1260 - What Size Carbs?

[Muddy]

I'm after the voice of some experience please.  If I was thinking of boring a 1100 Katana to 1260, what would be the recommended carb sizes ie 36, 38 or 40 mm or something else?  No track work, just street and twisty road use.

Thanks.

Regards

Muddy

[Gixer1460]

36mm's will be more than big enough for intended use (will retain enough bottom end and breathe well enough to support 150hp)

[Fazz711]

36 or 38.

I have heard that 40s can be a pain to set up. 

Personly I like 38s 

[GSX1100dreamn]

Hi Muddy,

I was running 91 GSXR750 38mm CV on my 1260 and they have round inlet (filter side) not the ovalish type. I used GSX1100 rubbers but new so they would stretch over and standard airbox with the inner metal ring removed again to aid fitment over the larger diameter. My engine had dialled in cams.

These are identified by the side adjuster for idle speed, they are shorter than the 1100 34mmand I had to cut flush the bottom drain tube so the airbox could sit forward.

Cheers Andrew.

[Gixer1460]

Good move retaining the airbox - solves a lot of jet faffing around when fitted to alternative motors. Won't solve ALL the problems but does help CV carbs work as they should.

Edited September 17, 2019 by Gixer1460

[Muddy]

Great info and nice to hear from the voices of experience.

 

Thanks muchly.

[Gammaboy]

On 9/17/2019 at 12:54 PM, GSX1100dreamn said:

These are identified by the side adjuster for idle speed, they are shorter than the 1100 34mmand I had to cut flush the bottom drain tube so the airbox could sit forward.

Cheers Andrew.

Watercooled 750/1100 Carb rubbers would have probably left the airbox in the right place - they're about 10-15mm longer from the looks of things.

[GSX1100dreamn]

Good tip Ben,

And I used the '91 GSXR750 hose clamps on the rubber at the carby side as they were a bigger diameter to fit over the 38's. The engine side is standard GSX.

And the mixture screws are on the underside facing down, I use a cut down screwdriver and most importantly a piece of thickish cardboard that fits on top of the gearbox and around up to the barrel fins to protect your hand when you adjust the mixtures when the engine is warmed up. Fricken hot !!

Edited September 19, 2019 by GSX1100dreamn

[HUM]

I have the 36mm from efe 120 main jet,   pilot screw 2,5 out, needle in middle, original airbox, V&H 4/1 racing baffle ,   on 1074cc engine with yoshimura stage I  cams ...  works good , but a bit thursty  :-) 

[Ibbo]

When you say what size carbs, are you refering to cv, or flat slides?

[Muddy]

Sorry, should have been clearer - I was thinking of putting in new Mikuni RS carbs with trumpets and Ramair filters.

Edited September 22, 2019 by Muddy

[Ibbo]

I had rs36's on a 1260 efe, and wished i had bought 38's mainly because it was so good on the street, and i thought i needed more top end. It had a cracking torque curve, and 135hp on the dyno. In the end i took the cams out when i sold it, and thought about keeping it, there was so much torque.

Now i would be happy with the 36's, but would struggle to keep them open for longer runs. If the alternator was better i would go efi, but it seems that its a struggle to keep the battery charged at low rpm.

[dago]

I would go with the rs 36mm for low down and mid range or 38 for top end you lose a bit of low down torque but still perfectly usable on the road