My '67 has this "dead" spot in the mid range where you can feel the power die off. Its not the off idle dead spot that the accelerator pump adjustment fixes.. This is like at just past 1/2 throttle to just past 3/4 there is a noticeable drop in power. Get it past 3/4 and it takes off again. Now the motor doesn't stutter, or die or anything.. you can just sort of feel the power die off... still runs clean in this range just no power.

Normal or is there something I should check?

 

I'd start by experimenting with a main jet increase. I've fixed this issue on a couple of trucks by doing this. I eventually went up 2 or 3 sizes. Todays' fuel doesn't have anywhere near the BTU content of the fuel that was available in 67.

 

I'd start with ignition, then work on carb calibration as required. If ignition advance curve is defective or just lazy it's going to act exactly as you describe. Need to know what it's doing and when from idle to 3000 or so. Lighter springs usually help a lot.

 

Hi there,

At 3000 RPM my timing appears to be 50

My initial is currently at 12 degrees.

Pertronix Dizzy, Coil & Wires. Vac lines hooked up to dizzy.

 

OK, but the vacuum advance needs to be disconnected and plugged for this test. We want to know what the mechanical advance alone is doing without interference from the vacuum advance.

Measure and record it at idle, say 500 RPM, then at 1,000, 1,500, 2,000, 2,500 and 3,000 etc. Make sure it's done advancing all the way. What you're doing here is mapping out the "curve", if you make a chart with RPM and Degrees on the X and Y that's what it will look like. There's usually around 34° or 36° "total" (without vacuum advance), but you can play with the "when" to wake up your motor. A lot.

There's two springs holding the centrifugal weights inside the distributor, usually a heavy and light or heavy and medium weight spring, something like that. The combination of the two, that's what makes it a "curve". Usually stock OEM pickups have a slow or lazy advance, because they are designed to carry heavy loads. A light weight car might have all of the mechanical timing in at less than 2500 RPM, where a stock OEM truck distributor might still be advancing all the way up to 4,000 RPM. The earlier the timing advances, it will add a lot more zing to your morning. Can do this by changing the springs. But, compression ratio and weight, fuel quality etc limits how much it will stand without engine knock or ping.

 

Done. Thanks for the info.

At 600 - 12 degrees
At 1000 - 12 degrees
At 1500 - 12 degrees
At 2000 - 20 degrees
At 2500 - 27 degrees
At 3000 - 34 degrees

 

That's about what I figured, it's a pain in the *** to recurve a Ford distributor, because everything is under the breaker plate. Have to remove the vacuum advance arm & clip, rotor, the felt oil wick, and the little circlip wire dealy bob (don't lose it!) that secures the reluctor to the distributor shaft, remove all that, the. breaker plate &c,, and then finally you can get an idea what's installed.

Usually the reluctor will have two "slots", these are measured in distributor degrees or, 1/2 the timing degrees seen at the cranks. If it's set on a 10L slot then the distributor advance will provide 20° timing + whatever the initial timing degrees is set to. The "when" though, is tailored by using lighter or heavier springs. Mr. Gasket 925D kit has a couple springs you can play with, along with the stock springs. If you look at the breaker plate itself, there's a hole that allows the arm that secures the springs to be tweaked a little looser or tighter with a special tool if you line it up. A flatblade screwdriver works. This will bring in the timing a little later or earlier too. The light spring lets the timing come in fast, then the heavy spring comes in, and slows the rate of advance down quite a bit. The heavy spring has more slack too, this is part of the "curve".

Can maybe try two medium springs, a light and a medium spring, or something like that. The idea is to bring as much timing advance as possible in as early as possible, though short of any knock or ping on hard acceleration. Make your test drives without vacuum advance hooked up. Can try advancing the initial a little bit too, the problem there is too much initial (above maybe 15°) will tend to cause starter kickback, especially when it gets hot. This is a problem with higher compression engines.

It looks to me like from your numbers, there is probably a 10L slot in use. That's a good thing, it gives lots more room to play around with the initial timing. Check to be sure and see what's installed. If you can get that "extra" 7° that's only coming in by 3000, to come in around say 2500 or so with lighter spring(s) that should help quite a bit. Just a few degrees one way or another can make a big difference.

Once the timing curve is optimized, then feed it some more jet maybe, see what you get. Should be a big grin on your face. When you're satisfied with the mechanical curve, re-connect the vacuum advance, and don't mess with the ignition timing further other than to adjust the advance of the vacuum canister itself. Sounds like it should already be close.

 

Distributor tuning

This explains it a little easier or better than I can. There's some other websites too if you dig around, that have lots of pictures that are helpful too. It's basically just using your engine as a distributor machine, to optomize the timing curve.

 

Another fuel related item worth checking is the power valve in the carburetor. If you have the 2 barrel Ford/Motorcraft the small cover under the float bowl is where it is located. If you find fuel inside the cover then the valve is blown out. If it is not replace it and make sure it is the exact one while replacing the jets as Mrpotatohead suggested. All it takes is one cough back in the intake manifold to blow out the valve.

 

Yeah, you've got plenty of ignition advance.

 

Put the lighter pertronix springs on and totally fixed it! I may mess with the jets too and see if that unleashes the beast more but already the mid-range bog is gone and I have more power throughout the range.

Pertronix makes it easy. Took me less than 5min.

Thank you everyone!