Have an OKO Carb fitted to my 199A which has generally worked well until recently in some longer sections on the throttle, the bike has behaved as if it was starving of fuel. From a quick Google this seems to be quite a common symptom of this carb in the scooter world. Anyone have any similar trials experience and related advice to cure?

Had a similar problem with a mikuni which turned out to be float height setting. The OKO is a pig for removing the float bowl and can easily bend the tangs if you're not careful. Have a look at this set up guide.
http://www.mid-atlantictrials.com/Instal.html

I would agree with the previous reply. Before fitting a new 28 mm OKO to a Montesa Honda MH349 we found the float height needed resetting before use.

The float height setting for the similar Keihin PWK carburettor is 19 mm from the float bowl gasket face to the highest point of the float.

Check the 19 mm dimension with the tang of the float resting on the float needle tip without compressing the spring inside the float needle. This 19 mm dimension also works well with the OKO flat slide.

To make checking the dimension easier start by holding the carburettor so the float bowl joint face is vertical with the float pivot pin at the top and horizontal. The float tang should be clear of the float needle, tilt the carburettor so the float moves towards the float needle. Measure the float height when the float tang just touches the needle tip. If the float height is out the adjustment is made by carefully bending the float tang.

Also check there is no water in the float bowl.

Hope this helps.

Edited February 17, 201412 yr by tayld

Good call on the water in the float bowl thought. I had this the other week and this gave the same symptoms, cleaned out the float bowl and was away again. I am always careful with petrol, using only new cans, (obviously not careful enough). I think that we are going to have this problem more often with the amount of ethanol in fuel these days.