FZR carb conversion

[Walt_M.]

I haven't had any problems that I could relate to float level.

[fret not]

That is my point, and thanks Walt.

[fret not]

If the carbs are not negatively effected by standing them straight up then the original air box (as YOU point out) should not need much if any modifications.  With the carbs from the YZF600r that I am using I chose the pair that has the bell crank and left them connected together as they were in their original application.  This caused me to make up new manifolds to fit the carbs.  It is MUCH easier to use original manifolds than it is to make new ones, but I didn't have to fabricate linkages and such between the carbs.  Since I have a spare air box I will modify one to accommodate the "new" carbs. 

[injuhneer]

People are pretty brave on pricing Vmax carbs while I have found FZR600 carbs around $100-125. And, as I found out, the first and third carbs were best for my purposes. Another benefit of this conversion, since I no longer have the airbox flapper, I have hardly any oil in the airbox from the crankcase vent, which makes perfect sense when you think about it

You can buy a rack of (V4) Venture carbs for a lot less than VMax carbs. They are nearly identical. VMax folks use the Venture carb bodies as spares.
Here is a thread:

http://ridersofvision.net/rovforum/index.php?topic=15881.0


Now I am wondering if a 2 cylinder version of V-Boost would work...

[livetoride21]

Just read through this whole thread, nice work!
I just picked up an first year Vision 550 and will be building a vintage race bike out of it.
The FCR carb conversion is very attactive for me because I already have a rack in stock!
Curious, what jetting did you end up at? I saw 32.5 pilot, 127.5 main, and 52.5 starter, is that correct? Did you ever do a plug chop?

thanks!
Hope you're still here on the forum.

Kevin

[fret not]

I just left the jets that were in the FCR carbs in place as they should be within the ball park if they are stock, which I believe they are.  Hopefully this will be a good starting point for fine tuning.  Also, it may be some time before I actually run the bike to find out as there are some other areas that need attention before that can happen.

[livetoride21]

Thanks for the reply back Fret not.
I actually slipped up and had FCR on my mind, but meant to write "FZR" as in the FZR600 carburetors.
Hoping Walt can shed some light on it.

[Walt_M.]

Yes, that's where I left the jetting. I never did do a plug chop as it ran pretty good there. Just a thought if you're thinking of track time, I believe it lost some power on top due to the smaller bore. but it could be the jetting.

[livetoride21]

Thanks for the reply Walt! I'll try it out. I have them in stock, so it be worth while to test.
Will try it out with your jetting and see what it nets. As far as losing power on top, I wonder how much air these motors can really pump through 34mm bore? I mean I have-to figure if two 41mm are enough to feed my 944cc ducati, two 34mm carbs should be adequate to feed the 550 up top.
Have you ever tried YZF600 (thundercat) carbs? I believe they're slightly larger bore, but very similar.

[fret not]

Yes, that is what I have.  From a YZF600R Thunder Cat.  Made by Kehin, and they have nice long trumpets.  As I recall, Tree Dragon said he put another set of the rubber boots in the airbox to lengthen that intake and smooth the air.  He reported it made a noticeable difference.  I miss his participation here, he had some good "tales" to tell about his marvelously developed bike.

[livetoride21]

Interesting, for some reason I thought you had put fcrs ( flat slide non cv carbs)
Thanks for the reply, you said youre running the stock thundercat jetting?

[fret not]

Not running yet, still in the "project" stage.

[fret not]

Walt and Ron, how did you attach the connecting rod/tube to the butterfly shafts?  I am guessing by drilling and tapping into the ends of the shafts, and using screws or bolts.  After looking at the shaft ends there is precious little room for ANY error in centering and drilling a hole, then threading it.

[Walt_M.]

Gee Mike, that was a long time ago. Since I used the Vision carb spacing I used 3/8" aluminum rod to extend the throttle shaft. I don't remember exactly how I attached it but I'm pretty sure I didn't modify the throttle shaft. 

[fret not]

Fair enough, I will  proceed with what I have here.  It's only metal, right? (it can be bent, drilled, cut, welded, etc.)
I have 'shelved' my welded up manifolds in favor of putting the carbs straight up and using the stock airbox as you and Ron McCoy have done.  To use the manifolds I made I would have to remove the bolts holding them to the heads to remove or replace the carbs because there is not enough room to put the carbs into the frame if the manifolds are in place.  Since the bolts are not so easy to access and in the interest of future service I will fab the connections between the carbs.  I will come up with a solution.  Thanks for all the inspiration. 

I am enjoying the anticipation of riding this bike "when I get it done".  Getting closer bit by bit, and each step is that much closer to achieving the goal of this journey.  I got a small set back with the triple clamps but should be back on track soon.  A friend with the facility will put a couple beads of weld in a strategic location so I can continue to carve some features.

[Ron_McCoy]

Mike, I just extended the tab for balancing the carburetors by tacking an extension on it with a slight bend in it to bring bit back into alignment for balancing. Tacked it with a wire feed welder and immediately cooled it with water to protect the throttle shaft seals. Works fine and still going strong after more than 20,000 miles. Picture on page 7 of this thread shows it.
 Good luck, Ron

[fret not]

Thanks gentlemen.  I had looked at that pic previously but didn't figure out what was going on until I read your explanation.