Quadrajet have to change metering rods

[Olds Eddie]

Re: Quadrajet have to change metering rods

I have 2 marked 42B. If these will do I'll contact you through e-mail.

 

[AdamB]

Re: Quadrajet have to change metering rods

Mine are marked 42, not 42B, I wouldn't know what the difference is, unless one if for auto and one if for marine?????<br /><br />The mixture screws are a little weird...

 

[rodbolt]

Re: Quadrajet have to change metering rods

I like the Q-jet. its been about in the sme basic design since 65. works on almost anything. and if your careful and study how and why carbs work to start with its a simple carb to modify. it will make power to about 500 HP if the correct parts are used. much more and the intake vacum at low speeds wont hold the primay rods in place. if ya really wish to complicate life use the motor craft duel inlet needle spreadbore that ford used in some of the 429-460 engines and jeeps used on the 401's.<br /> the Q-jet was the replacement for the troublesome and more complex rochester 4GC. but I have found the Q-jet to be solid performer for those that care to study how it works. it helps that I did a 5 day rochester course in the mid seventies as well. as far as changing from 42's to 43's if all else fails then open up the primary jetting a few thousanths. but the characteristic lag on rapid acceleration is just part of it.

 

[Olds Eddie]

Re: Quadrajet have to change metering rods

I agree with rodbolt. the q-jet is a fine carb. It's my understanding that the 'B' rods have a little different taper but the same size big and small diameters.

 

[AdamB]

Re: Quadrajet have to change metering rods

Rodbolt, could you elaborate on the characteristic lag on rapid acceleration problem... can I get rid of this with tuning or is it just an inherent rochester problem...<br /><br />I just read a web site that did say the B's were for auto, but with some modification they will work in marine use. I think I'll just start with the 43's and go from there. This carb was originally on a 305, and now a 350 and I'm not sure if the original owner changed jets at all. I guess I will play around a little.<br /><br />does anybody know what main jets and metering rods were used in the 350's??

 

[jimmbo]

Re: Quadrajet have to change metering rods

"B" rods have double or 2 step taper versus the single taper of a non B rod. The B rods were introduced in 1968, probably to have finer control of the mixture during light accelerations in autos. Whether these are used in marine/offroad apps, I don't know

 

[rodbolt]

Re: Quadrajet have to change metering rods

I just did a pair today on a 260 merc that used stepped primary rods.<br /> AdamB<br />the lag is most noticable during rapid acceleration from a medium speed.<br /> but was a wonerful sound on a 350 with the aircleaner lid flipped <br /> makes kinda of oooohhhh-whaaaaa sound<br /> its a momentary lag that is inherent with the design. there should be no popping or backfireing but if your crusiing at 3K and nail it you will get a momentary bog. its just the time lag to allow air pressure to overcome the secondary air valve and start raising the secondary metering rods. the "power" valve is also the primary metering rod hanger. on sudden throttle opening intake vacume falls and the spring pushes the hanger to the full up position. but all this takes a moment so you get a slight bog. a holley with mecahical secondaries and duel fuel pumps will bog a bit less but most likly will be to much for a stock motor. would require some serious playing with sqirters,pump cams and power valves. so if this is just a momentary bog you may be able to lessen it some by playing with the airvalve spring tension. if you do keep written records of how much you adjust it and which way. you may need it later . but yes the sound of a q-jet on a 350 was a fun sound

 

[jimmbo]

Re: Quadrajet have to change metering rods

You shouldn't get a lag, hesitaion or bog if the carb is calibrated correctly. Most of the time it can be corrected making sure the choke pull off diaphram is not bleeding off too soon. On a lot, if not most Q-jets this pulloff also holds the secondary air valve closed and prevents it from opening too soon. Tightening the spring that closes the air valve will slow the rate it opens and most likely prevent a leanout and resulting bog, lag, or hesistation.

 

[Peter J Fraser]

Re: Quadrajet have to change metering rods

AdamB,<br />From what I've read lately I understand that the 350 and 305 used the same carb.<br />I have a 350 Q'jet for the 305 engine I am going to fit into my boat next winter.<br />This link may be of interest to you. Qudrajet Tech Info <br />And this one More Q-jet stuff <br /><br />Both have a lot of info to help.<br /><br />Good luck<br /> <br />Peter

 

[rodbolt]

Re: Quadrajet have to change metering rods

I will bet I have sawed in half both lengthwise and cross wise and made more mods to a Q-jet than most people have seen. the bog is a fact of the design. it takes time for the secondary bleeds to supply fuel. it takes time for the primary circuits to fill to capacity. way more time than the throttle plates take to open. but there are many things that can be done to help lessen the chareteristic lag of the Q-jet. most require hours of playing.there are some mods that can be made to the bleeds,pump squirters and power circuits. however I have also scrapped more Q-jets than most have seen. people have gotten to used to the instant throttle response of todays EFI motors.we have even rigged electric solinoids on the vacum pull off to assist in opening the air valve while adding a secondary accelerator pump circuit. all the F and G stock rules said is that it had to be a Q-jet. did not say anything about modifying it. but any stock GM or Ford motors with a Qjet will give you the oooohhhh-wwhhaaaaaaaa if ya nail it from about 30 MPH.same in a boat<br />] if your tooling about at 2600 and nail it its going to lag slightly.<br /> how bad AdamB's lag is is unknown without actually hearing it.but it was a nice sound on a saturday night when cruising the stip or hanging out at the court house square. its a sound only a small block with a Q-jet makes. especially if the air cleaner lid had been flipped.one of the best mods were making our own seconday jets and cutting off the tips of the seconday metering rods. but we were not interested in midrange drivability nor fuel economy. we did not figgure the 4 gallon tank was going to go very far anyway. <br /> <br /> AdamB<br /> is your bog problem just on a rapid acceleration? and how long is the bog? does it happen from a mid-range to WOT or from an idle? is there any backfiring with the bog?

