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