Getting More Cowbell from the Rochester Quadrajet Carburetor in 30 Minutes!

To optimize the air/fuel tune on the 1967 Buick 300 Mule Engine, I create a QJet just as thrown together. I rejet it and add an adjustable part throttle to make that Mule WORK! Follow along as I recalibrate and educate on the QJet in 30 Minutes!

[@jakespeed63]

Most backyard mechanics don’t understand or appreciate all the engineering that went into tailoring these carburetors for different applications. They are a wonderful fuel metering device if used properly. Thanks for the tips.

[@glennmanchester5696]

Yessir the engineers at rochester knew what they were doing most of those carbs performed flawlessly for 20 yrs or better no power valve issues or jetting issues only two sizes fit all due to the air doors etc etc they would run a lawn mower to a big block lol

[@genehart261]

Hands-down the best carburetor for GM products! Can be tuned for other makes as well.

[@billiot425olds]

Only carb I will ever use engineering excellence I've got a 800cfm on my 67 olds 425 off a Cadillac 500 and she runs like a scolded dog.

[@waynep343]

If you have a 75 to 81 with a quadrajet. You will want to do some adjusting of the APT setting. Adjustable part throttle setting. This is the adjustment that limits how far down the manifold vacuum can pull the primary metering rods. If the adjustment is too far down the air fuel ratio goes lean and it lacks in the acceleration. If it's too high. It also suffers. Get it just right. Hang on. You only need 80 feet of space to tune the apt height. A quadrajet dipstick which is a hard to find tool nowadays. Goes down the round tube bowl vent tube. Push down against the power valve spring tension. Use a tractor big bore tire valve stem tool to turn the apt screw to lower the setting till the dipstick in the vent no longer gown deeper. Bring the adjustment up till you just feel the dipstick thru the vent start to rise. Bring the adjustment up 1.5 turns. Pull out the tools. Get in. Back up and give the throttle a quick push. Like if you were on the drag strip after the burn out and blip the throttle to check the traction of the tires. If it back fires thru the carb. Give the APT half a turn up . Back up and blip the throttle again. Give it another half turn up. You will feel the difference each half turn up. When it stops improving go back down in half turn steps. The seat of your pants will know the right setting as will the smile on your face with the crispy take off. This changes the quadrabog into your favorite carb forever. The 68 to early 75 carbs are much harder to do this with. As the apt adjustment is in the base plate and you bend a wire up that sticks up above the surface of the base plate. A much harder job. Using the carb dipstick to find the factory apt setting is also a great idea before you start screwing with this setting . #you should copy and paste this info into an email as you wont find this info on apt adjustment elsewhere. Only a few old timers like me who drag raced with quadrajets know this.

[@TheVenom8343]

Damn fella, that's some good info!! I copy and pasted this into a Word File and saved it to my computer. Thank you sir!!

[@reacp9114]

On 75 qjets, apt is an actutal ajustable rod and jet

[@CK-mf6du]

Too many people cast aside these carbs for a holley. I'm amazed at how much you can tailor these carbs, and most people overlook this and choose to curse them. I love how the secondary spring tension can be adjusted, and the vacuum delay makes it all blend together. Not many carbs can do both mileage and power the best.

[@ThomasELeClair]

,,,,,,,,,,,,,,,,,,,,,,,How about tellin us people how we can make these tools to adjust this APT setting

[@CK-mf6du]

@@ThomasELeClair they have a default position. Tool isn't necessary. Get the top of the adjuster flush with the carburetor (Top off obviously)

[@denniswalker4351]

As a teenager most mechanic friends did not understand Q-Jets. You have uncovered a long mystery of how these carbs work. Thank you.

[@Mech356]

Quadrajet carbs are the most tunable and most adjustable carb for the most applications ever hands down! 45 yr master tech

[@v1-vr-rotatev2-vy_vx31]

Used to love tuning these carburetors, lot of fun especially when that secondary is open, makes that big loud wushing noise.

