Topic: CB and CR carbs

[900WOT]

Has anyone put CR 31 carbs on their bike? I have a 1982 Honda CB900F Super Sport and Im getting rid of the CV carbs for CR 31s.  Looking for some thoughts on that.

[innovativems]

Quite a few people have.  For a stock street bike, 31’s should work but might be a bit big from conversations I’ve had.

What are you trying to achieve by swapping the carbs?


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[754]

Should work, do you plan on spirited use ?

[900WOT]

Should work, do you plan on spirited use ?

Thanks for responding.

Not turning it into a race bike or anything, I just want the CV carbs gone. Ive heard CR carbs make the bike run cooler and its a step up from CV carbs.

[900WOT]

Quite a few people have.  For a stock street bike, 31’s should work but might be a bit big from conversations I’ve had.

What are you trying to achieve by swapping the carbs?


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I spoke with the guys over at dynoman, who sold them to me, and did my research and it seems 31s are appropriate. A guy I know put 31s on his bike and said it runs great (pic below).

Mostly im looking for ease of tuning, for the engine to run cooler, easier start ups and maybe just a wee bit more on the top end.

[innovativems]

For a stock motor it’s probably a bit much with the 31’s and you will lose bottom end.  They aren’t much easier to tune but the main benefit is they are not cv carbs if you ditch your airbox.  As far as how hot it runs, they won’t help with that or start ups.  That’s all just proper setup on the bike. 


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[900WOT]

For a stock motor it’s probably a bit much with the 31’s and you will lose bottom end.  They aren’t much easier to tune but the main benefit is they are not cv carbs if you ditch your airbox.  As far as how hot it runs, they won’t help with that or start ups.  That’s all just proper setup on the bike. 


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Im not so sure 31s are too much. The guy whose bike I posted above (the black and gold bike) wrote this to me in email when I was debating. His first hand experience;

"For many reasons, this was the absolute best investment I made to my 900F. Throttle response is not crappy at all. One of the longtime and experienced members of the biking community told me that each person has to cross the threshold of when they justify getting the CR carbs. Most wish they had done so before spending time and money on the CV's. He was exactly right in my case. I did spend time and money on the CV and wish I had just upgraded to the CR carbs first.

Just like you I really wanted to get rid of the stock air box and love the look of pod filters on these bikes. For that alone, the cost is well worth it. Here are other benefits:

No more hard starting
Start to ride in less than 1 minute after starting up
No choke to mess with adjusting while the bike is warmed up
Performance is great (I am not going to say they make more power but they rev up through all gears as smooth as can be)

Do these things though as your bike will run rich even with the standard config from Dynoman"

[innovativems]

All of that comes down to using pods on cv carbs.  They don’t like it and can be difficult to setup.  And yes if you have poorly setup cv carbs or any carbs it will be hard to start and have poor throttle response. 

31’s will work but reduce your low end power as that’s a lot of carb for a stock 900f motor.  You will gain some top end at the sacrifice of low end power.  Which is fine if you aren’t doing mostly in town riding. 


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[900WOT]

All of that comes down to using pods on cv carbs.  They don’t like it and can be difficult to setup.  And yes if you have poorly setup cv carbs or any carbs it will be hard to start and have poor throttle response. 

31’s will work but reduce your low end power as that’s a lot of carb for a stock 900f motor.  You will gain some top end at the sacrifice of low end power.  Which is fine if you aren’t doing mostly in town riding. 


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I do city driving a fair bit. What type of low end loss are we talking about? Symptoms?

The dudes at dynoman also told me to change the baffle to allow more air etc.

Ive also upgraded to CBR600F3 coils and NGK Iridium plugs (which I am told I will never have to change).

And thanks for your thoughts. Much appreciated.

[754]

Unless you are considered a slow rider, it should not be a problem . It may suffer if you roll on hard in 3rd at under 3000 rpm.. that sort of loss of bottom end.
 We got a member on here, race bike with RS 34mm carbs on a 750 , and it works for him, but would suck in traffic in town.
 Intended use, is a big factor..

