Topic: CB550 & Keihin CR26 carbs or NOT!

[FunJimmy]

Hey gang

I'm considering the next stage in the CB550F Interceptor evolution and need (want) some real world opinions regarding Keihin CR29 carbs on a street bike.

My CB550F has been worked over a bit with a Mreick ported head, 650 cam, 59mm Yoshimura (slight raised dome) and a Kerker header & Megaphone fitted with a 1 1/2" competition baffle. I plan to swap out the 650 cam for a Webcam 58B profile and swap out the Kerker for a SS Yoshimura (replica) exhaust from Moto GP Werks. The other item that I’m considering is the Keihin CR29 carbs that you are running, but I’m a bit concerned that they may move the torque and power band into the WOT category at the expense of daily street use.

What says you?

Thanks
FJ

[754]

 Cant help with that..
 but a heads up.. when you head this way tomorrow bring a good jacket + a camera or cameraphone..  might get to - 18 C tomorrow and next few days,.....

[q2418130103p]

cb550fcafe has then, you may want to PM him.

[FunJimmy]

Cant help with that..
 but a heads up.. when you head this way tomorrow bring a good jacket + a camera or cameraphone..  might get to - 18 C tomorrow and next few days,.....

Camera? Got some secret project you wanna share?

[754]

Just the usual..

[bwaller]

I'm starting to wonder if you'll get the honest answer you're looking for Jim, too bad. I don't think I ever read about anyone here running a 500/550 with CR26's. The other option we have spoken about before is changing the intakes and mounting a set of VM26 on your 590. Not as glamorous, wider and real heavyweights compared to the Keihins though.

[FunJimmy]

Brent

My bike only has 59mm (555cc) Yoshimura pistons (with slight raised dome) in it and I am a little concerned with over carburetion.

Several SOHC4 members are using the CR29’s and report back that the bikes scream on top, which is enticing, but they are also commenting that the throttle must be gently administered until the revs get up there.
 
Now I know that the upper reaches of the RPM band offer up a ton of fun. But my bike is predominantly a street bike and needs excellent low to mid response too.

Another attraction to the Keihin CR’s is the new modern efficiency that they bring to the party. But at a pretty big expense too.


CHeers
Jimmy

[swellguy]

I had put a set of 29s on my kb 750 before tear down. It screamed all over the powerband. The general consensus was that the 31s were too large and better suited for the big bore kits. I just don't know enough about the 550 to predict how much jetting and timing issues you might run into though.

[FunJimmy]

I changed the subject to "CB550 & Keihin CR26 carbs 0r NOT!" because it's pretty clear from several private conversations and posts in other threads that the CR29's are too large for optimal performance and throttle response on a street going CB550.

There is however the CR26 carbs that Godfrey is using on his gorgeous “Café Overkill”. These smaller CR carbs should offer better velocity and throttle response from a mild to hot CB550 I would think, but they don’t come as a direct fit kit.

Seems that the spigots supplied are either a 30mm or 35mm OD and the CB550 requires a 33mm spigot. I know that custom spigots can be machined or perhaps the 35mm spigots could also be turned down, but they are also a bit long.

Others have told me that you require the shorter CB500 manifolds to obtain enough clearance for the pod filters too. That creates some additional cost and complication to the process, so I am considering something even cooler.

It looks like the CR carbs are mounted on adjustable (slotted) spacing steel rails. The Kawasaki KZ carb spacing is almost a straight match to the CB550 intake ports on the head.

How about making a custom manifold using a ½” plate of aluminum fastened to the CB550 head and then bolt on Kawasaki KZ rubber manifolds to connect the carbs. Keihin CR26 carbs can be ordered in KZ configurations so spigot will fit and the spacing should be adjustable for a perfect, straight shot at the intake ports.

What says you?

[754]

Dont take no for an anwer.. we can make almost anything fit..

 I will be there tommoropw, + its warming up...

[indycb450]

Got a '77 CB550 engine I am having bored over 1 mil with a polished/ported head.  Might drop a Webcam in too.  Still unsure myself whether or not to invest the $ on some Keihin's as opposed to jetting out my stock carbs.  This is an interesting thread that will play into my decision process.  Any input would be appreciated    ??

[Doctor_D]

I absolutely love mine.  Great throttle response, very tunable, and big power numbers.  The CR26's are properly sized for your application and would probably make you very happy.

The downside, they can be expensive to tune if you have to buy air jets, needles and mains. Get it as right as you can on your initial order.

[FunJimmy]

I did finally decide to go with the CR26 carbs set up with 77mm x 100mm x 77mm spacing for a direct fit to the intake ports on the head. This required either a modified (welded) intake manifold or custom manifolds. I went the custom manifold route using plate aluminum and Kawasaki KZ550 rubbers. 

Everything is installed, including the WebCam and I should have a ride report very soon, so stay tuned.

[bochnak]

What jetting did you end up with?

[FunJimmy]

I had an amazing opportunity to spend some time at Twinline Motorcycles with CR Master, Doctor_D and Jeff, AKA Tower.
These guys know CR carbs and dyno tuning like no one else in the PNW.

When I arrived my CR26 Carb jetting was: 

Pilot 60
Main 105
Needle YYO
Clip #2 (5th slot from top)
Air Jet 220
Air screw open ¾ turn


Post dyno tuning:

Pilot 65
Main 105
Needle YY8
Clip #2
Air 220 Inside 230 Outside
Idle Screw 1 turn

These jetting changes combined with a little ignition timing made big differences in throttle response and crispness. Idling was a different deal.
The bike just wouldn't hold a steady idle and required 1500rpm+ to stay lit, but that was found to be cam timing and an intake leak.
Not a fault of the carbs.


