Topic: 1977 CB550 K cafe racer build

[HalfFastMoto]

CV carbs will never have the same throttle response as a standard slide carb but they do provide smooth power, great fuel mileage and can be tuned if you know the tricks.

[Raef]

Its a shame that someone on here doesn't do later model carb conversions for our bikes, there are heaps of bikes that have carbs that would be better for our bikes than the old Kehins...

Mick

I am looking at putting modern carbs on the current build, I have alot of auctions saved checking, out many models. Any suggestions?

[Retro Rocket]

CV carbs will never have the same throttle response as a standard slide carb but they do provide smooth power, great fuel mileage and can be tuned if you know the tricks.

Terry in Australia has 34mm CV's on his 836 and from what he told me they #$%* on the stock carbs everywhere. They are off a 83-84  CBX 750 and the throttle response is better and lighter and they just run better overall. I think he has just had a second set made up to suit the old 750's, he is replacing the 29mm CR's with these CV carbs and just raves about them.....
Raef, i have mentioned what model carbs that Terry uses here but i bet there are others around, they will need modifying to fit but should end up cheaper than CR's and better on the street. Send him a PM and ask.....he doesn't bite....


Mick

[Raef]

I have been thinking about somthing from the mid 1990's cbr 600 maybe.

I have also been reading "mikuni vm24" may be a good choice, I have a while I just got the head, ordered gaskets and need to get my 550 jugs bored to fit the pistons.

and the bike is not done

Mark

[HalfFastMoto]

....

Terry in Australia has 34mm CV's on his 836 and from what he told me they #$%* on the stock carbs everywhere. ...


Mick

Man, those stock carbs must really suck!  Guess I'll have the joy soon enough or maybe I should just grab a set of CVs from a GPZ550 for my CB400F though 26mm seems big for a 400

-brad

[Retro Rocket]

....

Terry in Australia has 34mm CV's on his 836 and from what he told me they #$%* on the stock carbs everywhere. ...


Mick

Man, those stock carbs must really suck!  Guess I'll have the joy soon enough or maybe I should just grab a set of CVs from a GPZ550 for my CB400F though 26mm seems big for a 400

-brad

I wouldn't say they suck {well they do suck fuel.. } just old technology.

Mick

[Syscrush]

I have been thinking about somthing from the mid 1990's cbr 600 maybe.

They would be oversized for anything less than a modified 750.

When looking for a donor bike, pick something that made about the same power as your bike - cc's don't matter, hp does.

[Raef]

I don't know what kinda HP to expect but at right now I am working with a reworked 650 rotating mass in a 550 block. the head will have a good deal of work done and it will have a handmade 4 into 1


Mark

[Syscrush]

I don't know what kinda HP to expect but at right now I am working with a reworked 650 rotating mass in a 550 block. the head will have a good deal of work done and it will have a handmade 4 into 1

Something like a Bandit 600 might be a better donor.

[FunJimmy]

What i mean is that race carbs are more top end orientated and usually offer poor results for round town riding, you have to "feed" the throttle on when low in the rev range so as not to flood the bike and make it bog down. Terry has fitted a set of 34mm CV's off a 1980's CBX 750 Honda on his 836 and he says that it is the best conversion he has ever had, i am thinking of getting a set for my 1000cc build to run it in with then put them on my other bike for good....The 1000 gets fuel injection.....  There are lots of other carbs out there that would do a better job on the street than the CR's and probably a lot cheaper....


Mick

Mick

From your posts on the subject it would appear that you aren’t a big fan of the Keihin CR carbs on a 550 street bike. Most here that have used the CR’s on the 550’s have been using the 29’s and I agree that is over carburetion a 550, but Godfrey is using the CR26 carbs and reports good street manners.

It’s still a tight fit with K&N pods, but a custom (shorter) and straight direct shot manifold could correct that.

Do you think the 26mm CR’s would be a good choice on the street?
What effect does intake runner length have on the power characteristics of the engine?

Thanks
FJ

[Tintop]

What i mean is that race carbs are more top end orientated and usually offer poor results for round town riding, you have to "feed" the throttle on when low in the rev range so as not to flood the bike and make it bog down. Terry has fitted a set of 34mm CV's off a 1980's CBX 750 Honda on his 836 and he says that it is the best conversion he has ever had, i am thinking of getting a set for my 1000cc build to run it in with then put them on my other bike for good....The 1000 gets fuel injection.....  There are lots of other carbs out there that would do a better job on the street than the CR's and probably a lot cheaper....
Mick

Mick
From your posts on the subject it would appear that you aren’t a big fan of the Keihin CR carbs on a 550 street bike. Most here that have used the CR’s on the 550’s have been using the 29’s and I agree that is over carburetion a 550, but Godfrey is using the CR26 carbs and reports good street manners.
It’s still a tight fit with K&N pods, but a custom (shorter) and straight direct shot manifold could correct that.
Do you think the 26mm CR’s would be a good choice on the street?
What effect does intake runner length have on the power characteristics of the engine?
Thanks
FJ

FJ the CR26's would definitely be a better solution than the 29's.  The smaller throat, and venturi promote higher initial air velocity at small throttle openings.  It is the lack of this initial velocity that causes the part throttle flat spot(s).  Pods just make this worse, while stacks will promote air speed.

