So I bolted on the DCOE weber 6 months ago. When it's warm it runs well, but when it's cold it farts and splutters a bit. I need to pump the gas constantly to get it to start, and it sort of chugs a bit before the motors spins freely. The backfiring happens when I push the gas pedal to quickly, it seems to lag a bit.

Is this to do with my air fuel mixture?? The K&N filter i'm using is flithy and needs a good clean, could that be part of the problem? I ask that because it seems as though the problem is getting worse over time.
Thanks

could be a few things.. What heat range spark plugs have you got? they can make the plugs fuel up a but if they are the wrong heat range for cold starts. thats one idea, another could be that you have the mixture screw not open enough, the idle might need speeding up, or the idle jets might be to small.. just a few ideas..

When I first got the car running, I used a hotter plug and it ran poorly so I changed back to standard. The idle and throttle response is perfect when warm. Could it be running a bit lean?

The specs on my carb are as follows

65 starter, 35 pump, 45F9 idle, 40ex, 200 air, 130 main, 32 choke

If it's getting worse try giving the carby a good shot with carby cleaner, especially the air correctors. Readjust the idle screws and clean the filter. Was it backfiring/ sneezing out the carby?

For what its worth make sure there is actually a acel pump bleed valve in the bottom of the main fuel well. It is possible to get a carb to run without these bit but they will give the symptoms you are describing when left out of the rebuild.

Also for what its worth, a one 40 with a 32 mm choke is BARELY adequate for a 1600 (usually fitted to 998 / 1000 cc BL A series).

Cheers

Shaun B