That is why the #4 piston overheated and scuffed on the exhaust valve side only. No other damage, everything else looks good. Will need one piston, rings for one piston, pull the valves out and check them on that cylinder and some gaskets and engine will be good to go.

I swapped the stock 7.4L for a stock marine GenV 502 last winter. I used all the stock components including the Weber 750cfm carb.(Jetted way richer) Only thing I upgraded was the intake manifold and the oil cooler after finding that the stocker just wasn't up to the job of cooling the oil from the larger motor. Now I will need to upgrade the carb.

A Holley 850 is probably first on my list but I am also considering the 830 chokeless carb.

I don't do a lot of WOT running but, when I do I want it to run strong and stay together. Most of the 52 hours I have on this engine are at 3000-3500 rpms. I want it to run well at cruising speed, also.

What suggestions do you guys have for the best carb for my application?

Mac-I ain't buying it. If a carb is too small, then it will limit hp by it's airflow, not fuel flow. That 750 should have been close enough to work. Heck, I have a 850 on my motor, and the builder felt that that was even too much.

TEAGUE 830 marine carb.

Sounds to me more like a vacuum leak by #4 on the intake(either external or the underside toward the lifters). You say you had the original 750 carb jetted richer? You have a single plane intake? If so it shouldn't be just one cylinder. If your piston and block were trading metal it was definitely lean. Believe me..been there..done that . I still have the 4.55 bore piston on my desk for a paper waight(thats all it's goog for now).

Cord, that is what I thought, too. Either way though, I am going to a bigger carb just for more performance if nothing else.

mopower, I have an Edelbrock Performer RPM Dual Plane. The intake gasket was tight. I took it off myself. Possible vacuum leak? Maybe. Carb still too lean? Probably.

I suppose that in a perfect world all eight cylinders would operate the same. However, in the real world I assume that some run hotter than others and the hottest one is the first to go.

I think I was lucky and caught it right away before more cylinders started to get too hot. I shut it down as soon as I heard it start to make noise. A few more seconds and it might have been total meltdown.

Mac,
Was there a difference between the appearance of the plugs? obviously #4 would have been very white. How about others?

830 or 850 you will never see the diffrence the 830 is the choice it comes with all the cool parts out of the box. Idle on all 4 corners annular discharge front and rear power valves all the good stuff. The 830 was built out of a couple of diffrent carb shops before Holley offered them better driveabilty and all the parts to make it easer to tune. Unless your engine is 10 to one or more with a lot of cam a 830 or 850 will be fine.

mopower, I didn't pull the plugs right away, obviously I had to get back to the ramp. I ran it about 3000 rpm for about a half mile to get there. It sounded and ran fine except at WOT. When I did pull the plugs they looked pretty good ( light tan to darker tan) except the # 7 which had a slight hint of gray, which worried me, and the #4 which was as white as a new plug with a little puddle of tan on on side of the tip. I then did a compression test. It was only 140 on #4. The rest were 154 to 160. A leakdown test confirmed the damage. 50% on 4.

The white plug indicates lean, I know. Vacuum Leak? Lean Carb? Carb too small? Regardless, I am going bigger. The Holley 830 is sounding better all the time. I can live without a choke. I didn't have it hooked up on the Weber. Not much of a problem.

Mac,
You're right , the 830 certainly can't hurt any. It should supply a 502 with all the air it needs. And the choke thing...well I know I never had to start mine on a 10* morning Four corner idle carb generally start and run pretty good. Had a 540 with a 1050 Dominator and worked fine after I figured out the sequence. Same day...just turn the key. Next day...a little throttle. Next weekend...1 pump of the throttle.
I'd be real careful reinstalling the intake , by the plugs , it still seems like a single cylinder problem. I' hate to see the same thing happen again