Quadrajet Problem Solving > Dialing in your rebuilt Quadrajet carburetor
Tuning for a mopar 318
toocheaptosmoke:
Looking for any advice on a starting point for tuning a 318, doesn't seem to be a very popular combo. It's a newer style magnum 318 converted to a carb, the heads flow better than the old style. It has the stock cam, edelbrock performer rpm intake, headers, and an HEI ignition. The carb is number 17059247, off a buick I think. I rebuilt it stock with Cliff's kit, also got the book.
It fires up and actually idles pretty decent, but I haven't had the car on the road yet. Was hoping to get a reasonably close setup to get driving, or if you guys think it's close enough as-is I'll just run it and go from there.
Here's a video of it running, at the moment it doesn't seem to rev out very cleanly.
http://youtu.be/ImMFDtsFaOo
Cliff Ruggles:
Always best to do some driving and evaluate engine performance and fuel economy, etc, then go back and address any areas that need help.....Cliff
toocheaptosmoke:
Ok, have the car on the road now, think I have an idea what it needs.
Idle quality has always seemed surprisingly well, still have a stock cam so was hoping not to have many problems here.
Main jets were 73's. Primary rods have stamps that are hard to read, but looked like possibly 6-9, or 6-3, or 9-8? Anyways, they look to be quite a thick sectioned rod. The secondary rods were CZ, which again is a very lean rod.
Low and mid range performance was less than spectacular, engine reached operating temp. very quickly, and there was slight surge while cruising. I figured it was lean, and put in some 75 main jets, and some richer secondary rods from another carb I had. (not that I've really tried tuning the secondaries yet)
That made a big difference in performance, when the primaries were wide open, acceleration seemed decent, or at least it was much better than before. There was however still a stumble/hesitation whenever you gave it throttle while cruising. I turned the APT screw out another turn and that again made a big improvement, throttle response was much better.
Couple days later the temperature has dropped about 25 degrees, stumble/hesitation is back. Adjusted APT another turn out, didn't really help this time. Primaries at wide open don't feel quite as strong either.
I think I need to for sure try a richer set of primary metering rods, then also go up maybe another size on the primary jets, and possibly install a stronger power piston spring? I think the engine is still running a bit lean, sometimes it will pop a bit when downshifting. So the question is, how much richer do you think I need to go? Thanks.
toocheaptosmoke:
I purchased a set of the primary rods from Cliff's store, they were the ".044" ones. Anyways, they are smaller on both diameters, my old rods measured .036" dia. on the tip. I also used a stiffer rate APT spring this time around.
I put them in with the 75 mains and once again, it seemed to have maybe helped a bit, but the problem still persists. While cruising 4th gear and you get on it it, there is a half second where power is a bit flat, then there is a half second where it has a bit of a stumble/bog/surge, and after that it comes back and accelerates fairly consistently. Although, I think it should have more grunt than it does. I think what may be happening is, after the shot from the accelerator pump it goes lean, then catches up. I've also noticed that sometimes while accelerating hard say in 3rd, as it's pulling up around 3000+ rpm a slight drop off in in sound and power occurs. Not sure if this something related to my timing or not though?
Yesterday I went to 76 mains and a longer APT spring, again there was not much of a change, still has a stumble when under load. I am a bit surprised that all the changes I've been doing seem to have very little impact on the way it's running? I thought it should be running noticeably richer with the changes I've done. It's not belching black smoke and the plugs look brand new.
Cliff Ruggles:
75/76 jets would be HUGE for that carburetor number. 73's should have be plenty of jet. If you get lean symptoms I'd go back to "basics", float level, fuel pressure, check the power piston hanger arms to make sure they are exactly even and not bent up/down, power piston stuck/sticking in the bore, etc......Cliff
Navigation
[0] Message Index
[#] Next page
Go to full version