Non-standard carb internals

[The Duke]

Yay first post, and it's to ask about a running problem (Boo)

I've got a poorly running NC30 and set about checking the jetting and balancing the carbs with the drill bit method. Balancing was way out with the rear carbs so got them sorted and fitted 115/118 jets but when i went to look and the top end of the carbs they are different. The needles have a different number on them (J1GA) and the pistons are not all plastic, they have an aluminium inner and a red ring on the top of the piston where the diaphragm meets the piston. I guess because of the added weight, they have thicker and longer return springs than the standard carbs.

Has anyone any idea where these have come from. They look like an uprated set (Dynojet perhaps) but i can't find any reference to them anywhere. And do you think they are siutable for use. I have another set of carbs that are all standard but am reluctant to use them as the pistons are a bit sticky, the diaphragm rubbers seem to be holding them in and if you push them all the way up they stay there.

I'm after selling the bike but am not happy to untill i've got it running right. I'm not totally sure the problem is with the fuelling think it could be ignition related, but i'm not sure about the pistons and needles though.

Hope someone can help me.

[monkeywithaplan]

no idea whatsoever, which is of no help i am sure, lol, but get some pics up if you still have the carbs out. might jog someone's memory

[Cammo]

They will be UK spec carbs.

Check the uK bike sticky in the V4 general section for more details.

[Neosophist]

Yeah there UK spec carbs! (metal sliders instead of plastic is a dead give-away)

is it a UK bike? Your jetting will be slightly richer than Jap spec too.. (and worth more if its original to the right people... )

It should run ok with the standard UK jetting anyway so I would think your problem(s) lie elsewhere.

[The Duke]

Thanks for that guys. I had no idea about the difference with the pistons between uk/Jap bikes.

What about the needles though, there's no mention of them being different and they are a slightly different profile. I didn't take piccies though as i doubt it would show the difference. Also they have no washers on them at all ?

[Neosophist]

Thanks for that guys. I had no idea about the difference with the pistons between uk/Jap bikes.

What about the needles though, there's no mention of them being different and they are a slightly different profile. I didn't take piccies though as i doubt it would show the difference. Also they have no washers on them at all ?

The Shims (Washer) just raise the needles slightly, which richens up (adds more fuel) to the mid-range. After looking on the parts manual I can't see the washers in the UK model.

What jets were in there? 120/122 (at a guess) I can only speculate but since the jetting is richer anyway, perhaps the NC doesn't need extra midrange with the larger jets.. after-all the UK didn't have as strict emission laws as Japan did, hence the NC having smaller jets in its Japanese guise..