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Old 08-17-2016, 08:45 PM
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Exclamation Quadrajet M4MC Issues, new to Q-Jets

Hey everyone! I'm having trouble with a quadrajunk equipped 85' C30 454 that I'm trying to get operational for a buddy.

I've never tackled a quadrajet before, but I've been through quite a few Holleys and figured I'd give it a shot.

I'm slowly regretting this haha.

Here's the deal, neighbor asked if I could get his old pick up to run and I said sure. After a little trouble shooting and digging around it would seem it's not getting any fuel to the pump, so I assume the tank selector valve is crap considering when I hit the switch it hardly makes a noise.

I decided I'll worry about that later, and figured since I'm messing with the fuel system I might as well throw a rebuild kit at the old quadrabogger for poops and hahas. Long story short I rebuild it, it was a pain in my ***, but it has been rebuilt.

I get it slapped back on that old 454 and run a hose from a gas can to the pump and after a little bit of cranking VOILA it's running. It takes a bit to clear it out and it puffs a little blue smoke, which I assumed was from me filling the carb through the vent and spilling a bit over into the intake causing it to start up rich, No worries.

It runs like crap, wont idle much past 500 RPM, and smells nasty rich! I went through a whole gallon of fuel in about 5 minutes of idling

Seems to me the carb is consuming WAY too much fuel. I don't know crap about quardrajets, but I've read the well plugs can leak??

I didn't check those as I didn't know that was a thing..

I could really use a little help here guys, I have NO CLUE what would cause this carb to leak fuel internally and run through a gallon in 5 minutes.

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Old 08-17-2016, 09:06 PM
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Confirm that the secondary metering rods are seated in the jets. A lot of times the hanger gets bent, and the rods can be a real pain to seat properly. Easy to check, so theres one guy's idea to get started on.
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Old 08-17-2016, 09:59 PM
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I didn't even think about that.. is there a specific way to check those? Or do I just kinda look back there and wiggle em?
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Old 08-17-2016, 10:12 PM
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They should move freely when you poke a finger down at the back edge of the air valves, and close fully. If one side of the hanger is bent up, the rod can be unable to seat. I'd hate to say tear it back apart but theres a common error with the clip that holds the needle valve to the float also. But you didn't say it was dumping gas out the vent, so I didn't go there. I am no expert, just a long-time user and get-by-er but its been too long since I messed with one.

You'll get more and better suggestions after the guys have all seen your post. Patience and good luck with it. Hope its a simple fix once the issue is found.
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Old 08-18-2016, 12:31 AM
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i am hoping that you did not move the Double D shaped device in the float bowl known as the APT adjustment.. you would have had to use needle nose or a proper Double D shaped tool to do it..

quadrajet M4MC APT adjustments - Album on Imgur this is only a few pictures of the idle and off idle circuit control.

hint... taking quadrajets apart and putting them back together requires a trick... to free up the versions that don't have an easily released accelerator pump rod with a clip on them.. take the base plate off the carb.. flip the base plate around to allow you to disconnect the pump pushrod.. this makes life with quadrajets so much easier .. not having to knock the pivot roll pin in.. taking a chance to break the inner ear off the cover..

there are dozens of articles in various magazines.. there are several M4MC service manuals available online to assist you far better than the carb kit insert.

post a carb number if you can..

when you have the base plate off the carb... please hold it to the sun or the ceiling light to verify the throttle blades are properly centered and closing all the way in the bores.

as for the lack of fuel from the pump.. please read my reply on this post..

https://www.hotrodders.com/forum/65-i...ng-447345.html

quadrajets are a great carb... having one that has easy access to the APT lets you dial in amazing off idle response..... visit your tire supply and pickup the large bore farm tractor valve core tool.. bigger in diameter than a conventional tire valve core tool.. it will fit the APT double D screw head.

you will need to readjust the APT if you messed with it while you had the carb apart. to do so.. look at the images.. you can use a dipstick thru the round bowl vent. feeling the primary metering rod hanger depressing the power valve spring as you push down. turn the APT adjustment while holding the plunger so it drops until you cannot feel the plunger move farther down.. then start turning the adjustment up again while holding the metering rod holder/plunger down against the APT.. when you start feeling the APT screw starting to lift the metering rod holder.. try going up 2 hole turns. now its time for some seat of the pants adjustments..

have you ever seen a drag racer after the burn out as they are about to pull up to the lights... part throttle mash the gas for a split second.. if the carb spits out the top.. give it another turn upward.. back up and try another short blip on the throttle in drive.. keep going 1/4 turn at a time till you start to smile. or it does not get any better.. then go back to the spot where it is the best.. if you go up too far past the best spot. you will kill your part throttle fuel economy.. if you are too lean.. you will get lean surge part throttle and need more pedal to do the same work.
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