[@dirtyburd71]

I'll be building a Qjet in the near future. I pulled it apart and this one had the APT plug hanging low in the air horn. It also had a depression in the bottom so I used a small punch to knock it out from the bottom. What came out was a "nail shaped" piece with a large head. What remained in the air horn was a threaded piece. What I ended up doing was remove the threaded part, cut a slot in the "head" of the piece that came out, reinstalled it into the threaded part so a screwdriver can be used to take it out for APT adjustment. No threading or homemade plug! I hadn't seen one like that yet. Learn something new every day! Thanks for posting your videos!!

[@waltmoore3095]

After trying Holley,Edelbrock. I installed a Quadrajet on my 360 AMC CJ7. Couple days of tuning and this carb is awesome. Offroad, onroad,no complaints. Off camber climbing hills never sputters. Great carb.

[@markboyce1001]

When I build these carburetors, they work so well that a friend took his broken Holley off his Ford big block believe it was a 429 and made a adapter plate and put one my Quad GM carb,did not had to make no adjustment and laid rubber with his 15 in rear tires, ask me to build for his friends

[@mr.roddersneighborhood2740]

Some of those 429 ford engines came with Quadrajets, as well as the 351 Cleveland and the 400 Modified as well.

[@nicholasagnew2792]

Fun fact: They would use dual 401 Buicks to start the SR-71 Blackbirds.

[@bullriderinwrangler1]

@@Knucklehead4400 Yep, the AG330 start cart, 2 Buick 401 Nail Head set side by side to run the gear to spin the turbines in the J58 up to 3,200RPM to start them.

[@Lsx454]

Yea i thought it was a joke till i seen the engine on that cart.

[@Spiritof_76]

@@bullriderinwrangler1 340/350 would be a small block. Isn't the 401 a nailhead?

[@bullriderinwrangler1]

You are correct, the 401 is indeed the nailhead. I misspoke when I said 401 small block. @@Spiritof_76

[@Spiritof_76]

​@@bullriderinwrangler1 I'm a Buick power fan: 455, 350, 401, 425, 3.8 turbo. All a little different than the rest of GM, cool in their own way.

[@unclesquirrel6951]

Q jets are good carbs , great mileage and they sound great going to wide open . Plus a altitude adjusting bellows in some Q jet models

[@trillrifaxegrindor4411]

personally i blame q-jets

[@alleyoop1234]

@@trillrifaxegrindor4411 Knowledge helps

[@pauljohnson7may]

Used one off a Pontiac 301 on a 3.9L Rover v8 on a chopped down SU carburettor manifold,was surprised how well it performed as is and throttle response was amazing.

[@AryDontSurf]

Thanks Dallas! This is incredibly helpful.

[@alleyoop1234]

Good to see someone cover this topic. I worked in a carb and ignition shop back in the first half of the 80's & I always knocked out that aluminum plug for the APT. But I just covered the hole with a short piece of electrical tape

[@EYE_SPIDER]

Great video! Keep up the great content! 💪🏼🤜🏼🤛🏼

[@Tomcat71]

Im running the later E4MC electronic CCC setup on my Bonneville with the 350 I just built. I tuned it for 30 degrees mixture dwell at 2500 and then set my air bleed to get my 30 degrees dwell at idle. with 26 inch tires, and a good 2004r with 3.42's I pulled down almost 26 mpg doing 70 on the highway. last 227 mile round trip I just took. I love Qjets.

[@mr.roddersneighborhood2740]

Those are excellent numbers! I’ve never messed with the CCC Q-Jets. Sounds like they are not too different from the earlier ones.

[@Tomcat71]

@@mr.roddersneighborhood2740 they aren't ,only real difference is the primary metering rods are controlled by a solenoid, instead of by engine vacuum . other than that they are basically the same, You just think of the metering rods as having a window and you can adjust the window position leaner or richer by adjusting your lean stop and rich stop. long as you get your TPS set for the right voltage and set the dwell time for the 30 degree mark you are averaging the rods being fully up exactly half the time and fully down half the time and the ECM can control them to either stay down longer to lean it out or up longer to richen the mixture. but the rods are always pulsing long as the ignition is on and its plugged in.

