Running issue.

Hi I hope someone can help. So I moved to New Zealand nearly a year ago and shipped my cabby and all has been good. But the last few months it has been not quite right. When I start its all good and runs as it should but as its gets warmer and if I am say driving along at 2000 rpm it will kind of  judder this is like a slight misfire but it's not missing. I have checked the timing and its bang on its had new leads dizzy rotor etc and I even changed the o ring on the idle screw as I thought maybe it was sucking air once hot. Just to note if i am accelerating up through the gears there is no issue at all and goes like a rocket as it should, it is only when I am cruzing around.
Any ideas as this starting to do my head in.
Many thanks in advance.
Martin. 

Did you have the carb rejetted for the different atmospheric conditions?

Ignition timing done with a strobe?

Hi jelly belly I have a good quality strobe and set it 6 deg btdc all the timing marks align so don't feel it could be this.

Hi jusdubbin its k jet fuel injection so no carb it's got to be something real silly .

NGK plugs?

www.cabby-info.com  I would suspect the duty cycle.
possibly fuel restriction in the tank, and or fuel filter.

Does it happen more going up hill or down hill?  that would be a tank thing….

Is there a loud whine from the right side rear wheel arch when this is happening?  

If the fuel pump either gets noiser or quieter have a look at the lift pump in the fuel tank as it may be getting blocked or the lift pump is on its way out.
Also have a look at your fuel filler neck, shine a torch down it and look for any rusty holes.

Hi mark, I should have put on my post my car has had a full restoration which included a new filler neck Bosch fuel pump and a new lifter pump the tank was cleaned. I have a feeling it may be to do with the co2 level but I need to get it on a analyser.
Many thanks.
Martin.

Hi all thanks for your help so after a little more diagnostics it seems the car was running a little lean.  Many thanks.
Martin.