Balancing problems, HELP PLEASE! NC21

[Viffer77]

Hi folks,

Very new to all this but having a bloody good go.

I bought a cheap non-running NC21, got it started without too much hassle but it wasnt running to my liking (what do I know, never have a V4 B4).

Since I bought it last Thursday I have Changed oil/filter, spark plugs (bastard to get to), valve clearance, emptied the lumps from the carbs and put it back together again.

Since then she runs with much more torque low down but there are a few issues. The cylinder to the front right exhaust stays a lot lower in temperature (and yes, it is firing). In addition to this, after fitting the carbs back on and run for a while, I removed them again this evening to find the rear right cylinder full of petrol! Obviously i have strip and re-cleaned the carbs hoping it was some grit in the float valve seat.

I am also having a nightmare balancing too. When i get the vacuum close to the control cylinder, the bike revs up to about 4k!!!

I have called it a night now, but if anyone could PLEASE help me, I would be eternally grateful.

[Neosophist]

The idle speed will go up as you balance them, you have to turn the idle control screw to bring the idle speed back down to what your balancing them at (circa 2500rpm)

Spark plugs arn't really a problem to get to if you swing the front radiator forward like your supposed to, otherwise you risk damaging the rad.

If cylinders are running at differnet temps you might have a rich carb (more fuel / cooler running).

Firstly i'd check and set the valve cleareances, as you'll need to re-check the carbs anyway (see below) and you have to get them off to do the clearnaces, you'll need to swing the front rad forward too (or remove it)

The valve clearances are set by screwdriver and locknut so no expensive shims to get. Get all of these spot on first as if there off, setting up the carbs is a waste of time, it'll never be right.

When you stripped and cleaned the carbs did you reset the pilot screws and float heights and check that the jets / emulsion tubes are all in the right carbs?

What jets do you have in there.. it should have 110's in the front two and 112's in the rears.

If you take the emulsion tubes out of the carbs, the emulsion tubes with the most holes go in the rearmost carbs (they run richer to keep them cool)

Float heights should be at 6.8mm from base gasket and set the pilot screws to 2.0 turns out as a start, they'll prob need 1/2 a turn either way to fine tune them.

Once your clearnaces / carbs are set-up, balance it and see how it's running. (make sure you have the airbox on and filter is standard and clean)

If it still isn't running right it's either electrical, or compression.

Get back to me after the above and i'll advise.

[Viffer77]

Hi Neo,

Thanks for your time. I have already done the valve clearances, all of which went easy enough. Going back the idle problem, what I should have made clear is the idle screw in fully retracted so there is no more adjustment!

Also should the vacuum gauges fluctuate so much? I'm not sure what jet etcs are in there. I didn't think to check. Someone has definitely been playing around under here as most of the screws are nearly rounded off etc. (I hate it when people do that). But then it is 25 years old I suppose.

I'm going have another go at it tonight, I will let you know how I get on.

Again, many thanks for your time.

[Viffer77]

Oh and yes, I did reset the pilot screws, when you mentioned about the fine tuning the pilot screws, what am I using as a guide to adjusting them? Higher revs? Just to clarify, I am supposed to be balancing the carb from the carb linkage screws (or whatever the technical term is), aren't I?

Thanks.

Ben.

[Neosophist]

Right.

You mean it still revs at 4000rpm when you've turned the idle screw fullly out!?

This could be that all of the linkage screws (3 of them in the middle underside) are in too far, so even tho there balanced there naturally set too high which is bringing your idle up.

You may also have an air-leak on the carb rubbers.

What gauges are you using the balance the carbs... they should be dampened. (the morgan carbtube comes with a fine piece of rubber pipe you put inbetween the gauges and the pipes which stops the flutter) the gauge type usually have a dampner screw you tighten up to stop flutter.

If it's idling too high i'd back all 3 screws out a few turns and try to rebalance. Wouldn't be the first time i've seen them screwed in far too much

[Viffer77]

Perfect!

The manifold are at a similar temperature too!

Just one more problem to solve and that's replace the collector box where the MOT station jacked the bike up from to check wheel bearings. I am aware of what's involved with this and bloody dreading it! It will have to stay on a bit longer until funds and time become slightly more abundant.

Any one got a cheap NC21 collector box for sale?

Neo, you've been a legend.

Thanks

Ben.

[Neosophist]

No worries, i'm only in Wolves so if your stuck with anything give us a shout one of the weekends.

[Viffer77]

Appreciated.

[Viffer77]

Appreciated.