[@Randall-to8le]

I have one and if your car won't run you better listen for the ticking and replace the 10 amp fuse before you do like me and rebuild the carb and put a timing chain on and a fuel pump and plugs and wires she still ain't right seems like I'm getting detonation in the exhaust maybe I check the dwell

[@mvg-1776]

The q-jet sounds so good when it is wide open.

[@mr.roddersneighborhood2740]

I agree! an awesome sound to behold!

[@ThomasELeClair]

,,,,,,So you showed how to remove the plug and access the adjustment to prevent Quadrabog,,,,,,,BUT no details about how to adjust the height of the metering rods....@@mr.roddersneighborhood2740

[@jodypierson3137]

Great information, very useful

[@waynep343]

Tip. Accelerator pump rod. Stop driving the pin out. Take out the tear two long screws. Take out the 2 or 3 base plate screws. Take off the base plate. You can turn the base plate to unhook the bottom of the accelerator pump rod in 30 seconds

[@tonymaglio9376]

cool video very informative. Ex GM mechanic I used to clamp a long drift punch in the vice pointing up. Set the carb down in one of the back mounting holes onto the punch. You could spin it around 360.

[@mr.roddersneighborhood2740]

Great tip! I'm glad you liked the video!

[@VinnyMartello]

My 66 Chevy pickup rocks a 350 Buick and a quadrajet. It is my daily driver and tow rig. Much love for the Q-Jet.

[@mr.roddersneighborhood2740]

Perfect Truck engine! I love the 350 for that exact reason...Big Block Torque and Small Block Gas Mileage!

[@171apples171]

My God man i messed with that APT screw on the Q-jet on the 425 in my 79' Coupe Deville. Long story short, i didnt know what i was doing. Thinking back now (older/wiser) i never even put a timing light on it. Just a big open parkinglot and a tool i made out of brake line, in the dark... Seeing if it took off any harder after some adjustment hahaha

[@Ncaa67]

I actually love my Quadra jet, I have a 454 big block and I get 1000 miles on a tank of gas! Granted it is a 100 gallon tank but 10 mpg out of a 454 in a 36’ long 1986 Fleetwood bounded RV is great, and when I hit the gas it even picks up the front a little. But it won’t stop for shoot. And not I don’t cook up anything weird in it.

[@twobeards6714]

Never enough cowbell

[@thisisyourcaptainspeaking2259]

I run a QJ on my 231 Buick, it runs perfect and very strong.

[@dale116dot7]

I had no problem understanding the Q-jet. The front half acts like any other carburetor with a vacuum power valve or metering rods. The back half works kind of like a SU variable-venturi carburetor with the metering needles. That understanding makes tuning videos like this make a lot of sense to me. These days I work on EFI all of the time, but these carbs work quite well in my opinion.

[@carmudgeon7478]

Some things I like doing to the Q-jet is hone the accelerator pump well, use the close hole in the pump arm, use a lighter spring in the off idle piston, fill the air bleeds and drill them out for each vehicle until there is no cold stumble, all to make the primary as lean as driveable. Then fatten up the secondaries and adjust them to come in quickly. Gets 15-17 mpg city out of a 74 455 Grand Ville and 75 454 Monte Carlo. 23 highway on both if driven judiciously with the AC on.

[@mr.roddersneighborhood2740]

When they are right, a QJet is an awesome carb! Sounds like you have got them figured out! Wish I had the same experiences, sometimes they don't work out for me... especially when the combo of engine is too far outside of the normal factory calibration and I'm having to get one dialed in. Lot's of trial and error on my part. Thanks for the insight!

[@jonellwanger7258]

I had issues with my Buick 464. I pulled the idle tubes, and drilled them out slightly. Stumbled gone funny idle gone. I’d have to find the “build list” That lists the size I drilled to, but I’m in Colorado with no air.. you being lower Alt. might want to drill them larger.

