Main jet size for a NC23

[c7ll]

Morning all!

Got a 1988 NC23 running a standard air filter, and blue flame carbon end can on standard downpipes.

What size jets would you run?

It's on 116's at present and I think it may be rich.

The bike is a daily runner so looking for economy more than BHP

Cheers.

C

[BillingCBR]

had 110's for a stock system and open can, and that was a tiny bit rich (left some carbon deposits on the can) now on 110 dynojets for my full DIC alu system, apparently there was a difference between the J and K bikes, one ran 105's one ran 115s, best bet is to look in the haynes and go from there

[Wozza]

K runs 105 as standard.
116 sounds too big, I'd try 110 (Keihin) like C says - roughly equivalent to 108 Dynojets.

[BillingCBR]

Got 4 Keihin 110s as removed from my own bike, your welcome to them if you like :)

[c7ll]

I've got a 'J' model which I think run bigger jets than a K but i'm not sure what size as standard?

Anyone got a haynes manual to hand??

[Wozza]

J model is 115 as standard - ok that changes things! When you ride, does it accelerate better from low revs with WOT or with gradually opening the throttle? This will help to work out if it's running rich or lean. If you can't tell any difference it'll be a case of getting it on a dyno for an AFR reading. Or, like I plan to do, you could fit a wideband lambda sensor.

Sorry, I meant "like Billing says" not "like C says".

[The Novice]

Sorry to hijak thread, wozza - you refer to does it accelerate better from low revs with WOT (wide open Throttle) or revving slowly....

mine does exactly that - ie have to rev v slowly from idle or it bogs down and could actually stall. bit of a pain in the a55 in traffic when you want to get away quicker than the shed next to you.

does this mean its running rich? how do i cure that..... my carbs are coming off in the next few days for a clean and cause they leak fuel again (float bowl gaskets) and i need to reseal carefully with hylomar blue.

[Wozza]

Longmore - which part(s) of the rev range are affected? And have you tested from a rolling start rather than a standing start?

[The Novice]

it runs fine once going, its just off the line when it bogs down unless i am gentle with the accelerator. If i just whack it open from idle its as if its drowning in fuel if that makes sense.

I cant really test it at the moment through the revs under load etc as i have the brakes stripped down for a clean and to replace hoses with braided lines so the back wheel aint on it.

Only reason i ask is, i know the carbs have to come off anyway, so i wondered whether i just try and reduce the richness a little to see if that helps at all. But i dont know how to do it ! I will need to check what main jet mine is running but its got s/s headers and a slip on can. its an rrj.

[Wozza]

If it's right at the bottom of the revs it'll be your pilot screw settings.
If you rev the bike to around 3-4k rpm and release the throttle, do the revs 'hang' a bit before returning to idle, or do they drop below idle for a second and then return to idle?
If it's the former, it's lean - turn the pilot screws out half a turn and try again. If it's the latter, it's rich - turn the pilot screws in half a turn and try again.
You may not be able to get rid of the flat spot entirely but you should be able to improve it significantly by the sounds of it.