So, after the a&*'-kickin' that Donny Brass laid on me this weekend, it's apparent I'm going to have to learn to tune a Quadrajet. This GTO is the first car that I've owned with one and as much as it embarrases me to admit, I have no idea how to tune it, nor have I yet met anybody in the state of Ky that I trust to be near my car. I know they have metering rods vs the jets that a Holley has and I purchased some from Cliff Ruggles last year (gave him my engine combo and he had four sets made in the range he thought would work). However, I don't know how to access them and don't want to jump into the carb without a clue about what I'm doing. The car is off 8-10 MPH and 3/4 to a full second from where it should be. The car has great throttle response off of the line, with no bog, but it's running out of fuel (stops accelerating and surges) at the top of 2nd gear (about 4800 RPM) and again at the top of 3rd (about 4,000 RPM). It pulls strong in first gear, at least to about 5200 RPM, which was as high as I pushed it this weekend, but it should pull to about 6,000 RPM with what's in it. On the street, the car performs well, but I'm not making full throttle runs on the roads around here. Questions: -Should I get a fuel pressure gauge on it between the carb and the pump to see if I have a fuel pump or a fuel metering issue? - How do I access the metering rods? Once I have access to them, how do I remove them? -Is there anything that I have to be careful of when swapping them? -I see that the rods normally are identified by a letter code (CC, CE, CZ, etc.), but the one's that Ruggles sent me are identified with a # (I'm assuming the diameter). They also have letter codes, but he turned them on a lathe, so I'm not sure the letter codes still matter (Incidentally, they are CZ and DA). The rods appear to have differences in diameter, taper and length to what appears to be their seat. How do I decide which ones to swap next (it doesn't seem to be as easy as w/a Holley, just add two to the # you've got and pick that one)? I've got a junk old Qjet that I can practice on first, just to learn how to get to the bits, but figured I'd come here for advice first. Here are the specs on my engine, if it helps: 461 Pontiac Ported # 16 heads (roughly 260 cfm @ .600 lift, 250+ between .500 and .600) extrude honed, but otherwise stock Pontiac Q-Jet intake 9.5:1 compresson SD Performance "stump puller" hydraulic roller cam (.550ish lift and 230ish/240ish @ .050"lift)
Here is something I saved years ago, so some of the links have gone dead over time. The rear metering rods can be changed by just pulling the air cleaner and removing the small screw between the rear barrels, then lifting the tin hanger and rods out of the carb. I suspect some reading up on q-jets would help, but in general, they are rather simple once you get the hang of it.
X2 what John said, changing the secondary rods can be done easily w/o removing the carb. There are also different hangers for the rods that pull the rods out sooner...or later. Again that's a simple thing to change. More important...what number carb? What year car and engine? Stock fuel pump and lines? Has the carb been rebuilt? There are 750 + 800 q-jets, and some Pontiac carbs have a huge vent in the front. The size of the float can vary, it affects how nuch fuel is on hand in the carb. Some q-jets have a longer fuel filter housing, that holds a little more fuel, too. There is the size of the needle and seat that brings the fuel in. There is a LOT of stuff to mess with. Cliff is a good carb guy and we have a couple good ones on here, also. I'm no expert, that's a big engine that would need a lot of fuel. Just curious, what year is it and what kind of times is it running?
It's in a 68 GTO. The block is a 67 400 block, with 68 heads, intake, etc. The car weighed 3855 with me in it and a 1/2 tank of gas. I'm running a 3.73 gear and a 2500 convertor. The best pass of the day was a 13.35 @ 100.75 MPH, with a 2.12 60 ft. Somewhat ironically, its a Holley reman that I bought from Summit when I discovered my other Carb wasn't serviceable. cfm rating is unknown. Stock replacement Carter "Musclecar"pump. Stock replacement lines and tank.
I'd check the secondary well openings for size or restriction, make sure all of your pickup tubes are still interference fit in place in the airhorn and aren't drilled full of holes, your float level is correct (.250 for your application?) and you've got at least a .135 needle and seat. I don't think your issue is with the primary rods, you can try different size secondary rods but you still should be OK with anything in the .040 - .050 range. Also check secondary air valve tension and make sure it's not flopping around for whatever reason. The are great carbs when set up correctly, and you've got great resources on this board here in either Cliff, Ken (Everyday Performance) or Mark form Texas (?). Good luck, keep us posted.
You might want to check this link out to. It has to do with distributors and can make a big difference if you can get enough bite to hold the tires on the low end. http://www.highperformancepontiac.com/tech/1308_how_to_optimize_the_centrifugal_advance_in_pontiacs/ .