[@wesalker3479]

A set of wire gauge and machinist grade drill bits and a pin vise can come in very handy if/when access to metering jets isn't possible.

[@g2skinny]

Great video bro my boss has I bet over 100 of those carbs he loves them

[@blainesnider9089]

Brad urban actually did my carb back in the day. I met him.

[@GlennLittleford]

I swapped the pin for a screw in the accelerator pump lever fulcrum. Makes it a bit easier.

[@peterkovacs8654]

UTG did a Q jet video today too! Q jet Sunday!

[@mr.roddersneighborhood2740]

What! He’s dabbling in my Kool-Aid…ha! Great minds think alike!

[@carmudgeon7478]

Great minds run In the same gutter.

[@johnmcdonald3231]

How do you adjust the APT? What tool fits to adjust?

[@ezkempinkemp3467]

Thank you.

[@leightonfarms4962]

Excellent

[@waynep343]

Tip quadrajet stand. With some sections of all thread bolt together 4 or 5 old thick base plate gaskets. If the all thread is 2 or 3 inches long. You can put a nut on each. Half an inch from the end. Now you have a carb stand

[@tiledave621]

I just realized my SMI Q-jet carburetor already has a pipe plug installed. Pretty cool. Which way do I turn the screw to start my adjustments?

[@mr.roddersneighborhood2740]

Counterclockwise increases fuel, clockwise leans the part throttle mixture.

[@manicmechanic448]

I've got a 75 800 off of a Cadillac. It had that stupid altimeter thing. I tried running it on my 355 Chevy. It ran decent. Maybe if I'd tuned it a little better. What's weird is I used all the guts, metering rods and jets, out of my 72 750, off of a Checker cab. And it got horrible fuel mileage. So I put the 750 back on.

[@jtp682]

Very good video! I need some advice on something. I recently bought an 1986 chevy truck with a V6 4.3. It has a propane system on it and the original carburetor is no where to be found. I have a 78 quadrajet that I just rebuilt and would like to install it. the truck intake manifold is the original four barrel spreadbore quadrajet carburetor set up. Also this engine has the electronic spark control distributor without the vaccum advance. if I put this 78 carb I got on it do you think it will work just fine?

[@mr.roddersneighborhood2740]

It depends what the 78 carb is off of originally. The best stand to take is gonna be no, it likely will not work correctly without a rejet, change in metering rods and air bleeds. But that is not all that hard… finding the correct 4.3 v6 factory calibration information may be the tough one. Call Cliff Ruggles at Ruggles Performance or Quadrajet Power to get an idea of what calibration you would need for that 4.3.

[@artjones2498]

I never realized that buick quads were so specific....i got 1 off a 350 chev in a olde C50 series dump truck....and bought 1 at a flea mkt. With a ton of vacume hose's...the guy told me it was from a mid 80s 305 chev...im gonna use 1 of them on the 350 in my apollo..when i finally get the gaskets to swap the 4bbl intake on it....im gonna have to e-mail some questions to you dallas

[@mr.roddersneighborhood2740]

Don’t even bother with one of those carbs. It will likely run pig rich and you will hate the whole thing. Get a Buick specific carb or you are gonna hate life.

[@punch_bowl_turd3005]

didn't know that bout jet performance. i have their stage 2 on my gm crate L05 350.

[@toddmccarter45]

6:45 hey I have that same pin punch!

[@motorol5610]

Carter also lent a hand at building qj we had a 70 pontiac bonnevile with a carter stamped unit.thought that was interesting

[@mr.roddersneighborhood2740]

I had one of those too from a 1969 Pontiac. Apparently Carter was contracted to make them because the demand was so high Rochester could not keep up.

[@Rick-Williams59]

I love quadrajets, the only issue I've ever had with any of them is the small fuel bowl, I had big block Chevys run into a fuel bog, stock fuel pump can't keep up.

