Topic: cbr900rr to cb750 carb swap?

[NoXi]

has any body ever attempted to swap the carbs from a gsrx or cbr 600/900? i really don't like the idea of putting the slide carbs back on the bike, because im going to have to mess with jets anyways id like to do it with some nice CVs' for the added numbers.

[HavocTurbo]

You'll have to find a way to respace the carbs to fit the CB rubbers.

After that it's run cables and tune.

But I make it seem easier than it actually is.

[bradweingartner]

Sounds like a step backwards to me. These old carbs are simple and work well. All that CV nonsense is for emissions and you know, drivability.

Who needs it!

[faux fiddy]

Anything can be done, I've seen it happening.

Consider megasquirt of microsquirt if you want something different and custom, and that is What I dream on, is a  single throttle body and a single injector out of a 1.6-1.8 that is in every car junkyard.

A friend of mine does his own cnc machine work. He upgraded carbs on a RZ-500, and  tuning them became a screwfest- so he made curved velocity stacks so he could fit the original airbox with the aftermarket by slip on. Lots of retro-engineering, but he has a point.  If you have access to CNC, make it to where you can open it up and tune easy.


eccentric rz-500 stack


eccentric stacks fitted to airbox

[IMG]
cutting head on cnc.

The precice measurements and engineering of the adapters is the big part of making the first set.   After that everyone could have them cheaper by the dozen if tht is what they desire.

[BLUE71TURBO]

Sounds like a step backwards to me. These old carbs are simple and work well. All that CV nonsense is for emissions and you know, drivability.

Who needs it!

  CV carbs are know way a backwards step. They are very adaptable and tuneable and way more responsive for city driving. Also way more available and cheep.   

[Terry in Australia]

Sounds like a step backwards to me. These old carbs are simple and work well. All that CV nonsense is for emissions and you know, drivability.

Who needs it!

  CV carbs are know way a backwards step. They are very adaptable and tuneable and way more responsive for city driving. Also way more available and cheep.   

Agreed. I took the 33mm round slide carbs off my 1981 Suzuki GS1000S and installed 34mm CV's off a GS1000E, and got 25% better fuel economy right away (50 MPG now) with no loss of performance, and the throttle with only one cable and a lighter return spring is just so much nicer on a long ride. I'll put the slide carbs back on if I ever sell it because they're "original", but while I'm riding that bike, they can stay in a box. Cheers, Terry.

[bert96]

 I  bought carbs from a nighthawk cb700 85 and they have the right space,they fit right in.


Here's a pic


Bert

[MRieck]

The 900RR carbs are for a downdraft set up....you will need a side draft set of carbs

[NoXi]

Downdraft? does that just mean they are angled different on the cbr? because that was one of the things i was wondering about.  i want cv carbs because they arent jumpy like slide and they have great throttle response (because they combine slide and butterfly carbs)  and i have rebuilt tons of them and had great success with tuning them.

As for MS, i had considered it, but have been stalking a lot of builds around here and really have no interest in messing with the charging system, or the any electrics (the reason i got into manual machining and not cnc)

[razor02097]

Downdraft? does that just mean they are angled different on the cbr? because that was one of the things i was wondering about.  i want cv carbs because they arent jumpy like slide and they have great throttle response (because they combine slide and butterfly carbs)  and i have rebuilt tons of them and had great success with tuning them.

As for MS, i had considered it, but have been stalking a lot of builds around here and really have no interest in messing with the charging system, or the any electrics (the reason i got into manual machining and not cnc)

Yes most of the newer sport bike carbs ride on top of the engine in a vertical position (air flows from top downward into the engine) putting it horizontal will mess with the float level and may not operate properly.

[Aaron Richard]

Since we are talking about carb swaps, could a set of 650 or 750 cv carbs bolt on to a 550?
I like the cv carbs because they seem to be more responsive. No matter what I do with my older carbs, they always have a bit of delay. I know that's a characteristic but, not a fan of it.

[dtmmil]

Bert96, did those 700sc carbs fit the sohc 750 motor spacings, will they bolt right on? I am interested in doing that swap if they do, thanks, and I know this is an old post, but I found it in a search. thanks

[bert96]

 Yes,the spacing is the same,i bought these carbs because another member here did it.


Here,

http://forums.sohc4.net/index.php?topic=43294.msg449637#msg449637

Bert

[dtmmil]

Cool thanks, can I ask about your setup, are you running the stacks from the pic? If I do the swap I would prefer to stick with stacks. I tried a set of CV carbs off of a 550sc and they seemed to be much better for throttle response, not sure about upper end though. Do you have any pics of them mounted on the bike? thanks

[bert96]

 They are not on the bike unfortunately,i have added some ''filters''


I bought 4 spice infuser  it's cheap and it do the job!!


Can't do more to help you sorry


Bert

[dtmmil]

You have helped alot!! thanks And that is a cool looking setup, if you do use them they will dress up whatever they go on! thanks!

[m in sc]

has anyone done this to a relatively stock bike?
 rz500.. nummy.