I have a 1989 Cobalt 243. The boat came with a bum engine, which i believe was originally a 454 Mag, 365hp. I have a a Quadrajet 17059280 carb with a orange "454 MAG B" tag on it. It sits atop the correct Mag Rec port aluminum intake manifold, 6269318. Further investigation revealed "PASS" heads and a reman tag, so someone swapped in a standard 454 at some point. Due to the trouble of locating a "correct" 365hp Mag engine (weighing cost vs the extra HP vs availability), i decided to go with another standard 454, which is due to arrive early next week. In the meantime, i sourced a nice edelbrock performer intake manifold designed for the oval port heads, but have questions about the compatibility of my current carb.

I disassembled the carb last night for the rebuild and it looks pretty good inside. I removed both main jets and found them to be #68's, which from my research seems to be the correct jets. I did not look at the metering rods or measure their end diameter. I did a ton of research this morning and cant seem to find what the mains, meter rods, etc. are supposed to be for the standard 330hp 454. I am hoping someone can help me out here. Is what i have going to work OK? Do i swap some components out for better compatibility with the lesser HP engine? Should i source a carb from a 330hp engine?

Thank you!!

Quadrajets are very forgiving carburetors. I would bolt it on as it is and try it first. If you can borrow an A/F mixture gauge to see how it is doing once you get it running that would help but you could probably do just as well reading the plugs. The different manifold might affect it too so I would run it first before jumping into changes. If anything it might be a bit on the rich side but that is better than lean.

Take a look in here, hopefully it is in there.
https://drive.google.com/file/d/0B1T...dZMTRQTkE/view

Let us know if it is or not, so we can continue looking if not.

Ah very cool manual!! thank you for that. I took a look (cant attach the photo yet due to post count), page 440. It appears as though the jets and metering rods are very close in size, but cant say for the secondary metering rods. The carb is also a different part number all together.

edit: took a look at the secondary metering rods and thee DA is .0443 in diameter and the DB is .0700 in diameter, but the size of that depends on the carb it is in.

how is A/F mixture read in a riser/manifold?

You need to put it before the water is added. Water will foul the sensor. There are sensor blocks that can be bolted between the manifold and riser. If you have an inch of clearance you can use one.

Perfect. That certainly seems like a good way to go for piece of mind. Found the spacer on ebay for around 80 bucks and a new water resistant innovate gauge/sensor for about 160. Small price to pay to monitor whats going on in there.

To follow up, i did end up purchasing an Innovate wideband setup and the riser sandwich plate. I ran the boat for over two hours last week and it worked flawlessly. A/F ratios are spot on, barely creeping above 15.0 under light throttle. Under load, it will be between 14.5-14.8, then drop down to around 12 when the secondaries open. So, all in all, i think it works fine.

Keep a keen eye on cylinder # 3 spark plug, I dynoed a 502 w tiny cam and edlebrock performer intake and it ran 2 full afr points leaner than most the other cylinders on my 8 o2 sensors fwiw, Smitty

I'd fatten that midrange a bit. 14.8 is pretty dry. You might be able to do it with your primary springs. I forget if the springs or jets are easiest to change but I believe you will do best with a stronger spring which will pop up earlier and richen the mix earlier that way.. Haven't opened a quadrajet in a few years.