CR's, FCR's, Downdrafts.......I'm confused

[El Dopa]

Can someone explain to me in words of one syllable or less the differences between all the upgrade carb styles, and what works, what works best, and what doesn't work at all.

Keihin CR's - roundslides? sidedraft?

Keihin FCR's - flatsides? downdrafts?

I thought that downdrafts/FCR's didn't work on the B4.

But having done a quick search, it seems that Jay sold his racing CR's and upgraded to a set of 33mm FCR's.

I'm confused.......

[gsxr400 racer]

fcr make down drafts and flat slide down drafts lay horizontal flat slides lay vertical like our carbs down drafts are for like zx, fzr , cbr, new gsxr
cr's are usually called smooth bores older style round slides still mechanical racing carbs, no diaphragms you twist the throttle thats what you get if jetting right they work fine but they have no accelerator pump like the fcr or tmr's so you crack the gas you may have to wait or let off if the jetting isn't right on the bottom on fcr's you hit the gas they go instantly

[El Dopa]

so there are four fcr styles?

down drafts,
flat slide down drafts,
lay horizontal flat slides,
lay vertical flat slides (like the gsf400 carbs).

straight downdrafts are for e.g. - zx, fzr , cbr, new gsxr.

and the cr's are round slides, which are good, but because they don't have a pump, they aren't as good as fcr's (and can bog)?

"fcr's you hit the gas they go instantly" - because they have the pump, and are therefore preferable?

so what I'm looking for is a set of 33mm vertical flatsides?

[gsxr400 racer]

so there are four fcr styles?

down drafts, (1)
flat slide down drafts, (same as number 1)
lay horizontal flat slides, (same as 1 and 2)
lay vertical flat slides (like the gsf400 carbs).

straight downdrafts are for e.g. - zx, fzr , cbr, new gsxr.

and the cr's are round slides, which are good, but because they don't have a pump, they aren't as good as fcr's (and can bog)? (cheaper and sold here)


"fcr's you hit the gas they go instantly" - because they have the pump, and are therefore preferable? These are what drag racers used in the beginning simple jettingso what I'm looking for is a set of 33mm vertical flatslides?

[El Dopa]

so there are four fcr styles?

down drafts, (1)
flat slide down drafts, (same as number 1)
lay horizontal flat slides, (same as 1 and 2)
lay vertical flat slides (like the gsf400 carbs).

straight downdrafts are for e.g. - zx, fzr , cbr, new gsxr.

and the cr's are round slides, which are good, but because they don't have a pump, they aren't as good as fcr's (and can bog)? (cheaper and sold here)


"fcr's you hit the gas they go instantly" - because they have the pump, and are therefore preferable? These are what drag racers used in the beginning simple jettingso what I'm looking for is a set of 33mm vertical flatslides?

OK, so armed with a bit more knowledge I made friends with Google...

On stock carbs, the slide or throttle plate isn't actually connected to the cables, so when you twist the grip it lifts the diaphragm mechanism, and the engine vacuum lifts the slide.

In contrast, on the FCR when you twist it you are lifting the slide directly. Plus the carb assembly includes a pump.

So the CR's are a jump up from the stock option. And the FCR's are a jump up from the CR's.

Is that correct?

Jay, are you selling CR's? How much?

And what was the bike your FCR's came from?

[gsxr400 racer]

sold the cr's to JC
bought fcr's for a xjr400 yamaha from japan cheap as chip fit right on $400 shipped to my door used had to buy new velocity stacks but also found those cheap on ebay

CR's when tunned are better than stock but when not right you cant beat the throttle response of CV (stock ) carbs
FCR's way better response than stock come from 28 -33 size

[Banditmax]

Surely 33mm fcr's are going to give no more top end power than 33mm cv's?

[gsxr400 racer]

absolutely wrong mechanical carbs are a different animal than CV carbs you usually go smaller with than stock with mechanical carbs most I have seen sold are 28mm and 31mm for the bandits and gsx's. I believe its the gsxr 400 a 1992 spII model that runs 35mm CV's so there's some food for thought they don't fit on a bandit  or my gsxr but interesting to know that Suzuki put 35mm carbs on a 400 at one time for 1 year. I have also seen stock carbs bored out and had almost looked more into having it done on my stock carbs till i got the RS carbs.  (That would give you a 34mm carb if you have stock 33's)Now they sell those through SUDCO the RS carbs and i would definitely buy them a size or two smaller due to not having the accelerator pump .

[El Dopa]

Anyone got any idea if these would fit the gsf400?

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&ih=017&sspagename=STRK%3AMEWA%3AIT&viewitem=&item=270144683548&rd=1,1#ebayphotohosting

From an FZR400.  Looks like the inlet trumpets are a bit damaged. Dunno how much difference that would make.

Measurements are:

from the center to center of the outside carb intake = 9.5" center to center of out side to carb next to it = 2.9" and center to center on the two inside carbs = 3.9" also they will slip in the carb mounts up to about 1 1/4 " deep.

[gsxr400 racer]

these are down draft im almost positive they wont work but hey if you want to try

[gsxr400 racer]

down draft also meaning the carbs can lay flat and still hold gas in the float bowl with out it draining right out of the carbs

[El Dopa]

Downdraft carburetor:
A carburetor in which the air passes downward through the carburetor into the intake manifold.

Sidedraft carburetor:
A carburetor in which the air passes through the carburetor into the intake manifold in a horizontal plane. Contrasts with a downdraft carburetor.

Have got some pictures that show the differences. Will post them later.

[El Dopa]

Alright, think I've cracked it. I'm posting this as a guide for anyone who is looking at a carb upgrade and wants to know what they're looking at on ebay, okshon or whatever.

Apart from the spacing, there are two things you need to look at.

1) A side view. From the side, does the carb assembly look like you could draw two lines through it, aligned perpendicular/90 degrees to one another? e.g. a first (horizontal) line through the air inlet/engine mount, and a second (vertical) line through the float bowl, crossing the first.

If these lines are at 90 degrees, you're looking at side drafts.

If the two line are NOT perpendicular - they're more like 45 degrees - you're looking at downdrafts, which won't work, so move along and keep looking.

2) Can you see down the throat of the air inlet? Is the throttle valve/slide visible? If it is visible, is it flat face on to you, or is it rounded? Flat, you're looking at a set of FCR's - flatsides - your search is over. Rounded, you're looking at CR's, which you may also find acceptable.

[gsxr400 racer]

[El Dopa]

so what are those, Jay?

And:

What are these?

http://www.okshon.com/v.cgi?YYurl=http://page11.auctions.yahoo.co.jp/jp/auction/n52808347