back fire

[drivercar3]

Good Friday to all.
I put my rebuilt carburetors on my 67 roadster and I get a backfire through the back one. Can anyone help pinpoint the cause.
Thanks

[Gregs672000]

Lean condition. I'm not an SU expert, but check for dash pot oil and proper fuel nozzle to needle alignment and depth... air leak... anything that causes a lean condition.

[Gregs672000]

Confirm air flow/balance bewteen the carbs and good linkage operation.

[unklpat]

Make sure the feed line from the float bowl isn't kinked.

[Bwk2000]

The guys are right. As long as your floats are properly adjusted, dash pot oil is correct and needle valve seat is not clogged, valves are not totally out of adjustment, etc, it’s likely just a lean mixture setting. Turn the large mixture adjustment screw on the bottom of the back carb 1/4 turn clockwise (when looking down from the top). Drive it for a bit and see if the popping is eliminated. If not, repeat the procedure 1/4 turn at a time.
FYI: To avoid higher RPM carb popping due to a lean condition under load, it also helps to run a simple cold air hose/pipe directing fresh airflow from under the bumper to the drivers side engine compartment. Especially if you drive in a hot climate area. Your side-draft carbs will thank you.

[23yrRebuild]

I'm interested in a rebuild of my OEM R16 carbs....can I ask where or who rebuilt your carbs ? ...I don't know of any local shops that rebuild service SU's here in the Midwest. There were plenty who serviced the Volvo, SU equipped cars in the 60's thru 70's...