strange rev limit at 4500rpm

[Jimbo]

hi everyone
i recently replaced my 260 carbs with some new HS6 SU carbs and im having a few issues.
the car at the moment idels great and drives superbly untill you try and bury the accelerator.
for some reason at full throttle it doesnt seem to want to rev past 4500rpm and feels just like its struggling for either fuel or air.
if i use 2/3rds throttle it will happily rev right round to 6 and a bit thousand rpm.
its just the last bit of throttle it doesnt seem to want to run right.
i originally had SM needles but these style SU carbs arent the fixed type needle but instead fit into a kind of cartridge instead, but the same principle applies.
i am now running DX needles which again run beautifully and are little richer than the SM needles but i still have the same rev limiting issue.
i did wonder whether it could be an ignition timing issue?
i did set the timing to 10 degrees with the vac pipe on the dizzy disconnected and plugged which i believe is correct?

to be fair i could drive the car all day like it is and just not use full throttle (as im unlikely to anyway because i drive like miss daisy) but its annoying as i know its not right.

if anyone has any pointers i would greatly appreciate it.

 

[jonbills]

I'd check that the throttle butterflies are fully open at full throttle - specifically check they don't go past horizontal.
Next get a timing light and see what sort of advance you have from idle up to 4500 and on. about 35 degrees BTDC is the max and maybe 25 the min.

 

[Jimbo]

Cheers for the help Jon bills you were right to check the timing
Turns out the bloomin vac pipe had come off the dizzy!
I've just taken it out for a blast and seems to be ok.
Time will tell.