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

 

[Lou C]

Yet that’s what all inboards & I/Os are stuck with now a days!

 

[Scott Danforth]

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

my issue with aftermarket Holley EFI fuel systems is that they are only supported for about 5-8 years after they are sold...... then its so sorry, you must buy a new system. Been that way for nearly 30 years going back to the 2DI and 4DI pro-jection systems of the 90s. Its not just holley. went the route of a few stand-alone systems over the years, including ECM's from 034 motorsports and even megasquirt systems.

even most OEM systems are not supported after a few years

Nothing hurts worse than an email saying "we no longer support xyz system"

In 10 years, no mater what carb you have, you will be able to get service parts for it and maintain the system

 

[Lou C]

Agree 100%. For people with older boats, a carb is much easier to deal with, because they are all supported in the aftermarket, even the Quadrajet which has not been made since like 1990. And with carbs you have choices, if you have a Quadrajet that's too corroded inside to rebuild, you can switch to the Holley or Edelbrock, yes it takes a bit of searching for the right parts for the linkage, etc, but still not hard. The beauty is you can just go and buy a brand new one, and start over!
In addition to that, you have a simple mechanical or low pressure electric fuel pump, not an expensive pair of low and high pressure pumps as you would with EFI. The only true advantage of EFI for a boat is better cold starting and smoother running till warm up is done.

 

[Scott Danforth]

The only true advantage of EFI for a boat is better cold starting and smoother running till warm up is done.

If you boat in Florida, with only a 50 degree in temp swing, its not that big of a deal either. Some of us dont even run a choke.

 

[Lou C]

Those of us with older carbed boats have the collectable car hobby to thank for this, the demand for carb parts and new carbs, has kept this alive far longer than it would have because when EFI came out the 'experts' proclaimed that carbs were now obsolete.

 

[dingbat]

my issue with aftermarket Holley EFI fuel systems is that they are only supported for about 5-8 years after they are sold...... then its so sorry, you must buy a new system. Been that way for nearly 30 years going back to the 2DI and 4DI pro-jection systems of the 90s. Its not just holley. went the route of a few stand-alone systems over the years, including ECM's from 034 motorsports and even megasquirt systems.

even most OEM systems are not supported after a few years

Nothing hurts worse than an email saying "we no longer support xyz system"

Find it hard to believe in this day and age that nobody clones ECM modules.

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Car Computer Exchange - Replacement PCM, ECM, and ECU Parts. Car Computer Exchange offers ECM, TCM, and PCM auto computer control units for Chrysler, Dodge, Jeep, and Plymouth vehicles.

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[froggy1150]

I've built a few megasquirts. I do like them but can't see how they would be feasible on a boat