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Old 12-06-2008, 10:39 AM
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First Time qjet rebuild HELP

So today i am going to try and rebuild my Rochester M4ME Quadrajet off my 85' chevy blazer. This will be my first carb rebuild, although i am mechanically inclined to an extent i am always willing to learn new things. After diagnosing the problem of running very rich ( catalytic converter runs cherry red and black smoke from exhaust ) I decided to go ahead and rebuild the carb, with 108,000 origional miles under its belt i feel it would be good for me and the truck to try something new. I am posting this thread to ask anyone with related experience and knowledge to offer any helpful advice regarding teardown, rebuild and tuning to help make this first time aroud as painless as possible. Any tips and tricks and or helpful tools would be greatly appreciated.........

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Old 12-06-2008, 10:53 AM
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Are you sure the CAT is not clogged up?

I am no expert on the Quadrajet but I recently got a lesson on this subject . If you tun into any problems I will look thru my pix & see if I can help .




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Old 12-06-2008, 10:58 AM
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just had new exhaust put on and they did a compression check and came back normal, only thing left is carb problems hence the rebuild will help
......exactly how 'hard' is a carb rebuild????????????????
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Old 12-06-2008, 05:33 PM
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Just be methodical. Be careful not to lose any parts and remember how it all goes back together Famous last words.

I would also look to other sources, though. A carburetor is a manual device. It doesn't change over time to randomly cause a rich condition unless something physical has changed about the carb. I only say that so you don't get your hopes up when you find out its still running rich after a rebuild.

I suggest replacing the float while you have it apart. That is the most common cause of running rich in a Qjet.

Also, if the cat wasn't clogged before and you've run it cherry red and rich for a while, its toast. Rich mixtures kill cats in very short order. A compression test won't tell you anything about a catalytic converter, it only diagnoses engine ring and valve seal effectiveness.

But, a carb rebuild can't hurt. Things to look out for when re-assembling

1) make sure the primary rods go back down in their jets and not off to the side. You'll see what I mean. The rods are on little spring clips and they want to splay out to the side instead of hang straight down.
2) make sure you carefully install the primary step up piston in its bore while not tearing the gasket. Its a little tough to figure out the first time, but just look at it before you pull it apart and you'll see how it goes back together.
3) lube the accelerator plunger with engine oil to help it go into place, and to help it "break in" for the first few strokes.
4) Don't worry about removing jets unless you want to. I find that the soft brass will often times yield to the screwdriver before unthreading. Just stick the little red straw of some carb cleaner down in them and blow it out making sure you get good streams of stuff from the boosters.
5) Check the throttle shafts for play. The throttle shafts are steel and they wear away at the aluminum casting. If they wear too much they become a vacuum leak. Jet Performance sells a $60 kit that lets you install sleeves at home to fix it.
6) Don't try to take the throttle plates off the throttle shafts unless you have to for #5. The screws are mangled on the other side by a chisel so they don't fall out. If you just try to unscrew them, the heads will twist off and then you'll be looking for a new throttle shaft and screws. Grind the end of the screw threads off first to eliminate that deforming before unscrewing.
7) There is very little you need to remove from the outside of the carb to clean/rebuild it. The choke and vacuum brakes need to come off, but don't worry about removing all the throttle linkages. Too many springs and linkages to worry about and you can just clean them up with a toothbrush.
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Old 12-06-2008, 08:21 PM
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Quote:
Originally Posted by otero62986
just had new exhaust put on and they did a compression check and came back normal, only thing left is carb problems hence the rebuild will help
......exactly how 'hard' is a carb rebuild????????????????

A compression test is not going to diagnose a clogged catalytic converter.

The fact of the CAT running Cherry red is a good indication its clogged or broken/blocked.

You should check with someone revving up the motor about 3 G's & see if there is a sufficient amount of air coming thru.

A engine is nothing more than a BIG AIR Compressor/ pump, Air in ~Air out.

If the Cat is restricted its like You exhaling thru a kinked snorkel.

The theory being this.
A 400 CID {Cubic Inch Displacement}

Measure out 400 Cubic inches into a "cube" convert to feet =33.3333333~' by 33.3333333~' by 33.3333333~'

Quote:

I THINK PER MINUET NOT 100% on that.

This is in FEET {'} this is how much air is being pumped thru the motor .

The "COMPRESSION " is the piston compressing the air fuel mixture into a volatile atmosphere so that when the spark fires @ TDC {top dead center} then it rapidly expands & gets pushed out the exhaust.

NOW the CAT scrubs the exhaust by sending the hot gasses thru platinum which heats up to burn the wasted fuel off .

A motor using too much oil can clog the cat.

A resent conversion to synthetic oil will clog the cat.

Too much fuel will also clog it.

A blown head gasket or water in the exhaust will break the internals of a cat.

They wear out & break thus restricting the flow.

You might hear a load PFFFFFFFFFFT sound quite like a blow nozzle being used in the distance.





R
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Old 12-07-2008, 04:29 PM
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Ok well first of all thanks for all the help guys, autozone seems to have lost my rebuild kit for the 2nd straight day now.....sooooooo, i have decided to just go ahead and purchase a brand new carb, only problem is i am not sure what specs i am looking for there is an edelbrock performer series 500cfm that claims to fit the 305ci but again i have no idea what i am looking for, i know that it is electric choke and thats about all i know. Any help regarding CFM, and things of that nature would be helpful, thanks again......
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Old 12-07-2008, 06:02 PM
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My best advice would be to contact Cliff Ruggles and find out how much it would cost for his shop to rebuild your Quadrajet. In my opinion, spending over $200 for a carb that is inferior to the Quadrajet doesn't make any sense, particularly if Ruggles will freshen your carb for that or less. Fill out this quote request and shoot it off to him.....
http://www.cliffshighperformance.com/quote.html
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Old 12-07-2008, 06:34 PM
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I agree with the tekinspector. Also don't break the carb apart UNTIL you take the cat-converter out and give it a try. I tried all the things you are talking about to no avail. I gave up and found out the cat WAS bad. Replaced the system with new parts and bingo, it's just fine now. Its a whole lot cheaper and smarter to check the smaller item first. Good luck, let us know how it turns out. Building a quadrajet can cause you hair to come out.
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Old 12-07-2008, 06:47 PM
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Yeah... no reason to spend $300 on a new carb that will need to be tuned, when you already have the finest carb ever built that needs to be tuned.

They'll both need tuning, but the one you have is great.
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