Author Topic: hi performance carbs for cb550F (Read 7225 times)

shane · « **on:** April 09, 2011, 05:27:19 PM »

looking for some good carbs for my 1976 cb550F. Anyone have any good links for parts? Is there anyone that specializes in 550's? Seems to be mostly 750's or twins.

Let me know,

thanks,

Shane

FunJimmy · « **Reply #1 on:** April 09, 2011, 05:39:00 PM »

Shane

There are a couple of guys on the site that are having good luck with Mikuni VM28's and VM26's from the early Kawasaki KZ series, but you will need to modify or make manifolds as the spacing is wider than your stock 550 rack. The Mikuni spacing is a straight shot right to the intake ports on the 500/550 head, so this is a nice performance upgrade. Check out Bwallers build forum and some of the performance 500/550 threads, here in the High Performance section.

If you really want to toss the dough at your bike, you can always order up a set of Keihin CR26 smoothbore carbs. They’re available as bolt on or can be supplied with the KZ spacing for a straight shot at the intake ports.

FJ

Tintop · « **Reply #2 on:** April 09, 2011, 06:48:20 PM »

An other alternative is CB750 carbs, these are an inexpensive 550 bolt-on upgrade.

Kemp · « **Reply #3 on:** April 11, 2011, 03:16:37 PM »

Has anyone tried using CB650 throttle body carbs? These units have accelerator pumps and sport a variable throat diameter, looks like they might be interesting as an upgrade and possibly quite tunable with pods

fastbroshi · « **Reply #4 on:** April 11, 2011, 08:31:05 PM »

Kemp, from what I understand, those carbs are a proper pain in the ass.

Kemp · « **Reply #5 on:** April 12, 2011, 02:28:27 PM »

What are the issues with them? Have a set and am about to clean them. Looks like they were designed to flow more volume, thought they might be a little more "advanced" looking at the shape and sizing of the venturi. Is the accelerator pump a problem area?

TwoTired · « **Reply #6 on:** April 12, 2011, 03:39:45 PM »

I know the CB650 had two styles of carbs, the PD mechanical slide carbs and the later CV type carbs.
I don't know what "throttle body carbs" are.

The PD mechanical type will indeed work on the CB550 (I recall it being done). The larger venturi will be welcome if the engine also has cam, head work, induction, and exhaust improvements. The most welcome feature will be the accelerator pump, which should improve throttle response on an otherwise stock CB550. Since the carbs were jetted/adjusted for the larger displacement, different induction, and exhaust of the 650, it will be all wrong for the stock 550 and all aspects with have to be reviewed/optimized for its new role, (if you want any sort of optimization other than "it runs"). I don't see them giving you more HP unless you wind up the stock motor well past red line, where the larger venturi size will be of some benefit.

Cheers,

Kemp · « **Reply #7 on:** April 12, 2011, 04:04:39 PM »

Two Tired - Yes, I mean slide carbs not CV. Don't mean to hi-jack the thread, hopefully just add to it. The engine I want to try them on is a fresh 592cc Powrol kitted motor I just built. It has a a rebuilt head with 5 angle valve job not ported but decked. I'm also using a CB650 cam, Mac exhaust and unipods. I thought the 650 cabs might be a nice compliment to this kit for the reasons you've mentioned. I thought I'd try it with stock jetting first just to see where the bike is at and get a reasonable baseline to start. Does this sound reasonable?

TwoTired · « **Reply #8 on:** April 12, 2011, 04:13:38 PM »

Quote from: Kemp on April 12, 2011, 04:04:39 PM

Does this sound reasonable?

Yes, sounds like a good approach. You gonna do testing on a dyno? Probably be lean if the 650 carbs are stock jetted/adjusted. Have you noticed if the slide needles are adjustable on those carbs?

Cheers,

fastbroshi · « **Reply #9 on:** April 12, 2011, 08:04:33 PM »

I'd just heard those carbs might be problematic not so much reliability wise, but parts may be hard to find for those carbs, not to mention expensive when you do. Would you mind measuring the carb's openings front and rear when you get the chance?

shane · « **Reply #10 on:** April 13, 2011, 12:23:13 PM »

Quote from: Tintop on April 09, 2011, 06:48:20 PM

An other alternative is CB750 carbs, these are an inexpensive 550 bolt-on upgrade.

Nice! I didn't know these were interchangeable... Are all 750 carbs interchangealble? I saw some pretty cool options on this site... http://www.cyclexchange.net/Carb%20System%20Comp%20Page.htm

shane · « **Reply #11 on:** April 13, 2011, 01:42:45 PM »

Quote from: FunJimmy on April 09, 2011, 05:39:00 PM

Shane

There are a couple of guys on the site that are having good luck with Mikuni VM28's and VM26's from the early Kawasaki KZ series, but you will need to modify or make manifolds as the spacing is wider than your stock 550 rack. The Mikuni spacing is a straight shot right to the intake ports on the 500/550 head, so this is a nice performance upgrade. Check out Bwallers build forum and some of the performance 500/550 threads, here in the High Performance section.

