Please give me information on power valves.
The power valve’s function is to supply extra fuel for wide open throttle and other high load conditions. When manifold vacuum falls below the vacuum level stamped on the power valve, the power valve opens and enriches the main circuit by about six to ten jet sizes. The power valve number should be at least 1.5 to 2 in./hg vacuum under engine idle vacuum. If an engine produces 8-9 in./hg vacuum, a 6.5 power valve would be a good first selection. Using a power valve with a rating lower than this will delay the enrichment and can cause hesitation. However, on an oval track car with restricted carburetor rules, using a lower rated power valve can sometimes help performance coming off corners. Any drag race carburetor with a secondary power valve must be turned sideways to avoid fuel starvation. This is because the power valve is higher than the jets and is the first to be uncovered as fuel is pushed to the rear of the float bowl.