CR's vs. Keyholes

[shinyribs]

You can't help but notice how similar the two are.

Both made by Keihin, mechanical round slides, accelerator pumps...heck, the even look alike.

So what separates them? Cfm capabilities?

Seems 29+31 are the common sizes for our bikes, I wonder what size the 77-78 keyholes are?

[shinyribs]

Keyholes use the same intake boots as roundtops,right?

I know the matics are different, but are all the other SOHC carb boots the same?

[TOOLS1]

No, they use different boots. The CRs are easier  to tune, and work better.
TOOLS

[Re-run]

To be fair, the CRs work better than either of the stock carbs that came on the sohc. But you pay for it. Average of $600 for a rack.

[shinyribs]

Well, I was looking for a viable, more affordable option to plopping down big money for CR's. Thanks for bursting my bubble. Haha.

I do wish I had a rack of keyholes here to see what would be needed to fit them.

[Re-run]

Were you thinking of putting them on your dohc? Was that the idea?

Well, I THINK the size is 29mm for the manifold boots. I don;t remember for sure.
Now, I think the spacing is different between the engines, so I would get boots that fit and then fit the carbs to the motor. From there, make a template using something easy to mark and work with. Then transfer the template to some sheet metal and use that template to make the braces for the carb rack.

Essentially you just need braces to make sure the carbs maintain their position and are able to be supported.

If this IS your idea, you would probably need to change the petcock to a basic gravity feed instead of the vacuum style.

[shinyribs]

Bingo, Boss. You got it.

Petcock is already swapped out. Standard Res-off-on. No sos.

Making new rails to get the spacing sorted would probably be pretty simple. Not sure what would be needed as far as lengthening or shortening the actuator shafts. I don't have any too look at, but iirc, they are like CV's with the fuel supply tubes, accel pump fuel tubes, etc. All that would have to be custom made if any of the spacing was even slightly altered. Which would be a fun little project, but I don't want to sink weeks of fab work in to a rack of carbs that will perform poorly. I also don't want to sink alot of $$ into CR's,either.

A complete rack of CR 29's (or 31's) with the correct adapters (for the DOHC boots) run $730-ish. The do come ''pre-jetted" and, if you buy from Dynoman, the come with one size up and down main jets for tuning. Cool package,just pricey.

[Re-run]

Fuel rails would be simple. Just get ridged plastic fuel tubing that is the right length and some orings. Might have to cut grooves for the orings. As long as they seal, your fuel rails are good.

Actuator shafts would be the hard part. but who knows, the spacing might not be too far off that simple mods might work. Without having both racks for comparison, it's hard to say.

I agree though, carbs are just too damn expensive. Especially for how long they have been around. The r&d costs have easily been made back 10-fold.

[seestheday]

I'm pretty sure I read about a guy doing that on the other DOHC forum.  I recall that performance was "meh" but I could be wrong.  I remember reading that it took him a while to tune, but he ended up getting to run almost as well as stock carbs, with a minor flat spot.

That said, the guy trying it didn't seem to have as much experience as you.

They also say that early GSXR carbs work well.  Thread here: http://www.cb1100f.net/modules.php?name=Forums&file=viewtopic&t=41909 (bullshit login required to read)

Here are apparently all of the options:
BST 34,36,38 SS carbs-(GSXR/KATANA)
CR specials
FCR
And one fella who put SOHC carbs on his bike.

[seestheday]

Found the thread on the guy that did it: http://cb750c.com/modules.php?name=Forums&file=viewtopic&t=21444&postdays=0&postorder=asc&highlight=sohc+carbs&start=80

Here is what his setup was:

#170 main jets
#35 pilot jets
adjustable needles on clip slot #4
ALSO a slight modification to the accel pump shaft. I filed some off the top of the shaft SHORTENING IT slightly, not much tho, mabe 1/32 inch??
Plug chops at different loads and different speeds look light tan.
You "could" delete the accel pump entirely, however the bike don't wana start when she is cold. The accel pump circuit helps with this..

[shinyribs]

Prof. Sees, thank you for that. I'll register this evening and take a look.

[shinyribs]

Rabbit trail....

What about Nighthawk carbs on an early DOHC? Anybody have any info on this?

[shinyribs]

FYI: Nighthawk carbs wiln go on a SOHC with no changes to the rack. The spacing is the same.

Pull cable hooks up, push cable needs the jacket trimmed.

Not my research. Word of mouth. Supposedly, the are a nice match to an 836 in stock form. Accel pump feature improves cold start and throttle response.

Also, rubber diaphragm actuated slides vs typical early DOHC aluminum/sealing ring setup= pod friendly
 
Win, win, win and win.

[TOOLS1]

But they are still crappy CV carbs. I would still go with CRs.
TOOLS

[shinyribs]

Lol. Well, there are CV carbs, and there are crappy CV carbs. I would be tempted to try these due to cost alone.

CR's are silly expensive. And stock sohc carbs are getting pricey due to the whole sandcast and cafe thing. Saw I clean looking set of Nighthawk carbs on eBay for $40. Makes you have to think.