changing from a 2 barrel to a 4 barrel carburetor

[Lou C]

The other thing that can cause dark spark plugs is the carb running too rich (too much fuel vs the available air); and the causes of that are carb float too high, needle valve leaking and clogged air bleeds. A really thorough cleaning adjustment of the float level and and reassembly with new gaskets shouid make a big difference…might want to do that before converting to a 4bbl. While that will give the most improvement it’s fairly costly, a new Holley 4bbl is about $800, the Edelbrock is about $620, a used 4bbl intake manifold about $150-200, then there are small things needed for the accel linkage. By the time you’re done about a grand or a little more for the upgrade….

 

[rolmops]

Thank you Lou for this info. I just found out that Siera has an aftermarket Rochester Quadrajet for $869. Do you have any experience with that ?

 

[Lou C]

The other thing that can cause dark spark plugs is the carb running too rich (too much fuel vs the available air); and the causes of that are carb float too high, needle valve leaking and clogged air bleeds. A really thorough cleaning adjustment of the float level and and reassembly with new gaskets shouid make a big difference…might want to do that before changing converting to a 4bbl. While that will give the most improvement its daily costly, a new Holley 4bbl is about $800, the Edelbrock is about $620, a used 4bbl intake manifold about $150-200, then there are small things needed for the accel linkage. By the time you’re done about a grand for the upgrade

Thank you Lou for this info. I just found out that Siera has an aftermarket Rochester Quadrajet for $869. Do you have any experience with that ?

No, No and No! Cheap Chinese copy of Rochester's finest.
I would say this, go through your 2bbl make it as good as you can, and see what that gets you.

 

[rolmops]

I will certainly go through the 2bbl again and try to get that whole setup up to the best performance possible. Siera claims that its aftermarket quadrajet is made in Canada These are remanufactured carbs that's why I wondered if you have any experience with it

 

[Lou C]

Well to be honest I don't. But maybe the sourcing of the carb changed from when it was released.
If you have any Quadrajet questions, the guy to ask is Cliff Ruggles of Cliff's High Performance Quadrajets.
Google his website, they also have a discussion forum. I have used his rebuild kits, very good.
However, remanufactured carbs of any kind, are sometimes combinations of different carbs not tailored to your engine. Marine calibration of auto style carbs is very different. I would rather have a good original marine carb like what's on your engine, carefully cleaned and rebuilt than ANY reman carb.
The other options as we discussed, are the Holley 4160 and Edelbrock 1409, both of which can be bought new. The devil is in the details though. I think as I said that the Holley is easier to adapt to the OMC, due to clearance issues. The Edelbrock is a good bit wider and likely will interfere with the bracket for the shifter bellcrank and the trim relays. That can be moved though.
Look at the pic you'll see what I mean. The Quadrajet is the most compact of the 3 actually. A good one is really excellent, but they are now very hard to come buy. No new cores for 30 years!

rebuilt 37 year old Q-Jet, with a bit of external corrosion due to 25 years in salt water!
However, inside it was clean....no corrosion....

here you can see the relative size of the Holley 4160 and Edelbrock 1409

 

[Lou C]

Another data point I can recall from the past, not boats but cars.
2 of our family vehicles
1972 Chevrolet Impala 5.7 V8, 2bbl Rochester, 3 speed GM Hydramatic
1975 Olds Delta 88, 5.7 V8, 4bbl Rochester Quadrajet, 3 speed GM Hydramatic
the Olds weighed a few hundred lbs more than the Chevy, not sure if final drive ratios were the same it was a LONG time ago
But...the Olds was a much more responsive vehicle, even though you'd think a 2bbl should be perfectly fine on a 5.7 V8.
Emissions tuning might have also been different, as the Chevy didn't have a cat converter and the Olds did.
I think that the 4bbl will make the boat feel more responsive in the higher RPM ranges where fuel flow dramatically increases, but only you can decide if the cost is justified.

 

[rolmops]

Another data point I can recall from the past, not boats but cars.
2 of our family vehicles
1972 Chevrolet Impala 5.7 V8, 2bbl Rochester, 3 speed GM Hydramatic
1975 Olds Delta 88, 5.7 V8, 4bbl Rochester Quadrajet, 3 speed GM Hydramatic
the Olds weighed a few hundred lbs more than the Chevy, not sure if final drive ratios were the same it was a LONG time ago
But...the Olds was a much more responsive vehicle, even though you'd think a 2bbl should be perfectly fine on a 5.7 V8.
Emissions tuning might have also been different, as the Chevy didn't have a cat converter and the Olds did.
I think that the 4bbl will make the boat feel more responsive in the higher RPM ranges where fuel flow dramatically increases, but only you can decide if the cost is justified.

I am not overly concerned about the cost. After all, a shroud has no pockets.
What is holding me back at this point is removing everything on top of the manifold then replacing the manifold and after that is done,reinstalling everything. That takes quite a bit of time and with the winter coming in and not having a heated garage, it will have to wait until spring. Maybe for now I should just go with the old wisdom. If it ain't broke, don't fix it.

 

[Lou C]

If you've never done it before it can be intimidating. I had to do it because my head gaskets started leaking back in '16, and I wanted to try to save the engine, since it was always a good runner. And being that I am in salt water, raw water cooled engine, I didn't think I could get it apart. But after pickling the engine in the fall, come spring I started in on it. The hardest part was prying loose the intake. Those OEM GM gaskets were like Kryptonite, it was tough to get off. All the bolts came out with no problem. The head bolts were tougher, I had to use my De Walt 1/2" drive electric impact. But, didn't break one bolt or strip any threads. If yours was re-done not long ago, it shouldn't be hard. I did it in my driveway with the engine in the boat, in March/April in Long Island NY. The main thing is clean clean clean, keep everything clean. That and properly clocking the distributor. Other than that, not a hard job. In your case though, depends on which 4bbl you might use. Quad is easiest for the install, but the hardest to find a good condition one. The other options are the Holley 4160 and Edelbrock 1409 as we discussed. Personally from the point of view of simplicity and reliability I think of the those 2 the Edelbrock is the better one, although not so easy to adapt to the OMC engine. If my Quad acts up again though, I will make it work one way or the other.
This is what will be confronting you when you take off the intake.

At this point the remanufactured cyl heads were installed so I was ready to reinstall the intake but not before spending a long time getting the remnants of those dang OEM gaskets off. I used Fel/Pro head gaskets and intake gaskets.

 

[guy48065]

Has anyone here tried the Holley "Sniper" efi setup?

 

[jimmbo]

I believe it uses an O2 Sensor, kind of hard to do when water is dumped into the Exhaust