Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem

4.3L Mercruiser QJ

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Baylinerchuck:
Picked up the book y’all sell....lots of great information there. I purchased a remanufactured QJ from National Carburetors about 2 years ago and I’m learning how to dial it in reading the book. I still have the carb that came on my 1990 4.3LX, which is the 205hp V6. I absolutely intend on fixing that carb as I have a blockage in the primary side under those pressed in discs. That’s later as I am trying to get this remanufactured carb to work better first. It has a major stumble as the secondaries begin to open that’s been there since the day I installed it.

The guy at National Carburetor wasn’t a lot of help, but I’ve since installed the jets, primary and secondary rods, hanger, etc from the OEM carb into the reman carb. I had a small hesitation on the primary side that’s better now, but the secondary is still a major stumble, but runs strong at WOT.

Is there an exact or round about measurement aside from 2/3 open that is used to determine how far open the primary are when the secondaries begin to open? I used a 5/16” rod as a feeler gauge on the oem carb, and discovered the reman carb is way less open, around 1/4”. I’ve adjusted the linkage on the reman so it more closely resembles the oem.

Guess I also need to know where else to look for that secondary stumble. The air door spring is at 3/4 turn, the float seems right at 1/4”, and the accelerator pump is working.  What am I missing?

Thanks for any help, again, the book is great. 

Cliff Ruggles:
Common problem with "remanufactured" carburetors and that source turns out some horrible units, at least from what I've seen here. 

I'd spend my time/funds on the original Marine unit.  Get one of my Marine rebuild kits for it and a new choke pull-of if the old one is defective or opens too quickly.

You'll find when you are all done the time/funds were well worth the efforts and you didn't waste them messing around with a "hacked" up remanufactured unit.  I'd also add that the factory jets/metering rods would NOT be correct for the reman unit as they are "generic" for calibration.  Put all that stuff back in the original carburetor during the rebuild.

I do this for a living and will NOT work on or use a remanufactured carb or any non-Marine carburetor on a Marine application......Cliff

Baylinerchuck:
Thanks Cliff. I appreciate you taking the time to answer my post. Just to be clear, the carb I bought IS a marine carburetor.....putting a non-marine carb in a bilge is recipe for disaster.

I absolutely will rebuild the oem carb, as was the plan all along. Was just trying to make the reman carb play a little nicer until I get the oem done. The oem carb was polluted with oxidation from water in the fuel and sitting. I’ll need to drill out the discs on the primary side to reach the blockage, then use screws to seal per your book.

I’ll heed your advice and not put any money into the reman carb. It still functions, just not perfect.

I’ll search your site for the correct rebuild kit. Again, thanks for the response.

Baylinerchuck:
I found the marine rebuild kit.

Also, does the bottom plug kit repair both sizes of the plugs? The aluminum discs for the secondary wells, and the Front plugs under the primary jets. I need to drill out those front plugs in order to clean out a blockage of packed white corrosion from water most likely due to ethanol fuel. The previous owner wasn’t that great at basic maintenance.

Thanks again. 

Cliff Ruggles:
The bottom plug kit comes with two large plugs for the rear and 6 smaller plugs for all the other locations.

I would note that it is very rare to see a Marine carburetor leaking at the bottom plugs post around 1975.  I can't even remember the last time one failed a high pressure leak test.

The best way I know to clean out the insides of a nasty Marine or well oxidized unit that's had some water in it is to bead blast them with ultra fine glass beads.  No amount of soaking in any type of carb cleaners will do nearly as well and many chemicals or "recipes" folks come up with are very hard on the castings.  Since it's a Marine unit you can give the outside a nice coat of semi-gloss or flat black paint before assembly like the factory did to most of them......Cliff

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