So, the Cota has a 28mm OKO carb on it (the original carb came in a bix of bits, and has a big chunk missing out of it), and I have a couple of questions ...

Where can I find a rebuild kit for it?

What's a good starting position for the idle screw?

Where sould I route the tube that comes out of the float bowl?  I seems to get pretty full of fuel for some reason, so I'm guessing the float is stuck (?)

I'd really appreciate help with this so I'm not chasing my tail unnecessarily

Go to www.mid-atlantictrials.com and click on OKO Carburetors and Accessories.

Thanks, that's a lot of useful info (though they recommend I go to a smaller carb!)

Rebuild kits are plentiful on eBay & come with all sorts of bits

Your overflow problems could be caused by the tube inside fouling the floats, it's quite tricky to take the bowl off without catching anything, the keihin is just as bad. A clear float bowl can be helpful at times & last time I looked was only about a tenner 

Thanks I'll have a look, all the kits on ebay appear to be in the US or China though so I'm going to drop OKO UK an email to see if I can get one without a wait or excessive postage charge

I don't want to pull the float bowl without having a fresh gasket on hand, as I don't know the history of the carb and could end up with a worse problem!

First of all, I do not have an OKO carb but have Three PWK 28's and they are Awesome carbs if you keep your fuel clean. The OKO is a Keihin PWK copy and they are supposed to be very good quality, there are also copies of the OKO....which are supposed to be horrid with shoddy built quality and are marketed as an OKO and often sold cheaper...just a heads up here, be careful.. Try atlantic trials in usa, site is informative and good prices

The OKO is a Keihen copy and uses most the same parts. They are  available in different bore sizes such as 24 and 26mm as well as 28.

The tube coming off the float bowl bottom is simply an overflow, and willn direct fuel out instead of filling the motor with fuel in the case of floats sticking or tipping the bike on its side, however as mounted on many bikes, the sloshing around of a dirt bike will see a lot of spillage in some cases. Many folks simply plug the line to prevent this.

The bowl gaskets seldom require replacement, so I WOULD FEEL  FREE to disassemble and give the jets a good cleaning and see what sort of grunge you have in there.

Tube off the side is the bowl vent and you want it clean and unrestricted so it may vent properly and not let crap in, yout you CANNOT kink the hose, it can be short enough to diflect muck and that is all you want or need.

Properly sized jetting will give you a 1.5 turn out from full in on the airscrew as a good guide. Idle speed screw may vary.

copemech - I have had a Keihin on two bikes and an OKO on one and they all seemed very insensitive to idle mixture screw settings.  As long as I don't go below 1 full turn out, it does not seem to make any difference to the idle.  This is true even when trying different pilot jets.  They all ran fine but I have never had carbs so insensitive to this adjustment.  Is your experience different?  One day a friend went to adjust the idle mixture on his Beta and the idle mixture screw was missing.   His bike still ran fine.  Odd      

14 hours ago, mcman56 said:

copemech - I have had a Keihin on two bikes and an OKO on one and they all seemed very insensitive to idle mixture screw settings.  As long as I don't go below 1 full turn out, it does not seem to make any difference to the idle.  This is true even when trying different pilot jets.  They all ran fine but I have never had carbs so insensitive to this adjustment.  Is your experience different?  One day a friend went to adjust the idle mixture on his Beta and the idle mixture screw was missing.   His bike still ran fine.  Odd      

Strange as myself and others have commented in the past just how sensitive and finicky they can be, possibly requiring changes on the day and temps/baro.

The actual preferred range is 0.5-1.5 turns.

http://www.mid-atlantictrials.com/Instal.html

I followed the sdvise given on the above link,my 250 Bultaco Sherpa runs great on the OKO.

Apart from an intermittent air leak (I suspect the outlet rubber as it looks very sorry for itself, new one goes on tonight), and the stuck float, it seems to run nicely.

There's a severe lack of engine braking, but I'm guessing that's nothing to do with the carb!