Something I've been wondering about. Done lots of work on the car and it's running great and everything works. Last weekend we took a day trip up the PCH to Santa Barbara, did some site seeing, dinner on the beach then back to the barn. About 220 miles altogether and the car was perfect. AC even worked great in the 105 degree So Cal heat. Now for my question. When I first got the car running a couple of years ago after sitting for 18+ years it ran fine. At this point the only thing I did to it was change the belts and fuel pump. Didn't even touch the carbs. The idle mixture screws were between 3 3/4 and 4 1/2 turns out. (it passed smog with flying colors) Now after doing a bunch of work including cleaning the carbs (no new parts except jets). The Idle mixture screws need to be between 4 3/4 and 5 3/4 turns out and I'm wondering why the difference. (It passed smog but not quite as clean.) I suspected a vacuum leak but it pulls 20+ inches (upper end of normal) on my old vacuum gauge while hot idling at 980 RPM so no obvious vacuum leak. The carbs sync between 5 and 5 1/2 on my SK meter so no obvious imbalance. I have no problem getting it to idle down. I am running the following jets. Idle 60 up from 55 Main 130 up from 125 Emulsion Tubes stock F36 Air Correctors stock 200 Starter Jets 60F5 Accelerator nozzles EW 45 up from 40 Valves lashed middle of range to lower but within range. Cams set at 108 lobe separation angle front bank and 109 rear bank. No cats (empty) or air pump but it didn't have any before. (I install them for smog test) R1 and R2 points with micro switch giving about 10 degrees retard at idle. Dwell with both points at low end of range. Timing both banks 34 degrees at 5000 rpm. 5 degrees ATC at 1000 RPM. Stock exhaust exempt empty cats. Just wondering if anyone has any idea's about the idle mixture screws. Thanks Barry
Seems like a lot of airflow for those conditions -- IME, should be more like 4 Kg/hr. Was it the same idle airflow for those conditions before your carb work? Are you sure all the cylinders are contributing at idle?
Hi Steve As far as I know its always been between 5 and 6 kg/hr. One other thing I didn't mention is I put a restrictor in the vacuum line from the engine to the upper fitting on the carbon canister as I was having trouble getting it to idle slow enough. That may explain the higher than normal air flow through the carbs which may in turn explain the idle mixture screw settings. I'm not sure about any of this as the vacuum line I restricted is hooked up to the small vacuum tubes under the carbs which I believe have small metered outlets. I do know if I remove the restrictor the idle speeds up a bit. I changed the vacuum plumbing a little based on your recommendation which ties all the small vacuum tubes from below the carbs together. The idle mixture screws behave as expected. They are sensitive to 1/2 turn. All the plugs look great after idling for an extended period of time. As far as I know the vacuum system is stock with the exception of what I mentioned above. Something else I didn't mention is that the cams are 1 degree advanced. I don't know where they were set prior to all the work. Thanks Barry
That makes total sense as I previously measured that the orifices of the small vacuum tubes allow about 0.5 Kg/hr of air to enter each cylinder at idle IF they are connected to something with no airflow restriction. Plus you get a double effect -- allowing more air in increases the engine idle RPM, which increases the ignition advance, which increases the idle RPM even more. I was unhappy with the stock vacuum plumbing arrangement because the small vacuum tubes of cylinders 1, 2, 5, 6, 7, and 8 were connected to something with no/little airflow restriction (the charcoal canister) while the small vacuum tubes of cylinders 3 and 4 are connected to a closed thing with no airflow at all (the electrovalve + air diverter valve). Consequently, if you set the airflows to all be equal using the SK Synchrometer, cylinders 3 and 4 would really have 0.5 Kg/hr less total airflow. Here's that modified vacuum line arrangement again (that connects all of the small vacuum tubes to the charcoal canister and moves the vacuum source for the electrovalve + air diverter valve to the closed system serving the airbox flap) for other's reference: Image Unavailable, Please Login Since you report no operational problem/issues -- motor on!
Yup it runs great. I also have Derek Whites cam pulleys with round tooth belts on it just for good measure. His system makes it easier to degree the cams plus I managed to break one of the original cam pulleys fences, I didn't realize they were plastic, and even though I epoxied it back together I just didn't trust it. I'm about done with the engine stuff as it runs great and has no leaks and am moving on to the suspension. I already did the brakes as one of the rear calipers was leaking due to a 40 year old O ring on the E brake. I've also changed the rear shock bushings as one of them was so sloppy it let the shock bang against the top mount and repacked the CV joints while changing the diff seals. Next on the agenda are the front shock bushings then all A arm bushings. The ball joints seem OK . I'm also going to change the fans to more modern ones that flow more air and draw less power. Although the stock fans work fine and the car doesn't overheat ever I hope more air flow from the AC fan will help the AC during heavy traffic on those 105 degree days. I switched from R12 to R134 Freon which doesn't cool quite as well. Currently on the open road the AC pumps out 40 degree air but in heavy traffic on a hot day it pumps out between 55 and 60 degrees. I'll probably have to change the AC hoses as the R134 apparently is incompatible with the old rubber compound. Once all the mechanical stuff is done I'll start on the body work. Thanks for your help Barry
