When setting intitial timing with a light, the Vac Advance line should be disconnected. ( or at least I think so)
If you set the timing with a vacuum guage, do you still disconnect the vac advance line? or leave it connected?

 

The simple answer is yes...

Disconnect and plug the vacuum advance line, regardless of which timing method you use.

This is a must when sourcing manifold vacuum for your vacuum advance signal.

If sourcing ported vacuum for your vacuum advance signal it's not necessary to disconnect and plug the vacuum advance line (unless your idle speed is set so high that the transfer slots are exposed to a vacuum signal).

 

^ Agreed.
But....why would you want to set your timing with a vacuum gauge? Do you tune your carb with a timing light?
If you use a vacuum gauge for timing (setting it to the highest stable vacuum reading), you'll end up with your initial being too far advanced. Once you hook everything back up, drive down the road and punch it, you'll wonder why it's detonating.
If you don't believe me, test it. Set your timing with the vacuum gauge. Then use the timing light to check your initial.....I think you'll be surprised.
Stick to the timing light for timing and vacuum gauge for fine tuning carbs and troubleshooting.

 

Classic Inlines - Tuning with a Vacuum Gage

link that was given to me a few weeks ago that was very helpful. Give it a look. Hope it helps

 

Thanks for the input guys. Really appreciate it.
From my signature you can see I've concocted a little Frankenstein.
So I really don't have a manual stating "13 degrees" to use a light.
The heads literature says 34-36 total timing
The carb literature says 14-20 intitial timing
The msd ready to run distrib literature discribes the advance stop bushing
An msd generic timing guide says 6-12 intial.
I have been trying to get the initial dialed in, then I can set up the mechanical advance stop bushing.
In the garage ( not on road yet), the motor likes 18-22. If I go down to 15, it starts to really drop off. So I think i am tring to get lower on my initial timing.
I guess im wanting to see what the vac gauge tells me.

 

If you ask 20 people about timing you will more than likely get 20 different answers. One thing that I found consistent was you do want the 34-36 total timing. What I did was hook up the timing light and set my timing to 10 degrees (nice even number) then revved it to see how much mechanical advance I had. I saw that I had 20degrees so I set my timing to 34 which left me with a base of 14. Runs awesome now. I ended up with about 16in of vacumn. If I set the timing using the guage to get 20-21in (highest reading) that resulted in a base of 20 something degrees and over 40 total.. Was not good.

 

Thanks for the link. Good stuff.

 

^X2 Thanks. Reps comin.

 

Ok, thanks for the big picture. Not being a wise apple, just (now) understanding your question.
Any time one does any modifications, "The Book" gets flushed down the terlet. It's a good guideline but not a black & white rule. And every motor is different in what it takes to be happy. In your case, I would follow Miketaheny's suggestion. If you're sure you have #1 piston at TDC on compression and the pointer is at 0* on the balancer, then fire her up and set your total timing (with vacuum disconnected and plugged - even the one ported now) to 34 - 38 and take note of the RPMs at when the advance starts and when you've reached the total you want.
Once you've got that set, then you can play with the mechanical advance springs - red/blue/white/silver or any combination of both - to whatever makes the motor the happiest. Just be sure to take note of the RPMs every time you change springs at the desired 34 - 38 degree total. You can change at what RPM the centrifugal advance comes in/ends with the springs. Of which I'm sure you're aware.
Adjust the total timing first and where initial ends up, so be it!
Then play with the carb adjustments with the vacuum gauge.
Good luck, 'cause it's time consuming.....maybe a six pack or so.....hahaha

 

Best advice I've read all day. Reps sent.

 

Yeah that was pretty funny. Reminds me of "you can look up a butchers *** to ....."

Filthy Beast, I get what you and Mike are saying, about setting the total, then backing down to the initial. Which makes sense when you have a fixed degrees of advance. As Mike's 20 degrees. With my dizzy I
can select 18, 21, 25 or 28 degrees between intial and total. So I have some flexibility to optimize the initial.
Currently I have the 21 installed. So to get 36 total, the initial needs to be set at 14. But when I get down to 15 she chugs pretty good.
Long story short I had heard you can set timing with a vac gauge so I thought I'd play around a bit to see if I could optimize the intial.
If it needs the 17 initial, that it likes to run at, I can put in the 18 bushing and still stop at 36 total.

Initial timing of 16-18 seems high to me. But it certainly doesn't like sub 15.

Also yes TDC is zero on the pointer. When I degreed the cam it was verified. Brand new pioneer balancer too.

Thanks for the link and advice on using the the vac gauge, especially how it error to the advance side.
Learned a lot today. Too bad I got home too late to fire it up. Hopefully tomorrow.

 

I think it's all about tools in the bag and understanding how the tools relate.

 

Thank you, sir. Appreciated.

 

I applaud your desire to use every tool available to get as much information as possible when forming a course of action. One can never have enough information. This forum is one of the best tools around for that....good stuff, knowledgeable people.


Initial timing of 16-18 seems high to me. But it certainly doesn't like sub 15.
I have found that a "bigger" (relative term) cam likes more initial timing and the motor can handle it just fine. You might be able to get away with 38* 'all in' at 2500 - 3000 RPM. 16-18 would be a bit high - for a stock motor. Yours is not stock, so again, throw the "should be arounds" out the window and use your best informed judgement.

Use of a vacuum gauge to check/set the initial should be, at best, for your own edification - in my opinion. You have an LSA of what - 108, 110? With a "tight" LSA the timing would be advanced way too much by the time a high, stable reading is achieved.

I would still suggest you set your "all in" timing with a light, 34 - 38, at 2500 -3000 RPM. Then tweak it with the springs, cams and/or adjustable vacuum can - if you have one. Try to keep a record of each change, too. That way you can plot a graph of your curve(s) and find out which one works best. Good luck.

 

It would be if this were a stock motor, but it's not, so to paraphrase Filthy Beast, nothing is "by the book" anymore.

As long as your motor can tolerate 16-18 initial i.e. no starter kickback then it's fine to run that much initial. (as long as you're using ported vacuum for v/a)

If your motor's happy with 36-38 total... run 16-18 initial with the 21 bushing.

If the motor likes 34-36 total better... run 16-18 initial with the 18 bushing.

With that much initial (16-18) you can turn down the idle speed and get those throttle blades closed to prevent "dieseling" while still maintaining a healthy idle (750 rpm +/-)

MSD's come with pretty stiff springs that can delay total advance to around 4000-4500 rpm!, so spring changes are a must to be "all in" around 2500-3000 rpm.