Revs dying on full choke (Oil leak fixed? 12/06/12))

[missis sumner]

I have just a couple of minor problems with my NC30, and before I start ploughing through the Haynes, I thought I'd ask here, this being the place of greater knowledge and all...

Background : The bike had been running just fine, however over Christmas I didn't start it for what must have been over a month. When I came to start it, with full choke, no throttle, KILL SWITCH ON (D'oh!), not surprisingly the bike didn't start. When I realised what I'd done, I switched the kill switch off, and the bike fired up, but almost immediately the revs died down and it cut out. I tried to start it again (choke still on, no throttle) but no luck - probably flooded, so I left it 10-20 minutes. After this time it started again, but died down - a blip of the throttle with the choke still on brought the revs back up to around 4000.

This problem did seem to get better with fresh fuel, but as of Monday morning, the revs were still dying down on full choke, but I seem to have developed the knack of proper timing for a blip of the throttle, to bring the revs back up.

My secoond problem: as of Friday, after doing about 350km mostly on the motorway, the bike seemed to sound a bit rough at low revs. And on a run out on Saturday it was cutting out on idle, as I pulled up at junctions.

Before I start pulling it to bits, have I killed a plug by drowning the engine (trying to start it with the kill switch on)? Or could it be something else, with the two problems related?

TIA

[CRM]

Hmmm, i wonder if you have a knackered plug.
does it run just fine but cuts out at junctions or something Sarah ? can you get it to mine ? i am more than happy to have a look over it for you

[Man_Named_Dave]

I think the usual advice is to check the vacuum hose from cylinder 3 to the fuel tap to see if it's perished, in which case you'll get crappy fuel flow.

[missis sumner]

Hmmm, i wonder if you have a knackered plug.
does it run just fine but cuts out at junctions or something Sarah ? can you get it to mine ? i am more than happy to have a look over it for you

Dies down on choke, then when it is warm, cuts out at junctions, yes. Other than this it's still running fairly well.

I could pick up the clutch bits you have for me too? Although *I think* my recent oil change has solved the clutch drag issue, and I seem to have also developed a knack for sometimes anyway, getting it in neutral. :lol

[missis sumner]

I think the usual advice is to check the vacuum hose from cylinder 3 to the fuel tap to see if it's perished, in which case you'll get crappy fuel flow.

Fairings are off, so I'll have a quick look tonight. Ta.

[Man_Named_Dave]

Also my bike has always idled poorly, and last week I opened the pilot screws another 1/4 turn and it has improved.

[Neosophist]

Also my bike has always idled poorly, and last week I opened the pilot screws another 1/4 turn and it has improved.

They should idle like a swiss watch.

The pilot circuit (not the jet) the 3 small holes are often overlooked when doing a thorough clean.

Pilot screws need to be all together and set right as well as float heights and they need to be balanced well.

Besides that the engine needs to be in good condition (valve adjustment, plugs)

As for the op.. If it's suddenly started I wouldn't expect something to have gone off, perhaps vaccum tube, knackered plug.

Start with the easy things before ripping it apart.

[missis sumner]

I had a quick look last night, and from what I can see of the vacuum hose with the tank on, it looks in good nick. I've got a set of plugs on order...

[missis sumner]

Bloody hell, they're tiny!

While I'm waiting for my new plugs...

Plugs for 1 and 3:



They look ok to me? I think 1 is running hotter than 3, the insulator on 1 is off-white, while 3's is light brown. There was an oil/petrol mix at the bottom of the thread/collar, just above the plug gasket/washer, but the tips of the plugs are clean.




The airbox and filter (which seemed quite clean) did contain a little oil (assume from crankcase breather?), and part of the airbox gasket was slightly mangled and so not sealed, shown here:



I shouldn't have thought this would affect running? I'll try to get access to 2 and 4 tonight, and hope my plugs arrive in the post today. BTW, does anyone actually bother to set plug gaps these days? I thought they came set to the optimum gap, and once they've been used the electrodes get pitted so it's pointless doing it anyway?

Any thoughts so far?

[Neosophist]

You don't need to set the electrode gap.

Are the carbs clean (proeperly clean) and properly adjusted? (float height / idle screw)

When did you last check your valve clerances (with the carbs off it's a good time to do)

I'd check the carbs have the right jets and emulsion tubes, reset the float heights and pilot screws, ensure the pilot circuit (3 tiny holes to the butterfly) are spotless on all carbs and re-balance.

If they and the clearnces are fine theres no reason it shouldn't run perfect.