28/36 DHSA Backfires While Accelerating?

[TheBrokeEnthusiast]

Hello,
I am a new member to the forum and still a Fiat newb so if there is anything completely obvious I am missing (Either on the forum or my knowledge of car stuff) I would appreciate any correction!

I own a 1971 Spider with a 28/36 DHSA carb that I am trying to tune, I have a OEM air/fuel ratio sensor installed to help me out. I use the air/fuel mixture screw along with the idle speed screw primarily (I don't know squat about carburetors, and am not sure if I need to be adjusting something else or if something is wrong?).

Whenever I go to accelerate quickly the A/F gauge tops out on the lean side (It reads in like the 20s!) and the engine sputters and backfires through the carb. If I accelerate slowly the backfiring/sputtering is eliminated (although it hesitates a bit), but as the revs increase, the gauge leans out progressively (up to like 17-18).

I have messed around with air jets and the stop screw on the diaphragm thing, but as mentioned above I am completely newbish.

If anyone has anything to contribute I would be eternally indebted!

Thanks!

[rebar1111]

Backfire through the carb would indicate a lean mixture as confirmed by the a/f meter. If at steady speed, on a properly jetted carb, it would indicate plugged jet passages. If on acceleration I would look to the acceleration pump circuit. .

[TheBrokeEnthusiast]

Thanks for the response!

I have been looking at the accelerator pump, but haven't seen any way to make adjustments?
Is there anything I should look for? I believe I replaced the accelerator pump diaphragm when I replaced all the gaskets (not exactly sure, it was about a year ago.).

Thanks again!

[rebar1111]

Some DHSA carbs (32 DHSA} have a second pivot pin/hole in the cover for a different pump stroke length. Maybe you should recheck the float level\ first.

[TheBrokeEnthusiast]

Thanks for responding.

After pulling the carb, taking the pump diaphragm off, and soaking it overnight, I tried blowing compressed air through the inlet/outlets then reinstalled. It wasn't any better.

I messed with the pump while the engine was running with no change in engine speed/smoothness so I knew it had to be the accelerator pump, I pulled the top of the carburetor and tried to find where the accelerator channels were located. I was able to blow bubbles through the primary pump fuel inlet so I assumed there was a clog in the outlet somewhere, I pulled the nozzle that is on top of the primary barrel off and using compressed air, discovered that it was the nozzle for the accelerator pump, it was blocked!

After cleaning it using carb cleaner and a wire along with compressed air, I reassembled the carburetor and it is running beautifully!
It might need some minor adjustments, but the backfiring and hesitating is gone!

Thank you rebar1111 for directing me to the accelerator pump!