Topic: Keihin CR31 tickler carbs on 750 K head what's needed?

[napoleonb]

Hi guys, a search didn't come up quite with the results I was looking for.

The old Keihin CR31's have a 40mm diameter spigot on which the intake rubbers mount.
Earlier carbs (K1-6) are 37mm whereas K7/F0/F1 might be 40mm but I'm not sure, F2 seems to be 40mm.

K heads have different intake spigots to F2 heads (perhaps also K7/F0/F1) in regards to thread sizes as well as spigot outside diameter
Removing intake spigots seems possible: http://forums.sohc4.net/index.php?topic=115072.0

The rubbers have different lenghts between K/F besides different spigot diameters.
As I understand it the rubbers that belong with the CR31's had the earlier longer length

My K6 head will have some head-work done like porting and a valve job, but i would like to have this sorted before handing the head over.
My options and question are the following:
Option 1, using the standard K6 spigot fitted in the head with early K rubbers means I have to customize my CR31 carbs. But do they fit without altering spacing and only turning down the spigot?
Option 2, turning custom intake spigots with the thread fitting to K heads and the spigot diameter from a F2, using F2 rubbers. Do I have to alter the spacing between the carbs or can I use CR900 instead of CR750?
Option 3, using the standard K6 spigots, standard CR31's and adapting early K rubbers to accept a larger carb is this feasible?
Option 4, ...... ?

[johno]

Hi Napolean,
I have fitted a couple of sets in the early 70's, before the later 40mm spigots came out. All I done was get a sanding drum as close to 37mm as possible ( I think it was 35mm diamanté's drum) then mount the rubbers onto the head,  clamp head to bench , then work away slowly carefully bringing out the 1.5mm required. I remember it was hard to keep it perfect but with new soft rubbers you will be forgiven if its half a mm out.   Slow and steady, takes awhile, bout an hour for 4.
A whole lot easier than dicking around with spigots, they break, crack etc , not the best way that's for sure. Ive also used the grinding drum method to fit other carbs to Honda rubbers, ie RC webber manifolds and Mikuni carbs.
cheers Johno

[napoleonb]

I have ordered the early K rubbers and will open them up. Will let you guys know how it worked out.
Currently I'm also trying to figure out which felts, o-rings and rubbers are needed in order to revive these carbs.

[dragracer]

K7/8 intake rubbers.