My 1978 F100 has a 302, MSD ignition, and an MSD 8582 distributor without vacuum advance. Do I set the initial timing (say 8-deg BTDC) or do I set the total timing at around ~2500 or 3000 RPM (say 32-34-deg BTDC)? I can only adjust for one of these, right?

Beyond that adjustment, all I can control is the timing curve via a spring kit, which is more subjective - right?

Thanks!

J.

PS - the reason I'm messing with timing is because I have some off idle stumble and have chased a lot of other leads without resolving the problem.

 

There's kinda 3 lines of thought with setting timing.
1) Set the total timing (initial + mechanical) and let the initial just land where it may.
2) Set the initial and let the total be whatever it is. If it starts knocking or starts hard, back it off a little.
3) Set your initial advance as high as possible and have it still start cleanly when hot and then dial in the appropriate amount of mechanical advance (through weights/plates/ whatever your particular distributor uses) so that you end up with your targeted total advance (32-36deg?). Then dial in the curve with springs so that total advance number comes in by whatever RPM you're shooting for (~2800-3200).
Method 3 gives you the best result, by far, but it's also the most work.

If you're not willing to monkey with the mechanical advance or re-curve the distributor I'd say just set initial to 8-10deg and be done with it, that's probably safe. This approach, however, can leave a LOT on the table as far as power and mpg.

If you're going to set by total timing you have to keep reving it until your distributor is giving FULL mechanical advance. Some distributors have very lazy curves and if you just set it to 32deg at 2500rpm you may end up with considerably more than that at a higher rpm (that's bad!) and a crazy high initial setting (also bad) because at 2500 the distributor wasn't done advancing.

 

Thanks CaptainChaos. This is a great response! For option #3 - do you have an idea of the RPM range I should target for full advance? I don't have a tach, so I don't know what RPMs I'm hitting at WOT under load.

My distributor only has one option for replacement weights/plates, so I'm limited to changing the bushing and springs to impact the advance and curve. I'll open up the distributor and see what I'm currently running. Without knowing the POs maintenance history, it could be 25 years since the distributor was installed. Those springs may need to be replaced regardless.

Thanks again!

J.

 

Without any kind of tach it's gonna be tough to get any kind of accurate results. 2800-3000 is kind of a good, safe, general range to shoot for on pump gas but how do you tell what 3000rpm sounds like?
I'd err on the side of caution when setting it by ear. It's better to have a little lazy of a curve than too aggressive and have it spark-knock itself into oblivion.

 

CaptainChaos, thanks again!

I have a hand held tach, so I can check advance at a given RPM - I just don't know what RPMs I tend to hit when driving - like when I'm aggressively accelerating (for example).

The timing light I ordered got lost, so I placed another order. It's a shame the local auto parts stores don't have timing lights in their loaner program. I confirmed TDC today and took a look at the guts of the distributor. I have the two stock, heavy silver springs installed. I can't tell which color bushing I have (see pic below). The color looks more rusty than red. Assuming it's the stock blue one under that rust, that has my mech advance at 21-deg and all in at 4,000 RPM. I ordered a spring/bushing kit and will likely target all in around 3,300-3,500 RPM. After testing my current setup, I'm thinking I'll start with one heavy silver, one light silver and a blue bushing (~21-deg advance at 3,400 RPM).

J.


No idea what color bushing this is/was. Looks dusted with rust.


May start with this arrangement and a blue bushing and see how it performs.

 

I adjusted the timing this weekend. According to the PO's documentation, base should have been at 8-deg, but it measured at only 5.9-deg. I increased base to 10-deg and changed up the springs and bushing. I'm getting about 32-deg total advance now. The truck seems happier, although I'm still getting off idle stumble.

Question: The mag pickup is rusty. It seems to be working, but should I replace it? The reluctor looks ok, although a little oxidized.

Thanks,

J.

 

Rust on the pickup coil won't hurt anything. Most of the time on an MSD I end up using one light sliver and one blue or two blue springs with the large bushing(shortest curve) and that seems to work well if the engine has some camshaft.

 

Hey Dave,

With 2 blue springs and a black bushing (the largest, right?), that has you all in by 2500 RPM, but only about 17-deg of mechanical advice, right? What is your base timing? I have no experience with engine timing, so I took a baby step going from 2 heavy silver springs to one heavy and one light silver spring...but I stuck with the blue bushing. Maybe that is still too conservative. I don't think I have an upgraded camshaft (not the original owner). Thanks!