be a rod thru' the cases! So I always disconnect the fuel line completely when not in use.
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