Carb balance issues

[edwar65]

Hi all, when trying to balance my carbs found difference between 2 and 4 to be very high?
When I try to adjust to bring them closer together Idle speed drops off and engine starts to run very lumpy?
All valve clearances,carbs Etc have been checked and carb rubbers have a good seal?
I am using a set of mercury carbtune gauges that have not been used for a long time, could it be inaccuracy of gauges?
what sort do you guys use and is there anything else I could check I r am I doing something wrong??
Thanks.

[VtypeV4]

If two cylinders are pulling that much harder than the other pair, you may find you have to adjust your idle speed to compensate to hold the ~1350 rpm whilst you adjust the balance..

[edwar65]

Hi, no 4 is a lot higher than the other cylinders, almost at too of carbtune whilst other 3 are around 3rd/half way,
When I try to bring 4 down to match cyl 2 the motor starts running rough??
Cheers.

[krisztian_andre]

Are the carbs in all the way in their rubbers, pilot screws adjusted, float heights set, compression cheeked, leakdown test maybe.

You can check the instrument by swapping the tubes between cylinders.

[edwar65]

No means of testing compression, float heights ok,carbs in rubbers and pilots set at 2 1/4 turns out.
I'll swap around testers later and confirm if ok.

[krisztian_andre]

I just remembered that cylinder 4 is probably the one that has the fuel tap vacuum hose connected to it therefore it already had a nipple on it and that nipple might have a wider passage in it than the other three. But that will only cause the reading to be different if the difference is very large.

[Neosophist]

balance them at aroudn 2000 rpm.

adjust all 3 carbs with screws to match the vaccum of the carb that doesnt have a screw.

is this an nc30 / 35?

the vaccum line for cylinder 3 is shared by the fuel tap on these bikes, how do you this hooked up?

it sounds like everything is connected ok so just doubel check.

anyway.

you will have to adjust idle speed as you are balancing.

from the info it sounds like cylinder number 4 is way off and open too much.. this will be keeping the idle high.. as you back out the screw to balnce to the other carbs it will bring the idle down, which means you will have to turn the main idle screw up to compensate.

sounds normal for a bike with one or more carbs much more open than the others.. correcting them will lower the idle.

[edwar65]

I'll check everything again but I'm sure it's all connected up as it should be. I've run the pipe from cyl 3 straight into vacuum pipe 3 adaptor. Out of interest after bike been running for a few mins sprayed water onto all pipes front two are hot rear two are relatively cool, they don't evaporate the water instantly like the front two??
Carbs were stripped before run up and were perfect, no jets blocked etc.
Not sure what's going on here sparks good to rear cylinders too??
Could it be at idle rear carbs are not receiving fuel due to being out of sync so much???

[Neosophist]

yes.

balance them first and go from there.

just remember that if the one carb is much vaccum, as you back it out to balnce it to the others your idle speed will drop, yuo will have ot turn the main idle adjuster in to compensate as you are doing it.

get em balanced and go from there