Topic: CR carbs v. stock carbs on a CB750...

[camhello]

What are the advantages/disadvantages to running CR carbs (29mm) v. stock carbs on a stock engine?  Which are harder to tune?

Thoughts?

Just wondering, b/c I've got a set of CR carbs, and I may end up keeping them if it's worth it.  I'm not a speed demon or anything like that.  These would be for an old AEE trike w/ a stock CB750 motor.

Thanx in advance for any comments!!

 

[754]

Geez, can you post a pic on Inspiration thread..

 Trying to remember it, did it have a roof on it??


 Something of that era deserves Webers,, IMO..

[camhello]

If I only I had Webers, hey?

You can check out pics on hondachopper.com if you go into my profile and click on my yuku images album.

[Retro Rocket]

I would keep the CR's in the cupboard for a hotter build, after all they are racing carbs.....

Mick

[scunny]

they're trash mate, send them to me and save yourself some heartache.
I'm sounding more like TIA every day.......perish the thought

[lordmoonpie]

You won't run them on a street bike without a whole world of pain. They are peak poer items at top end of rev range and dead low down in the range. They are a nightmare to set up as well....if you're building a hot motor or a racer then go for it, otherwise sell them on for a fair price - i.e. not to Scunny

[camhello]

These are one of those small things that take up little space so I can store for a while.  I figure if I sell them, great, and if not, I'll just end up holding on to them and maybe one day using them.

Chances are I'll end up keeping them...

[gnarlycharlie4u]

it needs to be said:

are these the new CR specials or the old CR's?

I love my CR specials so far, they're excellent for top rpms but also do fine just cruising around town. Only down side is you can't whip the throttle open too hard.

[camhello]

These are the newer CR specials.  I don't remember the website offhand, but they look to be the newer/3rd generation of these carbs?  The website showed pictures.  Apparently the first generation were sandcast?

And nuts - you mean these aren't really good for low end gunning?  That means that they really wouldn't work on my trike if that's the case - I need more at the low end than the high end.

[754]

 You need accellerator pumps to get that weight moving..

[simon#42]

it needs to be said:

are these the new CR specials or the old CR's?

I love my CR specials so far, they're excellent for top rpms but also do fine just cruising around town. Only down side is you can't whip the throttle open too hard.

yes i agree ,  i find the cr's fine in the mid range [ even when i had a standard engine ]  they are very easy to work on , all the bits are readily available and when set up right give much better petrol consumption . the only downside is the tickover is slightly erratic compared to standard. dont get me wrong it still ticks over ok its just not as even as the standard setup . 

[camhello]

So CR carbs give better mpg than stock carbs?  That'd be nice.

Are the jets easy to find?  I've got full sets of jets for the stock carbs, but these jets are different.  And I'd prefer not to have to buy a bunch of sets of jets to find the 'right' setup...  BTW - these have 120's in 'em - is that stock for CR carbs?

Also, what is tickover?  I haven't heard that term before?

Thanx!

[Terry in Australia]

I had new 29mm CR specials on my 836cc engine and hated them. It actually ran better once I took them off and installed a set of stockers. I mucked around with jetting, needle position, yada yada yada, but couldn't get it to idle properly, (idle screw positions sucks too) and as has been said before, you snap on the throttle and ..... nothing.

I'll get Ken Piper to mod a set of 32mm CV's like the one's on my other 836 in my K2, so far they're the best carbs I've had on a CB750 engine, bar none. Light weight, light throttle, and light on fuel. I've got some modified Mikuni 33mm smoothbores for my RC 1060cc engine build, I had these carbs on a GS1000 Suzuki drag bike years ago, and they were very good too. Cheers, Terry.

[754]

Tickover = idle..
 ..used by the bunch that drink warm beer, and are prepared to camp on the side if the motorway, when they experience, yet another electrical meltdown...

 ..keep the smoke inside the wires, chaps...

[simon#42]

So CR carbs give better mpg than stock carbs?  That'd be nice.

Are the jets easy to find?  I've got full sets of jets for the stock carbs, but these jets are different.  And I'd prefer not to have to buy a bunch of sets of jets to find the 'right' setup...  BTW - these have 120's in 'em - is that stock for CR carbs?

Also, what is tickover?  I haven't heard that term before?

