arsey30 wrote:More likely carb than compression, but lots of testers on e bay, but with brass adapters [not nc size] but with 2 rod/rubber bung adapters included.

Put the bike in first gear with only the bad cylinder plug fitted.
Turn the back wheel, and compare the engine resistance/compression with just one of the 3 good cylinders with a plug fitted.
You could turn the engine with a torque wrench on the rear wheel nut to be more accurate, but the first way will soon show if there is any compression.
Don't put it in top gear, the engine will turn over too easily.

I think you are right, I'm not too worried about the compression. I started the bike up from cold today with choke and the problem cylinder fired up and header got hot instantly. When I turned off the choke it was back to lumpy idle and the problem pot soon got cold again.

Carbs off again, blasted through with a can of compressed air again concentrating on the pilot holes. I did see some air coming through all three holes but I suppose there still may be partial blockage.

Carbs back on, no difference.

Carbs off again (I'm now a pro and it takes me 5mins) lol. Removed pilot screws and can't see any o rings. Do these stay fixed inside the carb? All that comes out is the screw, spring and washer. On inspection I can't see any oring?

Will take carbs to my friends garage for a proper blast using his compressor tomorrow.

Even though this problem has been a pain in the ass I'm still enjoying getting my hands dirty and learning the bike.

The o rings normally stay in the carb but remove it to make sure it is seated correctly [fit the spring, washer and o ring on the screw for assembling]

Thin wire or the air canister will remove the o ring, but if blowing it out, then cover the hole to prevent loosing it as they are easily lost being so light and small.

Blow the airways out backward, covering the holes in turn with fingers to force air down each individual passageway.

I mentioned running on choke earlier as that is a quick check to see if the pilot circuit is working, as choke bypasses it.

Yes you were right on the money again lol. The o-ring was in there. Will get the compressor in there and blow out that carb in the morning.

Try the air canister first, you don't want it flying across the workshop.
Hold a piece of rag over the hole to catch it.

arsey30 wrote:Try the air canister first, you don't want it flying across the workshop.
Hold a piece of rag over the hole to catch it.

Yeah will do lol. Can the air jets get blocked. I was thinking maybe the pilot air jet is blocked? Where is the air jet? Is it the on by the big diaphragm at the top of the carb?

There is no removable air jet, only passages, the pilot jet is under the float bowl cover.

Blow through all the passages you can find.

Right carbs have been blasted with the compressor. Tons of carb cleaner, new plugs fitted. Still the same problem. If I cover the carb tops with my hand the bike cuts out instantly on the front cylinders and it makes no difference if I do the same on the rears. Could it be a fuel supply issue? Sparks look ok and I've tried swapping coils but no difference. Spraying carb cleaner into the air jets on the rears will sometimes make it splutter a bit. Idle screws set to 2.25 turns out. Did the rear wheel test for compression and there seems to be plenty, in any gear. Shall I try easy start into the carb throat?

Any suggestions guys? Feel a bit pi$$ed off ATM.

Maybe see if you can find a cheap set of carbs on ebay or something or maybe send them off for ultra sonic clean? It wont be the coils if its firing ok the other side. If its running on that cylinder on the choke ok then there fuel getting in that carb, but have you checked the little fuel filter in the fuel inlet pipe see if its blocked?

Easy start works well to get a cold motor running, but if engine starts and warms up, then I doubt if easy start will make a dead pot chime in.
Your last test indicates the rears not working.
Does the poor cylinder cut in at high revs?

Try to establish which ones are working.
Remove each plug lead in turn to see if it makes any difference. Fit a spare plug in the lead and lay it to earth to protect the ignition circuit.

Morespeedvicar wrote:Maybe see if you can find a cheap set of carbs on ebay or something or maybe send them off for ultra sonic clean? It wont be the coils if its firing ok the other side. If its running on that cylinder on the choke ok then there fuel getting in that carb, but have you checked the little fuel filter in the fuel inlet pipe see if its blocked?

Hi mate where is this filter? I was told NC's don't have an inline filter before the carbs?

Another thing is I turned off the fuel and placed the tank on the floor. Fuel was still pissing out and soaked my garage floor. I thought these bikes need a vacuum to flow fuel? Could the vacuum pipe be letting air in through a faulty fuel tap and causing cylinder 3 not to fire?