Total Timing Mystery 1969 Mustang 302

[YadiStang]

I have a mostly stock 1969 mustang, base 302. Mid length headers, Wieand Street Warrior intake, Quick Fuel HR-580 carburetor. Stock distributor and coil.

I've been bitten by the timing bug and because I was intrigued, I started to study the timing curve. I even swapped the springs to bring the total timing in quicker. Mind you, I'm not really expecting anything great and it is just a therapeutic tinkering thing to me.

The car runs good but probably on the rich side. I've jetted down and messed with air bleeds, but I still get carbon deposits on my garage floor from the tailpipes (on startup). The 580 is probably too big (technically) but I'm determined to make it work.

The first thing that I discovered was that my vacuum advance was broken, the diaphragm leaking. I plugged the ported source on the carburetor. I'm not really worried about this for now since I believe the most obvious effect would be mileage. Again the car runs fine. I will fix it one day when I can find the correct part.

My question... My reluctor arm that is being used on the slot is 13L. That would be 26 degrees mechanical, correct? My initial is usually 8-10. Wouldn't this make my total 36 degrees? When I charted my curve with a timing light, my total was 43 degrees (all in by 3,000). Does this make sense? What else could be attributing to the total? Could my broken diaphragm/advance plate be moving during operation? In all honesty, I've already run a 12v bypass to the pink resistor wire (tied up to the side) and will be converting to a Pertronix.

I'm interested in anyone's theory as to where the extra 7 degrees of timing is coming from.

 

[rbohm]

The first thing that I discovered was that my vacuum advance was broken, the diaphragm leaking. I plugged the ported source on the carburetor. I'm not really worried about this for now since I believe the most obvious effect would be mileage. Again the car runs fine. I will fix it one day when I can find the correct part.

My question... My reluctor arm that is being used on the slot is 13L. That would be 26 degrees mechanical, correct? My initial is usually 8-10. Wouldn't this make my total 36 degrees? When I charted my curve with a timing light, my total was 43 degrees (all in by 3,000). Does this make sense? What else could be attributing to the total? Could my broken diaphragm/advance plate be moving during operation? In all honesty, I've already run a 12v bypass to the pink resistor wire (tied up to the side) and will be converting to a Pertronix.

I'm interested in anyone's theory as to where the extra 7 degrees of timing is coming from.

you may have plugged the carb port for the vacuum advance, but did you lock out the vacuum advance plate? probably not, and i suspect that is where your extra 7 degrees is coming from.

 

[YadiStang]

I did not lock out the vacuum plate advance and suspected just as you describe - I wasn't sure how to do that. Now that I'm thinking more about this, it makes complete sense. Just out of curiosity, how do people lock out the plate?

 

[rbohm]

you can glue it in place, or use a self drilling screw. or if the vacuum advance can can be opened up, you can use a spacer to lock it down so it cant move.

 

[zookeeper]

I know "how" it's done, but what I can't figure out is "why" people do it for a street-driven engine.. My brother had a (supposedly) killer 406 ci small block Chevy built by a local engine builder that was a fan of this. Once we got the engine back in the car, it seemed to be a dog at all speeds and wouldn't rev to redline. I replaced the vacuum canister with an adjustable Crane part, then spent about an hour tuning it and the car felt like it picked up 100 hp! Plus mileage nearly doubled (9 mpg to 17 mpg)and it no longer had the part-throttle bog it had previously. But that's just my experience, I could be wrong.

 

[YadiStang]

I definitely would want it for my setup which is mostly stock. Soon I will be doing heads (afr165) and a mild cam, but still will use vacuum advance. With my recent posts, I was just learning as I go to see what is happening with my motor now. I actually just put a "stock look" pertronix distributor in the other day and that has the vacuum advance. I also learned a few other new things...such as, I had to change the steel gear for an iron gear, and apparently this new distributor does not have accessible advance springs. I haven't measured the curve and I'm hoping it its all in by 3,000 (for future considerations).

Do you prefer timed port or manifold vacuum?

 

[zookeeper]

Your vacuum advance needs timed port, otherwise it'll get an erroneous signal if you use manifold vacuum.

 

[rbohm]

I know "how" it's done, but what I can't figure out is "why" people do it for a street-driven engine.. My brother had a (supposedly) killer 406 ci small block Chevy built by a local engine builder that was a fan of this. Once we got the engine back in the car, it seemed to be a dog at all speeds and wouldn't rev to redline. I replaced the vacuum canister with an adjustable Crane part, then spent about an hour tuning it and the car felt like it picked up 100 hp! Plus mileage nearly doubled (9 mpg to 17 mpg)and it no longer had the part-throttle bog it had previously. But that's just my experience, I could be wrong.

I definitely would want it for my setup which is mostly stock. Soon I will be doing heads (afr165) and a mild cam, but still will use vacuum advance. With my recent posts, I was just learning as I go to see what is happening with my motor now. I actually just put a "stock look" pertronix distributor in the other day and that has the vacuum advance. I also learned a few other new things...such as, I had to change the steel gear for an iron gear, and apparently this new distributor does not have accessible advance springs. I haven't measured the curve and I'm hoping it its all in by 3,000 (for future considerations).

Do you prefer timed port or manifold vacuum?

in the end i agree with these posts. unless you are building a race only motor, you need the vacuum advance for the street for best part throttle performance and fuel economy.

Your vacuum advance needs timed port, otherwise it'll get an erroneous signal if you use manifold vacuum.

i agree with this also.

 

[bartl]

The timing can also be affected by wear to the breaker plate and the advance "post". It doesn't take much for 3* of distributor advance. FWIW, my '85 HO likes 44* total (8* initial and advance plate set on the 18L side...old OE dual point).