xivlia's thread of nc30 problems and questions

[xivlia]

the bike is ridable..although ive only ridden it on my gaden as i have no license yet...ive also inflated the tyres now.

[Cammo]

Did you put new plugs in it or are you using the ones you soaked in petrol for four days.

This!!

[spanky]

Turn the idle speed adjuster up so it idles at 2k or 3k revs, run it for a couple of minutes then check the temperature of the pipes - if they warm up now then your carb balance is miles out and the back cylinders just aren't getting anything through the carbs with the normal idle speed setting.

If they're still cold then my money would be on the rear coil pack. Either use an ht tester neon thing or if you're a cheapskate like me, take out a plug, reconnect it to the ht lead then crank the engine with the plug resting on something earthed. DON'T TOUCH THE PLUG OR LEAD WHILE CRANKING OR YOU'LL GET A SHOCK! You should see a nice fat spark - a weedy thin spark might not be enough and would point to weak coil or dodgy plug. Word of caution, I've had a plug that sparked but the cylinder wouldn't run at hoigh revs. If all is ok then check the other one.

Assuming the plugs are sparking then it's got to be either fueling (carb issues, leaky rubbers etc) or compression (less likley).

[xivlia]

i may have found out the problem guys...so i decide to remove my rear two plugs. i do it and bike runs on two cylinders, nice and smooth. slower revs it sounds all good...i connect one of the rear plugs..its sounding all dodgy and tinnie...like as if something was rattling inside the exhaust..and then plug all four then again its tiniie but even worse. i then try to remove one plug at the rear. and the ht lead litterally snaps in half....this might of been my problem.. loose connection in the lead. anyway. i satrt the bike up with 3 cylinders running. and its all of a sudden very LOUD and bikefires ALOT i thought the engine was exploding..i turned it off...and thats it...any suggestions?

[spanky]

When you say
'...so i decide to remove my rear two plugs.'

do you mean you removed the plugs and ran the engine with the plugs removed or you disconnected the HT leads and left the plugs fitted?

Backfiring is unburnt fuel exploding in the exhaust. That's most likely either because it's running too lean to fire properly or because the plug isn't sparking regularly/sufficiently, fuel is being expelled and then exploding when the plug does cause a proper detonation. Probably the latter given the other symptoms.

It could be carburation but I still think most likely a weak spark issue - someone else suggested swapping the coils front to back to see if the problem moves, check the plug gaps and rotate plugs front to back, check battery voltage with engine running is good (ideally above 14v), check coil connections, check leads.

One other thing.. I've just looked back at your earlier posts (plugs, valve clearances etc) Petrol soaked plugs would tie up with dodgy sparks, but then an air leak around the carb rubbers after you refitted them could also cause simillar problems, so could messing around with carburation when you had the carbs apart. I think you need to swap all ignition parts front to back and see what happens and either confirm its ignition or eliminate it as so much other stuff could have changed.

[CMSMJ1]

Where you at? I have a tub with loads of plugs in. I'll send you 2...

[xivlia]

i mean i only dissconnected the HT leads and left the plugs in there. i dont know whats causing this problem, il try a few things with the carbs again, but im pretty sure ive fittem properly back in.

[xivlia]

Where you at? I have a tub with loads of plugs in. I'll send you 2...

i live in scotland, it would be great if you could send me 2 plugs

[Neosophist]

i mean i only dissconnected the HT leads and left the plugs in there. i dont know whats causing this problem, il try a few things with the carbs again, but im pretty sure ive fittem properly back in.

It should run 1000x worse with leads disconnected.

I don't understand your explanation.

Do you mean it sounds smoother with only 2 plug leads connected? This is bizzare.

If connecting the plug leads makes it sound worse then it sounds to me like that cylinder is firing but you have mechanical problems with the engine.

Get somebody who is mechanically able to help you with the bike.

[xivlia]

what i mean is, i removed 2 of the rear HT leads and left the front HT leads connected, so the bike would only run on the 2 front cylinders. and the bike sounds smooth and mechanically fine. but, when i connect the rear HT leads back on. it sounds all dodgy and as if something is rattling inside the exhaust.