Carb Guys, Need Some Help

[bandt]

Got an AFR installed on my 72 340 Challenger.

Its a Proform 650 DP. The AFR's aren't to bad until I slow and come to a stop. The carb goes lean up to 18 even 22 a couple times if I can keep it running the idle will eventually pick up. It seems like it's the transition back from primary jets to the idle circuit. To compensate for it I have to turn up my idle screws to try and offset some of it. I can get it better, but the idle is rich like 12.9 - 13.1.

The exhaust always seems so toxic. Idle, on the gas off the gas. My AFR's really aren't that bad.

Any suggestions??

Thanks,
Brian

[Chryco Psycho]

I am not sure what you have access to but I would install a smaller bleed in the idle circuits ,  you can buy blanks in packs of 10 & use numbered drill bits to dial in the sizing . Idle is probably toxic due to cam dropping cylinders & loading the exhaust with raw fuel

[bandt]

Wouldn't smaller bleeds richen the idle circuit? How would that help?

Any other suggestions Neil? Air bleeds are out of my comfort zone but if it would help I would try it.

[cudabob496]

I've been playing with my 850 DP and a new AFR for the last two weeks.
Seems I can get the WOT at 12.5 pretty easy.
But the best I can do right now at idle and when cruising at 2500 to 3000 rpm
is around 13.0.

I'm not gonna mess with it much more, and the WOT reading is my main concern.
A little rich at the cruising lower rpms is not gonna be a big deal to me. Seems when
I try to lean out the lower rpm cruising stuff, my WOT goes up above 13.0.

[Chryco Psycho]

you are gpoing way lean as the throttle closes & compensating with idle screw so yes smaller bleeds will richen the idle , I though that was what was needed as the throttle closed ?

[bandt]

Oh I see. On that transition from primaries back to idle what exactly happens? I'm trying to get my head around what exactly is going on. Does the carb go right from primary jets to the idle circuit with no other transition of fuel?

Brian

[Chryco Psycho]

ok as the throttle blades close down the air flow drops to the point where it will no longer draw fuel from the boosters which is where it goes lean so raising the float level may help a little but as it closes down the fuel is drawn through the idle transfer slots , if the cam is lumpy it will have very low vacuum at idle & there is not enough fuel drawn in from the idle circuits so by reducing the bleed size the low vacuum will have more effect on pulling fuel in .
Kapiche

[bandt]

That helps, thanks.
I usually have a better chance of making the right changes if I understand how it works.