Thanks. I will look into the intake again. However, I did rev the engine high last night and sprayed carb cleaner all over the intake and there was no change so I'd be surprised if there was a leak there. I did notice yesterday that if the bike is on its stand with wheel off ground, I can give it plenty of throttle and it's fine. But when I actually get on it with the wheels on the road and give it a throttle, it loses power when I give it more than a bit of gas.
I'm beginning to think I may not have gotten all the rust out of the tank and make give that another go. I did it with the tank still on the bike last time but will see if I can figure out how to take the tank off this time.
Apart from air leak or fuel flow, could it be anything else? I'm very new to mopeds and haven't tackled adjustment of timing yet. Could that have something to do with it?