Anyone running Keihin CR special 29mm carbs?

I just bought a set and was wondering if anyone had experience with them?

Hey Mike, I know this is an old post but I thought I'd share anyway. When I first got my KZ750H2 it needed the usual carb work as it had been sitting a while. Well a friend-who knew more about bikes than me, or so I thought at the time-and I got into them and proceeded to wreak havoc on the poor things. We're talkin' broken of bits of brass, gouged venturis...it was a wreck. All of a sudden I'm in the market for some new carbs. At the time I was not benefitting from the founts of wisdom found here at KZR and I'm sorry to say that I dropped almost twice what I paid for the bike on a brand-spankin'-new set of 29mm Keihin CR Specials. They sure are pretty, but I had a bit of a time getting everything to play nice. I adjusted the needles and airscrews and eventually got the bike running fairly well. However I eventually started fouling plugs left and right. At first it was once a week, then every few days, then I couldn't even make it out of the garage before the plugs were all black again. I ended up throwing up my hands and took it to a shop...(don't tell anyone, but it was actually a Honda dealership). They managed to get it all running right with some rejetting and slight adjustments.
To make a long story just a little bit longer, I've been pretty pleased with their performance. The only catch is that they really are a racing carb and on the street I have to keep the ol' girl revved pretty high. 5000rpm and up...LOOK OUT!
Don't know if all that helps or made any sense, but I thought I'd throw it out there

Wirewulf wrote:

I dropped almost twice what I paid for the bike on a brand-spankin'-new set of 29mm Keihin CR Specials. They sure are pretty, but I had a bit of a time getting everything to play nice. I adjusted the needles and airscrews and eventually got the bike running fairly well. However I eventually started fouling plugs left and right. At first it was once a week, then every few days, then I couldn't even make it out of the garage before the plugs were all black again. I ended up throwing up my hands and took it to a shop...(don't tell anyone, but it was actually a Honda dealership). They managed to get it all running right with some rejetting and slight adjustments.
To make a long story just a little bit longer, I've been pretty pleased with their performance. The only catch is that they really are a racing carb and on the street I have to keep the ol' girl revved pretty high. 5000rpm and up...LOOK OUT!
Don't know if all that helps or made any sense, but I thought I'd throw it out there

When you bought the carbs, were they pre-jetted for your bike, and you still had problems?

My 78KZ650C2 came with a set of these on it. I had no history on the bike or carbs (it came from an estate sale), and I now have the bike running pretty well, but like yours it hates to be below 5k. My understanding is that when you order the carbs, they are setup for your particular bike by the distributor. There is very little info that I could find anywhere on setup. Mine seem to run a bit rich as I can start with minimal choke, and I get about 30 mpg whether I drive hard or easy. I bought a set of stock carbs to try out but have to refurb them before I can put them on and see how the CRs compare.

I was wondering if our resident carb guru has an opinion on these.

Yeah, I told 'em all about my bike when I ordered them and they were supposedly setup for the engine(stock) w/ 4-1 and pods. I took their word for it that they were pre-jetted properly, but I believe the mechanic changed the pilots and mains, not sure what to.
I also only get about 25 to 30 mpg and thought that was a little low, especially since I can smell unburned gas from the pipes when I pull up to a stop sign. But after all my failed attempts at resurrecting a functioning bike, I'm just happy that it pushes me down the road(the speed is nice too!). Although I have been pondering whether I should get/make a larger tank. Having to stop every 50-60 miles is a drag.

Any idea what slide cut out is in this carb and what size pilot air jet? Sounds like they are big numbers that require a real big set of pilot jets. These are often hard to tune at the low end. What size pilot jets and main jets do you have? Bigger gas tanks are expensive!

If I'm reading the dyno printout properly, I've got 110 main jets and 1.75 Pilots...and 60HP at the rear wheel, is that respectable?

The pilot jets will likely be #17.5 and not 175 but that ain't bad for a KZ750. I doubt that the racing carbs are buying any horsepower over the stock carbs as that is about what I would expect for a 750 w/pods and pipes. The OEM Keihin CV34 or Mikuni BS34 carbs will likely make about the same horsepower (at rear wheel). Guess some 750 owners will have to chime in.

The jetting sounds about right... maybe a bit smallish mains for pods but I have little experience with these carbs. If it will pull redline on the dyno, the mains must be big enough.

wiredgeorge wrote:

The pilot jets will likely be #17.5 and not 175 but that ain't bad for a KZ750. I doubt that the racing carbs are buying any horsepower over the stock carbs as that is about what I would expect for a 750 w/pods and pipes. The OEM Keihin CV34 or Mikuni BS34 carbs will likely make about the same horsepower (at rear wheel). Guess some 750 owners will have to chime in.

The jetting sounds about right... maybe a bit smallish mains for pods but I have little experience with these carbs. If it will pull redline on the dyno, the mains must be big enough.

If I get some time, I will pull mine out and see what jets are in em. I am leaning toward going back to stock carbs if they will get the bike running better at lower RPMS. The way it runs now, if I grab a lot of throtle anywhere under 5k, it bogs down and then seems to clear and pull like heck to redline.