Hi,

I am suffering from carburation issues on my race nc 30. I am running stock carbs with the whole cutout in the plastic tray in front of the airbox snorkel, the air filter element has been chopped out. I have slowly increased the main jets from 120 front and rear to what im running now which is 125 front 127.5 rear and apart from this flat spot which iv had all along this choice of jets seems to be the best so far. The problem i'm having is in fast corners where the bike is lent over, for example cascades at Oulton , church at Anglesey. If i approach the corner say hard in 3rd or 4th and roll off the throttle tip in the bike just at the apex where you start to roll the throttle back on there is nothing there it stutters and i have to wait a fraction for it too start pull again its off putting as you have to anticipate this or you end up having to sit the bike up a bit as the power isn't instantly there to help do that job for you, then you obviously have lost some drive and often i get out dragged down the straight. It only seems to happen on this kind of bend with a high revving approach and the bike lent over. I have checked carbs all seems ok i'm thinking some sort of fuel starvation possibly because it only happens when the bike is on its side can anyone advise on float heights or should i just stick to what the haynes manual says, the fuel tap has had the mod done so any advise towards a possible solution would be great as its really annoying. I do have 6 months to sort out though is it worth fitting a fuel pump? I know some people say they aren't needed but it cant hurt.

Thanks

Could it be the air flow when you get it into yaw round the corners? it should starve itself at high revs, at least some times, if it was that thirsty?

Have you got an HRC air tray? the piece that sits beneath carbs and has a tongue over the top rad? the removal of the flaps and snorkel, when I was messing with all this back in the day I found that the tray was very good indeed.
I slowly went from open RVF carbs with single sheet of HRC Air foam - good for keeping flies out... to a full airbox, filter and standard VFR carbs. it fuelled so nicely that I was able to be on throttle and take the gains there and it didn't really lose much up top.

Just a thought, but from your description of the changes to the airbox and ducting, could you have created a disturbed airflow. You could try the F3 HRC airbox and ducting mods. You also mention a flat spot, this may be a symptom of an airflow issue if present after the airbox changes or exacerbate the airflow issue if present before the changes.

The airbox is standard apart from element being chopped out and im still using the original bell mouths the only mod is that the flap in front of the snorkel has been chopped out which is a common mod. Oh i have drilled the hole in the slides and got a washer under each needle. 125 front mains and 127.5 rear mains.
Its weird that it only happens in certain lean angles and when i roll off the throttle, if i am on a fast straight flat out in top then brake hard and go down the gears into say second gear corner lean it over and get on the gas there is no fault at all it pulls clean its only when you roll into fast or faster corners on the over run then slowly feed the throttle in and thats when the flat spot rears its ugly head whether its high revs on the overrun that is fouling the plugs or whether it is due to the lean angle and fuel level in the carbs due to prolonged time with the bike lent over that is what im trying to suss out.
I have checked diaphrams all seems good but they are old now wondering if the diaphragms are getting stiff wondering if that would be an issue on delicate throttle input i.e breathing on the throttle coming out of faster corners?
I got talking to a fellow racer about this and he said he had a pair of hrc carbs with tray that i can have for £200, i have agreed to, but setting up hrc carbs will be a challenge so i was hoping to iron out the original set up before moving onto an even more tricky set up. I think i will strip fuel tap and make my own blanking plate instead of the looped tube, strip carbs again do float heights then get it on a dyno.
Hate carburation issues

My money on the air as magg also suggested.

Hrc drilled carbs and open airbox is surely still digging a hole.