Quadrajet Stumble or Timing Issue?

[savatreatabvr]

My mid 70's 454 had it problems and I've fixed most with the help of this forum but of course all good things come to an end. Now at idle it will stumble, well, I should say it's cut outs more than stumble but it drive fine. Any idea's?

[INSIDIOUS '86]

My idea ditch the quadra bog. They are the number one source of problems on these trucks. With holleys and edelbrocks available there is no reason to run a soggy quadra jet. They get good gas mileage and that's it. But so does a Holley two barrel and a proper tuned carb period
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[beamn7]

I mean this honestly when I say no offense Insidious but I get so tired of hearing Quadra-bog or Quadra-junk, etc. Quadrajet's are a very efficient and properly tuned an excpetional performance carb but so many people are scared of them and don't know how to properly tune them that they opt for the Holley or something else. Many people dislike the ThermoQuad or the AFB, etc (actually 2 other very good carbs). EVERY carb has it's pros and cons. Myself, I prefer Rochester products.

Having said that, as for the stumble I would check several items:
-EGR for proper operation (be sure it is not engaging at idle either due to a failed diaphragm or spring tension)
-plugs / wires / cap / rotor? Good condition?
-check for proper base timing
-connect a vaccum gauge and check for fluctuation (could indicate misfire, flat cam lobe, burned valve, etc)
-check for vaccum leaks
-check for proper choke operation (be sure it is fully open when engine is at operating temp)
-with the engine running, look down the throat of the carb and be sure the float level is not too high (I.E. dripping / pouring gas down the venturi's)
-IF all checks out, set the base idle and then turn the idle mixture screws all the way in and come back out 3 COMPLETE turns on each one (many people confuse a 1/2 turn for a complete turn, if the screw is a flathead and you start straight up and down, the next time you come to straight up and down is only a 1/2 a turn) With the vaccum gauge connected, start the engine and adjust each idle mixture screw out one at a time VERY slowly until you reach your highest steady vaccum reading and then turn it back in 1/4 turn. Do not go out more than 4.5 COMPLETE turns. (in other words, no more than 1.5 turns from where you are starting since they will already be out 3 turns)

Hope this helps.

[savatreatabvr]

Hey thanks Beamn7, I agree, I've had Quad's on Z28's, Chevelle's, Camaro's and 4x4's and they've always performed great! Yeah they are a little tricky to fine tune but all in all I'd take a Quad over a Holley any day! Another great carburetor is the Edelbrock Performer, I've got one on my 440 Moho and it performs flawlessly! Now back to my 454 Quad, the carb originally came off a 350 so I'm wondering if the jetting can be my issue? Next question is, as far as I know the Quad was put together from a box of miscellaneous parts so should I just buy another Quad off Craigslist or ebay? I know I'm taking a chance finding a good Quad but I'm tired of my truck running different everyday!

[dmwphoto]

the Q jet is a great carb. It powered WAY more cars over the years than Holley or any other brand. Some can be challenging and in some cases the holley is a better choice but the q jet is a great carb

[86customdeluxe]

Originally Posted by beamn7

I mean this honestly when I say no offense Insidious but I get so tired of hearing Quadra-bog or Quadra-junk, etc. Quadrajet's are a very efficient and properly tuned an excpetional performance carb but so many people are scared of them and don't know how to properly tune them that they opt for the Holley or something else. Many people dislike the ThermoQuad or the AFB, etc (actually 2 other very good carbs). EVERY carb has it's pros and cons. Myself, I prefer Rochester products.

Having said that, as for the stumble I would check several items:
-EGR for proper operation (be sure it is not engaging at idle either due to a failed diaphragm or spring tension)
-plugs / wires / cap / rotor? Good condition?
-check for proper base timing
-connect a vaccum gauge and check for fluctuation (could indicate misfire, flat cam lobe, burned valve, etc)
-check for vaccum leaks
-check for proper choke operation (be sure it is fully open when engine is at operating temp)
-with the engine running, look down the throat of the carb and be sure the float level is not too high (I.E. dripping / pouring gas down the venturi's)
-IF all checks out, set the base idle and then turn the idle mixture screws all the way in and come back out 3 COMPLETE turns on each one (many people confuse a 1/2 turn for a complete turn, if the screw is a flathead and you start straight up and down, the next time you come to straight up and down is only a 1/2 a turn) With the vaccum gauge connected, start the engine and adjust each idle mixture screw out one at a time VERY slowly until you reach your highest steady vaccum reading and then turn it back in 1/4 turn. Do not go out more than 4.5 COMPLETE turns. (in other words, no more than 1.5 turns from where you are starting since they will already be out 3 turns)

Hope this helps.

