Too much vacuum advance at / near idle? SCV valve plugging?

[aribert]

I have a L-O-M distributor and (still temporarily) my 1904/1908 Holly carb on my newly installed 200. The turns out that the very new looking vac cannister on the distributor was shot and there was no advance at all. Now I have swapped in a vac cannister from a core distributor (and while it has a minor leak and does not hold vacuum, it does advance the timing - a lot. How much vac advance sould there be at idle (say 750 / 800 rpm)? How much vac advance should there be at say 1200 rpm? The factory shop manual for my '61 Falcon gives various values depending on year and trans type, but generally 2 to 4 deg advance at 700 rpm. I am seeing about 10 deg adv at idle when I reconnect the vac line. FWIW, at idle there is about 14 inches of vacuum, at about 1500 rpm it peaks out at about 20 inches.

I had intended to swap in a '73 dist last night instead of swapping vac cans but it looks like I need a newer style dist cap - the rotor was making contact with the LOM dist cap. When I make this change I know that I need to block off the SCV valve. I have read the stickys and several other postings but am unclear as to what to block off - do I simply block off the approx 0.060 dia hole in the side of the SCV just below the threads?

 

[james singleton]

Is your vacuum line connected to manifold vacuum or your carb??? I believe you should only be seeing 4-7inches of vacuum @ idle; but not sure about that with your particular carb. I know the Autolite 1100 w/SCV and LOM dizzy is suppose to be between 4-7" at idle; and the vacuum line goes to the carb; not to manifold vacuum. Jim

 

[aribert]

Thanks for the response James. From memory, the vac specs for the 1904/8 are comparable.

Since posting, I have swapped in a '73 distributor and am now running just on mechanical advance. Last night I epoxied up a SCV valve and will install tonight and check the overall advance with the vacuum connected. The vacuum is taken off of the carb port to date. I have marked the balancer with marks at 14 and 28 degree advance. With the dist set to 6 deg BTDC, I am seeing more than 28 deg of total advance from the mechanical advance. Does anyone have specs as to the total advance limit for these engines for the mid/late '60 or early '70s time period.

 

[BIGREDRASA]

Vacumm advance cannisters on Fords are typically advanced by inserting an Allen Wrench inot the hose nipple of the can. I think you tern clockwise to decrease the amount of advance for a given vacuum. Could be ounterclockwise. Use a vacuum pump to take your readings.

 

[66 Fastback]

The shop manual publishes ignition advance specifications in distributor degrees and rpm. So a spec of 4 degrees at 700 rpm would actually be 8 degrees and 1400 rpm on the crankshaft.

When you say 28 deg of total advance, I assume you are talking at some elevated rpm say 2500 to 3000 rpm. I imagine the vacuum advance when hooked up to manifold vac will yield 15 to 20 deg of additional advance at idle.
Doug

 

[aribert]

Yes, the total advance of 28+ deg is at about 2500+ rpm. I just reread 66 Fastback posting as I was previewing this response - it is slowly beginning to sink in. If the advance spec is at the distributor then things are begining to make a bit more sense. I am looking a crank position advance when I perceive that there is too much advance.

What I am interested in is what the total advance limit should be (in other words how far advanced is too far). Advancing and listening for detonation (pinging) is not working - I can not hear any - I am clearly able to hear detonation on another (Triumph) 6 cyl engine that I own when I do not run mid-grade. So for now I am content to limit the advance to factory specs. And since my Ford shop manual is for a '61, I am asking for some one to post max advance specs for a later engine / distributor - preferably post LOM and pre DS1. Thanks