So what carbs do you run on your 1600/1641 engines and what is the biggest carb you can fit to these?
If you go too large the engine will not move enough air to develop vacuum to keep the carb working properly at full throttle. Unless you uprate components to rev well into normal redline territory. This shows up as flat spots combined with a tendency to go well past the redline in low gear. Also the cooling cant keep up as well as you try to cruise at 67 mph with a roofrack and a poptop.. The 32/36 progressive on my 1641 bus is not a large carburettor but the total venturi area is about twice the original 34pict-3. Result is that it took a lot of tuning (as well as preheater reimplementation because its centremounted )to get rid of flatspot on wide open throttle and my peak reading rev counter shows 5500 (60 in 3rd) to 5700 rpm on days when I drive with too much enthusiasm and with the stereo up too high. Top speed is still about the same but the acceleration in first and second has improved. Fitting a freer flowing exhaust will also help. The JK stainless single quiet pack and the empi twin rust pack I had before both help the flow.
The EMPI progressive has a design problem that will cause a bit of a flat spot when flooring the throttle, in that it only has an accelerator pump on the primary 32 mm inlet and none on the secondary. If you floor it and open both butterflies at the same time, the single pump is not enough to stop a momentary leaning of the mixture, leading to a flat spot. When I had mine set up, the carb guy put a genuine Weber accelerator pump on and that did give a better 'squirt' than the EMPI one, so this is worth a try as well. The other reason for flat spotting on this carb is the length of the inlet manifolds and you can't do anything about that.
you can adjust the volume and timing on the accl pump jet...or fit one of these but a larger idle jet and no air leaks will normally reduce flat spot on 32/36 (so I've been told) Maybe use a little less stomp when you drive it?
