Hesitation When Accelerating

[eschaider]

Anytime you are experiencing a throttle response issue in a 7 liter or thereabouts sized engine with a single four barrel carburetor in the mid to high 700 cfm range your problem is almost never inadequate accelerator pump shot size. The problem is almost always low speed or tip in fueling delivery through the powervalve fuel enrichment circuit.

In the old days (middle to late 60's) before low vacuum point (2.5 or 3.5) power valves were readily available the fix was to block the power valve fuel delivery circuit with a powervalve plug and go to the largest accelerator pump available (at the time that was one step down from the 50cc REO pump) and start adjusting accelerator pump nozzles to produce the required fuel flow during the off idle fueling transition period until the vacuum signal at the boosters was adequate to pull the fuel needed through the main jets.

The only thing different today is the low vacuum powervalves are widely available and the large capacity 50cc REO accelerator pump diagphrams are too. Both approaches work. The correct powervalve and powervalve metering is the more flexible solution to the problem.

Your chosen powervalve should open at ½ your idle vacuum or lower. If you idle at 12 inches of vacuum or higher you can use a 6.5 power valve. The 6.5 means it opens at 6.5 inches of vacuum.

If your idle vacuum is 7 to 12 inches of vacuum then you need a a 6.5 powervalve at the upper end of that range and a 3.5 powervalve at the lower end of the range. If you idle vacuum is in the less than 6 inches category, you only have two choices — the 2.5 and 3.5 inch opening power valves.


Ed