Hot Rod Forum : Hotrodders Bulletin Board - View Single Post - Rochester Quadrajet 4MV Carburetor: Removal, Disassembly, Rebuild (Rookie Level)
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Old 03-01-2011, 02:00 PM
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cobalt327 cobalt327 is offline
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Quote:
Originally Posted by lt1silverhawk
In the book, Cliff says: "Simply dabbing epoxy over the leaking plugs does not work as a long term repair. The epoxy eventually comes loose from the aluminum after many heating-up and cooling-down cycles of the engine." (chapter 5, page 71).
I've been saying that about using JB Weld forever. Then I hear back, "Ruggles uses Marine Tex epoxy". All I know is, epoxy has failed in the past and I will not use it on my carbs. And I'm glad to hear he seems to think that, too.

Quote:
It seems like there is a gap between the air horn and the fuel bowl in the rear of the carb. The book says this can be fixed using a belt sander (chapter 4, page 68). Anyone feel this carburetor needs to be sanded or is it negligible?
I cannot see the gap, so I cannot offer an opinion- but if it's significant, you'll want to either replace parts, or... I suppose sand it down. Although I will readily admit to never having done this. That said, it sounds easy, but somehow I doubt it actually IS easy. At least not to get it perfectly smooth and square. But that could be just me.

In any event, this means removing the down tubes from the airhorn (unless, God forbid, you want to sand on the main body ). Measure their installed height before removing them, and be careful when you remove them.

I don't know what procedure he uses for this. If you would, post what it is. I would insert a solid piece of wire the same size as the ID of the tubes into them so they could be gripped w/o crushing them.

The inner tubes are bottlenecked on the bottom, so you will want to go in from the top w/the wire "reinforcement", should you try to remove them this way. The inners are also small, it may take a bit from a numbered set to do it, or maybe a cut down pin, etc. Make sure the end of the wire extends out of the tubes, after gripping them for removal the wire will be trapped and you'll want to be able to grip the wire for removal.

All that said- unless there is a gap that will not close up when the screws and bolts are tightened, don't worry about it. They mainly will be warped downward at the corners where the long bolts go through the airhorn down to the intake flange. These get overtightened, and the corners will 'droop'. Unless this is bad, I usually do nothing. I have had to VERY carefully tweak the corners back up some- but this always makes me nervous, cast zinc is brittle.

Quote:
One of the mods mentioned is making sure the throttle plates open up a full 90 degrees. Here are pictures of my carb and the secondaries are opening almost 90 degrees. Sufficient enough?
You want them to be 90 degrees. Yours aren't.

Quote:
Another mod listed for throttle plates is drilling small holes in them to add additional air at idle. It is mentioned as an alternative to another mod, which is adding an idle bypass air system.But these are not necessary if the idle bypass air system is already in place. (chapter 6, page 95). I need to check to see if this car has this system already. If not, I may just drill the plates since adding the idle bypass air system requires alot more work and precision.
Do not drill the throttle plates unless as a last resort. If your cam isn't radical (I don't recall any specs on your engine, sorry), this won't be an issue anyway. The more duration/overlap, the more need there is for the bypass air, but there are other ways besides drilling the plates to accomplish this, same as a Holley.

I got a chuckle out of using a machinist rule to hold the PP down in position while reassembling the top of the carb to the body.

My thoughts on this are that it's bad enough already- you have to keep the gasket in position while the return spring of the accelerator pump piston is fighting to extend, plus aligning the down tubes into their proper positions, and at the same time you're aiming the pump through the hole in the airhorn, etc.

I would do most anything to not add yet another procedure to all that- you'd be running short of hands, I think! lol
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