Series 3 2.6 petrol, standing still fine, under load cuts out

hi folks, looking for some of your wisdom... my s3 109 2.6p 6cyl has been standing for about 8 months. Wouldn't start initially but I found water in the tank, drained all out, good petrol back in and now running well, sort of... The problem I have is that while the engine runs idle sitting stationary, as soon as I get into first, then begin to drive off, the revs die, engine cuts out and I say bad words... I've tried leaving the choke on full, engine revs like a sports bike, I get about 3 meters before it cuts out in this case. If the engine is up to temperature and the choke is fully off, ticking over ok standing still, it won't stay running as soon as it begins to move forward unless I rev the living daylights out of it... It has a stromberg 175CD carb which I've tried various settings on the mixture screw on the bottom but no luck yet.
Any pointers out there or something obvious I'm missing???
thanks in advance
Pete

The brakes ain't binding are they? Have you done a compression test? Does the oil look ok, no sign of mayonnaise.

Col

Check the points, and little coil, distributor advance retard could be stuck through standing

Did you clean the float bowl out (on the carburetter)? May be water in that too.

Try it with the air filter hose disconnected in case it is collapsing and starving engine of air.

needs a service mate

Fuel lift pump clogged/not working right.

thanks for the details guys, some good ones in there for me to work through!
Col, No sign of mayo on the oil cap, I replaced the head gasket 14 months back, hasn't travelled many miles since, but all looks ok. The brakes are ok, all wheels turning jacked up off the ground, and I've pushed it along the driveway without it complaining. I'll get a compression test sorted shortly.
Freelance, I'm suspicious of the advance retard, it fell out a few times way back, I have it well anchored to the post inside the distributor but it looks a bit limp, it does move back and forth when the choke is moved around, but it doesn't look 100%... the points are ok, I'll have to investigate the coil a bit further though.
Boguing, good call, I didnt drop the float chamber out on the carb, will try that today.
Blackburn, I tried without the air filter on, unfortunately the same thing happens, same thought as you about starving of air, but I think its a fuel starvation but happy to try anything!
tottot, I've a new pump to try, the current one seems to be pumping ok, and plenty of fuel is getting through to the carb, but agree, it could just be weaker than it needs to be.
Cheers fellas, back to the motor between the showers!

I have a transparent fuel filter on mine just before the carb, it ideal for seeing fuel flow.

Col

Duff coil

quick update on this one, the winner is - boguing !
the carb float bowl was gunged up with a mix of water, petrol and a congealed jelly like substance (no sure what or how...), all now cleared out and the landy going like a dream again! thanks for all the help!