Ask Away! with Jeff Smith--Carburetor Conversions and Vacuum Advance Redux

Jeff Smith tackles a couple of really good questions this month. Well, it's more like one question--how to convert a draw-through supercharger carburetor to a blow-through design--and a refresher course on the the importance of vacuum advance for ignition timing. Let's get to it.

Converting a Draw-Though Blower Carburetor to a Blow-Through Design
N.B. from Sweden has a nearly new, 850 cfm Mighty Demon carburetor set up for draw-through type supercharger (much like a traditional Roots blower) that he wants to convert to a blow-through design for a centrifugal supercharger system.

The good news for N.B. is that modifying the carburetor isn't that difficult--a simple change from hollow brass floats to nitrophyl floats that won't collapse when boost pressure is forced through the carburetor.

But the real fun begins with tuning the carburetor for part-throttle operation. Jeff explains what to do--and why you're doing it.

Vacuum Advance and Part-Throttle Operation, Explained (Again)
Back in 2015, Jeff got a question on ignition timing that started a very, er, lively debate on timing and part-throttle operation. It was lively enough that Jeff has done another column to help clear up misconceptions on ignition timing and how vacuum advance is important for part-throttle operation. It's worth a careful read--maybe even a couple reads.