I am running a late model 800cfm quadrajet on my BBB. I have idle, cruise tuned exactly where I want it. WOT power is good, but I am running at 13.2 to 13.6 A/F from 4250 to 5500 rpm. I would feel much better if I could get it down into the 12.7 range especially at the higher rpms. I am already running the smallest secondary rods I could (CC). What options should I pursue at this point? Carb info: Carb number 17057553 0507 74 main jets 50m primary rods CC secondary rods TA 290-94h cam 1.6 roller rockers Edelbrock stage 1 heads TA 1 7/8 headers Edelbrock performer intake Factory ram air cleaner
Be careful, use calipers, and chuck the rods in a drill and turn then down another few thousandths. Till you get it where you want it I couldn't find my q jet book to see what cc's were, i have a set here i turned down to .036 or so, if you want to try them, they are yours.
whats your air flap open distance set at, and do you have a good(not worn out) secondary air flap cam?
CC is .0303 so it is small. Do as mentioned above and check the cam, opening distance and hanger. You can adjust the rear hanger height by raising each side one at a time. For reference point, you can measure from top of air horn to rod hole. You may be able to relax your air horn spring to get more opening also. Good luck. Keep us informed. I would like to hear what helps you get what you want on it.
The hanger...of course. p I have an M in there right now. I have a few others. The chart I have shows that the earlier in the alphabet the letter, the more secondary fuel you should get (so more with B than M). I will try my H and F hangers tonight. (The carb is new....secondaries confirmed to open all the way).
Not to sure about the file down the rods in the drill method. Those rods have a coating that will be ruined when you do that. The rod will then wear fast. CC rods are already like needles anyway. ---------- Post added at 12:30 PM ---------- Previous post was at 12:28 PM ---------- You may also want to look for a 71-74 455 carb. They are better. ---------- Post added at 12:30 PM ---------- Previous post was at 12:30 PM ---------- You may also want to look for a 71-74 455 carb. They are better.
The rods i did that to were not original qjet rods, not marked and different metal, they did not wear after 3 years of use.. Could possibly drill the jet a bit larger, if you wanted to try that. A racer here witha rather fast GS used a q jet, he said he had the press in stainless jets removed and replaced with Holley jets, go big and tune with rod again. Now i wouldn't try that myself, but maybe others have done it.
The "M" series primary rods are most of the problem. I'd reduce the main jet size to 73 and install our 44 primary rods with .026" tips. Check the size of the main airbleed tubes, they should be in the .026-.036" range. Smaller tubes will fatten up full throttle A/F some. Not keeping the carb full on hard runs is another tuning issue. .030" CC secondary rods would typically be "pig" rich in that carburetors for what you are doing, so most likely there are other issues, or something fundamentally wrong someplace, fuel pressure, float level, size of the fuel inlet seat, etc......Cliff
Ok, here is where I am at. Determined the problem was that the secondaries not opening completely....the adjustment spring was too tight. I am embarrassed to admit this....never thought to check it. I bought this carb from a company that supposedly built it custom for my specific engine.....I learned my lesson. I was trying to save some time by buying the carb I did. I have now spent so much time in this carb I would have been many hours and hundreds of dollars ahead if I had just rebuilt one and tuned it myself using cliff ruggles book as a guide. So.......I decided to start over......used "recipe 2" as my base from the book. I still need to measure the various tubes and restriction orifices next time I am in there....but it was very late and I was pretty sure I had found the smoking gun. Ended up with 45 primary rods (had a set of no step, full taper, long rods in my spare parts), 72 primary jets, H hanger, and AY rods. I think I may still try the 44/73 recipe that cliff suggested above, but I went with what I had on hand and used the APT to bring it in. I live at 5500 ft elevation, so the 72 may be good here. Pretty happy. Smooth off idle, good part throttle response, and 14:1 A/F at highway cruise speeds. (Keep in mind this carb was shipped to me with 76 primary jets, 47k primary rods, and CE secondary rods with a M hanger......supposedly custom built for my application) So, all should be good, right? Well, I experienced something interesting when switching from the CC to larger secondary rods (I tried .440, .527, .567). With each larger set, while 4500-5500 rpm power improved, and I ultimately ended up with good A/F in the 12:5:1 range at WOT, I lost noticeable power in the 2000-3500 rpm at WOT. With the CC rods, even after i adjusted the secondary spring tension, I could light up the tires at a rolling 15-20mph by flooring it. Considerable power. Not any more. I kept messing with the spring tension to get the secondaries to open faster, but I would eventually experience bog and never got that lower rpm WOT throttle response. I want the lower and upper rpm WOT power. I am open to suggestions. I think I will play with some smaller secondary rods and longer (higher alphabetical) hangers as well as spring tension so I get more fuel in initially but limit the max flow. ---------- Post added at 09:28 PM ---------- Previous post was at 09:14 PM ---------- Uh...oh....I really feel like captain obvious now...."Cliff R" = Cliff Ruggles? If so, wow, what a resource. I really appreciate the advice from someone like you. Thanks.
