Thanks for the input guys. I'm starting to understand. Where are there jets available for these 2 barrels? I have an old 4 barrel Autolite from the early 70's; are the jets and metering rod interchangeable? Should manifold vacuum be going to the air cleaner for the air door? I want the truck to start and warm up as fast as possible in the winter.

 

"Should manifold vacuum be going to the air cleaner for the air door?"

Mine connected to a vacuum tree behind the carb, which was manifold vacuum. However, there was an inline temperature switch in the air cleaner lid that controlled the flow of vacuum to the air door.

 

Thanks jade. Mine has the temp switch also. Not sure if it works. Too much to do on this truck. I guess that's what $800 gets you.

 

My 302 done the same thing when you hit a hill or gave it more gas. I thought it had something to do with the vaccum advance. I had a 351w laying around and it had a round regulater on it. It would let it pull vaccum but not let it shut fast or the vaccum lrak off when you let off the gas. I took it of and put it on my 302 and it fixed it. It took gas better and the pinging stopped. You see them on the older 289's and 302 and the 351w.

 

I figured it was a lean mixture making it ping since I have it set at 4* with 36* total advance at 4500+. Took out the 59 jets and installed 62's, made sure the power valve is ok and that no passages are plugged. Carb seems to be in fine shape, went for a drive and it still pings. No change at all. Back timing off to 0* and ping is gone. Hook up vacuum advance and ping is back, turn out screw in vacuum diaphragm which reduces the vacuum advance but not enough to eliminate ping. Why do I have to run this thing at 0* to stop the pinging? Pistons don't have any carbon on them and I tried 91 octane. A fellow told me a stretched timing chain could cause it. Is that possible? Thanks.

 

A stretched timing chain will most likely cause the cam to be retarded a bit and the distributor is driven off the cam, however, it will also cause the timing to fluctuate quite a bit due to the play in the chain. Do your timing marks jump around when you aim the timing light at them? Also caused by worn distributor shaft / bushings.
It might be worthwhile to richen up the power circuit by replacing the current power valve with one that comes in sooner. Scroll down the bottom of this page Motorcraft 2150 2V Carburetor and check out the enrichment circuit. See which power valve you have in there now and replace it with one that is rated at a higher number. Vacuum is high at idle, and when you open the throttle, vacuum gradually goes down as you accelerate. So a power valve rated at 4 in/Hg won't open until vacuum has gotten way down to 4 in/Hg. A power valve rated at 9 in/Hg will open much sooner as you accelerate since vacuum goes from high to low as you accelerate. I'm assuming you have the Autolite / Motorcraft 2150 2 bbl. Here's a chart that lists various power valves. Motorcraft 2150 2V Carburetor You might want to hook up a vacuum gauge to manifold vacuum and put the gauge in the cab. Have a passenger note the reading on the gauge at the point you notice the pinging. Then select a valve that opens one step higher.
It's just a thought, easy to do, and can be easily changed back if it does'nt cure the pinging.

 

No, the timing marks don't jump around at all. I came across another carb that seems to have a stiffer spring in the power valve. It has a 7 and 75 stamped on it with no color. I didn't look close enough at the power valve I'm using now to see any numbers. I also have another distributor with a 13L reluctor arm I can try. I will give your suggestions a try, Jade. Thanks again.

 

I installed the other power valve and hooked up a vacuum gauge in the cab. Accelerating in second gear and with the vacuum climbing it started pinging at 10 Hg and continued until 14 Hg. So now I have 62 jets and a power valve that comes on sooner and a huge flat spot on initial acceleration. I'm sure that it is plenty rich. Next I put in a distributor with a 13 reluctor arm and the pinging went away. Hooked up ported vacuum advance and it came back but at least I'm getting closer to figuring this out. Tomorrow I will hook vacuum advance to manifold vacuum instead and see what happens. I like the idea of lots of advance at low power for throttle response and fuel economy but not at the risk of detonation. Not sure why the vacuum advance won't work for me as I'm sure plenty of old trucks still have it hooked up with no problems. Thanks for the help and if you have anymore ideas please let me know. Feels good to be making some progress.