Thank You! im tired of them being called names to. i have a Quadrajet sitting on a edelbrock intake on my 350. i have never ever had a problem with mine.. so theres no reason for me to change it.. keep it old skool

[beamn7]

You know, I'm not so sure that would be the cause of the stumble at idle but you certainly would be running lean on the primary and secondary circuits. If it was me I would either re-jet the primary circuit and calibrate the secondary circuit by changing out the secondary metering rods and the hanger OR...... just pick one up for a 454 which is actually, probably the better decision. Like you said, if it's a hodgepodge of parts to make one, could be a mess to monkey with....
Quick search on Ebay pulls up a few. Some cheap rebuildable ones (fingers crossed) or some a little on the higher side....
My truck had a Quadrajet for a 4.3L on a 5.0L when I bought it and had no idea until I installed the 350 and ran the numbers off the carb.... I ended up getting the proper one, rebuilt it and dialed it in... Runs great and real clean and it's the other QJ everyone hates, a feedback / ecm'd carb! (amazing how great you can dial them in with a dwell meter, just can't be scared of them. But still, dang Calif emissions are a pain.......that's another story for another day!)

http://www.ebay.com/sch/i.html?_nkw=....c0.m270.l1313

[1LowToy]

The california emissioned ones are the easy tweekers. The are very much adjustible. As for your stumble your probably looking at a very lean idle mixture problem or an a accelerator pump issue.

[beamn7]

You and I both believe them to be but most people think QJ's and especially computer controlled QJ's are junk. I love 'em personally....

[lurch115]

i agree with you guys also. quadrjets are a great carb. as long as the person working on it knows what they are doing. Personally the first place i would look for issues is the most common place. The accelerator pump plunger. if the carb. has sat dry for a period of time the plunger is known to dry out, crack and split.

[sethv]

I loved the Qjet on my truck, but when I got a squarebore aluminum intake, I had to dump it and get an Edelbrock. I can tell ya that the Qjet performs better and you get so much better mileage. I went from 18 mpg highway to a measly 14 mpg.

Anyways, I'd rebuild it and get bigger jets for it. See if that helps at all. Good luck.

[savatreatabvr]

How can the accelerator pump effect the idle?

Originally Posted by lurch115

i agree with you guys also. quadrjets are a great carb. as long as the person working on it knows what they are doing. Personally the first place i would look for issues is the most common place. The accelerator pump plunger. if the carb. has sat dry for a period of time the plunger is known to dry out, crack and split.

[lurch115]

sorry about that. misread your original post. was thinking off idle for some reason. if it is stumbling while idling the first things i would check are #1. to make sure all the screws holding the airhorn body (or top plate) are tight. they can come loose sometimes and it creates a large vac. leak. #2. would be to make sure the choke buttlerflies for the secondaries are closing all the way.

[raws67]

Quadrajets are Awesome! I used to think they were junk but then I started to figure them out. Lets look at the idle circuit first. As far as the accelerator pump is the pump arm already in contact with the plunger when you are at idle? also try squirting a little starting fluid around the throttle blade bores at idle to make sure they are not leaking. If they are leaking it will not let the carbs idle circuit function properly.

[savatreatabvr]

Never thought about the secondary's not closing all the way, kinda makes since because now under hard acceleration it stumbles! Can it be starving for fuel since the Quadrajet originally came off a 350 and is now on a 454?

Originally Posted by lurch115

sorry about that. misread your original post. was thinking off idle for some reason. if it is stumbling while idling the first things i would check are #1. to make sure all the screws holding the airhorn body (or top plate) are tight. they can come loose sometimes and it creates a large vac. leak. #2. would be to make sure the choke buttlerflies for the secondaries are closing all the way.

[cheguevara]

Hi everyone can anybody help me figure out what I am missing from this 4bbl rochester quadrajet. I am trying to mount it on my 81 C10 it currently has a 2bbl carb..... any help is greatly appriciated. Email cheguevara778@gmail.com. I dont know why I can't post the carb pics here

[savatreatabvr]

Originally Posted by cheguevara

Hi everyone can anybody help me figure out what I am missing from this 4bbl rochester quadrajet. I am trying to mount it on my 81 C10 it currently has a 2bbl carb..... any help is greatly appriciated. Email cheguevara778@gmail.com. I dont know why I can't post the carb pics here

You just need the 2 barrel to 4 barrel adaptor between the carb and manifold! Edelbrock, Holley, Mr Gasket they all make one!

[donut]

Or hit the junkyard for a 4bbl intake. Not like they're rare. Any smallblock, spreadbore will work.

[mrolds88]

First thing I noticed in your picture was that you don't have the vacuum advance hooked up. That needs done first. I believe you have a short hose with a screw in it in the right port. Its the small one in the main body low on the drivers side. With that done, tune your idle mixture screws. turn them in til it runs rough then back out about a 1/2 turn. Both sides. Now on to the air doors (flaps on the back barrels). There is a small socket head set screw that needs loosened that is located on the underside of the airhorn on the passenger side. Once loosened, the screw that adjusts the air doors can be moved. They should be set to where the are a shade tighter that just coming closed when you tap them with your finger. You may have to adjust a little bit here and there on this, but it will get you in the ballpark. Once its dialed in, look out!! You should be pleasantly surprised.

[motornut]

Always been Quads for me,and if two,swap to four.
keep an eye out for this type with the extra holes,takes both
this ones a small block
some people play with screws when they shouldn't lol thats one reason they bog
another I've seen
is when the choke pipe, off the intake rusts out the choke stays on,thats why before messing with settings i tie off the choke...
cause that keeps secondarys from kicking in if you don't bend the rod on the side or tie it off