Keihin CRS smoothbore carbs for Norton

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Hi Jim

You wouldn't have the clearance problems with the Featherbed frame like you would with the Commando frame, looking good but, I am still happy with my PWKs and I think I will be staying with them for the time being but will keep a intrest in this projet.

Ashley
 
Any plans for a kit for Atlas motors? I've got the Monoblocs on my Atlas but honestly don't know if they are going to work or not since I'm still building it.
 
Johnnymac said:
Any plans for a kit for Atlas motors? I've got the Monoblocs on my Atlas but honestly don't know if they are going to work or not since I'm still building it.
Click to expand...

The clearance problem is with aircleaners and the stock Atlas oil tank. Bare twin carbs will fit but with aircleaners you need a Manx type oil tank or similar.

Someone else is interested in Keihin CRS carbs for an Atlas and It will require straight manifolds. When this happens I'll be trying them on my Atlas test bike with modified oil tank.
 
Is that brass balance tube the best way to go? I'd be concerned about vibes and seal quality.
Would tapping into the manifold be a better option like the original manifolds?

Also, is the balance tube necessary? The flat slides don't have them.
I'm ignorant I'll admit but what are the benefits?
 

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Dkt26 said:
Is that brass balance tube the best way to go? I'd be concerned about vibes and seal quality.
Would tapping into the manifold be a better option like the original manifolds?

Also, is the balance tube necessary? The flat slides don't have them.
I'm ignorant I'll admit but what are the benefits?
Click to expand...

I've been tapping into the boots with a brass tube since the mid 1980s and its always been reliable and airtight. Tapping into the manifold is just fine but its unsightly and the rubber connecting tube can fall off or deteriorate - I have several old manifolds with rotting rubber balance tubes on them. The heavy duty rubber boots I use have a wall thickness of over 3/8" and the stepped brass tube is trapped, airtight and quite secure - there is no connecting rubber tube to come loose and the stepped brass tube is practically invisible.

No you don't really need a balance tube and there are plenty of Dominators, Triumphs and BSA twins without them. But to make a carb kit user friendly and easier to tune - a balance tube helps.
 
johntickle said:
http://www.allensperformance.co.uk/crs-35-860.html
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Looks OK but notice that its not mounted on a Complete Commando.

The throttle cable bracket will not clear the gas tank. Look at the photo below and you will see that the bracket needs to be modified and a new cable wheel fabricated in order to clear the gas tank. To set up these carbs for Commando I have to make a new cable wheel and a new cable bracket as well as modify the original cable bracket. See details at website (bottom).

Keihin CRS smoothbore carbs for Norton


Keihin CRS smoothbore carbs for Norton
 
And I think 35mm is a bit big for most, I have a set of 33's on the way and I'm wondering now whether I would of been better off with the 31mm carbs.
 
T120 Steib said:
Application for a 750 T140V? Are there smaller bore sizes like 30 or 32mm?
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They are in odd sizes ie 31,33,35mm. so you can take your pic, a lot depends on the tune of your motor. I ran 34mm smoothbore Amals on Triumphs very successfully. I know guys who ran 38mm!
 
I am using 29mm CR specials on my Rickman CR750. These are great carbies on my slightly worked 836cc Honda four engine. My experience is much improved flow at higher revs and they really improve performance throughout the rev range. It must be remembered that these are race carbs and as such the idle circuit is basic and some slight popping does occur when backing off the revs, although under excelleration they provide smooth and strong power. Most racing Honda fours use these carbs and they are very tuneable for standard and worked engines. I'm restoring my MK111 and will be interested to see how they perform on a Norton.

Johno
 
Indeed Johno they are good carbs. I ran some on a 988cc R3 motor and they were great.

However, if I were spending tis much time and effort fitting exotic carbs to a Commando... I'd go the FCR route... well actually I did!
 
As luck would have it I was just given a pair of 33 CR's that came off of a gsxr ltd. Will you be sharing the setup process? I just finished modifying the stock Norton manifolds to suit. I still have to make a set of 33-32mm adapters. The bought ones are too dear for me.
 
flying-w said:
As luck would have it I was just given a pair of 33 CR's that came off of a gsxr ltd. Will you be sharing the setup process? I just finished modifying the stock Norton manifolds to suit. I still have to make a set of 33-32mm adapters. The bought ones are too dear for me.
Click to expand...

I am a week or two from putting them on the test bike and checking jetting. Just waiting for some special straight manifolds from England so they'll fit my featherbed. Then I'll have some more info for you.

Matchless already gave us jetting specs and that should help you a lot. But these specs are for a 920 so beware.

Tell me how they clear the tank and post some photos.

current settings are:
125 mains
yy8 needles clip 2nd from bottom (at bottom for 920)
68 pilots
230 slow air jets
Float height 14mm
the throttle slides are 3.0.
 
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