[900WOT]

Unless you are considered a slow rider, it should not be a problem . It may suffer if you roll on hard in 3rd at under 3000 rpm.. that sort of loss of bottom end.
 We got a member on here, race bike with RS 34mm carbs on a 750 , and it works for him, but would suck in traffic in town.
 Intended use, is a big factor..

Its not going to be a racing bike. It wont be a DAILY commuter, as I have a few bikes, but I may use it to commute into the office a few times a week, weather permitting.

[BomberMann650]

I got mikuni CV's to work with pods.  Just sayin.

[900WOT]

I got mikuni CV's to work with pods.  Just sayin.

My switch to CR's wasnt necessarily about getting the pod look. I wanted to get rid of the airbox and I had heard what a nightmare CV carbs are vs CR carbs.

[DaveBarbier]

The testimonial quote you posted seems only like a description of properly tuned carbs. The CR’s won’t make your bike run cooler, unless you’re very lean with the CV carbs. A proper tune would cool that down just because it’ll give you a better mixture.

CR’s are race carbs and are designed to run at like 3/4-WOT. The larger carbs you go with the more that will be true. I’m using CR26’s for my 674cc build, as recommended by MRieck, and they’re great. Dynoman recommends 29’s for the 650 but I’d think that’s a hair big unless it’s a track bike mainly.

Another option is finding carbs off a different bike with an accelerator pump. That would give you better throttle response off the line. But I know it’s nice with the CR’s because the racking is customizable...just giving you an alternative.

CR’s aren’t easier to tune, per say. They have easier swappable main jets, needles and air jets so that will make the dyno operator happy but the design of the carbs doesn’t make it more forgiving as far as getting the right air/fuel ratio goes. If anything, because there’s so much you can change it could make it more frustrating. Also, I totally recommend doing a little bit of butt dyno just to get it going and then getting it tuned on a dyno.

What I’m essentially trying to say, the tune process is the most important. You can get CR’s with a half ass tune job or some conventional slide carbs with a great tune and of course the slide carbs will run better.

[Scott S]

 Why do you want to get rid of the airbox?

[900WOT]

The testimonial quote you posted seems only like a description of properly tuned carbs. The CR’s won’t make your bike run cooler, unless you’re very lean with the CV carbs. A proper tune would cool that down just because it’ll give you a better mixture.

CR’s are race carbs and are designed to run at like 3/4-WOT. The larger carbs you go with the more that will be true. I’m using CR26’s for my 674cc build, as recommended by MRieck, and they’re great. Dynoman recommends 29’s for the 650 but I’d think that’s a hair big unless it’s a track bike mainly.

Another option is finding carbs off a different bike with an accelerator pump. That would give you better throttle response off the line. But I know it’s nice with the CR’s because the racking is customizable...just giving you an alternative.

CR’s aren’t easier to tune, per say. They have easier swappable main jets, needles and air jets so that will make the dyno operator happy but the design of the carbs doesn’t make it more forgiving as far as getting the right air/fuel ratio goes. If anything, because there’s so much you can change it could make it more frustrating. Also, I totally recommend doing a little bit of butt dyno just to get it going and then getting it tuned on a dyno.

What I’m essentially trying to say, the tune process is the most important. You can get CR’s with a half ass tune job or some conventional slide carbs with a great tune and of course the slide carbs will run better.

Thanks for your response. Ive already bought the CR carbs. They are being delivered today.

[BomberMann650]

Everything DaveBarbier said is spot on.

CV carbs aren't the bane most would have people believe.  They are a go-to kit piece for a whole lot of stock bikes in virtually any displacement and configuration.  The "bad rap" is undeserved.

You'll certainly notice a difference going from CV to CR parts.  But don't let the hype or the butt dyno convince you the CV's were an inferior part.  It's all apples and oranges.