I have a poorly NC35 in my garage, carbs are utterly mong. I've plonked on a set of known-to-be-good NC30 carbs and it fired up but only on 3 cylinders. The front 2 cylinders, the back left, but not the back right.

Am i right in thinking that it will only run on 3 cylinders unless I have blocked the vacuum feed from the back right cylinder, considering that i am firing it up with a temporary gravity fed petrol tank (aka a robinsons squash plastic bottle).

Hi, that may help if you block the pipe up, but id try cleaning the plugs and maybe swap them across.
Cheers

Ian

Alex, I have always been told you cannot cross these carbs as you can't put Nc30 carbs on a NC35 or 35's on a 30 so it may be giving you a bum steer. It's all to do with how the velocity stacks work on each set of carbs and35 carbs have a smaller bore. Depending on where you are I have a couple of sets of both carbs if you want to try a set

Regards

Paul

P.S if you can run 35's on a 30 and it gives you a better power delivery I'm all ears


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It sounds daft as you sound like you know what your talking about but some months ago there was a thread on here with the same fault and they found after lots of tests a valve got bent some how it's very strange but it had identical firing order as yours


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Yep - block the feed. I scratched my head for ages trying to figure out why mine would only run on 3 and that was the culprit

Thanks Luke,

As expected, that cured the problem.

FYI - NC30 carbs will work fine on an NC35 and vise versa

phs187 wrote:Alex, I have always been told you cannot cross these carbs as you can't put Nc30 carbs on a NC35 or 35's on a 30 so it may be giving you a bum steer. It's all to do with how the velocity stacks work on each set of carbs and35 carbs have a smaller bore. Depending on where you are I have a couple of sets of both carbs if you want to try a set

Regards

Paul

P.S if you can run 35's on a 30 and it gives you a better power delivery I'm all ears


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As already been said thats bunk... a lot of racers fitted NC30 carbs to NC35.

They both work on each but are different carbs so depending on how you are setting the bikes and carbs up and you can achieve optimal results with appropriate carbs.. the nc35 carbs are more road-tuned..

now adays it doesnt really make much difference and probably should stick with the original carbs for your bike unless you have appropriate carb tuning parts and knowledge as they dont just bolt on and give anymore power.