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Old 09-03-2004, 12:30 PM
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383 Marine project. QJet rejet?

Well
I got the stroker running and in the boat, and it actually runs quite well! No dead spots, no idle problems. I am only able to get 4800 RPM out of it WOT, as compared to 4200 with the same prop with the old 260HP 350. (9.8 compression Sportsman II heads, comp XM-262h -12 cam) I do however have way more torque, all the way up to 4800. this baby will go from any RPM to 4800 RPM pretty quickly! I am running the original QJet marine carb, and an original cast iron stock intake, which seem to run fine, but should I put bigger jets and/or metering rods in that carb? I know where the secondary metering rods are, and happened to have a smaller pair of those laying around that I have put in, but what about the primary rods and jets? Can they be changed and should I even mess around with that? I am thinking that an edelbrock performer type intake and a rejet would probably put me at or above 5000 rpm. Any thoughts? I am at about 14 degrees initial timing right now, and don't currently have a way to measure totol timing. I will try to get some timing tape to see how much timing advance my Mercruiser distributer throws at it. The thing that made me think about the carb jetting, is that the mercruiser tag on the carb says 260/270 which would refer to the 260 and 270HP motors available in those years. This is a 1984 Qjet pn 17080561 which decoded, just says it is from a manual transmission Chevy truck. The date code is 3273, which means it was made in the 327th day of 83. How do I tell how many CFM's it is. Are all Qjets 750's? I know some of the big blocks and Caddies had bigger ones, but I assume this is a 750 right?

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Old 09-03-2004, 01:24 PM
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It's a 750. Did you take a look at the plugs? the primaries are changable, there are umpteen combo's, the performer rpm will help also, if your pulling that hard you should be able to up the pitch more for top end, but watch the outdrive if it's an alpha, they're only rated to 300 hp! Check the knowledge base or pick up a haynes rochester manual, there are plenty of simple mod's to do that will wake that Q-jet up!

Last edited by Wrencher; 09-03-2004 at 02:24 PM.
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Old 09-03-2004, 02:53 PM
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Pull the intake and carb and get an edelbrock air gap intake and a 750 Edelbrock carb and don't look back. Also the merc distriburtor has 20 degrees. So don't go anymore. You may want to back it up to 10 or 12 initial. Beware of your drive if it is an alpha, to many hard starts and she will blow the top gears. If you don't have one, get a drive shower for the lower unit. It will prolong the drives life.


Chris
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Old 09-05-2004, 09:29 AM
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I think I may just leave the intake and carb alone. I was out last night and with 4 adults and 2 kids, I had it up to 5100RPM (briefly, don't want to blow the outdrive). Not sure why the jump from 4800 last time I had it out, by myself I might add, but it may be getting broke in, or it may have been from having more weight in the front of the boat last night, which is where 1 of the adults and the 2 kids were riding. Either way, I really don't think I need any more top end. I may switch to a 23 pitch prop, but that will probably make it tough to get out of the hole when the boat is loaded down. Anyway, I would say going from 4200RPM max with the 21 pitch prop and the old motor, to 5100rpm with the same prop with the stroker is pretty damn good! I think I'll just leave well enough alone before I blow the outdrive (again). I have replaced/rebuilt the upper unit 2 times in the last year due to an oil leak in the lower unit that I didn't discover until the second outage! I think I will probably get a drive shower as well.
Thanks guys!
Tom
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