Topic: Keihin CR carb history?

[kayaker43]

I know there's old and new style, I have the new ones now. I'm collecting parts for a vintage superbike project and the old style CR's are what I need. I understand they went through many upgrades and have heard of sandcast, diecast with no idle circuits, diecast with idle, and CR750 carbs which may or may not be special,.. then the new style carbs.

Can anyone give me a brief history and tips on identifying the various types, I googled but there's little to nothing out there.

[nippon]

http://www.satanicmechanic.org/carbs.shtml

[kayaker43]

Thanks for the link, that must be the one I found a while back? I'm still not clear though if any of the older style diecast carbs had idle circuits? I keep hearing "early CR carbs" don't , but does that mean just the early (sandcast) models of the first generation design, or all of the first generation carbs?

This link says they have no idle stop but the early diecast pictures clearly show they do? They also appear to have idle mixture screws?? I've seen these on several street bikes, did the owners live with no idle??

I would abandon my search if none of the first generation CR's would idle,.. that would make for a lousy street bike???

Also I know there were 26,29,31 sizes but some I see don't have the big red CR logo cast in the side while others do? I think the 26 and 29's do, is it the 31.s that don't?

[lordmoonpie]

Thanks for the link, that must be the one I found a while back? I'm still not clear though if any of the older style diecast carbs had idle circuits? I keep hearing "early CR carbs" don't , but does that mean just the early (sandcast) models of the first generation design, or all of the first generation carbs?

This link says they have no idle stop but the early diecast pictures clearly show they do? They also appear to have idle mixture screws?? I've seen these on several street bikes, did the owners live with no idle??

I would abandon my search if none of the first generation CR's would idle,.. that would make for a lousy street bike???

Also I know there were 26,29,31 sizes but some I see don't have the big red CR logo cast in the side while others do? I think the 26 and 29's do, is it the 31.s that don't?

Regardless of the configuraion, old style CR Keihins are meant for racing, put them on a street bike and you'll be regretting the huge cost of the carbs. They don't allow for good idling and are a pig to set up. Stick to the new CRs if it's a street bike - they are great and will give you trouble free motoring. If on the other hand you want a racer - the early CRs are defiintely the trickiest bits to have!

[kayaker43]

Yeah, that's the vibe I keep getting, early CR's are race carbs but then I've heard they went through like six revisions. Still can't get a definitive "No" to the rumor that the later versions did have reasonable idle circuits?

I'm not building a commuter bike, but a full race replica that might see a couple hundred street miles a year or a few track days. To put things in perspective, it will have a Yosh close ratio six speed with bump start only, so a poor idle doesn't concern me too much. I may even run total loss ignition with Lipo battery for 1-2 hr run times? Practicality means nothing, I have other bikes for that. I just want to re-create my old race bike but with all the stuff I couldn't afford then.

Depends how lucky I get with other parts. If I can scare up some period Dymag wheels like I used to run, I'll try to keep it very authentic and will want the early carbs. Otherwise I'll fudge a little and use CBR three spoke wheels for a similar look and use the modern CR's,.... still collecting parts but I have a lead on some old CR's and need to know for sure how to identify the variants.

[Geeto67]

I had a friend who used to run early CR carbs on the street without idle circuits. They were lousy in stop and go. The modern stuff is so so much better for street duty. If for no other reason than you don't have to keep whacking the throttle at a stop light or deal with the bog as you pull away.

6-speed tranny? hmmmmmmm I would love to see pics of it.

[lordmoonpie]

I had a friend who used to run early CR carbs on the street without idle circuits. They were lousy in stop and go. The modern stuff is so so much better for street duty. If for no other reason than you don't have to keep whacking the throttle at a stop light or deal with the bog as you pull away.

6-speed tranny? hmmmmmmm I would love to see pics of it.

6-speed on a 750 - very interesting. Mine's close ratio but 5's enough for me - what is the top ratio like then in a six speed? Is it similar to the top on a five just to get closer ratios and better power band control?

[kayaker43]

Settle down guys,.. I should have been more specific. I have a 6 speed close ratio trans for a CB550, not sure if Yosh ever made a 750 one?

I also have their CR 5 speed, and some of the gears came in OEM honda bags with part numbers. I think I scribbled down the numbers somewhere too. I suspect its made up of parts from other models??

The 6 speed came in an engine I bought but was never used. I wonder if it uses parts from a CB400F 6 speed, like the drum and forks. It sure looks factory stock, not machined from billet, but Yoshimura surely had the connections to get special parts from Honda vendors?

If I can dig the gearboxes out of storage, I'll start another post. Maybe with the help of others, we can match it up with OEM parts using these for refrence??

[HB-1fan]

Hey Kayaker,
 If you have not got an answer yet and you are in Fl. for the winter this year you can surely get an answer in the infield on vintage race day at Daytona during bikeweek. Hope to see ya there!! Live here and never miss it!!
 Would love to converse on your project. Although I don't have the carbs, tranny or the header, I do have quite a few of the other kit parts you mentioned in that post you replied to last year about the Yoshimura CB500 kit.
 Could you by any chance measure and post header dimensions like: Primary and secondary tube diameters and lengths(on centerline). I have a serious interest in the near future to start fabricating some serious "race replica" parts.
 The AHRMA superbike class is growing by leaps and bounds each year at Daytona.
 Good luck with the project and hope to see you there!!!!!!!!!!!!!!!

Rick

[kayaker43]

Rick

You bet I'll be there for the Ahrma races and I'm sure I'll see a few CR carbs too. Hopefully we'll run into eachother. No one around here wants to hear me talk about hot rod cb550's

Here's some specs on the Yosh header, round the dimensions up or down to fit stock sizes.

Primary tubes. 1.260-1.270 ID and 1.385 OD, 24 to 24.5 long

Secondary including collector 27 inches long and appears to be 2.5 OD straight tube with .050 wall.

[HB-1fan]

Thanks for the header specs. Can you get me some more pics and specs sometime when you get a chance? Different angle pics of the headers. The next time you have the 6sp. tranny out could you take me some good pics of it and list the individual part numbers. Let me know or post for all what it takes to make it work in your bike. I have been looking for years for this info!! I'm guessing its a mix and match of parts from different bikes. Wonder what clutch basket works with it, also.
 I'm gonna try to make a casting mold from one of the "POPS" intake manifols and hopefully reproduce them, also.

Rick