If you really want to toss the dough at your bike, you can always order up a set of Keihin CR26 smoothbore carbs. They’re available as bolt on or can be supplied with the KZ spacing for a straight shot at the intake ports.

FJ

Thanks for the info Jimmy, just looked at your build thread, amazing work! Where is a good source for the carb options you mentioned? Also, a little off topic, but where did you find your exhaust?

Pinhead · « **Reply #12 on:** April 13, 2011, 06:34:49 PM »

The '79 CB650 carbs have 90 main jets from the factory and will run terribly lean with your pod air filters. In fact, many 650 owners have to go straight up to 98 mains just by removing the air filter cover.

There's nothing really wrong with those carbs, except for the price of rebuild kits ($45 per carb last I checked).

Kemp · « **Reply #13 on:** April 14, 2011, 10:13:15 PM »

Did a 550/650 comparo. 550 carbs ID 27mm, 650 carbs ID 29mm. 650 carbs bolt directly onto 550 intake manifolds. Can use 550 intake boots also although they are a tighter fit on the 650 carb mouth. Will try and post 3 pics of the comparo[/img]

Kemp · « **Reply #14 on:** April 14, 2011, 10:30:45 PM »

http://i559.photobucket.com/albums/ss37/kemp1111/550-650%20carb%20comaro/550650carbcomparo003.jpg

Kemp · « **Reply #15 on:** April 14, 2011, 10:40:35 PM »

Previous pic has 550 carbs on left and 650 on rt. Shows big difference in airbox side of carbs 35mm ID for 550 and 43mm ID for 650. The next two pics show spigots and difference in size 550-650. I think the 650 cabs are the same size as the CB750 (29mm) but might have the advantage of a lower profile and accelerator pump.
http://i559.photobucket.com/albums/ss37/kemp1111/550-650%20carb%20comaro/550650carbcomparo002.jpg http://i559.photobucket.com/albums/ss37/kemp1111/550-650%20carb%20comaro/550650carbcomparo001.jpg

TwoTired · « **Reply #16 on:** April 15, 2011, 12:37:00 AM »

Where does the third air jet go on the 650 carbs?

bwaller · « **Reply #17 on:** April 15, 2011, 04:10:37 AM »

There is obviously a complicated venturi section on these Keihins and tough to measure but Honda claims the 550 carbs to be 22mm, the 750s 28mm. Not sure about the 650. The 750A's are 26mm as another option. The Mikuni VM26 venturi is nearly straight round and closer to 27mm. On a stock engine I'm afraid these will be too big and a nuisance on the street.

In the seventies I tried to help a friend sort through jetting CB750 carbs on his CB500 that had a 4-1 but otherwise a stock engine. Although it ran well on the top it was a pig everywhere else. We came to the conclusion that on a street bike they were obviously too big. They are a choice of many racing these bikes however.

I'm waiting for Funjimmys report on his new 26mm Keihins.

FunJimmy · « **Reply #18 on:** April 15, 2011, 07:21:47 AM »

Quote from: bwaller on April 15, 2011, 04:10:37 AM

I'm waiting for Funjimmys report on his new 26mm Keihins.

Fired it up yesterday for the first time, and it sounds impressive.
Number 2 primary pipe isn’t heating up as fast/much as the other three so I’ll sunc them today and let you know how it goes.

First impressions are good. Throttle blips with authority and drops to idle quickly.

Flying J · « **Reply #19 on:** April 15, 2011, 08:54:42 AM »

I came across a CB550 at the junk yard the other day that had a set of carbs that i was not familiar with. They turned out to be the 650 carbs. After a little research i found that the rebuild kits plus what the carbs would cost and the time to jet them properly would be counter productive. If i ever upgrade it will either be the vm26 or the CRs but for now ill run a set of stockers.

Pinhead · « **Reply #20 on:** April 15, 2011, 12:12:22 PM »

Quote from: TwoTired on April 15, 2011, 12:37:00 AM

Where does the third air jet go on the 650 carbs?

I believe you're referring to the air jet feeding the air-cutoff valves.

TwoTired · « **Reply #21 on:** April 15, 2011, 12:36:02 PM »

Quote from: Pinhead on April 15, 2011, 12:12:22 PM

Quote from: TwoTired on April 15, 2011, 12:37:00 AM
Where does the third air jet go on the 650 carbs?

I believe you're referring to the air jet feeding the air-cutoff valves.

Yes, of course, I forgot about those on the 650.

Thanks,

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Author Topic: hi performance carbs for cb550F (Read 7225 times)