well a funny thing happened today I was driving along and noticed a bit of a miss or flat spot at about 6000rpm under hard acceleration, I took the car home and checked base ignition timing, spark plugs, electrical connections and high tension leads, I took the car out again and now it starts to miss at about 4000rpm and won't rev past 4500rpm.
The engine is an A15 with a lumpy cam and running about 11.0:1 compression ratio. I am using a bosche HEC 715 coil with a datrats modified bluebird series 2 distributor set at 5 degrees base ignition timing and weber 38 dgas carb with F6 emulsion tubes, 50 idle jets, 185 air correctors and 145 main jets
It ran fine for past 2 weeks but now this issue has just appeared out of no where
very stumped on this one

what happens when it gets to 4,500rpm?

kinda sounds like my old a15 when I blew the headgasket

Dropped a cylinder ?

loose harmonic balancer?, my old L18 won't rev past 3500rpm when the balancer came loose

cheers for the suggestions, I will check the compression of all 4 cylinders and check the harmonic balancer too.
When it hits 4500rpm it misses quite bad and coughs and splutters but performance from idle is pretty normal idle is smooth at about 800rpm.
I have a feeling it could be a dose of crap ultimate 98 juice, I put $20 in her today and I can recall it started to miss soon after, my wife had a little 250 cruiser a while back and when I rode it home from the seller it had been sitting for 2 months, all seemed normal around 60kmph but once the motor reved up to highway speed the thing started doing the same as my datto. Turned out to be crap juice because it all went back to normal as soon as I filled it up with fresh fuel

Is it not running out of fuel? Clogged filter?

sounds exactly like my a15 with a blown headgasket. Put your hand in front of the exhaust and see if you get little bits of water and #### on your hand. With mine it didnt blow smoke or steam but lots of little drops of water

yeah i guess a dodgey fuel pump could do that. I've had a few issues with mine recently.... leaky diaphram and not holding vacuum.

Worth a look

Try checking the fuel filter and make sure the dissy is still set properly. My A15 had a similar problem and I found that the dissy had moved, retarding the timing.

Cheers. Adam.

it sounds like a carby problem.
sounds like the float has a small hole or crack in it
Happened to my old A14 that was a similar set up mild cam 32/36 webber then again I could be wrong