weber hottroding (problems)
 

So after having my car out of comission for most of the summer after a carb swap and rebuild, my mechanic tells me today that the idle transition ports have been modified from a port to a slot. Anybody have experience with weber mod's or know a weber hotrod guru. We already spoke with richard at pmo.
Thanks,
Phil

Are these 40IDA carbs? What is the problem you are having with tuning them? Too rich on transition? Stumbling off idle w/ black smoke? If the transition ports were slotted out, that probably means someone was trying to richen the mixture on small, partial throttle openings, before there is enough signal to get the main jet circuit to kick in. Unfortunately, I don't think you can easily repair the carb body after these ports are altered like that. Usually, people just drill them a little larger instead of slotting.

The transition circuit is fed from the idle jets, I believe, so you could try going as small as possible on the idle jets if you are too rich on transition. That may slow down the flow of fuel to the transition ports when the butterfly uncovers the slots. You may also be able to build up a little ridge out of solder on the back side of the butterfly to keep the ports covered longer or something. That may let the engine build up more revs and airflow before the extra fuel is dumped in from the transition circuit as the butterfly opens. Lessening the accelerator pump volume may help, too.

Good luck,
TT

you're screwed.

John,
I think you've nailed it. These are 46 IDA on a 3.5 L rsr motor, ran great on old carbs runs like s#@* on new carbs, ain't rocket science, well maybe a little.
Phil