Vacuum advance connected to ported or manifold vacuum?

 

the distributor has a vacuum advance plugged into the carb if that’s what you’re asking

 

Which port on the carb?

 

left of the mixture screws

 

🤦‍♂️ What carburetor?

 

lol sorry I don’t know the difference in the vacuum ports. its an edelbrock carb I’m not sure what model though you can kinda see from this picture I had it’s plugged into the far side

 

Looks like it's on ported vac. kip

 

Okay. That's the "timed spark" a/k/a "ported vacuum" port.

I would set my base timing to 12*BTDC to begin with and have your centrifugal advance provide an additional 24* by 3,000 rpm. If it starts and idles fine at 14* or 16* that's fine, but you'll probably need to dial back the amount of centrifugal advance accordingly. A total of 36* is a good starting point.

 

aluminum edelbrock heads

Which Edel heads? The Performer RPM heads only like 28-30°, total. Add about 12° vacuum advance.

 

They’re performers

 

Okay great info thank you! I’ve never dialed an advance any tips on best way to do it?

 

Sure. Remove the distributor. Pack it carefully in a box. Ship it to Dan Nolan at the Mustang Barn. Provide your engine specs.

 

@W427 made a very good comment on timing. I have a GT40P engine in my 66. The GT40P heads also are very combustion efficient and like no more than 30*. Now as we both have a roller cam motor converted to a carb that means you probably have a distributor for a 85 Mustang 5.0 , 5 speed since it has vacuum and mechanical advance and the correct gear. The Mustang 5.0 is also EGR equipped which likes a lot of vacuum advance. My distributor was set up for 24* mechanical advance leaving 6* initial. It also has a very lazy rate of advance. I also have a Edelbrock that’s old and bought used. And also had a little stumble that I was playing around with jetting.

Getting your timing curve right will have a dramatic effect. The more timing you can run initially the more it’s going to help in throttle response and low end torque along with it coming in quicker. So I welded up my mechanical advance slot to limit mechanical advance from 24* to 16*. That allows me now to set initial timing to 14*. That extra 8* does wonders! Not to mention having the rate of advance come in much quicker by changing the springs. Not only does the engine feel like it’s 30 inches bigger but that hesitation is gone.

As far as vacuum advance. I prefer manifold instead of ported but have it on ported. The reason has to get back to what I said earlier about EGR. EGR motors like a lot more vacuum advance than non EGR and sooner. Compared to my old points 289 distributor it has a bit more advance and even adjusting the rate I couldn’t slow it enough for a smooth idle.

I would highly recommend having your distributor set up for best performance. That alone may take care of the hesitation but at least will make your car far more responsive

 

I've outlined how to tune timing here and elsewhere, and there are various references on the web with a search. A couple YouTube videos also come to mind. They're mostly creative ways to determine either best acceleration (power) at accel points, or best efficiency using indicators such as vacuum (economy) at various points of operation. Simple and quick ways to test two values for which is better. Diagnostic. Worse - go the other way. Better - keep going until it gets worse and back-up to best. Then configure the distributor to hit those values at those points.

An experienced person can throw a generic curve in there for some pretty reliable and decent results, but you can do the same in about an hour. Whether you do or not depends on your curiosity and willingness, time and budget. If someone else can do it, why not you? But that's not for everyone. Do your thing.

 

Once it comes back from Dan, all you need to do is dial in the initial time. Start with, say, 10°. Lug the engine uphill (low rpm) and see if it pings. If not, advance 2° and try again. Continue until you get ping, then back off 2°.

 

Dan has instructions and spec's to set exactly. With unknown spec's (e.g., aftermarket or parts store rebuilt distributor), you can use procedures for unknown curves, by setting for total advance (vac disconnected) to the general spec total timing for your engine - say, 36° for classic SBF, Lima, etc. Do this with parked warm engine revving above the point the advance stops adding. Let it idle-down to corrected warm idle rpm to check and note the idle (base) timing for future setting.

Don't buy a custom curve then mess with the curve away from what was intended for your engine to work best. When you change the whole curve range, you may seemingly improve one area, but pooch another. Timing is about maximizing efficiency, extracting maximum energy from the supplied fuel and air at every operational point. Knock (detonation) is about temperatures and octane, not most efficient timing.

 

Lots of help here. Unfortunately I’m still completely lost I’ll just have to read up on it. I’ve even called shops near me and no one will touch it lmao

 

Set your all-in timing as-above. See what results for warm idle timing, and note incremental advance with rpm, testing the curve you have now. Go from there. You need a starting point. That's it.

 

so from what I could tell was I’m some where around 11 degrees idle I had someone bring the car up to 3k rpm and the marker was on 30. How would I determine how much advance my vac advance is providing? I’m really trying to understand I think my brain could use some advancing lol

 

How would I determine how much advance my vac advance is providing?

You test it. On the engine, we would use a hand-vacuum pump to the vacuum canister. With a timing tape or plenty of damper markings, you can apply vacuum incrementally to the canister at low warm idle, and read the amount of advance on the timing marks with your timing light. If the rpm changes, take care to also note any added mechanical advance added-in.

Likewise, you can tune your vacuum advance on the road with a hand-pump, while driving at steady part-throttle loads. Add or subtract timing with the pump at a specific speed and load. Note the vacuum applied at the point the engine made best vacuum. Repeat at a different speed. I might do 30, 50 and 70 mph. When you get home, plot those speed and vacuum values and the relative advance (from the idle testing) to get best vacuum. Configure your vacuum advance canister to (as closely as possible) hit those values at those points. Bingo - tuned vacuum advance.

If you had previously tuned part-throttle fueling to max lean just shy of lean-surge (the job of the main jets in a Holley, Autolite, etc), then your ride will have the most potential for peak economy. If you also tune your fueling with the power valve and PVCRs, you will get both max economy and max power potential in the same tune.

Tuning vacuum advance is very important to not only best performance, but much longer engine life, especially the valves and seats. I recall some long (and a bit draggy) but thorough videos on this if it helps.