Why use NC30 carbs in a 35 race bike?

[Old Painless]

The exhaust isnt self cleaning but the plugs are.

[Cammo]

but the plugs look spot on. Is there a reason why it would look like it's running rich in the exhaust(being black with soot) but the plugs are a lovely buiscuit brown?

Did you do a plug chop from wide open throttle or did you let it return to idle before checking the plugs?

[Jon]

The NC30 carbies have 32mm butterflies, the NC35 carbies have 30mm butterflies; this does not quite tell the full story though.

The most restrictive part of these carbies is not actualy the butterfly area as can be seen here.


The circuitry of the NC35 carbies is quite a bit more advanced and is generaly a lot easier to get on with if not running a fully standard air cleaner and housing.

A couple guys on here have full HRC NC30 setups but bits are very hard to get, Cammo has some nice pics in his bike pics.

Rick Oliver does a full HRC Carby setup for the NC35 carbies.

[Drunkn Munky]

Skinnydog, you say your going to run standard jets for a while but 120 is not standard, 110 is standard on rvf carbs.
Jon is also right in what he is saying, the rvf carbs may be smaller but are a little more advanced than the Vfr carbs, rvf carbs are more forgiving and generally give better midrange hence a lot of people fit rvf carbs to their vfr's. What is it your building? Road bike or race bike? If you want every last bhp out of it then vfr is the way forward, if not then I think I'd be tempted to stick with rvf carbs.

[skinnydog0_0]

but the plugs look spot on. Is there a reason why it would look like it's running rich in the exhaust(being black with soot) but the plugs are a lovely buiscuit brown?

Did you do a plug chop from wide open throttle or did you let it return to idle before checking the plugs?

Hi Cammo, i checked the plugs after it had been left to idle for a few minuets. I hadn't run the bike at full throttle since the day before. The following day i started it warmed it up and then let it cool and checked the plugs.

[skinnydog0_0]

Skinnydog, you say your going to run standard jets for a while but 120 is not standard, 110 is standard on rvf carbs.
Jon is also right in what he is saying, the rvf carbs may be smaller but are a little more advanced than the Vfr carbs, rvf carbs are more forgiving and generally give better midrange hence a lot of people fit rvf carbs to their vfr's. What is it your building? Road bike or race bike? If you want every last bhp out of it then vfr is the way forward, if not then I think I'd be tempted to stick with rvf carbs.

Hi Drunkn Munky, Yes you are right with the not standard 120 jets. I didn't really explain what i ment very well at all. I will start with the standard 115 - 118 vfr jets then try what i have at the moment (my standard 120) as i know it works kind of okay with the porting i have, and go from there.
I am building a F400 race bike, this will eventually (fingers crossed) be a bike i want to run at the Manx, so it needs to be reliable too.
The engine is a UK spec NC30 engine with ported NC35 heads and cams. I have also removed the quitening gears and have a Micron race can. The CDI is a HRC copy with no rev limiter and flat spot remover.
I plan to get the bike running 90% right, then get it to a dyno, to get it set properly.
If you run the air scoop and no filter, can the dyno give you a proper set up or do you need to go to a specialist dyno?
Cheers

[Cammo]

but the plugs look spot on. Is there a reason why it would look like it's running rich in the exhaust(being black with soot) but the plugs are a lovely buiscuit brown?

Did you do a plug chop from wide open throttle or did you let it return to idle before checking the plugs?

Hi Cammo, i checked the plugs after it had been left to idle for a few minuets. I hadn't run the bike at full throttle since the day before. The following day i started it warmed it up and then let it cool and checked the plugs.

That will only give you an indication of how it's running at idle (rich or lean).

You can save a bit of dosh by getting it near right before taking it to a dyno. 95% of getting the jetting right on these bikes depends on what sort of induction setup you're running....

E.G: do you have the intake flap, intake snorkel, airbox, filter (what type?). What size pilot jets, main jets, what needles, etc?? The answers to these questions will get you in the ballpark for jetting.

[Cammo]

If you run the air scoop and no filter, can the dyno give you a proper set up or do you need to go to a specialist dyno?

You can get the jetting 'fairly' right before a dyno, but further carb mods are needed for this setup.

[skinnydog0_0]

Thanks Cammo. I think i will run the rvf carbs as i have them now as i know they are kind of right (have them set properly on the dyno though).
The NC30 carbs i have will be the full HRC spec(i hope), no airbox or filter, drilled intake/velocity stack plate and air scoop jets needles and so on. But that will take a bit of saving and time so i have time to read up on all the threads on here about it

[Drunkn Munky]

For what its worth your current jetting sounds about right for your spec, the previous 35 i had had ported and gasflowed heads, run 120 ish jets, standard airbox, no snorkle or rubber flap with a token guesture piece of foam to stop the bumble bees being swallowed up and a yammoto system. Went really well if a little boggy down low.