cb650 keihin crs29 carbs
If you have a cb650 (or any jap 4cyl) and you’re looking to splurge close to an extra $1000… This post is for you.
79-80 cb650 actually have pretty good stock-oem carbs IMO: 29mm bore, mechanical slide and accelerator pump. However, if yours are getting shitty and want a nice upgrade, brand new keihin crs29 smoothbore race carbs are the way to go.
If you have the shitty 81-82 constant velocity carbs, bummer for you. Def upgrade to the keihin crs.
Benefits of keihin crs smoothbore carbs
- Brand new. Still made today. Every and any part is available still
- Every single circuit is tunable to a fine degree
- They’re not too difficult to tune
- You’ll prob get a few horsepower assuming you tune them properly
- Choke is on the carb body so no more shitty cb650 pull choke near handlebars
- Nothing beats brand spanking new carbs… Best upgrade for any bike IMO
Keihin crs29 jetting for cb650
- 115 main jet
- 220 main air jet
- 68 slow jet
- yy6 needle – middle
- Air screw 1 turn out
If you have a 4-1 exhaust, and you’re basically at sea level, above is the jetting I recommend to get you in the ballpark… to then fine tune.
Things to note
- Intake spigots need to match up: if you have 79-80 you’ll want Keihin intake spigot number 020-024 (below pic) for a Suzuki gs850. Needs to be long enough to clear the petcock as seen in below photo. Also need to shave off 1mm from the end that sits into the intake boot so it seals properly.
- Pod filters won’t really fit. They hit the frame on cylinders 1 and 4. So I’m running the velocity stacks that come with the carbs.
- You’ll need a different “pull” throttle cable. Use the “push” from the CB650, and then buy a “pull” from a 78 Kawasaki kz1000. KZ cable is slightly longer looking but the cable/housing ratio is what you want.
- Where the cables thread into the carb holder…You’ll need to bend the tabs up and to the left a hair, so the cables clear the frame of the motorcycle. Seen in below pic.
- Get a pair of new rubber intake boots. Might as well, right.
Yea, if you have a 4cyl jap bike… These are the best carbs you can pick up, hands down. I also have a set on a 74 Kawasaki z1 and I love them. Don’t put carbs on your bike that are too big bore. Some people upgrade to the Mikuni RS34, which are too big. For a 4cyl, I love the Keihin CRS, and for a twin or single cylinder, I like the Mikuni VM.
These carbs will work great on any 70s Honda CB 500, 550, 650, 750 4cyl.
However, on 500, 550, you should run the keihin crs26. Slightly smaller bore will work better.
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Published - Nov 26, 2010
Karl was a longtime Philadelphia area vintage motorcycle rider that frequented Two Wheel Tuesday from time to time. Some of you may have met him or saw him in his wheelchair last year at the Norton Gathering in Washington Crossing State Park. The photo above is of the gravestone Karl had pre-ordered the beginning of […]