As said above ^^^ Check your basics particularly your valve clearances (lash) . Clackety does sound like they need a good adjustment and if you’ve got one or two clacking, there’s every reason to suspect there may be one or two too tight which could rob you of your compression hence power. It’s also possible that you are over fueling by the description of a petrollly smell and that could be your needle and seat letting in tooo much fuel and swamping your motor, this could be caused by poor float level adjustment or knackered floats. Amongst other things.
So first things first, adjust your valve clearances and this must be done stone cold. Second, check your oil firstly by sniffing your dipstick for that petrol smell and also is it cleanish and when was it last changed and what has gone in there ?
Then wizz your dizzy cap off and have a good look inside the cap, is it clean ? Any hairline cracks, are the contacts on the cap all nice and bright. Is the rotor arm clean on the top contact and on the side contact . Are the points opening fully and rub a little very fine emery or similar in between them, check how much they open when the square bit (cam) tries to knock the heel open on the points, and the tiniest drop of oil on the cam, more of a smear.
Ozziedog,,,,,,, then we can go from there.