Timing light operation question

[92470]

Can anyone tell me if you are supposed to dial the advance degree dial on your timing light to what you are trying to hit, like 8 degrees BTDC and then adust timing. Or are you supposed to dial it to 0 and then adjust timing?

I bought a used light, and can't figure out which to use it. Today I dialed it to 0, then adjusted my distributor until it was 8 degrees BTDC on the tab like the factory spec says. It seems to run O.K. But I could also dial the light to 8 degrees and adjust my distributor to 8 degrees on the tab and it seems to run alright that way also? Any advice is appreciated. Thanks

[powell72]

If you dial in the degrees on the light, than you adjust the timing until it says zero on the tab. If you had the light at eight degrees and it reading eight degrees on the timing tab you had sixteen degrees, which would explain your truck running good. I like twelve to sixteen degrees on SBC's with HEI's.

[92470]

My engine is the stock 350 completely original and unmodified to my 71' Super Cheyenne other than I converted to a HEI distributor. I also opened the plug gap to .045 vs. .035 as factory spec due to the HEI and this seems to have given it a bit more power, but no better mileage as has been suggested.

I just assumed that I should set timing to 8 degrees BTDC as factory, but should I set it different being it has an HEI now? I try and keep and set everything as original as possible, but I'm open for timing adjustment suggestions if they improve the performance.

[hvychve]

The wheel on the back of the light is usually for checking advance, ie. vacuum and mechanical advance, if you were to check your timing while holding RPM's up, you would see your timing mark move, so to move it back to where it was before you reved up engine , you must turn the dial, if you remove the vacuum advance before you do this, you will be checking the mechanical weights under the rotor (mechanical advance)and when you rev it up w/ vac. advance on this will give you total advance, I hope I didnt confuse you , however, if you were to run your engine with pickup lead (inductive probe) on cyl. #1 start engine (warm) off fast idle, you could do it either way, you can dial your light to read whatever you want timing at, if for instance you wanted twelve degrees, and you had dial on tiiming light showing twelve degrees and your mark on balancer was aligned with zero, you are actually 12 degrees, also you can have your dial @ 0 degrees and the mark on balancer could be showing twelve degrees, that too is the same..... hope this helps.....

[hvychve]

forgot to mention, that when you check your mechanical totals, and than hook up your vacuum and check again, you will have a greater number, subract the two, this will be your total vacuum advance.

[92470]

All responses have answered my questions. Now if I could only find a cheap way to acccuratly guage my RPM's so I could adjust correctly I would be set! The stock tachometer isn't the best method I'm sure! Thanks!

[PanelDeland]

On rpm's I use a tach/dwell meter.You may be able to find a used one at a pawn shop or yard sale.I bought one at Sears.I think it was about $60.00 or so.It also works well if you are still running points.I haven't installed the HEI for my 6 yet.