engine/ Carb Gurus. 502 crate motor carb choice?

[JayZ]

Hey guys,

The carb off my OMC 7.4 330 H.P. motor seems to not be to happy. Rather than a tear down and rebuild I'm thinking a new carb may be in order.

Anyone have suggestions on carb choice size, jetting etc. to get me started. As mentioned int he subject line it is a crate motor (marine) 502. ...no cam etc.

Thanks,

Jay

[duckhunter]

I would guess that a 1410 Edelbrock marine carb @ 750cfm would be pretty close right out of the box. Is it a spread bore or square bore flange on the intake?

[JayZ]

no idea if it is spread or square bore. ...not even sure the difference really.

It is an edlebrock air gap intake that much I know.

I can tell you that I want to be able to idle this thing real low just in case I have issues with the shift assist module on the OMC boat.

I like my stuff to run well and have typically been a fan of not over -carbing motors but most of my experience is with triple down draft webers not four barrels.

Thanks again,

Jay

[Conquistador_del_mar]

http://www.jegs.com/i/Edelbrock/350/1410/10002/-1

[duckhunter]

Air gap intake will be square bore. That's a good thing - gives you more options. Spread bore means the secondary holes are larger than the primaries, ie on a Quadrajet.

As far as "plug and play" goes, it's hard to beat Edelbrock, and if you decide to tune that's fairly straightforward as well. Tuning the idle is a matter of adjusting two screws on the front of the carb for mixture and the idle speed screw on the throttle arm itself. Super easy.

The Edelbrock website has the instructions for their carbs online, well worth the read as they are pretty well-written.

[BUIZILLA]

a 7.4/330 is not a 502....

[duckhunter]

a 7.4/330 is not a 502....

My understanding is that he is swapping parts from his old 454 over to a new crate 502, but not positive.

[joseph m. hahnl]

You always go with the spread bore manifold it's Bigger and a square bore carb will fit

[Pat McPherson]

My 502 crate engine has a 750 Edelbrock on top. I've been told she may spin a few more rpm with a 800 or 850 Holley but those cost about twice.

[JayZ]

a 7.4/330 is not a 502....

No it isn't but the 8.2/415-ish crate motor that I installed is a 502

[smokediver]

The Holley will make more horsepower and once u get it set up will last a long time. The initial investment will pay off. The air gap manifold and Holley carb combo is really tough to beat.

[Ghost]

I'm curious roughly what HP/RPM the crate motor was intended to make.

[VetteLT193]

What's everyone's feeling on mechanical Vs. vac. secondaries? I had a Barry Grant mighty marine demon on the minx and loved it. No choke to deal with. pump the throttle a couple times, turn the key, fired right up. With the "idle ease adjustment" it was a snap to install and ran great through the whole RPM range.

In cars the vac. secondary probably makes more of an efficiency difference because boats are always running under so much load anyway. You can also figure out exactly where the secondary will start to open on the throttle for cruising purposes (get the boat on plane then back it down to where you know the secondary is closed) so why bother with a Vac. secondary?

And a related note, I also had an electric fuel pump and I don't ever want a boat with a carb with a mechanical pump again.

[biggiefl]

Never had a choke on any of my boats(except outboards) nor my hotrods. Easier to just pump it a few times and maybe have to restart it a second time than mess with a choke. I would think mechanicals would be better even on the water. First off you have much better throttle response, especially if running a cam. Second you can dial in where the secondaries open so you know to stay under that RPM for cruising. Air gap should be square. I would not go too crazy searching for the best, etc as this is not a car. We are always under load and get 4mpg at best so dialing it in is not going to be a science. Don't run too low of an idle as this will ingest water. Low idle on BBC's can also wipe out cam lobes.

[miike]

I have the carb off my 1992 OMC 454 right now so if you need some measurements let me know. It has a 750 Holley


BTW my 502 came with a jetted up 750 Edelbrock (free) and I'll prob upgrade next year once I get things dialed in. It will run with that carb but if you plan on doing anything crazy you may need more.