Hi all, my nc30 has an erratic idle, the revs drop and then recover and i cant seem to get rid off it. The carbs have been off separated, ultrasoncally cleaned, new slow jets and mains, float height checked 6.8mm and a litetek seal kit fitted all done by me. They have 2 x 0.5mm washers fitted and the slides drilled to 2.5mm, these were done previous to my ownership. New carb insulators, carbs balanced and valves also checked.

The bike runs well except the idle. I have checked the battery 12.8v, tickover 14v, tickover and lights 12.5v, 5000rpm 14.5v and 5000rpm with lights 14v. It has new plug leads and plugs and the rubber flap is in place.

All jets etc are in the correct carbs, slow jets are 35 and mains are 118f and 120r , air screw 2.25 turns out. Standard exhaust fitted but can has been gutted so pretty much straight through can.

Any suggestions as to what the cause may be or what to try next?

A gutted can may adversely affect the air flow and fuel mixture at idle. Do you have access to a stock can or you could try restricting the outlet of the gutted can.

As back pressure has already been mentioned in a round about way, have you checked the air box is seated and sealed properly? Unregulated air intake can also cause erratic idle. Not so much of an issue when accelerating as you're forcing the induction.

Thanks for the replies. I checked the airbox which appears to be sealed correctly but the air filter is an aftermarket item so have ordered a genuine one.
The standard exhaust idea will have to wait a while and I'm not dismissing it or trying to start an arguement as i know your trying to help but wouldn't that happen with any aftermarket end Can? I have a 12v extractor fan (no mains electric) on the exhaust so i don't choke in my shed, do you think that may be making matters worse? I'll put no extractor and restricting exhaust on the list.

I'll let you know how I get on when the air filter arrives. Thanks again.

Check the vacuum hose as well, if it's got even a tiny pinprick hole it will affect fuel delivery.

Haven't been able to do much lately but today had a bit of time. I decided to fit the new air filter first off but was surprised to find it didn't fit very well. Certainly not in a Honda way, seems too small whereas the aftermarket one fitted straight on and is physically bigger. Anyone else encountered this before?

https://ibb.co/5TvNT0d
https://ibb.co/RCWzmfg

The vacuum hose is new and i also get the same problem using an auxiliary tank. The air filter made no difference to the idle.

After market cans are not necessarily "gutted" and many have a baffle of some type to keep noise to an acceptable level. The mixture screws may need adjustment for altered exhaust flow. Substituting an OEM can would be a method of diagnosis but only if available.

I have an original system on its way so will try that. Still concerned over the genuine air filter not fitting very well, can't imagine you should have to force it to fit.
Thanks

Where did you buy the air filter from? There's a lot of fakes floating around on the likes of eBay that are listed as OEM

I got it from nutjob.ie , an online shop who deal in Honda genuine parts who I've used before. It all looks genuine as do the other parts i ordered. Am I right in thinking the filter should just fit in the grooves around the airbox , no force required.