Hey, already tried the above ^ have even tests the plugs under compression. Unsure when they where last changed as it would have been the previous owner but they look fine.

So with a different plug in there its still the same?.compression test would be next unless you check carbs..try float valves..good luck

Agree - I'd check the float heights first and then maybe the valve clearances on that cylinder.

Yes i did change the plugs over and is still the same. Just done a compression test: 170 psi on all cylinders except the front left which was 150, which just happens to be the cylinder that's having the issue!

Like you said Luke, valve clearances next on the list

Ah,do valves then and you should be ok hopefully...probably they're tight and not closing properly...