[@mr.roddersneighborhood2740]

I try and not use them for a hot street application or racing. I use them for daily driving and for that purpose, you would be hard pressed to find a better carb.

[@72chevelle156]

I have a video on my channel called "does your qjet lean out on the top end" it's a simple fix, costs $0.

[@ivanr5436]

Ive got a chevy 350 mildly built. Mild cam, longtube headers but a stock emissions era qjet carb 1977. What would be an ideal jet set up and tune. Would Edelbrock jets work on a qjet?

[@mr.roddersneighborhood2740]

No, Edelbrock jets are not the same. The easiest thing to start with when trying to find your correct jet and rod combo on a 1975+ QJet, is to start with the stock calibration and slowly adjust the APT (adjustable part throttle) to determine which way you need to go in your combo.

[@partymanau]

Best Carb ever made, forget Holley for ur streeter. Learn these and u will have power and economy depending how u drive. Infinitely adjustable once u know how.

[@partshoard72]

Thanks!

[@jorgegomez4608]

The idle air bleeds better have them Lean if have rich condition off idle Fill them and drill in steps to Adjust throttle tip in

[@TOMVUTHEPIMP]

I want a Q-jet for my 84 C10. Problem is there's 80,000,000 different designs. Findings 3 or 4 of the same design to build 1 good one is not easy. The one that came on my truck is trashed.

[@mr.roddersneighborhood2740]

The one that came off of it can likely be saved. I saved my 71 stage 1 carb and it had corroded away half the main body.

[@ClintsStreetMachines]

More cowbell...Howling, too funny.

[@davidcallahan5157]

What was the number on the metering rods?

[@mr.roddersneighborhood2740]

48K rods

[@kingcosworth2643]

Technically that's the cruise mixture adjustment isn't it? All the Quadrajets I have had access to in Australia has the cruise adjustment in the base plate, right in the middle between the idle mixture adjustments.

[@mr.roddersneighborhood2740]

As far as I know, that is called the part throttle adjustment. I guess it could be considered a cruise mixture, but it does effect the entire off idle mixture.

[@Joe-xj2tb]

What is this cowbell you speak of??

[@831Batman]

I have a 88 chevy g30 van with the same carburetor I need parts for it but can't seem to find and any. Problem being the secondaries ain't opening when going uphill or trying to gain speed if anyone has any info on that I'd appreciate it. Thanks in advance.

[@M45Rider-tl7cu]

I believe I have one

[@Spiritof_76]

Cliff's performance, quadrajet parts, quadrajet power, Mike's carburetors: these websites all sell parts.

[@forthwithtx5852]

Do you need a pin punch set for Christmas? Maybe start an Amazon wish list.

[@mr.roddersneighborhood2740]

Did my ground screw not do the job? LOL! I'll start a wish list on Amazon...

[@67L-88]

Q-jets always run good but I never liked taking them apart or fixing them. Do they still sell Jiffy-Kits? I had them run 250k mi and never need a thing I have had them on boats too, 454s always ran well with them just try to keep the secondary from opening. or youll go from 15 gallons an hour to over 30 per hour, not fun when you have two burning 60 gallons an hours. Even short bursts make the gas gauge drop.

[@gotrust4741]

What happens if those little air bleeds get clogged

[@mr.roddersneighborhood2740]

It will run fat! Really fat!

[@briansd2772]

Try extra-thick .062" gasket for warped air horns.

[@mr.roddersneighborhood2740]

Yes, I've found those helpful too. They are available from Quadrajet Power.

[@72chevelle156]

I wish qjets had 1100 cfm option

[@mr.roddersneighborhood2740]

YES! That would have been an awesome Carburetor... could you just imagine the noise it would make when the secondaries opened if it was 1100 CFM? It would have been an even more awesome sound!

