Don't waste your time or cash with anything smaller than an 850, we sell the blueprinted(by us) chineese clone Holley HP type carbs new for $459.95 set up specifically for each engine. The stock Q-jet is either about 735 or 790 cfm depending on which model you have, don't go smaller. You can install a 950 on your jet boat with no ill consequences because the jet doesn't load the engine much at all below 2500 rpm. With an 850 or HP series 900+ the primary bores flow over twice as much as the Q-jet ones do, and that allows you to cruise and drive faster on the front two barrels. Your Q-jet with its small front barrels won't even stay on plane on just the primary barrels. Sooooo you have the front small ones most of the way open, and the large secondaries about half way open, and that causes distributition problems, uneven cylinder loading, and a higher fuel consumption. Those carbs were designed for light throttle cruise in a car or truck on only the front 2 barrels at up to about 70/75 mph. The boat takes much more hp to even stay on plane, so all 4 barrels will always be open. A Weiand Stealth dual plane, Performer RPM air gap, or an import copy of them will provide more horsepower, higher top speed and better fuel economy than the junk Q-jet intake. The early cast iron high rise Chevy intake makes good HP, but you will still run on all 4 barrels all of the time, so leave that one to the collector/restorers. Most jet boats won't run at any reasonable cruise speed with a 750, so all 4 barrels will be open on that too and thats why I recomend the 850 or bigger HP carbs. The bigger carb will absolutely pay for itself in fuel savings. I modify all of my carbs linkages on my boats to allow more primary opening before the secondaries "kick in" to allow even higher cruise speeds on the front two barrels. Don't even think of a vacuum secondary Holley either, its too small, and their design allows the secondaries to open to the same primary opening amount under load, again, all 4 barrels are open to some extent during cruise. Don't forget to have the distributor curve checked or modified for the new setup, again, a higher top speed and lower fuel consumption are the results, and its cheap! TIMINATOR
