Secondary lean tip in?

[toms73novass]

I know not the standard setup up, but....
I have 140 blow through turbo engine. Finally getting back to logging data.

What I am seeing is that when the secondaries open I get a lean spike in the AFR's. I do not feel it but I would like to eliminate it.

I did NOT have the accelerator pump cups in my secondaries (which are 62-63 bases), after seeing the lean tip in I put the cups in. It may have helped some but the peak is still there.

Ideas?

Top line is the AFR, middle RPM, bottom (blue) boost.

[66vairguy]

I'm assuming you are blowing boost pressure through stock carburetors. Excuse me if you thought of this ------ back in the days of blow through carburetor turbocharging one issue was the fuel float bowls were pressurized (as they should be to make the cluster work) which in effect was like lowering the fuel pressure into the carburetors and would cause a lean condition. My favorite fix was Rolls Royce who put the carburetor and fuel pressure regulator in a BIG BOX that surrounded the carburetor and pressure regulator. It looked awkward, but worked like a charm.

Now systems use a computer, or fuel pressure regulator with an input to the boosted air pressure to adjust fuel pressure as boost (and float bowl air pressure) increase.

I'll have to say that after decades of engineers dealing with turbocharging via carburetors, going to fuel injection and computers was a huge improvement in engine performance, including just cruising around town.

[vairmech]

Increase your pump shot on the secondary carb. Easy adjustment by bending the rod. Where the marks are supposed to line up put the line a thickness or two further ahead. 1/32"-1/16"

[toms73novass]

I'm assuming you are blowing boost pressure through stock carburetors.

The carbs have been heavily modified to handle boost and I do have a variable rate fuel pressure regulator that increases pressure as boost increases. I agree modern setup with FI can overcome these issues easily. The car runs great actually don't notice the tip in just on the logs.

[toms73novass]

Increase your pump shot on the secondary carb. Easy adjustment by bending the rod. Where the marks are supposed to line up put the line a thickness or two further ahead. 1/32"-1/16"

OK will do. Thanks

[Frank DuVal]

Studebaker also put the carb in a box with the supercharged engines.

[66vairguy]

First - I goofed as it was a Bentley that used the box, not RR. Back then they were basically the same car.

Second - I've noticed that these old carburetor accelerator pump bores are getting worn and sometimes you don't get a shot of fuel until the cup moves some. Also there is a check ball in the bottom of the plunger that can cause issues with a poor "squirt".

[toms73novass]

It seems to be working well.