OEM FCR Float Bowls

S

sixstring

Well-known member
This is a bit of a long shot but here goes nothing.

My ZX7RR came from the factory with Keihin FCR41s. They arn't quite like the aftermarket Keihin ones as they have fixed spigots, two accelerator pumps on carbs 2 and 3, a fuel enricher circuit and a set of retarded float bowls. Furthermore, they have tiny main air bleed jets and massive main jets. In a word, they need work out of the box to ride smoothly.

So I get some aftermarket keihin main jets which are long hex shaped things unlike the short round jets that came in the carb to start with. The advantage of using a longer jet is to allow the main jet to sit lower in the float bowl so that when the bike is leaned over or under hard acceleration, there won't be a sitation where the fuel level drops below the level of the main jet.

The problem is my #4 float bowl for whatever reason is shorter than the float bowls on my other carbs and as a result, the main jet hits the bottom of the float bowl, preventing me from closing it up all the way.

I like the longer main jets and don't want to modify them. At the same time I don't want to go and buy a single aftermarket float bowl because it will mean that my #4 bowl holds a different amount of fuel than the rest of my bowls. I'm hoping that someone here can either
a) sell me a set of four FCR float bowls or
b) let me know if you can help me cut/press out the OEM drain sumps and tap threads for a bolt type sump like the aftermarket FCRs have

Aftermarket jets (bigger) vs original jets (smaller)
IMAG3132.jpg


Aftermarket jets installed
IMAG3168.jpg


Float bowl #4 is too short
IMAG3178.jpg


Float bowl #4 won't close
IMAG3172.jpg


I'd be happy if I could cut/press out the OEM drain sumps and replace them with bolt type sumps like 99.99% of FCRs have. Some ducati carbs are used below to show what they look like
fcr_main.jpg


There are more details of my FCR struggles on my blog http://zixiaozx7.blogspot.com/
 
Try calling winners circle in Markham. They have tons of stuff for FCR's. Im quite sure there is a spacer made for this type of application.

Your going to need something like on the FCR for dirt bikes like this... http://www.tntracing.co.uk/product_view.php?id=6503

Just an example, im sure you could find something local but just an idea.
 
Last edited:
  • Like
Reactions: TK4
use the shorter jets, and set your floats heights to spec, you shouldn't have any issues with the short jets sucking air
 
RonnieRev said:
use the shorter jets, and set your floats heights to spec, you shouldn't have any issues with the short jets sucking air
Click to expand...

The proper float height according to the Keihin manual is 9mm which just barely submerges the whole jet in fuel. The round jets work okay-ish with stock 6mm float height but simply won't do with 9mm. From what I understand float height and needle dimensions are key to getting FCRs to run right - especially large bore 41mm FCRs so I need the lower 9mm float height setting.
 
I’m a bit late, but They do make carb bowl extenders. One company that makes some are called Thunder Products, idk if they will have one for your specific carb but maybe.

thunderproducts.com

Mikuni Float Bowl Extender - Thunder Products Carburetion Performance

Mikuni Float Bowl Extender for VM round slide carburetor provides 20% to 40% more fuel capacity for better performance, long hard pulls or when using alcohol.
thunderproducts.com thunderproducts.com

I’ve realized they only have mikuni carb extenders, but I’m sure someone else makes something for keihin
 
Last edited:
nokturnal said:
+1000

Use the proper style jet
Click to expand...
These are both "correct" jets.
The long ones are Keihan 99101-357, the short ones are 99101-393. Both are Keihan FCR jets.
The short ones came in OEM optioned carbs that appeared on stock bikes.
If you bought a pair of FCRs off the shelf, or aftermarket, they came with long jets.
They both work. Yes, you have to play with float height to get them to work right... like ANY carb.
There are bowl extenders and deeper bowls available, usually used on dirt bikes, I've never seen them on a street bike.
I'm running aftermarket FCRs on a 900SS with xxx-393 jets without issue.
 
disable one of the accel pumps. trust me. and do what ever you can to be able to use red stacks. if you have to run an airbox, find a set of 2003 gsxr1000 stock stacks
 
'357' carb parts were used on first generation (1974 ?) Honda CR250M.
'393' parts came from last generation single cam Honda CB750s, specifically the Automatic.
I don't know whether looking at the appropriate parts schematics will help, but can't hurt ?
 
TK4 said:
'357' carb parts were used on first generation (1974 ?) Honda CR250M.
'393' parts came from last generation single cam Honda CB750s, specifically the Automatic.
I don't know whether looking at the appropriate parts schematics will help, but can't hurt ?
Click to expand...
HUH?
I'm pretty sure the early Honda single cam ran Mikuni VM29s and the early Elsinores ran a Mukuni VM34
You are using Honda part numbers, I am using Keihan part numbers
I don't think we saw FCRs till the mid to late '90s, after Lectrons and TMs
 
bitzz said:
HUH?
I'm pretty sure the early Honda single cam ran Mikuni VM29s and the early Elsinores ran a Mukuni VM34
You are using Honda part numbers, I am using Keihan part numbers
I don't think we saw FCRs till the mid to late '90s, after Lectrons and TMs
Click to expand...
Honda has always used Keihin carbs. They OWN Keihin, just like they own Showa.
Carb internals have been used across many different models, same as Mikuni does.
I'm just suggesting that OP takes a look, there may be some hints to point him in a direction.
 
You must log in or register to reply here.
Back
Top Bottom