Thanx!

unfortunately if you are going to do it yourself you are going to have to buy alot of jets .i just bought a full set from 98 to 122  two needles each side of standard and some smaller pilot jets . took me an hour on the dyno to get it sorted . as terry said the idle adjustment screw is in the middle of the carbs and is a pig to get to , you can buy a remote adjuster that makes things much easier . if you really want to use them it might be worth finding a good dyno shop local to you , usually they will swap and change the jets and then just charge you for the ones you need . on a stock engine fitting the carbs gave an extra 4 hp in the mid range and 7 hp the top . when i fitted the 836 kit it made no difference to the jetting at all , when i fitted the megacycle cam it cocked it up completely , had to come down one needle size 7 main jet sizes and 2 pilot jet sizes .  i did find that changing the needle clip position didnt work , if you want to go richer or weaker in the mid range change the needle itself  . hope this helps ,dont be afraid to try its not rocket science but if you havnt done it before it can be a bit confusing .

[Howell]

I have 31 mm on my 822cc F2 streetbike and they work very well even at low rpm's and speed.
I use 115  mainjets and lowered the needle with the clip in the third position.
You can buy jets etc here:http://www.pjmotorsports.com/

[camhello]

Thanx for the comments! 

I'm thinking, though, that I may be really done w/ bikes for a long time to come...I'm considering spacing my trike, too, since I don't have a garage and it's stored at a friend's place (as is my bike...) - and that's a PITA b/c I can't even really work on it.

Damn...to think I may be more interested in diesel landcruisers now...I would have never guessed...sheesh...now to find one...in the US...yeah, right...

[Ace]

Start of hijack - those of you who run CRs, VM29s and other non stock carbs, do you used pods or stacks or an airbox of some type? 

End of hijack 

[Terry in Australia]

Start of hijack - those of you who run CRs, VM29s and other non stock carbs, do you used pods or stacks or an airbox of some type? 

End of hijack 

Hey Adam, got to Tin Tops thread (link below) regarding the new "Anti Pod" filter setup he's manufacturing, it's the best of both worlds and he's sent kit #1 to me for testing, so once my K1 is back together (hopefully tomorrow) I'll be able to start the rigourous testing that Brian (Tin Top) has planned. I can tell you, that they look heaps better than the stock air box, and are better engineered than most pods. Cheers, Terry.

http://forums.sohc4.net/index.php?topic=79491.new;topicseen#new

[MCRider]

Start of hijack - those of you who run CRs, VM29s and other non stock carbs, do you used pods or stacks or an airbox of some type? 

End of hijack 

I ran K&N Pods with VM29s and 888cc. Required minor rejetting: main jet and idle circuit tweaking, less than a few hours work.  I thought they ran wonderfully, though I never put it on a dyno. Out on the interstate in steady cruise mode with a side wind, I could feel the slightest of occasional surge. Great gas mileage, easy start with little choke, fast warmup, and accepted full throttle easily.

I think pods on a 750 esp with increased bore, work better than smaller engines which are more sensitive it seems.

[gnarlycharlie4u]

Start of hijack - those of you who run CRs, VM29s and other non stock carbs, do you used pods or stacks or an airbox of some type? 

End of hijack 

uni foam filters.
however when it comes around i'm thinking of getting Tinpop's Anti-Pod

[Retro Rocket]

These are the newer CR specials.  I don't remember the website offhand, but they look to be the newer/3rd generation of these carbs?  The website showed pictures.  Apparently the first generation were sandcast?

And nuts - you mean these aren't really good for low end gunning?  That means that they really wouldn't work on my trike if that's the case - I need more at the low end than the high end.

Cycle X has some mikuni's with accelerator pumps ffor the price {or cheaper} than the CR's..\

http://www.cyclexchange.net/Carb%20System%20Comp%20Page.htm

Scroll down and look at the 34mm Mikuni's....

Mick

[Terry in Australia]

I've got a set of those carbs in a box Mick, I got them off a guy who drag raced a Suzuki GSXR750. They are very light, compared to CR's and the older 29 or 33 mm Mikuni smoothbores. I decided to use my 33mm mikuni smoothies on my 1060cc engine though, just becuse they are more "period" than flatslide carbs. Cheers, Terry.

[cbrfunk]

back to the CRs...Would you not have a quicker reaction with pods and a fully ported head?
I'm putting together a hot street CR750 overbored to 836, ported heads, wicked cam etc... and just bought a set of 29 CR carbs because the guy sold me on the full range of power that I could expect with my motor.

Was I misinformed??

thanks for any advice
Chris

[754]

 Is full range of power & wicked cam, even Allowed in the same sentence..