'Nother thing, if the rear upper flaps on your carb don't look like this with the openings in the upper flaps and the enrichment holes in front of them, I'd bet the carb isn't correct and isn't letting you make as much power as the factory carb was possible of. There are other solutions if the notches aren't there though. :Brow:
I also forgot to add the link to my post waay up above. Some of the links have gone dead over the years, but you should be able to gain some info on q-jets. Moral of the story is; Never drink and post at the same time. http://www.florida4x4.com/tech/quadrajet/
Buy Cliff's book.....Its what I did several years ago and it taught me the ins & outs of Q-jets....Very easy to understand and do As to your problem, your runing out of fuel, quite possibly the fuel pump, buy a Stage 1 replacement, pushes more fuel than regular BB one.
If it is not pulling at higher rpm, you may be running out of fuel. Set the float level to 9/32". Make sure you have a high flow needle/seat to get fuel in the bowl. You need about 4.5-5# of fuel pressure is all for the Quadrajet. Changing the secondary rods has been covered, so you can go with smaller tip. You also want to make sure secondary throttle blades are opening all the way to 90 degrees at WOT. Last thing to check is the secondary air valve spring, make sure it is loose enough that the air valves will open all the way.
Hey Randy, I don't know if this applies to your car or not, FWIW, try filling the tank up. I had a lean mixture problem with my 70' Olds last year, several Oldsmobile guys told me to stop running with a half tank. Apparently, the fuel pump pick-up sock will starve under hard acceleration. I filled it up and and got some relief, got some more relief from being pitted next to Greg Gessler. He walked me through setting the proper float level and loaned me some of those hanging metering rods. Car picked up 7-8 mph if I remember correctly. Nice to see you out with a car again. Steve
If you haven't done it, I would definitely watch fuel pressure and see if your pump is keeping up. If you ain't getting fuel to the carb, it's going to be hard to do much tuning to compensate.
Have you considered sending your carb to a pro like Carmantx for a custom rebuild to your cars specs?
I've contacted Cliff Ruggles re: building me a carb, but as most on this board now, there's some significant wait time there. I played with my old carb yesterday and found/removed/replaced the metering rods. I also pulled the air horn off, just to peak around inside. I checked the linkage to make sure that it had full travel when the carb was put on, but never thought to check that full linkage travel=full throttle blade travel. Will check that this weekend and maybe throw a pressure gauge on it. If I have good fuel pressure and the blades are fully opening, I'll try playing with the rods. I have Cliff's book and scanned through it last night. As I understand rod/jets need to be somewhat matched. I didn't see the secondary jets in my old carb when I pulled the air horn off last night and didn't see them pointed out in any of the illustrations in the book. I thought the metering rod went into the jet? Do they thread in from the bottom, between the base plate and the main body? Hodges, Good to see you too. Your Challenger seemed to hook really well. What were your 60 ft. times like?
Take it off the engine and completely rebuild it, then you can be 100% sure it's all good, otherwise you're still just guessing, but you are on the the path to enlightenment grasshopper!
Secondary jets aren't screw ins and they aren't normally changable. They look look like little different colored metal circles on the bottom of the float bowl.
yes, no factory interchangeable secondary jets, only the rods are easily changed. Primary jets and rods are matched for each build. The Quadrajet has a very small fuel bowl and it is not uncommon for high horsepower engines to run out of fuel unless the Quadrajet is prepared correctly. if you need parts, get them from Cliff, he is my source for all parts. I don't know what you have now, but you should get from Cliff (if you are doing this yourself): 1. new float, smaller body 2. set float to 9/32" 3. new high flow needle/seat 4. new jets/primary rods 5. possibly go ahead with His HR kit make sure you have good volume on fuel pump, but keep pressure below 5#. good luck, hope this helps. my basic adjustment sheet might be helpful View attachment Quadrajet Power Adjustments.pdf
I'm with Mark on this - but also check the passages that allow the secondary wells to fill with fuel - check them for blockage obviously, but they often can be like .025 from the factory. You'd want to open them up to at least .035 and allow those wells to fill quicker under WOT. While it's always a good idea to make sure you've got full opening of the secondary air valves and butterflies of the baseplate, I don't think that's your issue here - they would just rob you of power, but not create a intermittent condition.....unless the spring tension of the air valves is so screwed up that they bang open and shut during WOT...could be either too tight or too loose that would do it, but you generally see that as more of an issue in 4 speed cars. Cliffs book will give you all the info you need to confirm proper tension, but I use 3/4 turn past initial contact, and that's too loose for a lot of people. And while it's also a good idea to make sure you've got the correct primary jets and rods, I don't think that's the issue either - I'd think they'd show up on launch or part throttle......
I got to play with the car for a little while today, then ended up working until the evening: -Double verified that wide open gas pedal equals full travel on the linkage. I also verified that full travel on the linkage equals full travel on throttle blades. -Set fast idle while I was there. I'm sure that's unrelated to the issues I'm having, but it was just bugging me that it wasn't set. -Pulled metering rods. The very tip on the one's in the car were .0120" inch. The one's that Cliff made me are .043-.054, so thicker than what was in it. The rods in my old carb were .0115 at the tip, so I put them in. That's as far as I got today. Still need to pick up a pressure gage. I didn't get a chance to take it for a drive today, maybe tomorrow.
