NC30 Only running on 3 cylinders.

[TheRehabKid]

Hi, i'm having a right pain trying to get my nc30 runing right.
It just won't fire on all 4cylinders, it is cylinder number 3 which won't fire (rear right), after running bike for 5 minutes the rear top downpipe will only have heated up a tiny but (i can touch it with my hand no problem).
I've had the carbs off (1989 model with 110 jets atm), adjusted all the pilots to 2 turns out, balanced the carbs using a drill bit, checked all carb rubbers are sealing, and tried swapping the front and back coils but no joy.I've also had plugs out, cleaned, re-gapped them and swapped the rear two over but still have the same problem?
The bike starts fine, but with it only being on 3 cylinders it splutters and revs seem to be taking to long to return to idle.
Any ideas would be much appreciated!
Richie

[CMSMJ1]

So, it does not fire using a known good plug?

You sure that it is getting fuel? Is the plug getting wet?

[TheRehabKid]

I flooded the bike whilst trying to get all four cylinders fired up, and all 4 spark plugs were wet so it is getting fuel.
The plug in the cylinder which isn't firing up has a spark, and i have tried another known good plug in as well with no joy. Although when i flooded the bike, both rear cylinders fired and neither of the front ones did because of the wet plugs. So i have had number 3 cylinder working very briefly, but when i cleaned the front 2 plugs and tried again, it was back to not firing .

[Neosophist]

So if you swap two plugs over now it still doesn't run on the same cylinder?

[TheRehabKid]

Exactly, i have tried swapping the spark plugs around between the two rear and it is still the rear right one which won't fire, i will double check the gapping of the plugs tomorrow but i dont think that's the problem.
The spark plug does spark, just seems like it won't ignite the petrol which is definately running through.
Is it worth a try heating the plug up with a heat gun b4 putting in and starting up?

[Cammo]

Sounds like the plugs are fouled or fouling in that cylinder. A new plug will probably sort it.

[Conica]

I've got the same unresolved issue on one of my nc30's, Always the same cylinder, Tried different sets of coils known to be good, Swapped plugs around and always the same cylinder which doesn't fire, I know the carbs are good as they've had a full rebuild and are currently on my road nc which runs like a dream. Tried two ecu's, Both with and without an M-max restrictor box and still no clue.

Valves & Cams seem good too, been some serious head scratching over this one :/

[CMSMJ1]

New plugs...

[karl BKK]

HT cable parted from it's connector within it's boot?
Found mine had done this on the rear right cylinder and after fixing it the bike ran fine, but you had said you have replaced the coils too....... What are the chances that both coils have this problem?

[TheRehabKid]

I've just solved my problem.
Picked up some cheap second hand carbs, fitted them and worked perfect straight away!
Now to try and fix the old carbs!