 

[AdamB]

Re: Quadrajet have to change metering rods

I think mine is a problem because the carb needs to be re-built. Although, when I did take it apart it wasn't that bad, and the gaskets didn't look too worn either (except around the accel pump)<br /><br />I am talking about a bog from just having it in gear to tighten the ski rope, and nailing it to WOT instantly. Bog to the point where I'd have to back off the throttle for it to overcome the bog. Sometimes, it would even backfire, but very rarely. I am hoping the carb rebuild I am in the process of doing will eliminate this for the most part. I just finished JB Welding around the metal caps and hopefully when I get home tonight I'll get the carb back together. I hope to have her running this weekend and will post a follow up.

 

[AdamB]

Re: Quadrajet have to change metering rods

Update, well while assembling the carb last night, I some how managed to lose the spring in the power piston assembly. I had to borrow a spring from something non carb related. I guess this will be hit or miss, but I made it so the power piston goes all the way up, without popping out of place, also, will go down to ride in jets with vacuum pressure with a little bit of pressure on my finger. If this doesn't work, I'll have to order a new one. I am just trying to get this back together for this upcoming weekend.<br /><br />I got called into work early today, so didn't get a chance to install. Will hopefully get done tomorrow or Sat a.m. early.

 

[jimmbo]

Re: Quadrajet have to change metering rods

Originally posted by AdamB:<br />[QB] Update, well while assembling the carb last night, I some how managed to lose the spring in the power piston assembly. I had to borrow a spring from something non carb related. I guess this will be hit or miss, <br /><br />Oh Oh

 

[Olds Eddie]

Re: Quadrajet have to change metering rods

That spring determines when the valve opens under load to enrich the mixture. It functions like the power valves on a Holly. They come in different tensions to calibrate for things like radical cams and short gearing.

 

[AdamB]

Re: Quadrajet have to change metering rods

Oldseddie,<br /><br />I don't know what you mean by "determines when the valve opens under load" It seemed to me that the spring will hold the power piston assembly and metering rods out of the main jets when there isn't any vacuum (like when not at idle), otherwise, when the vacuum is high, it sucks the piston down and the metering rods go into the jets to lean the mixture when at non peak power demading times, like idle or just off idle etc. I figured the worst that could happen is it would run a little rich at idle, which I could hopefully tune out with the mixture screws. Do I Have this wrong?? I know it's a finely balanced mechanism that won't be perfect, but hopefully it'll still run until later time when I can get the proper parts (like a non Holiday weekend).

 

[rodbolt]

Re: Quadrajet have to change metering rods

it may<br /> we used to cut them up and add small washers under them all the time. especially when the rules allowed some of Luanati's cheater cams. we had to run the Q-jet. however we could chop on them, weld on them and modify them anyway we wished. sometimes it worked sometimes it junked the carb. lucky one of our sponsers was a rather large wrecking yard outside FT worth TX and Q-jets were free. but if it does not allow the rod holder to raise fast enough be prepared for a heck of a pop and if the flame arrestor is off you will see why its supposed to be on.

 

[AdamB]

Re: Quadrajet have to change metering rods

Rodbolt,<br /><br />Couldn't be worse then the pop that blew an exhaust elbow while on the ocean. I got to see first hand how much ocean water can come into your boat through a large exhaust tube. On the plus side, I did notice the flapper was loose and not stuck, although it didn't keep the water out. Thank God I made sure the bildge pump and float were working prior...

 

[AdamB]

Re: Quadrajet have to change metering rods

Hey, started and idled great. Unfortunately I managed to ruin my impellor. I tried to sink the outdrive into a bin of water, but it didn't work and the impellor destroyed itself. Should have stuck with the muff method.

 

[Olds Eddie]

Re: Quadrajet have to change metering rods

It may work without the right spring under the 'power piston' which holds the rods, but as I stated, it is supposed to be calibrated so as to enrichen the mixture when the throttle valve is opened and the vacuum drops. I would recommend you replace it before any serious time is spent trying to tune it. My friend that builds Busch engines says that in a boat where the engine runs at a steady speed, the vacuum will build back to the point that the power valve/piston will close. You may want to put in a stiffer spring while you are at it. Jegs and Summit both carry tuning parts for the Edelbrock q-jet.

 

[AdamB]

Re: Quadrajet have to change metering rods

I didn't get a chance to run it long, since I watched my temp guage climb steadily upward I figured my impellor must have sucked air from the bucket I was running it in.<br /><br />I had planned on reaching into the vent to see how far down the power piston was sitting while the engine was idling. I was going to use a pair of long bent needle nose (I practiced before installing so I think I can do it relatively safely) I put in a pretty stiff spring, and not sure it'll even seat fully into the jets with full vacuum.