Possible faulty fuel tap NC30

[Vincent]

Hi there,

I've been noticing that after extended higher rpm operation, my bike will sometimes stall when returning to idle. It idles fine otherwise, and will happily idle when hot (90 degrees+). My carb setup is good, and carbs have been recently balanced.
I am thinking it is a fueling issue, where the carbs are emptying too much after higher RPM riding. So when I come to a halt the level in the carb bowl is too low, which causes the stall.

When I balanced the carbs recently, I tested the fuel tap to make sure it was flowing when vacuum was applied. It did, but it wouldn't hold the tap open. Sucking on the pipe and then sealing it resulted in a spurt of fuel, rather than constant flow. Even sucking on it and blocking it with my tongue right away only resulted in a single spurt of fuel.

Correct me if I am wrong, but I am under the impression that the diaphragm should stay open when vacuum is applied and the pipe is sealed. It seemed that there was a vacuum leak on the fuel tap end.

I checked the vacuum line and there were no splits or holes in it, so I assume this means I have a faulty fuel tap diaphragm.

Are there any clever ways to fix this? Or am I going to need to buy a rebuild kit.
Any other thoughts or advice on this, please feel free to chime in.

[Dynamohum]

You say hose is OK but would change that first it could have a pinhole or split that's hard to spot no harm in trying that before getting the tap rebuild kit which is a good idea anyway.

[Neosophist]

Interesting one, as above a new hose first of all is a good idea but it does sound like you mihgt have a hole in the diaphram or a bad seal, have you taken the tap apart and had a look?

you can bypass the diaphram temporarily to check that this really is your issue, if it is then id rebuild the tap.

[Vincent]

Interesting one, as above a new hose first of all is a good idea but it does sound like you mihgt have a hole in the diaphram or a bad seal, have you taken the tap apart and had a look?

you can bypass the diaphram temporarily to check that this really is your issue, if it is then id rebuild the tap.

Not yet, I filled her up the other day, and the jerry can is full too
Ok thanks for the help. I'll temporarily do the 'HRC' fuel tap mod to diagnose the problem. Don't really want to leave it like that though.
Although I do like the idea of throwing in a 12v solenoid fuel valve.. Hmm.

[nc30racer]

Don't do the HRC mod. It happened to me, that the diaphragm snapped over and the bike stopped. After that, I removed all the internals related to the vacuum thing and the rear cover. I cut a piece of 3mm aluminum in the right shape, added a gasket and since then there is no more trouble.

[Vincent]

Update:
I pulled the fuel tap apart, compressed the spring a bit so make it easier for the diaphragm to open, tested it to make sure it wasn't leaking, put it back on the bike with a new vacuum hose.

Seems to be working fine!