Anyone know at what RPM the boosters should come on? I free rev the engine as high as 3300rpm and hold it there, the boosters are not on and I thought they would be as I found my 4150/850 the boosters come on at 2800rpm on my 408.

I know relatively nothing about carbs...... but I’m pretty sure it has nothing to do with RPM, it has to do with vacuum signal. Free-revving a motor is not going to pull a much vacuum. Thus, boosters may not be drawing much fuel.

We need Dom......

Booster start point is controlled by the signal generated by the booster, the amount of emulsion/kill bleed above float level, float level, and the main air bleed size. The same carb on two different engines may start booster flow at different RPM's as the pressure difference may not be the same at the same RPM.

ok. kill .028 Emul .028 Mab .028 with float at mid window. I was able to check this on a 4150 on my 408 and boosters started up at 2800rpm steady free reving . I usually cruise at 3000rpm and thought I was on the booster at that,but not so. Looks like i'm cruising on the Mixture screws and T -Slots instead. Just trying to figure and tune all the circuits and want to fully understand each one. Tune is really coming around now and after a long cruise yesterday this 511 has put a big smile on my face. In a nut shell, it just wanted more fuel.

Did you buy and install an O2 sensor?

If you did, do you mind posting what the O2 said before and after you added fuel??

Thanks.

Bigger t slots but smaller pcvr and added 5* timing. Was 12.5 before and after last tune. 45* air temp. I think there is more tuning left and i have a few more ideas. Dom has been a big help in my learning curve as well.1st

Most of the previous tunes were 13 on an avg. And i tried different timing settings which made nil changes in performance. It seems all these circuits have to be well tuned to all work in unison, even w.o.t and the way it comes up on the vert clean and fast.

Thank you.

As Mark stated, different carb and motor combos change the signal strength and therefore will pull fuel sooner or later depending on the additional holes/bleeds in play. I know a 1050 Dommy on my car is way more sensitive to idle and hi bleeds compared to the 1150's I've tested which are more stable across the board w/similar bleeds and settings and the t-slot really helps a bunch in low rpm steady cruise before booster start up. BLP says they use a certain size in just about everything both 4150's and Dommys but my testing proves bigger as in the .070's I tested recently giving me 9.9-10.5 afr's compared to the .055's that produced steady 12.8-13.5's. I now am trying .059's and it's 11.2-12.0 so this alone on a street driven car has a Hugh influence. The pressure differential between emulsion holes and the bleed pack and the amount and sizes of given bleeds affects booster start up and yes, the boosters will be active w/out being under load. I'm still learning a bunch of stuff and sometimes a change that SHOULD do this or that, does not then the fun begins............I did a Dommy for someone on here w/.600 id boosters for a Hemi and it just could not pull enuff fuel no matter what bleeds or jets were used on the dyno and street. He sent it back for .0500 id boosters and an external linkage kit and boom, lots of controllable fuel now..........fun stuff.............