http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=370354074797&ssPageName=STRK:MEWAX:IT

Price seems to good to be true. Considering a shortcut here as I don't really want to spend 330 on an msd.

Looks like a good deal.

MBHD

I bought one for a V8 from that outfit on ebay. Quality seems pretty good for the price, but I have not installed it yet.

These stock distributers are good to 5500 RPM. You can run them with confidence. In the future you can get parts from Performance Distributers in Memphis to hop it up. The only problen I ever had with an HEI was it blew a hole in the rotor after 35K miles. When it failed to start I opened the cap and changed it. (had an extra on in the glove box) Make sure to use a quality wire for HEI's; a stock one will put out 40,000 volts and higher.

I bought one of these in February and installed it in May I called them today and I did get a 65,000 V coil!The ad does not mention that the vacuum advance is adjustable. You get a smallallen wrench in the box but no explanation. Screw in to advance screw out to retard. These are made in China but with a lifetime guarantee I doubt that it's a problem.

If the vacuum can is like OEM, the adjuster controls the spring rate, not the amount of advance.

Panic - ??? I'm confused

I sent a question to the seller of this unit asking if the vaccuum advance is adjustable. They replied that it was.

I assumed/guessed that 'adjustable' meant that I could control the amount of advance. Are you saying that it controls the 'rate' of advance instead of the amount?

Currently I'm running a stock HEI that the vaccuum advance is too large. Inorder for me to be at 32-34 degrees at 3K I have the base timing too low (retarded) which affects my low end takeoff until about 1500(also, I don't think that it's helping my mileage either.)

How do I limit the amount of vaccuum advance so that I can get proper timing at both ends of the spectrum?

Can it be done with a stock unit? Can I purchase a different vaccuum advance to accomplish this?

p.s. I'm sending another question to the seller asking this. I'll let you know what he replies. (Also - 'Made in China' is never a selling point for me)

The allen screw tensions the return spring, which determines how much vacuum is needed to pull the advance plate. Completely relaxed (screwed in) means any vacuum at all advances it, full tension (out) means no advance until high vacuum.
Crane used to make a snail that went inside to adjust the actual plate travel.

Those cheap distributors have stamped out mechanical advance units that usually wears a lot faster than a quality unit with hardened parts.What Panic says is correct,you need to build an advance stop.This photo shows what I do on a V Hei distributor,same as the inline unit.Usually limit the vacuum advance to about 12-14 crankshaft degrees(trial and error with a timing light)use intake vacuum ,not the ported carb vacuum if doing an advance stop.

Here's the Crane part.

Why use intake vacuum vs. carb ported vacuum?

If I do use intake vacuum, then I should be able to plug the vaccuum port on my Holley, correct?

Thanks

Intake vacuum source gives more advance at idle.This can help off idle response on modified engines.The the extra advance also speeds up the idle,to compensate,you close down the throttle opening,this helps some engines that run on a few seconds after the ignition is shut off.Extra advance can also make the engine run a bit cooler at very low speeds if this is problem.
On some carburetors the ported vacuum can recieve a false vacuum signal at high speeds and bring on the vacuum advance when you don't want the extra advance.
Be aware if running a very small carb the intake vacuum might rise up enough near maximum RPM's to start the vacuum advance.This is something you may want to check out with a vacuum gauge during actual running conditions.
And of course,every tuned engine is different,run yours the way it wants to be run.........

the intake vacuum might rise up enough near maximum RPM's to start the vacuum advance

True - this is potentially dangerous.
A high vacuum level under power will also shut down your power system (pull the metering rod down, or close the power valve) and lean it out.

The choice of ported or manifold vacuum is also a way of "cheating" the throttle blade angle position at idle. Depending on the cam, PCV-based carb or not, etc. your idle setting may place the disc edge too far into the transition slot for best response, giving a flat spot off-idle.
Increasing the idle spark sometimes allows the disc to be re-positioned where it should be - about .020" to .040" into the transition.
Pre-PCV carbs frequently don't tolerate the extra air added by a PCV very well, and lowering the idle speed manually causes the disc to retreat too far away from the transition slot. In this case, more spark may make the problem worse.

Horses for courses.

And the only way to really check it out to to rig up a vacuum gauge and do a few test runs.How many guys messing with engines actually do this,probably very few.Some spend a lot of time looking for high speed misfiring or power loss,and they might be looking in all the wrong places.
The limited vacuum advance running off the intake is more often than not used on cammed up V-8 street engines.It almost always has a positive effect on part throttle performance.
It's simple to do and worth a try .........

For the last several days I've been reading all I can about vacuum vs mechanical advance and how they interact and about ported vs manifold vacuum. I've learned that I know alot less than what I thought I knew. Most of the info that I've come across is discussing V's, but I'm pretty sure that the same principles will apply to inlines though.

Based on what you guys have said and what I've been reading I'm going to do the following this weekend : 1st - limit my vacuum advance enough so that I can set the base timing to 4 - 6 degrees BTDC (near factory) and still maintain 32-34 at 3K; 2nd - move the vacuum advance to the manifold and readjust the carb; 3rd - install a line so that I can run my vac gauge into the cab.
Then drive it and fiddle with the mechanical advance springs (I have 4 sets that came with a kit I bought) and moving the total advance at 3K up some and down some and drive it after each change.

My carb is 390 Holley, mild cam, zero decked, cast iron headers, Offy intake.

Now it's time for questions!
Tony P - do you consider a 390 to be a 'small' carb and should I expect vacuum at max throttle (4200 - 4600 rpm's)?
Panic - are you saying that I may have to increase the idle spark higher than 4 - 6 BTDC? If yes, then I'll also need to limit the vacuum advance further to keep my total timing near 32 - 34, correct? I'm not aware of what your talking about when you say 'disc edge too far into the transition slot' (excuse my lack of knowledge/ignorance - I'm learning as I go!) You said vacuum advance at max throttle is 'dangerous', dangerous to what?

Both of you - do you agree with total advacne at 3K near 32-34 degrees? Is it possible to have both good performance and fuel economy or is one the sacrifice for the other? Is it worth my time to get an adjustable vacuum cannister?

I'm open to all suggestions and thanks!

Dangerous, as in makes holes in the pistons in less than 1 minute.
The mechanical advance is never enough for maximum mileage. Depending on temp and mix, over 50° total with vacuum may be useful - but it has to vanish almost instantly with falling vacuum.
The throttle blade angle is more likely to be a problem with a cam bigger than about 240° @ .050". The symptom is typically that if you have to increase idle speed to prevent a stall due to roughness at 7-800 RPM, then you get a flat spot (perhaps a pop) above idle. If you have neither, don't worry about it.