[@t-rodshader9593]

They have made them 1,000 so I've heard, I do not however know where you'd ever find one.. but I've heard a few people bring up the fact that there have been modifications made to them over the years that has made this possible before

[@mazterplumber2549]

Did you and uncle Tony plan this

[@mr.roddersneighborhood2740]

It was all coincidence. If ya go fishing in the pond, your bound to catch a fish… he never showed interest in a Quadrajet video. I’ve done a few, never thought he would do one.

[@N2YTA]

I'm missing something. You knocked out the plug, then tapped it and added a threaded plug. What was the difference between the hole being sealed with a pressed in plug or a threaded one?

[@mr.roddersneighborhood2740]

I can access the pipe plug from the exterior of the carb without removing the air horn or carburetor from the engine. This allows you to adjust the adjustable part throttle on the fly to improve the drivability without a carburetor breakdown.

[@daledavies2334]

Threaded plug is easily removed to make an adjustment.

[@briana3467]

I use chapstick on my gaskets to keep them from sticking.

[@luispina4012]

👍👍

[@rmg3008]

What is the difference between a Quadrajet and Rochester Quadrajet

[@mr.roddersneighborhood2740]

It’s the same thing, Rochester is the manufacturer.

[@rmg3008]

@Mr. Rodder's Neighborhood thank you I didn't know i bought one at the auto fair in Charlotte last Saturday, it had Quadrajet on it but when I was younger and the early 80s I had a 69 nova the best I remember the carburetor had Rochester Quadrajet on it, I wasn't sure if one produced more horsepower, thanks for the information.

[@shootermcgavin2819]

"go home ball"

[@nicksnarski5973]

Do dad aka float block.

[@mr.roddersneighborhood2740]

Excellent! It does have a name besides doodad. Thanks!

[@briansd2772]

Float Bowl Insert. Shave 1/4" off bottom to free up space better used for more fuel.

[@stephennichols4815]

Isn't that a 1/8"pipe tap

[@mr.roddersneighborhood2740]

Yes, did I say otherwise? I can’t remember.

[@ThomasELeClair]

,,,,,,,,,,,Ok ,,,you showed how to access the adjustment,,,,but left us hanging.......How do you adjust that strange lookin double -D screw , which controls needle depth and height of travel........

[@mr.roddersneighborhood2740]

Start at 3 turns from the bottom and then adjust it in 1/2 turn increments up or down to get the fuel needed for quick acceleration. If you find yourself with greater than 5 turns up(richer) go to the next smaller metering rod and start all over. Driving it is the best to get a feel for what it needs in regards to fuel.

[@elebeu]

So where is the cowbell info.? This was a disassembly video that anyone with a Quadrajet already knows. A two minute video on the plug conversion would have been sufficient.

[@dirtyburd71]

BTW, haters may send their Qjets to me if they would like! 🤪

[@SSGTDSG7]

WOT

[@unclesquirrel6951]

Personally I blame squirrels

[@SpecialAgentJamesAki]

Hi uncle squirrel

[@manicmechanic448]

I blame Biden.

[@jamesbennett9654]

Q jet carbs are junk, small float bowl that can distort causing the float to stick down, holding the needle valve open, leaving raw gas to pour out all over the motor, which in turn catches fire; have seen this happen at least two times, 59 Chevy truck with a 400 Pontiac motor, then a friend's 1965 Chevy convertible burnt to the ground because of Q jet carburetors with stuck float, and failing to shut off fuel supply , flooding carburetor all over the intake manifold and down the spark plug wires and "Hot" exhaust manifold!!!

[@repete2362]

warped top plate yess how would you warp the main body? i'd guess more of a didn't get the needle valve in correctly .

[@gregrenner3228]

Could be problem in boat.

[@josematanzo5879]

I used to have a Chevy nova 1977 with a 350 cu and jets on the quadrajet were 75. Any below you just trying to save fuel.

[@mr.roddersneighborhood2740]

Not at all, the jet size is directly related to air bleed size. Chevrolets use humungous air bleeds, hence huge jets. This is exactly why taking a q Jet off one combo and putting it on the next generally never works out well.