Keihin cr33 carbs

[Bigleo]

I finally got my 1980 xs1100 running yesterday after a 1197cc installation. I had never gotten the stock carbs to run all that great. Tried for seven years though. So I bit the bullet and got some Keihin CR33 carbs from Dynoman.net. I must admit I was a little concerned about comments about usabilty on the street etc. However they work great!!, pull hard from 2000 rpm. Haven't got into it too hard yet, as I'm still breaking in the motor. But have grabbed a bunch of throttle at 4000 rpm a few times, and no bogging issues what so ever. This is the best mod I've done!!! Yes!!! The weird throttle responses and jerking at low speeds that the old carbs had is totally gone. The throttle response is so excellent, you would never guess they are not CV type carbs. I also put in 1978 cams and individual K&N pods, with a 4 into 1 Jardine. Many thanks to AUDIO_MEKANIK for the pod air filter and gas line interference fix. I used a 2" of fuel fill hose hose clamped to the carb mouth, then 2" of stainless tubing was inserted into the fill hose and hose clamped, but left 3/8" of the stainless tube sticking out to mount the pod filters. In effect it makes a 3" velocity stack, and moves the pods back to fill in the unsightly gap left by the missing air box, and no petcock to carb issues with the gas line.

[geniusloerts]

I would like to see a picture of the tube extenders....

[TopCatGr58]

Hey Genius,

Check out This Tech Tip in the MODS, Carbs Section . Sorry about the thumbnails "ONLY" in my reply, but Photodump changed their photo linking format, and I haven't updated them, but you can get the idea from the text, sounds very similar to what BigLeo did.
T.C.

[Bigleo]

cr33 carbs

Hi Genius,
Topcat is right, that link is fairly similar to what I did, only he used the stock velocity stacks. I just wasn't sure how he did the filter hose clamp. Was it only clamping to the rubber stack or did he have some kind of sleeve inside the stack for extra strength? I did what audio_mekanic did, except I used stainless tubing and he used copper pipe. Also he did it using stock carbs, so he used a different diameter fuel filler hose. I will try to post some pictures in the next few days, I have not posted pics before, so may take a few tries to get it right.
Leo

[Bigleo]

Keihin cr33 carbs

So its been a few days now with the new Keihin carbs. Starting the engine is instantaneous, cold or hot, never have to use the choke. With the old CV carbs, starting always involved some cranking, sometimes lots, sometimes not so much, but it was never consistent. These carbs have transformed the bike for me. The pod sound when you get on the throttle is great too.

[Mathh]

iginition hose

I'm wondering what you did with the vacuum hose going to the ignition?

[mro]

I'm wondering what you did with the vacuum hose going to the ignition?

On my hot rod XS with the flatslide carbs I have a screw in it...

mro

[Bigleo]

I currently have the vacuum advance line disconnected, as there is no ported vacuum provision on these carbs. My plan for a vacuum advance, will be to hook it up to the intake boot vacuum outlets. Hooking it up to only one outlet will be unsatisfatory, as it will pulsate too much. What I am going to do is to remove the insides of the fuel system octopus that I am no longer using, then hook the 4 former gas line fittings on the octopus to all 4 vacuum outlets. Then I will use the vacuum fitting on the octopus as my vacuum source. That should provide a fairly steady vacuum through 360 degrees of crank rotation. The only problem I see is that the vacuum signal may be to strong. I have a adjustable restrictor valve from an old vacuum guage that I will install into the vacuum line to address that issue. If there is still pulsing in the vacuum line after all this, I will put a paper cartridge fuel filter into the line to provide further damping.
Leo

[Bigleo]

Well I have now driven the bike long enough to get a reliable gas mileage rating withe the new Keihin CRS carbs. With the stock carbs and stock engine I got between 32 and 38 MPG highway driving. 38 if I kept the speed down to 55mph and down to 32MPG if the speed was 80mpg. With the the new 1197 kit, (tight motor), the 1978 cams, bigger carbs etc, I assumed that the mileage would be worse. I was pleasantly suprised to get 42 MPG. This is even with the vacuum advance unconnected, which I figure is costing me about 2 MPG. Once I hook up the vacuum advance and the motor loosens up a bit, I am hoping for 45MPG at highway speeds.
But best of all, the irritating driveline snatch which is caused by the stock carbs is gone!!!! Yes!!! And the massive unwanted compression braking you get with even small throttle closings on the stock carbs, also gone.

[mro]

Keihin CRS

If the opportunity arises that you can put your XS on a dyno...
would be very interested in the results


mro

[thewiz]

Vac advance ...

.... " unsatisfatory, as it will pulsate too much. ".....

I'm running VM33 smooth bores on my G and even though it does have a ported vacuum port, it still pulsed too much causing some hammering. Someone here suggested putting an old pilot jet in the line, which I did, and that did the trick !!

[Bigleo]

Hi MRO,
I will be putting it on a dyno when I get some larger main jets. The local Harkey dealer will do three pulls for $60. So I will be able to try 3 sets of main jets. I still have to install the low restriction baffle into the Jardine 4 into 1 exhaust I am running as well. The dyno is paired with an exhaust gas analyzer, so I will be able to see how the mixure is doing. I will post the dyno results when I get them. Hoping for 100 hp at the rear wheel.
Leo

[Bigleo]

Hi Wiz,
thanks for the pilot jet tip, some sort of restriction in the line will definitely be needed.
Leo

[rogermOS]

CR33 Throttle cable routing

I have a 79 XS11. After reading your post I decided to junk the stock carbs. My bike had a pull throttle only, so I got a push/pull kit from motion pro. Everything was going great till I had to route the cables at the carbs. What looked like it would work was the opposite of all instructions I found on the web. Please tell me how you routed your cables. The throttle arm is shaped some what like a > sing with 3 holes on top and bottom. I would greatly appreciate it if you could tell me, and also any tips you may have found to make it easier. The MP kit was specific for Yamaha models, so the cables should be long enough, but being an after market, who knows.

Thanks

[TADracer]

I currently have the vacuum advance line disconnected, as there is no ported vacuum provision on these carbs. My plan for a vacuum advance, will be to hook it up to the intake boot vacuum outlets.

Good morning.

Hooking the vacuum advance dashpot to the carb boots will not give you the vacuum curve you need, even if you get rid of the pulseing. Vacuum will be high at idle when you need zero vacuum on the dashpot. You mist tap the carbs immediately behind the throttle butterfly to get ported vacuum.

Do a search on ZRX carbs and you should come across what I did when I installed my Keihins. Though you have a different kind, you may still find a place for a vacuum tap.

And like you, changing out the carbs was the best mod I ever did for my machine.