What's the purpose of the metering plates I see for Holleys?

Also on the vac. secondary carbs.....for a '71 Chevelle should I go with the heaviest spring or the lightest?

As far as spring are conserned I wouldn't go with the lighest because it will most likely cause a bad bog. If you have the stiffest in now I would step it down one or two. It all depends on your setup. Most 350's will run well with medium plain sring. It's right in the middle and gives a little punch. AS far as metering block are concerned, All standard holley "VS" carbs excluding street avengers have a metering plate inside the fuel bowl. That why the back is not as long as the front. This acts as a constant jet setting, it can not be changed, don't try and drill it. The metering blocks they sell seperately allow you to change the jets for the secondary venturis. Basically turning it into a 4150 carb with vacuum secondaries. This comes in handy cause when I dyno'd my car at low rpm's it was way rich and the top end it was way lean. This allows you to infinitely tune and make some power. Also If you have a duel fuel inlet holley you'll need to buy a fuel line for a 4150 carb, becuase the block makes its length longer. If you have a single fuel hookup you don't have to worry.GL graemlins/thumbsup.gif