Is this carburetor tuned for race gas?
Race Fuel is specially formulated with different characteristics based on racing conditions. The carburetor itself should have no problem running a race fuel regardless of the octane, but octane rating is not an indication of added performance, just the ability to reduce detention. However, oxygenated fuels or containing accelerants may need additional tuning due to changes in the air-fuel ratio. It's best to contact your race fuel provider to ensure the chemistry works for your application and if there is any need for tuning adjustments.
Can this carburetor run or be tuned for E85 or other ethanol blends?
We don't recommend ethanol for any carburetor used for small engine engines. Ethanol percentages are seasonal and regional, and you may experience significant changes in performance and struggle to stay consistent with carburetor tuning. Ethanol also draws a lot of moisture. You may have a higher water content from pump stations, or if the fuel is bought from a race shop or fuel blender that isn't properly stored, it will be contaminated with water over time, which hurts performance. Since lead has been removed from many of our polymers used for o-rings, inlet needles, etc, ethanol can cause them to shrink, grow or disintegrate over time. If possible, use pure gasoline.
What is the barb fitting for on the intake?
The fitting is to get a vacuum signal for external fuel pumps. The intake is the recommended place to get your pulse rather than the crankcase or valve cover.
Is the carburetor for gravity fed or by a fuel pump?
Both. If you are using a stock fuel tank, the fuel tank outlet needs to be above the fuel inlet of the carburetor. In most cases, it is not, so the tank needs to be raised. When relocating the tank or using a remote tank for gravity feed, keep the tank within a couple of feet. If the tank is too high, it may pressure the fuel enough to force the inlet valve open, causing a rich condition. When using a fuel pump, use a round-style vacuum pump. Do not use electric fuel pumps, or if using some dual feed pump will have too much fuel pressure and will force the inlet valve open, causing a rich condition. The best pump to use is the Walbro FPC-1.
How does this carburetor compare to Tillotson or Diaphragm Carburetors?
Properly tuned Tillotsons designed for your application have performance and tuning advantages. However, Tillotsons or diaphragm carburetors on 4-cycle engines are not made to idle and will be finicky if not used properly. Unless you are kart racing(oval or sprint), we normally recommend using a bowl carburetor.