Engine Miss: Part Deux - Distributor

The only way that'll run right on manifold vacuum is if the distributor is modified. Lighter springs I believe and the aforementioned vacuum stop. In stock form on manifold vacuum the timing will retard briefly giving you the bog you had. I can't see how you couldn't run it ported. Of course when I come into some extra $$$$ I'm gonna get a Dave distributor and quit concerning myself with this issue.

 

uh....ok.




Back to square one....kind of.

So I need to put the stop on the adavance like Dave said...


Would lighter springs help? Where do I get them?


Dave this thing may be coming to you sooner than I thought.:gt:

 

I'll take a stab at this... vacuum goes away at WOT. So when you stomp it you only get mechanical advance.

Ported vac only operates once you are off idle. So if you use that for vacuum advance, you will have no vac advance until you accelerate MODERATELY (remember, WOT makes it go away). So you will have to have your timing set a little advanced to get the idle you want, which can make starting difficult.

Using full vacuum for the advance allows less initial timing (mechanically) because as soon as the engine starts the vac advance gives you a few more degrees to bring the idle up.

I don't see where a bog would occur if you have your mechanical advance set to come in early enough. Yeah, as soon as the vac advance goes away your timing drops back, but with a correctly setup distributor the mechanical advance will compensate.

So bump your initial timing back and use full vacuum and set your idle speed where you want it.

 

Ok Just to clear my head....


The arrow is pointing to WHICH vacuum....ported or full?

This is the one it is currently plumbbed to, and runs well...to my knowledge (it cleared up the miss). The fitting on the opposite side is the one it was attached to when I had the miss.

I want to cover all my bases here so I don't step on my.........trying to figure things out the wrong way. I've been chasing this damn miss for 2 weeks with no success. I even pulled the intake and resealed itou:



See picture in next post:

 

oops...forgot to add picture::::::::::::::::;

 

The port that the arrow is pointing to is not pulling full vacuum at idle, so I am assuming it is "ported" vacuum.

Dave, you have mail.....againou:

 

Just a quick note regarding WOT vacuum. I connected a long hose to a manifold vacuum port and drove around with a vacuum gauge connected and vacuum never dissapeared totally at full throttle. The least that it registered was around 2 and 5 HG. 2-5 HG might not be worth anything as far as pulling the vacuum advance but I just thought I'd mention that at no time was I not registering any vacuum. There was always some present.

 

That is correct Adam.

 

Yes...that is the spark port.

That kind of vac is normal. You would need a real big intake and carb combo to get zero. If you read the 455 build-up in what ever mag that everybody is talking about in other threads, that engine was still pulling vac at WOT at peak power on the dyno (means it could use more carb cfm). also, If you were to put a timing light on your engine and a vac pump on the vac advance, you would see that it takes more than 2-5 HG of vac to make any real timing change. A vac advance is there to help part throttle drivability and gas mileage. On my own engine, I have my mech adv all in by 2700 and set my timing at 34deg at anything above 2700 w/vac disconnected. Don't remember what base is, don't really care, it idles & starts good. My vac adv gives 10deg at 10hg of vac. So, when I'm cruising I get 44deg of advance. I do have a small nos system on the car and I bring the timing back to 28 total (no vac adv) when I plan on using the nos. My car gets 17 mpg hwy, 13 city. Runs 12.44 w/nos. (Thats all with a 3.73 gear and t400 trans).
As far as "what is the correct way to run the vac adv" goes, I almost always run ported on any close to stock application unless OEM was not. So, if it has a TVS giving it manifold vac when cold (to add in cold idle), and ported when warm, thats what I do. I will advance base if the engine will let me.
I've been a auto and truck tech for the last 20 years specializing in drivability and have lots of happy customers. Both people looking for a stock driving car, and the guy's looking for a little more power and fuel economy.
This seems to work for me, but, you can do and try what ever you want. Hey, you may find & love something else.