Rochester Quad. adjusting and tuning - Hot Rod Forum : Hotrodders Bulletin Board
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Old 11-04-2003, 04:17 PM
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Rochester Quad. adjusting and tuning

I'm trying to set up my Rochester Quad. Carb. on my 85 C20's 454. I have 2 square trype screws in the front of the base plate. I think when I bought the truck I messed with them and may have them way out of wack. also my choke feels like its stuck and will never shut off I tied back the arm that goes to the plate on top to hold it open. that seems to shut the choke down or maybe just give it more air to compinsate for the richness. I've tried alot of thngs. I wish I could just the carb back to factory default. I'm not looking for a tweeked carb just one the has a choke breifly that i can hit the throttle and shut it off like a normal car.

am I asking to much at once. I feel like I'm opening a can of worms. thanks guys BTW Its the original rochester so its around 800cfms right? I have an oval port heads. and its in a 3/4 ton so no smog BS (heat risers, restrictors ect.) my truck didnt even come with cats. =)

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Old 11-04-2003, 04:33 PM
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hey man those 2 screws at the bottom of the plate are the idle mix screws, to adjust them turn them in untell the engine runs rough, then back them out 1 and a half turns and thats it. you may have to play with the choke to get to work all fine and dandy.
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Old 11-04-2003, 04:49 PM
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Here are a few sites that describe a Qjet.

http://www.recarbco.com/technical/ (better site)

http://www.73-87.com/garage/myqjet.htm

http://500cid.com/mts/tech/Quad.htm
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Old 11-04-2003, 05:12 PM
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so those 2 screws have to be the same?
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Old 11-04-2003, 06:20 PM
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I feel more confused now
1BAD80 this is a 454ci truck engine not a 500ci race engine or a SBC. I know this can be fixed without tearing my carb apart and drilling things. i just want to how to turn my choke down. and if those 2 idle mix screws need to be the same?
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Old 11-04-2003, 06:49 PM
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The 2 screws need to be the same turns out. Just gently seat each one then back them out 3 turns. Then get a tach and let it idle warm, then start tuning each one in 1/4 turn at a time. When the rpm starts to drop, stop, back each one out 1/4 turn, re-ck your idle speed and its done.

As far as the choke goes, it should have an index mark thats usually a good place to start. Make sure the choke pulloff is good too. Its imparitive that it works right for the choke, and for the secondary butterfly too.

If its an electric choke, make sure it has power going to it and gets hot.
If its a hot air choke, make sure the pipe gets hot going to it too.
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Old 11-04-2003, 09:21 PM
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it's a hot air choke. a tube goes into the intake and loops back into the carb. there is a mystery tube with a hose on it that i cant seem to find a home for. one tube goes strait to the carb from the plate. the other makes a 90 deg. turn and swivles (that is the one connected to nothing. also the back of the carb. has a vacume line about 1" long going to nothing and is it possible to block off a PCV valve or do I need that for the engine to perform correct.
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Old 11-04-2003, 10:07 PM
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The choke tube that goes around back to the carb, should have about 1" of hose on the end and will plug in to a short metal pipe on the rear/top of the carb.

Hot air is pulled through the choke housing.

The air actually starts at the rear of the carb, comes through the long rear tube, down into the intake box where its heated by exhaust that crosses through the bottom of the intake. Next it goes to the front of the choke housing, heating the coil inside the choke housing, then into the carb.

You DO need the PCV valve. Don't remove it.

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