Hot Rods Rejetting Dual Stromberg 97s

My 29 roadster has two 97s on an edelbrock slingshot manifold on an 8BA flathead
Cam is mild but not stock, minor lope
If I let let it idle for any amount of time it would load up the plugs

I went to a hotter plugs NGK B-4L and this helped with the plugs loading up
but
the plugs are still showing rich with carbon on the plugs

the engine runs very well, that being said I would like to rejet and return to standard heat range plugs NGK B-6L.
I am currently cleaning and resealing both carbs, what I found is the primary carb has .048 jets and secondary has .045 jets.
Being relatively new to the flathead and Stromberg carbs is it normal to have two different size jets and do I reduce each carb by one size or just the primary?

the way the linkage is setup the secondary doesn’t kick till about 1/4 throttle
Dave

 

I have a 1929 coupe, 276 59A flathead, two Stromberg 97's from England, Eddie Meyer hi rise intake and running an Isky 400 Jr. cam. I went through the jetting process this past summer. Engine has the NGKB6L plugs as well and was running way too rich. The England 97 carbs come with .045 jets right out of the box. Way too rich you could smell gas and slight popping or backfiring out the exhaust. Replaced the .045 jets with .043 jets . Better but still rich. Replaced the .043 jets with .041 jets. Much better but still a little bit rich. Finally took out the .041 jets and installed .039 jets. Engine runs perfect now. Gas smell is gone and backfiring has stopped.

I found fuel pressure made a big difference too. I'm running 1.5 pounds fuel pressure. I had the engine at 2.5 pounds fuel pressure. Too much pressure. At 1.5 pounds it is just right.

All I can suggest is getting a few additional sets of jets and keep lowering them until you have found the sweet spot.

 

I’d change to straight linkage for a dual carb setup. Jets should be the same size.
Use a carb synchronizer to allow both carbs pull vacuum exactly.
Unhook your linkage totally. Set each carb individually at idle to a perfect vacuum.
Reinstall your linkage and adjust the linkage so it fits your carb throttle without moving it one slight bit. After both carbs pull exact vacuum at idle recheck with synchronizer.

 

So both carbs should have the same size jets
That’s what I expected to see
This car has no choke and starts very easily down to about 60 f.
I plan on adding a choke.

maybe the thing to do is start at .044 in both carbs and go from there

 

Any other comments would be appreciated

 

I had run dual 97s on my flathead with high rise Thickstun manifold. Straight linkage, did run very rich, lowered the floats a bit, then used smaller mainjets to get mixture correct on wide open throttle but the tickover needed modified idle jets as well. As none were available I soldered them closed and redrilled smaller. Now the plugs stayed clean, no black soot anymore.

 

8ba, with Offy 2 carb, and mild cam. Running .043 currently. Thinking of going down a size.