Hi , I'm Dave. Can anyone tell me what i should use for jets, rods and rod hanger on my 1973 455 non stage 1 q-jet? the car runs to lean. It runs rough at idle, gets hot and cuts out at high rpm and still gets 13 miles to the gallon even when doing 90 miles an hour. If i cover the choke with my hand the idle gets better. I'm thinking that the carb is to lean because its a stock non stage 1 carb. Here are the specs on my car... 1973 regal with variable pitch turbo 400. Stall speed is 1800 and 3000 . 323 posi with 245-60-15. 73 455 block decked .040 with 8.5-1 factory pistons, 71 stage 1 cyl heads, 1970 factory intake, stage 1 fuel pump, poston gs116 cam, factory lifters, crane cams chevy 454 exhaust valve 7/16 harded push rods(perfect length) , stock dist with points and msd 6al , accel 8.8 wires, msd blaster3 coil, acdelco plugs gapped .055 . stock exhaust manifolds with 21/2" dual exhaust with thrush glass packs. How should i set up the carb for this? Most of the work was done to this car before i got it. Does this seem like a good setup, is there anything i should change? Does anyone know how much compression I have with 8.5-1 pistons, stage 1 heads and .040 decked block. How much Horsepower should this thing be making? Also when i tried a holley 4160 750 cfm carb it still ran like crap and the only difference was my gas milage dropped to 9 and my top end power got worse. Could the holley have been to lean as well or do i have a totaly different problem.
Whether it is a Stage 1 carb or not is not the issue here. it appears that the issue here is that the mixtures are lean throughout the rpm and load range. Under these circumstances, I suggest trying a one or two steps larger jet, which will likely enrich the entire range. This will need to be done in steps, as a larger jet will also slightly enrich WOT mixtures. Rather than concerning yourself with what should be there, let's work from what we have, especially since the engine is not completely stock, nor is the emission package known. Let me know...
I just checked for vac leaks and i have none. I decided to check the size of the rods while i was there. When i went to put them back in they fell off the hanger and into the carb. So now i'm going to have to take of the carb anyway! It had size DR on an F hanger. the motor seems to run better when cold. I'm confused! If the carb was to lean would it run worse when cold and better hot? My car has lots of power when cold and acts like its too lean when hot. No vac leaks. I Have messed with the timing with no luck. I Tried changing back to points. I even put a new stage 1 fuel pump on. The only thing left i think i can do is replace the distributor and screw with the carb. Anyone have any ideas before i try changing jet sizes?
It sounds to me like you were messing with the secondary metering, which will not affect the performance at part throttle. Your improved performance is due to the choke limiting air flow when engaged. Be awae re of some things before jetting changes. At light throttle, either the idle passages or the part throttle are down stream from the jets. I suggested the jets because of two things. One, they are easier to change than the passages, and two, if they are too small, it will affect ALL of your non WOT metering. If you find that the moderate to heavy metering is improved by the jets, but the light throttle metering is still too lean, the other passages will need enlarging, but carefully. A little goes a long way, and too big will require their replacement, which is nearly impossible at best. BTW, the secondary metering rods will likely be accessible by simply removing the air horn. Have a gasket handy, obtained by carb part #. It is also VERY likely that the power piston is sticking, causing ALL of your problems. This can also be checked by air horn removal. Ray
Thank you for the advice. I will check it out. How do you fix a power piston? Why does this problem happen when the motor is hot and not when it is cold?
If the problem is a stuck power piston, it can be repaired by gently tapping the piston and spraying carb cleaner in to the bore containing it. Be gentle. The problem is more aggravating when hot because the choke is adding fuel when cold. Since this is the purpose of the power piston, at all times, the additional fuel could cover the problem when cold. I cannot be sure of this diagnosis, however, Q jets are known for this problem, though it is not widespread. Ray
I'm Going to take it apart and check the jet size. I had it rebuilt about three months ago and it ran perfect for a few weeks and slowly started getting worse. So mabey it could be something simple. Berfore i take it off i will check the power piston with carb cleaner and see if it worked. I just ordered the right size secondary rods off e-bay (cv) for a stage 1. I will change the main jets to stage 1 specs and see what that does too. Also its hard to start when cold but starts on the first crank when hot.
Hard starts are typically due to sticking choke linkages. I would not recommend the use of metering components for anything other than the application unless you know exactly what you are doing. I would first be sure that the original combination, when it works properly, still has a problem. You may find that the original combination is correct; you might create another problem for which you could chase your tail. If you want to try a combination, make sure you keep track so you can get back to square 1. Keep me advised, I'll help where I can.
I think i found most of my problem or all of it! I hooked up a vac guage to check things out. the needle was jumping between 19 and 20.5 HG at 750 rpm. I checked the distributor and put my secondary rods that fell out back in. I let the engine idle for about ten min and then i pulled the spark plug to check it and it was black carbon. I guess its not lean after all. I then took it for a hard drive shifted at 5200rpm and got it up 110mph. It had power until i got of the highway and then it was running rough at low rpm and hot. Drove home at normal speed, very sluggish. I checked the same plug again and it was clean. Then i decided to screw with the timing. I set it at 12o btw. I then checked the mechanical advance. My total advance was only about 28o. I raised total advance to 34o and was now reading 21HG of vac at 750 rpm and steady. I took it out for a drive and it lit up the tires when i punched from 20mph! I beat the crap out of it 40 mph in low 1 at 5000 rpm for atleast a mile, got home and it was alittle hot but not running rough anymore! I'm going to put brand new plugs in and consider it fixed! I also found shortly after i got home , the paper work that came with the car , telling me to set the timing at 18o initial and 34o total. ( lucky guess!) I feel like I am the one that is retarted now!
Food for thought... it frequently occurs, especially for a carbureted vehicle, that fuel builds up in the oil, since it is heat that keeps it clean. I have a vehicle presently that is driven 4.5 miles to work; if I don't get it out on the highway twice a week, it is not happy. It loads up and runs rough. A note to all readers; it is an emission control to limit advance rates and amounts, to limit HC's, and CO. Do not be afraid to experiment with advance curves. I have fixed my share of driveability problems by advancing initial timing and quickening both centrifugal and vacuum advances. Removing controls on vacuum advances such as TCS, will wake up any engine. There is a fine line between performance and clean air. It is usually not necessary to mess with the carb, but making changes to timing will make almost any engine happier, adding both power and mileage. No one is retarded if they learn from experience. The retarded ones never learn, nor do they want to. Definition of insanity: Doing the same thing over and over again, and expecting a different result. Good show!
