holley 750 mechanical

« **on:** November 27, 2009, 10:24:14 AM »

i need some help guys before i go run my boat for the first time with the new engine i built. 21 centurion cruiser with a 30 over 454 10.68 to 1 compression big oval port heads thru transom exhaust 550 lift hyd. cam duel plane intake manifold and a marine 750 holley carb.i bought the carb rebuilt from a guy it has 72 primary and 82 secondary. the primary seems a little small to me. if anybody has a simillar set up to this please ring in,shane

« **Reply #1 on:** November 27, 2009, 10:32:14 AM »

72 seems a little small to me as well....the carb in general seems a little small to me for the motor...my 429 ford tunnel ram intake i run an 800 double pumper on it and i am at 76 primaries and 80 secondaries...one good way to test this is run it on the water...you will not get the results needed on the trailer because you need a load on the motor then do a spark plug reading on it...like alot of people say on here is it is almost impossible to over-carb a jetboat motor they will take almost anything you throw at them...im actually looking at going up a carb size or two, but that is just me...do you by chance have a jet kit? what i did was took a jet kit with me to the lake and ran the piss out of the boat and kept doing plug readings till i got the plugs where i liked them and liked how the boat was running

« **Reply #2 on:** November 27, 2009, 11:24:04 AM »

Quote from: 4EST PERFORMANCE on November 27, 2009, 10:24:14 AM

i need some help guys before i go run my boat for the first time with the new engine i built. 21 centurion cruiser with a 30 over 454 10.68 to 1 compression big oval port heads thru transom exhaust 550 lift hyd. cam duel plane intake manifold and a marine 750 holley carb.i bought the carb rebuilt from a guy it has 72 primary and 82 secondary. the primary seems a little small to me. if anybody has a simillar set up to this please ring in,shane

What is the list number on your carb? You have to be cautious just arbitrarily changing jets, if you have the list number I will look up the factory settings and let you know what's what. Sometimes jet sizes will be odd, normally on a square 850 we see 76/76 to 80/80, there are a lot ov variables.

Also I'm thinking that a 750 is pretty close for a thru transomed, oval port dealio.

GT

« **Reply #3 on:** November 27, 2009, 11:31:00 AM »

The factory Holley jetting it a good place to start.

70pri 80sec is found in several of the 750s.

72/82 Sounds like a good place to start.

4EST PERFORMANCE

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