NC30 - First Ride - Fuelling issue maybe?

[Growler]

Ok finally got to ride the bike. Its been 6 months stripping and rebuilding but got out for a couple of miles. Problem is bike starts and runs fine. When revved at stand still in neutral when cold it stutters around 5 -5500rpm and is slow to rev. Once warmed it revs out in neutral no probs. Took the bike out and pulls cleanly and strongly to around 5000rpm then seems like its running out of fuel... It does rev out to the redline but takes a while. It is running on reserve but seems like plenty! Will half fill tank tomorrow just in case though!

The speedo drive cable is disconnected(waiting on replacement from Rick O) but the electronics are connected. Carbs have been stripped/ cleaned and balanced by me and intake rubbers show no sign of leaks using carb cleaner method. Would the restrictor be cutting in if the mechanical drive cable wasn't connected? Didn't think this would matter?

Where should I start checking? Fuel starvation maybe? How would I check this out?

The bike is completely standard/ standard jetting and pipe with new plugs/ filters and valve clearances all done. Bit gutted after all the hard work that it didn't run A1 from the off but suppose thats half the fun getting it sorted... Want to get it on track before summer ends so any help would be great...

Thanks in advance...

[Growler]

Any ideas?????

[Growler]

Can anyone tell me at what point in rev range the main jets come in to play? Is it just above idle or could it be around the 5000rpm mark? Possible a blocked jet causing this? Odd that it pulls cleanly til 5k then seems to struggle for fuel?

[Cammo]

Main jets won't come into effect until above 8-9000 rpm. The speedo drive is isolated from any restriction, it won't matter if you remove it.

When cold, nc engines don't like to rev out cleanly. Was the engine hot when you took it for a spin or just warm?

Fill the tank with fuel, get it up to proper temp (3/4 or more on the temp gauge!) and see how it goes.

[Growler]

OK thats great... Was sure I'd cleaned carbs properly so will look elsewhere. I did notice the regulator/rectifier getting very hot and one wire (Red and White) was off When I re connected the red and wite wire it blew the 30Amp fuse on the Pulse Generator. Will need to see where the wires all go and if Reg/rect is knackered? Would that cause limp home mode by any chance? Does Limp home mode stop dead at 5500rpm or will it still rev but very slowly and on half power (two cylinders?)

[rich1988]

i wouldnt have thought so but if the reg rec is dead surely there wont be enough power to provide a proper spark ?

[Growler]

Ok so can rule out Reg/Rec I think. cleaned up all contacts and replaced some melted spade connectors and getting 13.95v at 5000rpm so seems OK there. Noticed that vacumn hose from fuel tap is perished at air intake albeit there is good strong vacumn pulsing at idle. Gonna get a new length of Vacumn Hose today and try that and failing that its got to be dirt in the carbs surely??? Any thoughts?

[Keysie]

I recently just had similar problem and kept taking my carbs of to re clean and balance etc (they are bloody gleaming now) and still had the problem I also kept annoying a certain Mr Oliver for advice who eventually gave me the right answer one of my diaphrams on top of the slides had a small tear in it that was 3 weeks ago Rick said have you checked the diaphrams and i said yeah but I didnt check them carefully and only noticed it the other day there whilst cleaning and re checking balancing , so dont do what i did check each one carefully perhaps hold them up to the light etc cause it only needs to be a small pin hole sized tear and thats enough to give you problems.

[Growler]

I recently just had similar problem and kept taking my carbs of to re clean and balance etc (they are bloody gleaming now) and still had the problem I also kept annoying a certain Mr Oliver for advice who eventually gave me the right answer one of my diaphrams on top of the slides had a small tear in it that was 3 weeks ago Rick said have you checked the diaphrams and i said yeah but I didnt check them carefully and only noticed it the other day there whilst cleaning and re checking balancing , so dont do what i did check each one carefully perhaps hold them up to the light etc cause it only needs to be a small pin hole sized tear and thats enough to give you problems.

Tried the fresh petrol... When bike is warm and in neatral Revs out cleanly but does give the slightest stutter around 4500-5500rpm. When on the move pulls well to 5000rpm ish then loses power. It does Rev on and will rev out to Redline but seems to be working hard...

Just had Carbs off again and double checked all diaphragms and all appear OK. Bottom of float bowls had gathered some crap so cleaned again and back on bike. Will need to take it for a spin tomorrow to see if its cured but a quick start in the garage doesn't fill me will confidence! Bike still stutters at the 4500-5500 mark.. Only other think I can think of it HT leads plugs etc. Plugs ae brand new but plan on checking continuity of HT leads tomoorow?

Any other ideas folks its doin my head in!

[Growler]

Just out of curoisity does anyone have a pic of a standard airbox? The airbox design doesn't appear to let much air in as the tray seems to seal around the V of the head stock... Is this normal... It certainly looks standard?????