My truck pings at higher rpm's. Mechanical advance increases the timing by 12 deg and ported vacuum advance increases it an additional 30 deg. I believe the problem is the vacuum advance and would like to decrease it to about 14 deg advance. That would give me 26 deg advance plus the 10 deg initial setting for 36 deg total. I think this would eliminate any pinging. Is there something I could get at the parts store to put in the vacuum line that would decrease ported vacuum? I tried searching this but couldn't find anything specific. Thanks for the help.

 

In the past I have seen some replacement adjustable linkage vac advance. You might do an internet search.

 

I don't believe that's causing it. :/

Might be wrong, but that advance doesn't sound like very much to me.
You set it back very much from that and it seems like that makes the
engine have extra hot exhaust temperatures?

My 360FE pinged to beat hell before the rebuild because Ford's valve
seals leaked oil "to beat hell"! LOL :) So, the tops of the pistons were
covered with pretty bright glowing carbon deposits. :)

"thank you Ford :/" -Alvin in AZ

 

Are you sure you don't have those numbers reversed? 30* mechanical and 12* vacuum? the vacuum canister only advances timing in the neighborhood of 6-14* (if the adjustable type) in order to only have 12* of mechanical advance you would have to be using a 6L reluctor arm and i don't believe they even come that small, pull your breaker plate inside the disributor and see which reluctor arm you're using, a 15L would give you 30* of mechanical advance.

Initial+mechanical advance=total advance, vacuum advance doesn't factor into the total, by the time you're at full throttle vacuum advance is no longer part of the equation.

 

This sounds like it should have manifold vacuum hooked to it. The distributor had ported vacuum to it so as the rpm's went up so did the timing. All the books I looked at showed Ford using ported vacuum rather than manifold. I checked the reluctor arm and it was 16L. It had full movement, nothing seized but when I checked the timing again it would only advance to about 25* with the initial timing set at 6*. I reved it to about 3500 rpm(no tach). It should be fully advanced by then, right? Once again when I hooked up the port vacuum it would go over 50*. All the vacuum lines have been messed with. I'm sure none of it is right. The vacuum line to the distributor comes straight from the carb, nothing in between.

I went for a drive with the vacuum line unhooked from the distributor and it still had a slight rattle climbing a small hill. I didn't think there should be any detonation with only 25* of advance. Might there be another problem. I have yet to replace the plugs and suppose it could be a lean fuel mixture. Truck has been sitting for the last year. Does anyone have an easy explanation how the vacuum advance should be run. My Chilton manual only goes to '76 (mines a '79) and the Haynes manual just plain sucks. Thanks for help

 

That would be cool; would be able to easily set the total advance to whatever you wanted it.

 

Here's an excellent article explaining how initial/mechanical/vacuum advance all work together and it also touches on manifold vs. ported vacuum and the use of ajustable vacuum canisters....FORDMUSCLE webmagazine: Timing is Everything - Distributor Curving for Maximum Power

 

I was just reading that link, thankyou. Sounds like I should hook up manifold vacuum instead. First, I gotta figure out why I'm still getting a little detonation with only 25* advance and then figure out why I only have 25* advance with a 16L arm. I'll be foolin with it again tomorrow after work.

 

Ok, after carefully reading that article I think my distributor is working properly. Makes sense if stock advance curve may take 4500+ rpm before reaching full advance. Engine still pings with new plugs and advance backed off to 4*. Manifold vacuum is at 18" so don't think there are any vacuum leaks. One plug had oil on it but compression was good on all cylinders. Could the carb be running too lean because none of the emissions are hooked up? Could the power valve not be working properly from sitting too long? If it is a lean mixture ping would richening up the choke and test driving eliminate the ping? Engine isn't running hot. Can't think of anything else.

One other question; which is better for fuel economy and driveability?

04* initial + 32* advance = 36* total
10* initial + 26* advance = 36* total

I found a 13L reluctor arm amongst all my junk.

Thanks.

 

If you're running 6* initial and only getting 25* mechanical for a total advance of 31* you shouldn't even be approaching detonation territory so i'm guessing you may be running too lean, you may want to fatten up your mixture a bit with a jet and/or metering rod change.

I like to run as much initial as possible just to the point of starter kickback then back off a few degrees which in my case is 12* and i use a 13L reluctor arm for a total of 38* through trial and error i know my motor will ping at 42* total so this gives me a 4* safety margin, my vacuum advance (ported) kicks in another 14* of advance (at part throttle only and therefore is not part of total timing) keep in mind this is on my FE (390) and every engine will be different, it just takes experimentation but you'll eventually get it dialed in where your engine's happiest.

 

Thanks highboy, I will tear into the carb next and see if I can figure out how it works. I don't understand how ported vacuum increases timing at part throttle. Doesn't ported vacuum increase as rpm goes up?

 

I have two vacuum connection on my distributor. One in front and one on the top. What does each one do?

 

Engine vacuum is at its highest from idle to part-throttle and eventually decreases to near zero at WOT that's why it's not factored into total timing, the only time manifold and ported vacuum are different is at idle, after the throttle blades are cracked open ported vacuum is exposed to manifold vacuum and they function exactly the same.

 

Yeah but. ;)

While you're just bopping along the highway the vacuum comes back
up and advances the timing again. So that the vacuum advance and
the mechanical advance are -added together- to get the real timing. :)

As soon as you open the throttle plates again, very far, the vacuum
advance backs off again.

Alvin in AZ

 

My 302 (2 barrel autolite carb) used to ping like crazy on even the slightest of hills. I used to run premium fuel, which helped, until gas prices went sky high, then I unplugged the vacuum advance and ran mid grade. Our trucks were calibrated lean due to the fuel shortage and increasing emmisions standards at the time. I recently put on an Edelbrock Performer intake and 4 barrel carb which has eliminated all of the pinging and I can even run regular grade gas now. I've spent some time tuning the carb and this truck runs better and has more power than it ever has. The only trade off is that I've dropped 2 mpg.