Went back out tonight and tried to finish tuning. I decided to stick with the 72 primary jets, 45 primary rods, CC secondary rods (.300), and the M hanger after testing tonight. My WOT A/F at 3000 to 5500 RPM is 11.5 to 12. I know it is richer than I want but given my available parts, that is the best I could come up with. I actually observed that my WOT A/F got richer as I INCREASED my rod size according to final width. This had me scratching my head until i got home and read the full chart on rod size. After looking at my full rod chart, I suspect that I observed this because of the length of hanger - the M hanger is not pulling the rods up far enough to make a proper difference given the taper of the various rods I have. At 70 deg taper, which is where I suspect they are pulling up to with the M hanger, the CC rods are actually the LARGEST at .599, even though they have the smallest final dimension. The CV is exactly opposit-smallest at 70 degrees, largest at 90 degrees full open. That would explain it. The only other hangers I have on hand are a H and F and those cause the car to get too rich with those rods and I lose some low end response at WOT. I am going to try one more round - maybe next week. I will order in a K hanger and DA rods and see what I can do. Ideal might be something like a CD rod with my F hanger....but not sure I can come up with those rods by next week since they are no longer produced. Learning a lot about tuning these carbs. Having fun.
The motor wants what it wants.... I played around today with a few final combinations for the secondaries. My goal was to get the lower end WOT response I got with the CC rods but lean it out to the mid 12s for A/F in the higher rpms. I tried 3 new combos: CC (.300) rods with a T hanger DR (.567) rods with a C hanger CL (.667) rods with a C hanger My idea was to lean out the CC rods with a longer hanger or try better throttle response but target higher rpm WOT A/F with the larger rods but shorter hanger. End result...I was able to get the CL rods with the C hanger about right (on paper): decent throttle response with 12.5 WOT air/fuel. I say "on paper" because even though that is supposed to be more ideal...my seat of the pants and rolling 20mph burnouts still suggest that the CC rods with the T hanger running 11.7ish A/F still perform better....so that's what I am sticking with for now. I hope to get to the Dyno next month and will test both combos....will update then.
The later carburetors use shorter primary rods. The longer primary metering rods are too deep in the jets. You need a J, K, L, or P rod for that carb, not the longer B series rods. We sell .044 tapered rods for those carbs with the correct .026" tips. You are finding out that it is difficult if not near impossible to tune the secondary side by changing metering rods. They will have different dimensions on the upper portion of the rods, tip length, included angle leading to the tips, etc. I found this out decades ago on the dyno, when we say leaner A/F by installing rods with smaller tips on them. The best deal is to use a set of rods machined from the same cores. All of my customers who are serious into tuning do this. Typically we will machine a full set from about .030" to .055", in .003-.005" increments. Then all you have to do is find the hanger that works the best, and dial in the full throttle A/F by changing the metering rods. If your set-up likes the CC rods in the lower range, it's because they have a wide upper section, then taper down quickly to tiny tips. They are lean until they get at full lift and some fuel flowing by them. I don't like or use CC rods for this reason. In most cases it takes a pretty high hanger to get them to work effectively, then you'll find other rods, AX, CE or DA (for example) will be too rich as the secondaries come in, making tuning difficult, if not near impossible with going to a shorter hanger.........Cliff
Well, got to the Dyno....my seat of the pants tuning for the secondaries is not worth diddly..... Ended up going to CL .667 secondary rods on M hanger to lean it out enough. Picked up 40 horsepower from first run after tuning. 12.7-13 across the range. Still more work to do, but ok for now.
Did you use a set of fully machined secondary metering rods for the dyno tuning? If not, it is very difficult, if not near impossible to nail down the tune swapping out secondary rods pull to pull......Cliff
