Greetings Gareth and
1: Try it briefly without the air filter fitted
2:This doesnt make sense
"in 1st and 2nd gear the power valve will kick in around 8K RPM, (2nd splutters unless i let off the throttle a tad)
3rd 4th 5th and 6th all have now low end power ( expected) but wont reach 8k rpm, and wont take off,
top speed reached is about 50mph on a flat, it has no yvps control servo, and i have no idea what the problem could be, i took the carb off and cleaned, all seemed fine,"
I assume the power valve will never kick in because it's not functional...you mean it will take off in 1st and 2nd (Hit a power band) ?