NC21 still not running right

[Viffer77]

I'm starting to get quite disheartened with my VFR.

After lots of hard work and effort she still isn't running right. When she gets upto a reasonable working temperature she runs great. Shortly after, she gets very hot although the water temps gauge seems ok. When she is hot, she has flat spots all over the place and generally runs crap.

Here is a list of works carried out so far.

Drained all the fuel and replaced with fresh.
Oil, filter and spark plug change.
Stripped the carbs and cleaned and set the pilot screws to 2.25 turns out.
Carb floats set to the correct height.
Balanced the carbs.
Valve clearances.
Run a fair amount of Redex through it.

I don't know what else I can try. The emulsion tubes etc all seem to be correct. It's almost like it's running lean, but when she starts up from cold she smell quite rich! (and yes I know choke may cause it a bit, but really smells).

Any thoughts!?!




Can anyone shed any light please.

[Neosophist]

Sounds like it's running rich and the extra mixture at temperature is causing the flatspots.

What are you float heights set to?

Try the pilot screws at 2 turns out to start with.

The emulsion tubes with more holes go in the rear.

[Viffer77]

I was wondering that, but with my limited RC car knowledge, richer = cooler and vice versa.

I can try.

Thanks.

Ben.

[Neosophist]

You could have an airleak between the carbs and the engine.

What are the inlet rubbers like? Is there any rev-hanging.

Cooler? Confused :-)

[Viffer77]

The carb rubbers seem ok, but I would guess the originals. The revs are hanging a bit.

Sorry, what I meant is if an engine's mix is lean it will run hotter and if it's rich, it will run cooler. That's right isn't it?

Any simple tests you can suggest for air leaks? Spraying something combustible at the rubbers?

Ben.

[MexicanGringo]

Get the bike up to temperature, gun it hard back to your house and dont let it idle at all when back.. Then check the plugs once its cooled down a bit, if theyr whiteish its running lean in the mid to upper rev range & that explains the high temp.. My 30 runs at 70-80 when up to temperature and riding, if it then idles the water rises to 90-95.. Id also check for air leaks as suggested..

EDIT: what iv read is, if the revs hang at idle when throttle blipped, idle screws are set LEAN, and if it drops & then rises theyr RICH (factory pro website), they say that applies to 1000 or lower idles tho... Try 1/2 turn out

[Viffer77]

Ok, so where are the idle screws? Sorry for the newbie question. I've located the pilot screws ok.

I will give your idea a bash tomorrow (weather permitting).

Ben.

[Neosophist]

Those are what he means (pilot screws) 2.25 is already on the rich side for the 24 though so I wouldn't really go higher than that.

Hanging revs suggests you have an airleak aroud the rubbers... that'll explain your revs hangin and your lean mixture, richening up the pilot screws has compensated for this a bit.

they get really old and hard and can be a right buggar to seal properly.

Something like easy-start thats really flammable, spray it around the rubbers and look for RPM changes.

I've had them look fine but leak no matter what.. fortuantly the new rubbers are only like £5 each or something silly, not £15 like the kawasaki ones.. :-)

[Viffer77]

That would make sense. As the bike warms up, the rubbers would get loose and let more air in!

Are you sure it 2 turns out though. It an NC21 not 24. The book states 2.25 turns.

I will give it a try tonight.

Many thanks.

Ben.

[Viffer77]

Also noticed that the oil smells of petrol again!

The carbs have been out many times now and everything seems to look ok!