1980 F250 with 351M and Motorcraft 2150 carb. A few months ago I replaced my stock timing set (was well worn and had broken tooth) with an aftermarket one and installed it straight up. At the same time I replaced the distributor since the old one got a little messed up removing it. I also replaced the carb with a reman unit from NAPA because the old one had a crack in the base. Now I get pinging only when the engine is at operating temp and going up hills. I verified that the timing is set at stock specs (10 BTDC) and the EGR valve is working. All emmissions stuff is hooked up and working. The jet size on the original carb was 53, the reman unit came with 55 jets. The spark plugs came out completely white so it looks like too lean, I put 57 jets in but still have the pinging. The plugs are still mostly white with a tiny bit of light tan so it looks like I'm still lean. I'm having trouble getting larger jets and am wondering if there is something else wrong. I don't think there are any vaccuum leaks. Should I have to keep going up in jet size? I had no pinging before replacing this stuff, what size jets are normal for these carbs? Any help would be appreciated.

 

This happened with my '72 400 after I replaced my distributor. I advanced the timing, retarded the timing, over jetted, under jetted, ported vacuum, manifold vacuum, it didn’t make a difference still pinged. What it ended up being was I was given the wrong distributor. I got one that had only one vacuum port on the advance instead of 2. I assume that the mechanical advance was different as well. I swapped it out with another distributor and problem solved. Apparently they do not distinguish between the 2 but there is a difference.
If you have tried all that other stuff try the other model distibutor. Simple to change and doesn't take long.

 

Exactly. If you have EGR, both the distributor and the carburetor are calibrated for it. It is very likely you are having problems because your distributor isn't calibrated to work with the leaner mixture caused by EGR.

 

I have had simliar expereiences where the reman distributor did not have the factory stop on the vacume advance. If there is no stop it will advance the timing way up when vacume is applied. Try unhooking the vacume advance and then make the trip uphill and see if it pings. The stop is simply a small piece of metal that sticks through a slot in the arm of the vacume advance canister inside the dist housing.
Zac
77 F-250 351M 4spd
All Stock
77 F-150 472ci
Comp 280 Magnum Cam
Holley 850
Headers
3 inch Flowmaster exhaust
Loc-Rite 9inch 3:50 gears
C-6 Auto Shift Kit
2,500 Stall Conv

 

You guys are right, my problem is with the distributor. I put the original one back in and no more pinging even with the base timing set at 15. I made some measurements and it looks like the original distributor has 5 degrees mechanical advance and 25 degrees vaccuum advance. The new one has 15 degrees mechanical and 30 vaccuum. Thanks for the help.

 

You should have about 12 distributor degrees at 2000 distributor rpm or 4000 engine rpm of mechanical advance.

You should have 11-12 distributor degrees vacuum advance at 25" vacuum.

You need to double distributor degrees to get engine degrees.

It sounds like your old distributor with 5 degrees mech advance has a stuck or worn out advance mechanism.

 

How does one determine how much advance their distributor has?

 

you can map out the distributor by using a tach, timing light, and a timing tape on the balancer. a timing tape is a stick on decal that goes all the way around the balancer and has degree marks most of the way around it. by watching the tach and increasing rpm, the timing light on the timing tape will tell you how much advance is being applied. do it first with the vacuum disconnected and you will be reading the mechanical advance only. then you can connect the dist vac advance to direct intake vacuum and read the total advance at idle. you can set base timing at 0 or subtract base from total at idle and this is your total vac advance. or take the dizzy to a speed shop and have them map it on a distributor machine.

 

thanks for the info..just getting my carb dialed in, so the dizzy is next to play with!

 

ive had the same problem with this engine. my problem after everything was fixed (as it seems you have done) was the tappets. the adjustments are easily obtainable and should be checked every 10,000 miles even if they arent the problem. i have no idea if this will be useful but i figured i would let you know since that was the problem with my engine.

 

First of all, you guys rock - nice job diagnosing this problem.

But I was amazed at the differences in the amount of timing between the two distributors; original had about 30^ total, the new one, which I assume was for EGR, has 45! You would have to turn the static timing way back to make that work, and the curve would probably be way off.

I'll bet there was a huge jump in performance when you went back to the old one.

 

The valve lash is non adjustable on the stock 351M/400, and is set with shims at build time. Are you perhaps thinking of the 351W???

 

I finally got another reman distributor and compared it to the previous reman distributor. I was trying to avoid dist reman by Cardone but they are the only brand the stores have around here. I noticed that on the 1st reman distributor the magnetic pickup assembly advances two times further than the one I just bought when vaccuum is applied. The mechanical advance is the same, advance plates are both marked 16L. This new distributor works fine, no pinging. The strange thing is both the distributors have the same Cardone part number but the vaccuum advance is much different. By the way this also fixed my intermittant stalling problem, I found out that the 1st reman distrib has a bad ground, when I move the wires where they go thru the grommet into the distrib body the ground wire loses continuity.

 

Good I am glad you got it fixed, That was the same problem I had with mine they where the same part number but very different advances