Author Topic: tuning CR's (Read 6202 times)

turboguzzi · « **on:** July 07, 2009, 04:12:56 PM »

OK, getting nearer to mounting my set and when talking with another tuner / racer about 29 CR's jetting he came up with an interesting idea.

He said that he cant understand why the CR's come stock with solid (undrilled) emulsion tubes. No other cabs have undrilled emuslions tubes.

so his idea was that maybe Keihin sells them that way so that tuners can drill them by themselves......

Hei carb gurus, what da'ya think, ?

TG

a CR's emulsion tube pic....

nokrome · « **Reply #1 on:** July 07, 2009, 04:22:27 PM »

i am very interested in this thread because i have a set of cr 29s that i will be using soon

ive heard that they are very tricky to tune

scondon · « **Reply #2 on:** July 07, 2009, 05:28:35 PM »

If it ain't broke, don't fix it. I can't say as to how they work, just that they work really well as is. Two things I think of as necessities for these carbs are a remote idle adjuster, so you can adjust idle without pulling the tank, and brass nipples drilled into the carb boots so you can vacuum synch the carbs.

I got both these tips from Mrieck and am glad I did the work before installing the carbs. They can be a pain to get on and off due to tricky cable routing.

turboguzzi · « **Reply #3 on:** July 08, 2009, 12:25:32 PM »

scondon

Thanks for the tips, on my 500 the 29's adjuster is quite reachable while I will be putting vacuum nipples on the manifolds for sure.

If it ain't broke is a fine logic, but inquiring minds want to know.....

Look at any carburetor diagram and you'll see drilled emulsion tubes,

The CR's got only the little hole in the small part that sits on top of the tube but when you think about it, there;s not much length where the fuel can get mixed with the air to nebulize BEFORE it exits the tube.

So the idea that the CR's emulsion tube needs extra holes along the shaft is not a stupid one.

More opinions/experience?

TG

turboguzzi · « **Reply #4 on:** July 08, 2009, 03:06:34 PM »

getting interesting.....

just found a diagram of the CR's in the german keihin site and it shows emulsion tubes with holes......

so the question is not THAT silly.

Mike or any other of the big guns?

TG

Jerry Rxman Griffin aka MuthaF'er · « **Reply #5 on:** July 08, 2009, 05:42:41 PM »

Sudco.com

The US importer and distributor.

turboguzzi · « **Reply #6 on:** July 09, 2009, 11:44:15 AM »

Jerry,

The only "emulsion tube" in sudco's catalog is the one in my first post, no - holes

been reading more on the subject, including, John Robinson, Dellorto manuals, Hondaman's take on emulsion tubes and the ommission of holes in the CR's makes even less sense.

Could it (making your own holes) be the great secret that makes them easier to tune?

Hondaman? Mrieck?

TG

MRieck · « **Reply #7 on:** July 09, 2009, 12:38:04 PM »

This pic shows the needles and needle jets for 3 of the most modern and popular flatslide/smoothbore carbs. The last needle/needle jet is from a typical CV carb. The first thing that stands out is the overall length of the needle jet and needle....they are huge compared to the CV combo. I would think the length and the fact the signal is stronger in the aftermarket carbs is the reason....maybe it is very difficult to control precise fuel metering with strong intake signals and long needle jets with emulsion tube holes? Personally I haven't found the CR's to be to bad to tune. The FCR have idle mixture fuel and air screws just as an example

paulages · « **Reply #8 on:** July 09, 2009, 12:49:11 PM »

Are they even "emulsion" tubes if there are no holes for air to enter and mix wih the fuel? Where do the air jets end? It seems like this is an important clue.. obviously they work as is, so the air is mixing in somewhere. It does seem strange though. I wonder if you could get a keihin rep on the phone... Anyone in japan?

turboguzzi · « **Reply #9 on:** July 09, 2009, 01:05:34 PM »

Hi Mrieck

nice pic! Was indeed wondering how do the Mikuni smoothbores tubes look like and now I see that they are also blank....

needle length is less of an issue, CV's , like non smoothbores have the clip near the bottom of the slide, so that automatically makes the needles shorter.

what is true in your observation is that the tubes themselves are rather long.

got a set of VM's appart, gonna shoot a pic of their tube next to a CR's.

Paul, indeed, they are called "nozzle holders" (39 in the pic). The emulsion / air mixing happens in the “Noozle” which is a small replaceable part that sits on top of the “noozle holder” (no 43 in the diagram)

The noozle has a big hole on the side that is fed by the main airjet.

So there is an emulsion set-up in the CR’s but it is very high up.

From much of what I read, the holes in emulsion tube serve as a fuel reservoir for fast throttle openings by connecting the tube to the extra volume around it.

The little holes in part 39 in the diagram are still a mistery...... japanese draughstmen dont make mistakes....

Cheers

TG

MRieck · « **Reply #10 on:** July 09, 2009, 01:26:49 PM »

There are several nozzle types for CR's if I remember correctly.....one delivers more fuel for sustained high RPM use (I think that was the description). Keep in mind the age of that drawing.....it is probably very old and an "approximation".

ev0lution7 · « **Reply #11 on:** July 09, 2009, 02:41:54 PM »

tunning them is not that hard just use a Wideband O2 its really easy just adjust when it gets lean or rich... course it helps to understand how the CR's work i think there is an extra "air" port in the intake of these carbs that helps "imulsify" the fuel and air together they are truely a nice carb and pretty advanced for a non feedback carb!

turboguzzi · « **Reply #12 on:** July 09, 2009, 03:08:47 PM »

OK! Paul gets the "Keihin 2009 Star" award for the right answer.

