Response

Float levels: Float levels basically affect the point at which the crossover from idle to main metering occurs. It has essentially no affect on overall fuel metering. Way too high, and fuel will slobber into the venturis. Way too low, won't meter properly. Actual metering is controlled by the main jet, metering rods on some carbs, air correction jets, and emulsion tube calibrations. Only the mains are usually available replaceable. Engines that stumble at about 1500 rpms are usually victims of low float levels, as the crossover is too lean. The idle circuit only meters when the throttle plate is adjacent to the idle port/slot. Good ol' Bernoulli at work.

I rebuild and dial in carbs as a sideline. I've got vacuum gauges on my twin 302's w/Holleys to observe actual conditions. After decades of dialing carbs in, I've learned marine applications have so many variables it is dangerous to say one setting fits all. The printed settings are a great starting point, but don't assume they are perfect or even adequate.

Choke settings: Those bimetallic thermostats are notoriously inaccurate, whether electric or heat well heated. Be aware that many times there is a fast idle cam attached to the choke..the more closed the choke is, the higher the idle is. A COLD engine won't idle slowly..not enough velocity in the intake to keep the fuel vaporized.

Accelerator pump: Marine engines run relatively cold. As such, fuel vaporizes poorly in the intake system. The only way to get a decent shot is to make the pump fat. This is very important on carbs with secondaries, as they tend to bog. The amount of fuel momentarily injected is insignificant in the big picture on marine engines, as the throttle is not moved very often.

Frankly, I have little experience with AVS's. Like quadrajets, the secondaries are easily adjustable for opening point. I think quadrajets are great carbs, but limited by unavailability of tweaking parts. The tiny primaries are great for street applications, but are marginal for marine applications without opening the secondaries. I evaluate each carb and application on its' own merits or disadvantages, and proceed accordingly.

Enrichment circuits: I've yet to plug my Holleys power valve, but it doesn't open until 3" of vacuum. A holley power valve is good for 4-8 jet increments of enrichment. We agree these are relatively useless on marine applications.

Secondary opening: if your secondaries are open at cruise, it may be caused by other factors such as overpropped, restricted flame arrestor, lazy timing. If the secondaries open prematurely, a fringe detriment is as the manifold vacuum drops, the power valve/enrichment circuit opens. This causes a richer mixture than needed, which removes money from your wallet rapidly.

So, has anyone reading these threads learned anything? There's a test at the end of the week.................

Bill