I work on a base where the fastest you can go is 15mph! Been no problem in the past but last 2 months i have found hat the bike is becoming lumpy at that speed.
I can't seem to get a happy balance on the throttle to cruse at lower than 20mph even off base when filtering.
It feels like I am gunning the throttle then shutting it off in quick succession. While its doing this the engine sounds like its running smooth.

I have adjusted the chain
Adjusted the throttle to remove any play in the cable
Fitted new Cush drives

These did improve it slightly but it still does it.

I will be putting carb cleaner (in the fuel tank stuff) thru this weekend to see if that helps but I doubt it.
Am looking to replace the Cush drives as well... When I find a set cheap enough.

Any further ideas?

As a temporary measure I packed the play in the cush drive rubbers with a cut up bike innertube. I say temporary, mine is still like it a year on as i cant find a decent set.

I got slated for doing it but as a bike mechanic at a main dealers told me to do it I thought i would try it. In fact he also mentioned cutting plastic from a milk bottle to do the same job, but i went with innertube as i had one lying around.

It got rid of the play in the wheel anyways. Try it, its free.

Well if it fixes the problem I know to get them replaced.

Cush drives did not fix the issue.

Anyone got any ideas?

Maybe crap in the fuel filter? What do your spark plugs look like colour wise?