I thought I'd post this up here, since I've been looking for info like it everywhere on the Internet, and not found anything. To get to the point quickly - I've found that the accelerator pump jets need to be modified and re-drilled at an angle of about 10 degrees left or right, and about 15 down on my L6 engine & manifold (& I expect this to be true of all others, and probably weber DCO too). This is because the accelerator pump jet needs to land a squirt of fuel in the inlet port, and the shape of the L24 manifold prevents this with stock pump jets. I bet now I've posted this, loads of you old skool fellas will tell me this is common knowledge. Go on then . There's probably a thread on here about it somewhere too eh? The longer story: I've got an L24 with triple dellorto DHLA 45s with 36 mm chokes. It is 'over-choked' for sure, and I'd always put the stumble in the acceleration phase down to that (I mean giving it full throttle in any gear from below about 3k resulted in a complete loss of power!) However, when reassembling the carbs on the manifold last summer, I noticed that although I got a nice squirt out of the carbs on their own, as soon they're on the manifold there's no stream of fuel coming out. Looking at the manifold, it's obvious why - the runner curves left or right, AND down quite a bit, and the fuel stream hits the inside of the manifold and does no good at all. I did lots of googling for this at the time, but found nothing and gave up, assuming that in a running engine, perhaps the airflow would help the fuel into the engine. After all, the Internet would surely have highlighted such a glaring design mismatch. So I dropped it. a couple of months ago, I got round to installing an AFR gauge. It was quite revealing - it confirmed that when I open the throttle fast from low revs, there's no fuel, just air. so I decided to do something about it - I've now redrilled the jets and the squirt comes cleanly out the other side of the manifold and the stumble is gone in many cases. It's much better accelerating up through the gears. I've still got more to do - I think with my large chokes I need to make the squirt duration last much longer to be able to snap the throttle open in 4th at 40 mph- currently it's less than 1 sec, and it probably needs to be twice as long, but I hope that's just a matter of finding the right spring combinations on the pump rod and diaphragm. Much more fun than all this talk of 500 bhp hybridz eh?