Best carb combo for 750 big bore kit and Shell #1 cam?

[zrx1100]

I had the VM34 on a 750 kit bike and they seemed to work OK. They had been set up by a previous owner so not sure of the jetting. Since then I have built a number of bikes, and never had any problems getting the stock BS38’s to function properly. A stock bike with open pipes needed one size up on the pilot and I left the mains alone as it ran fine. A 707 kit bike with pods and open exhaust, 1 size up on both jets and I got a nice colour on the plugs, but possibly 2 sizes up on the pilot might be better as I have a tiny hesitation off idle.

I had good experience with bs38 as well. On the jetting I found that exhaust/intake combo affects jet size hugely. I went from 135 to 152.5 on the main by changing from commando/stock air box to open cone mufflers/Uni pod intakes to maintain AFR in the 12s. The pilot and the needle hardly changed

 

[Kevin Werner]

I was told by the gentleman from Brazil that VM34s flow much better than BS38s. Both are easy to rejet as you are tuning your build.

 

[GLS4004]

I have a 750BBK, ported head and Shell #1 cam. I opted for VM34 carbs and that all seems to be working very well - I also have a stock clutch which has been holding up fine so far (about 1000 miles on the motor, so not too many when fully run in).

Can you tell me your VM 34 carb set up, jetting and so on, thanks CM

 

[GLS4004]

Can you tell me your VM 34 carb set up, jetting and so on, thanks CM

 

[jay760]

I always use dellorto pumper carbs, but have manifolds made for them

 

[nighthog]

Can you tell me your VM 34 carb set up, jetting and so on, thanks CM

Hi CM, sorry about the delay, I've been biking abroad .
My carbs came from NicheCycle and this was the spec as supplied:

Jetting Specifications
Carburetor #	Venturi Size	Main jet (VM4/042)	Pilot Jet (VM22/210)	Needle Jet	Jet Needle	Throttle Valve	Air Jet	Needle Valve
VM34-275 & 168	34	175	15	P-6	6F9	2.0	2.0	3.3

A bit lean for my setup so I upped the jets a little: PJ 20, air jets removed, MJ 180. Air screws out 1.5 turns.
The bike ran wonderfully but natural caution about running lean at WOT made me change the MJs to 185. However I'm not convinced this has made any improvement, and it was maybe better with the 180s. I'll have to change back and compare.

Good luck with yours, I'm sure you'll find them a great solution!
Cliff

 

[GLS4004]

Hi CM, sorry about the delay, I've been biking abroad .
My carbs came from NicheCycle and this was the spec as supplied:

Jetting Specifications
Carburetor #	Venturi Size	Main jet (VM4/042)	Pilot Jet (VM22/210)	Needle Jet	Jet Needle	Throttle Valve	Air Jet	Needle Valve
VM34-275 & 168	34	175	15	P-6	6F9	2.0	2.0	3.3

A bit lean for my setup so I upped the jets a little: PJ 20, air jets removed, MJ 180. Air screws out 1.5 turns.
The bike ran wonderfully but natural caution about running lean at WOT made me change the MJs to 185. However I'm not convinced this has made any improvement, and it was maybe better with the 180s. I'll have to change back and compare.

Good luck with yours, I'm sure you'll find them a great solution!
Cliff

 

[GLS4004]

Thank you kindly sir, much appreciated!