<a href="Not a valid vimeo URL">CB550 Interceptor - Dyno Tuning[/url] from FunJimmy on Vimeo.

[bochnak]

Here is the current jetting:

Pilot 50
Main 100
Needle YY8
Clip #3 from top
Air Jet 220
Air screw open 1/4 turn

The above yields a crappy idle, bogs everywhere in RPM range, zero crispness.

Before ordering parts I tried the following:

Pilot 50
Main 100
Needle YY8
Clip #7 from top
Air Jet 220
Air screw open 1/4 turn
Masking tape blocking 50% of carb intake

Huge improvement! First w/o tape, it really woke it up in mid-top as expected. The tape was added and low end bog was almost gone.

I will try the following when jets come in:


Pilot 65
Main 105
Needle YY8
Clip #5 from top
Air Jet 220
Air screw -? Tune for best idle

Also, this bike has a cam as well. What timing did you go with? I'm timing it with a strobe, full advance @2500, stock settings.

Did the air jet make that big of difference on outer 2?

[FunJimmy]

Also, this bike has a cam as well. What timing did you go with?
I'm timing it with a strobe, full advance @2500, stock settings.

Did the air jet make that big of difference on outer 2?

Interestingly, I discovered that my cam was mistimed by one tooth, so ignition timing was way off to compensate.
Once resolved the ignition timing was set to factory settings and all was good.

I don't think the mismatched air jets did anything at all and will likely match them before spring.
I also have a nicely ported MReick stage 2 head.
That might be a big contributor to these carbs working so well.
 

[bochnak]

Also, this bike has a cam as well. What timing did you go with?
I'm timing it with a strobe, full advance @2500, stock settings.

Did the air jet make that big of difference on outer 2?

Interestingly, I discovered that my cam was mistimed by one tooth, so ignition timing was way off to compensate.
Once resolved the ignition timing was set to factory settings and all was good.

I don't think the mismatched air jets did anything at all and will likely match them before spring.
I also have a nicely ported MReick stage 2 head.
That might be a big contributor to these carbs working so well.

OK, thanks for all the info. All this should save me a couple of jet changes. I also will install 35 starter jets.

I'll report back this weekend.

[andrewk]

Does 48 RWHP make sense for your build?  I see a ported head, big bore kit, big carbs, big cam, free-flowing exhaust....  Seems low to me.

EDIT-  I bet that's before the cam timing change- nevermind.   Did you put it back on the dyno after?

[FunJimmy]

Does 48 RWHP make sense for your build?  I see a ported head, big bore kit, big carbs, big cam, free-flowing exhaust....  Seems low to me.

EDIT-  I bet that's before the cam timing change- nevermind.   Did you put it back on the dyno after?

Ya, that cam issue really sucked. I've got it sorted and running much better (seat of the pants dyno) just need to get back to Twinline to see what it's got.

[singedebile]

sheesh, every time I think I am getting somewhere with my bike I see yours... and then you go and do all this to it!

Keep it up!

Given stock wheel HP to be 39, I really would have expected yours to be comfortably above 50 (in my limited knowledge)... but am very curious to find out what it finely is. Please update us when you find out!

[FunJimmy]

sheesh, every time I think I am getting somewhere with my bike I see yours... and then you go and do all this to it!

Keep it up!

Given stock wheel HP to be 39, I really would have expected yours to be comfortably above 50 (in my limited knowledge)... but am very curious to find out what it finely is. Please update us when you find out!

Me too. 
I was a bit disappointed, but I'm sure it's in the 50+ range now.

[matt mattison]

sheesh, every time I think I am getting somewhere with my bike I see yours... and then you go and do all this to it!

Keep it up!

Given stock wheel HP to be 39, I really would have expected yours to be comfortably above 50 (in my limited knowledge)... but am very curious to find out what it finely is. Please update us when you find out!

Me too. 
I was a bit disappointed, but I'm sure it's in the 50+ range now.

48 RWHP is a 20% gain. That seems to be a pretty appreciable increase.

[greenjeans]

How were they able to diagnose the air leak and cam tooth by the dyno ?     Just curious.   Had it been off by that one tooth for long time ?

Really wish there was a dyno in my town -  I'd like to think I'm getting an ear for tuning these things - just not 100% sure I've seen/heard one dialed

in perfectly.    Always loved that bike of yours - seems like it just keeps getting better and better.

[FunJimmy]

How were they able to diagnose the air leak and cam tooth by the dyno ?     Just curious.   
Had it been off by that one tooth for long time?

I wasn’t able to diagnose the cam timing or the air leaks on the dyno but we just couldn’t get the bike to idle below 1500 rpm and even then it was rough and would periodically fall off completely and stall. The bike was a lot stronger and throttle response was great, it just wasn’t perfect, so that got me thinking and poking around. Being out one tooth on the cam is a lot easier to do than it sounds and when I did get the cam timing right idle got noticeably better but still not the way you’d expect. It’s been out that tooth since I first installed the Webcam a couple seasons ago.
Part of me assumed that there wasn’t enough air speed at idle to get a good signal in the carbs and it is what it is, but when I pulled the plugs I noticed two rich and two lean plugs. Close inspection suggests air leaks between the rubber carb boots and the aluminum manifold but confirmation of that and the results will have to wait until I get my head back from Mike and run it up.

Always loved that bike of yours - seems like it just keeps getting better and better.

Thanks