Just bought an NC21 off a mate which was used as a track bike.
Has stood idle for the last three years and I am putting it back on the road. Lights, indicators etc.
The problem is the tickover. Once the bike is warmed up (choke off) the tickover is all over the place.
I can set it with the throttle stop screw to a comfortable 1000rpm but every now and again it will race up to 3000 without me touching it. A good blip of the throttle brings it back down but sometimes it will then stall.
It also seems to take an age to return to tickover after a right good handfull of throttle (in neutral and on the stand) compared to inline 4s I've owned in the past.
Any thoughts???

Air leak on carbs somewhere.

Yer likely carb leak, but I would get the carbs off and give them a very good clean as they are likely gummed up if the bike been stood for a few years.

Thanks Guys

probably best to replace the rubbers as they will be so old.

Assume you mean the seals between carbs and inlets?

Yup.

Cheers

Also make sure your carb linkages are all well lubed, as they can bind and cause the carbs to lose sync and operate very erratically at tickover. Only requires a squirt with WD40. Made an amazing difference on my bike.

Ben.

Cheers Ben