Went down to the garage and:

Tubes of a 26 VM and a 29 CR are not that different in length

BUT

the area around the tube of the CR just doesnt have any air intake, it's totally closed, so no emulsion can happen, even if there were holes in the tubes.

the only air entry is indeed in the very top, stright into the noozle jet, so Paul, you were pretty close..

Evo, they are sure very easy to work on, everything can be changed real quick,

the only tyhing that i havent grapsed yet is the mutual effect of the main jet and extrnal air jet, seemingly you can alter top end A/F ratio with both of them. currently I am with a 120 fuel main and 250 air main. It's a 500 mind you,

We'll see, am about two weeks away from closing the engine and heading for the dyno, need to check how the new piston and cam tensioner work too.

TG

paulages · « **Reply #13 on:** July 10, 2009, 12:35:35 AM »

woohoo!

in regards to the air jet vs. main jet: it seems like you could use each to slightly different benefit... the fuel isn't going to change much except in temperature, but maybe you could change the air jet if the barometric pressure suddenly changed? like at those rainy races you seem to do so well in?

i don't know... i don't fully understand their relationship maybe. the air jet controls the amount of air that mixes with the fuel before the throat, thereby controlling its ability to atomize, right? does a larger air jet with the same main jet lean the mixture out significantly?

jhasewhite · « **Reply #14 on:** July 13, 2009, 07:42:19 PM »

I will be following this one closely... I have tuned my CR's to an acceptable 8/10 but perfection is needed.

turboguzzi · « **Reply #15 on:** July 13, 2009, 11:11:05 PM »

J,

it will take awhile as I am closing the engine only now and have still to build the deicated manifolds.

Will surely post about the continuation of the saga
TG

bwaller · « **Reply #16 on:** July 14, 2009, 04:36:01 AM »

I found an old Yoshimura catalogue that offered a set of manifolds for an early set of 31mm CR's. I'm sure you have something in mind, but thought you might like to see the pic. Not as straight as what you used before!

turboguzzi · « **Reply #17 on:** July 14, 2009, 02:59:15 PM »

nice one brent!

though not quite sure that i understand what i see.... something about the position of the manifold ears doesn't make sense.
and why the eared rubber flanges?

to get the straighter shot, the distance between the two center crabs should be bigger too.

I guess pops tried to keep the carbs tidy and narrow, within the frame rear down tubes, mine stick out big time and are quite unprotected from rain and such.

In any case, the parts for the new manifold are almost ready but now i realize that I need another throttle!

Want to keep the old set up intact just in case the CR's dont work well, so i want to get a spare throttle assy. does anybody got a recommended throttle assembly that works well with CR's? Would like to get really quick opening, 90 degrees to WOT or less. used a cagiva/ducati thotlle with the VM26's, not sure that this will give the quick opening I want with the CR's.

Thanks

TG

MRieck · « **Reply #18 on:** July 14, 2009, 03:39:19 PM »

As a side note....are you measuring the float at full drop (at it's lowest point)? Float height is 14 to 16mm but the float height when extended should be between 26 and 28mm. I mention this because I was working on a set of CR31's today and those extended heights were all over the place.

bwaller · « **Reply #19 on:** July 14, 2009, 03:54:18 PM »

TG, never saw a set of these, but I expect if those manifolds were turned to mount on the original studs it would aid in a few degrees downdraft, not unlike your own. The inlet tract would be a lot longer than the ones I set up too.

Retro Rocket · « **Reply #20 on:** July 14, 2009, 03:59:50 PM »

I bought an old Honda drag bike with sandcast CR31's on it and it also had a quick action throttle on it, half a turn from stop to full throttle.

Mick

Jerry Rxman Griffin aka MuthaF'er · « **Reply #21 on:** July 14, 2009, 04:41:57 PM »

Guys, am I looking at the wrong thing? The cast manifolds I see say CB900 below the picture?

bwaller · « **Reply #22 on:** July 14, 2009, 05:43:26 PM »

I'm not going to ask about your eyesight Jerry, no no no I'm not!!

Mind you I need to increase the size to see it too, but it does say 500 or 550.

turboguzzi · « **Reply #23 on:** July 14, 2009, 10:48:10 PM »

Quote from: retro rocket on July 14, 2009, 03:59:50 PM

I bought an old Honda drag bike with sandcast CR31's on it and it also had a quick action throttle on it, half a turn from stop to full throttle.

Mick

half turn would be regarded as slow opening.... race some and you'll see why.

Quote from: MRieck on July 14, 2009, 03:39:19 PM

As a side note....are you measuring the float at full drop (at it's lowest point)? Float height is 14 to 16mm but the float height when extended should be between 26 and 28mm. I mention this because I was working on a set of CR31's today and those extended heights were all over the place.

Interesting.... why is extended height important? the floats bottom on bowls anyway, no? What is stranger still is that a few tuning guides talk about adjusting float height to control low-mid range.

Retro Rocket · « **Reply #24 on:** July 14, 2009, 11:35:04 PM »

Quote

half turn would be regarded as slow opening.... race some and you'll see why.

Actually i checked and it is closer to quarter turn.
What type of racing are you referring too..? If you mean circuit racing, i have ridden a few race bikes {FZR 1000, GSXR 750 and so on, on the track} and none had the shorter turn throttle.
Drag racing is a different thing altogether..

Mick

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Author Topic: tuning CR's (Read 6202 times)

ev0lution7