Rochester Quadrajet Rebuild and Adjustments

[Baylinerchuck]

Got the OEM Quadra-Jet bolted back onto the manifold and hooked up. Took a bit of cranking to fill the bowl, but once fuel was there, she fired right up. So far on muffs the engine idles perfect, and there is absolutely no hesitation or stumble in any throttle range. I can watch the secondary quickly open and the engine returns to idle smoothly. The engine starts quickly.

We’ll see what happens once the boats in the water. The initial idle mixture setting seems close. More on adjusting that at a later time.

Below is an exploded view of the carbs with proper nomenclature. Hat tip to Cliff Ruggles.

 

[oldboat1]

Is it a stumble as you throttle up, or more prevalent when the throttle is steady near WOT? How long has it been since the carb was rebuilt?

Thanks again. I would say steady near WOT. Carb was rebuilt last Spring (I didn't do it -- left it to the marina shop.) It's time to have the boat pulled anyway, so will get back to it next year. I have a feeling it's close.

Great thread!

 

[rad1026]

So funny, I just did the same thing Chuck. Bought the book, read like a maniac. Did exactly the same rebuild as you. Put it back on the boat and primed the fuel bowl and it fired right up. Idled great and absolutely no hesitation on hard acceleration. I didn't touch a thing. Its a lot of parts but once you have done it not really that bad. Plus now you completely understand how it works and what adjustments need to be made if any. I applaud you for doing it and documenting it. I didn't have the patience for documentation. From the very beginning when I saw you bought the book I knew you were going to be successful. You were much more organized then me. Cheers!

 

[Baylinerchuck]

Thanks for the compliment. Hopefully others can use this thread as a guide.
Next is a Rochester Mercarb. Rebuilding it for a friend, and will document the tear down and rebuild for this forum, (in a thread of its own of course).

 

[Baylinerchuck]

As a quick update and refresh.....the Quadrajet I rebuilt is 100% perfect. Throttle changes are seamless between idle and WOT. The only issue I see is now I have more power, and tach over 5k at WOT. This was a surprise I wasn’t expecting since the secondary fuel load should be the same between carburetors as the fuel nozzles are both 1/4”. More power is a pleasant surprise and may require a change to a 23” prop to contain the RPMs.




The sun has set on this boating season. Sadly it’s time to winterize.

 

[Scott06]

How far above 5 k are you.you are better off being a tad under propped than over propped. if you haven’t might also be good to verify the tach vs a shop tach fore you add more pitch, if the boat is weighted down with people when it’s warmer you may be better off with the lower pitch prop.

 

[Baylinerchuck]

How far above 5 k are you.you are better off being a tad under propped than over propped. if you haven’t might also be good to verify the tach vs a shop tach fore you add more pitch, if the boat is weighted down with people when it’s warmer you may be better off with the lower pitch prop.

I’m hearing ya. All things to consider. Luckily I own the 23” prop so testing is no big deal. The engine was about 5100 before I throttled down slightly. It’s rated at 4600-4800, so I’d prefer to be in that range. I rarely run the boat at that RPM as it lives in the 3k to 3.5k throttle range.