The intake runner length has minimal effect, as long as the rest of the intake system is matched (tuned) to it.  This is were TwoTire's oft quoted Helmholtz Resonance comes into it.  There are power pulses in the exhaust system that a properly designed pipe uses to empty the cylinder, and draw in the new charge.  Those same pulses exist in the intake track.  NASCAR engineers use a 3 wave model, (think I've got this right ) were the 1st 2 waves cancel each other, so that the 3rd can carry the full new charge.  Changing the runner length changes the parameters.   From my perspective the biggest problem is not the length, but the bends, which slows the charge. 

[Retro Rocket]

There is a direct correlation between intake runner length, stack length and performance,mainly changes in torque and where the bike likes to perform, these type of changes are usually only looked at in racing so street bikes tend to be a compromise or a "happy medium"
Its not that i don't like CR's, its just that they are a racing carb and lack the finesse of a street carb, so they can take some dialling in.
TT covers why the 26's would be a better carb for the 550 on the street and i agree..... Now, if it were me i would be looking at some later model CV's to go on the 550, just look at the way modern bikes accelerate compared to our old war horses, just like electronic ignitions, the newer technology is much better through evolution......

Mick

[traveler]

On my 550, you couldn't go full throttle without bog until you are at 6,000 RPM or higher.

When you would hammer the throttle, sometimes, I had toroll the throttle back just a hair to "lean it out" and get the rev's up.  Once you are used to doing it, you do it instinctively.  The prerormance of the bike was VERY strong, but with the lower gearing, I was capable of only about 90 MPH flat out.  But on a long 40 degree hill, coming up it, I was able to accelerate up it like nothing!

The best route would be Fuel Injection, but how easy would that be?  You'd have to fab up an intake, a crank fire setup for the EFI controller to use to fire the fuel spray....big bucks.

On these bikes (the 550's), it just seems, once you take the airbox off, everything goes to hell QUICK.  The CR's are a nice setup for a cafe'd 550.  cams, headwork, etc. ADD air, and make the CR carbs work better.  I had to play with the throttle, because I had a stock head and cam.  Th work on a Cafe bike, because they are all about performance, not reliability or drivability.

I used to wind the crap out of that poor motor!  it really came alive above 8,000 RPM.  Good thing I never snapped a rod, huh?  I always made sure the cam chain was tight, and had plenty of oil pressure!:D

I think it's best to just build a 750 if you're looking for a bike to build.  

~Joe

[Really?]

How come I just noticed this build thread?  And there are 45 pages of it!   

it all started with the filter on another thread and I landed here.  I think ffjmoore layed out th elink in a nother thread.

Well, I made it, whew!

[Tintop]

How come I just noticed this build thread?  And there are 45 pages of it!   

it all started with the filter on another thread and I landed here.  I think ffjmoore layed out th elink in a nother thread.

Well, I made it, whew!

Kind of like getting through War & Peace, TipperT.

[Really?]

I don't read much but for some crazy reason I want to read that sometime in my life.  I better hurry up, time is running out lol.  But the way kids are getting reading shoved down their little necks, I expect my 8 year old to be reading that in the next three years, lol.

[Raef]

I don't read much but for some crazy reason I want to read that sometime in my life.  I better hurry up, time is running out lol.  But the way kids are getting reading shoved down their little necks, I expect my 8 year old to be reading that in the next three years, lol.

I have one in the 10 grade and one in collage and to this point I think the 2nd grade was the worst for homework and reading, well AP calculus and chemistry were a little tough around here as well

[ace1204]

So if one is building a cb550 and wants to remove the airbox what is the most affordable solution that works with improved or par response to stock settup with airbox?

[Flying J]

the stock air box. Thats it. There is no equivalent replacement.

[Godffery]

I have to disagree, K&N pod filters vastly out perform the stock air box when the Cabs are jetted properly.

[Zaipai]

Tintop is working on a darn good replacement for the stock filter, however it wont be cheap.. I believe its going to be like $250 or around there.

Personally I replaced my stock air filter for pods with foam filters and am loving them more then the stock, and other then a problem idling when cold they are perfect it idles fine when warm. just how I feel about them tho, I am sure others would disagree.

.: Scott :.

[Retro Rocket]

I have to disagree, K&N pod filters vastly out perform the stock air box when the Cabs are jetted properly.

I would love you to elaborate on that comment ....

Mick

[Tintop]

I have to disagree, K&N pod filters vastly out perform the stock air box when the Cabs are jetted properly.

I would love you to elaborate on that comment ....
Mick

It can be done Mick, but you and I both know its going to be a PITA.  Zaipai pointed out one alternative (actually more like $235 probably).  You and I have debated the pros & cons of the HA bread box, in the same filter thread.  Each to there own, but to me 'vastly out perform' means from idle up, and with clean transitions, not just 1/2 to WOT.  The stock system (550 & 750) was designed to use stacks, you loose those with Pods.

[FunJimmy]

The stock system (550 & 750) was designed to use stacks, you loose those with Pods.

But not with your's 

[Tintop]

The stock system (550 & 750) was designed to use stacks, you loose those with Pods.

But not with your's 

    didn't want to sound like I was schilling, but thanks.