Carb size on a big bore

Hi

Building up my street bike. 7s cam Maney barrels venolia pistons. I have looked at all my manifolds ie 2 into 1 etc & have a dilema
34mm mk2 with matched manifold 33mm mk1ss with velocity stacks but in my box I have 38mm Amals?
To Much?
Lots of racers run them (I run 36mm) but will they work on a road bike?
You know what its like its only cos I have them.

all the best Chris

Hi Chris,
Over the years I have tried MK1s in twin 30mm, twin 32mm, single 30mm, single 32mm, MK2 single 34mm, & 1/3/4" SU. On the 920 I am now using Keihin CRs 33mm. These are the best I have tried but the twin 32mm MK1s were pretty close on performance with good idle & pickup. I have never tried huge carbs on the Norton but BMW airheads use 38 & 40mm Dellortos & Bings to good effect.

Martyn.

I'm running a pair of 36 mm Mk2 Amals on my MK3 with 883 engine. With ported head, 9.1 CR, Trispark ignition, stock exhaust, and medium cam, they work quite well, with a good idle, very broad torque band and great top end. You can get a bit of hesitation if opening the throttle too quickly at lower rpm. I have no problem with that in normal street riding, but you might find it worse with a pair of 38 mm, particularly if you have a 750. Like you, I used them because I had them. If starting from scratch, I probably would have used something in the 33 -35 mm range, mostly for a little better low speed response. It's not like the big carbs will make it unrideable, but they might not be as pleasant for low speed putting. I have run a pair of 38 mm Mikuni flat slides on a 920 race bike, and really liked them, but not sure how they would be on a street bike.

Ken

Hi Martyn Ken

Thanks for the reply's.
I have decided not to go the single carb route as all my manifolds with a bit of length, leave the big Dellorto & Amal hard up underneath the spine of the frame. If I use the shorter Stewart manifold the throttle cable has a better route.
I will be fitting the 33mm MK1s as I have a pair of bored out manifolds for these. Might use the 34mm Mk2 later on but have always found a Norton easier to start on a MK1.
Still not sure where this bike is going as I am still swapping parts about as I go :roll:

Chris

Chris,
Get a few spare slides for your Mk1 33 Amals coz with on the road use they'll eat'em.

Try the Mk2 34 Amals with 25# or 30# en-richer jets.

Dave

Hi Dave

Thanks mate.

I am going with the MK1s cos thats what I have. Everything can be changed later & probably will be.
I now have a pair of manifolds for the 34mm MK2's now & a set of rubber connectors. I will have a look & see what jets I have. Two sets of cables to make.
Building a bike while trying to use up all those odd bits you accumulate in the garage.

Chris