340 Distributor Timing

[kawahonda]

Been chatting with Cody a little, but I think I'm a little lost.

I'm at 2700 feet elevation. Running 91 Octane.

Initially without my digital timing light, I set my 340 at 9 BTDC. This was pretty much the max I could advance it before I got any pinging.

Now that I have my timing light, I'm able to see what my total is. At 9 BTDC, my total is 45 degrees "all in". Disconnecting the vacuum from the advancer (and plugging it) sets my "all in" to 26 degrees. So my vacuum advancer is adding 19 degrees. My mechanical springs are adding 17 degrees.

I was told to bump my initial to 14-15. That seems to be the sweet spot for 340s I suppose...

I bumped it to 14, and as imagined, my total timing went up to 51. I then took an Allen wrench to the vacuum advancer and tightened it a few turns. Checked again, and it didn't seem to get any better. Tightened it again, and it bottomed out. Rechecked my total and it's at 53. Weird how it went up. May have been "within" error. I will say that it didn't get any better. Oh well.

So......now what? I will eventually send the distributor off for a rebuild/recurve/pentronix, but shouldn't I be able to get more advance out of the stock one?

I'm pulling about 16 inches of vacuum at 800 RPM (Idle)--at 9 BTDC. I haven't checked how much vacuum I am pulling at 3,000 RPM.

Should I revert back to 9 BTDC, and just live with knowing my total advance is way over spec? Should I leave my screw in my vacuum canister all the way in like it is now? I turned it about 4 turns clockwise in order to hope to reduce advance, but didn't seem to make much difference.

[Cuda Cody]

What is the total timing when you back the allen wrench all the way out?

[Cuda Cody]

If you back the allen all the way out and there's not a change that would lead me to believe that there might be an issue with the vacuum canister, right?

[kawahonda]

Loosening all the way it continues to add 19 advance. Still at 53 BTDC at 3200.

So...it's basically adjustable, but not adjusting!

I did check that it holds pressure, and that the vacuum advance is working.

But what causes the adjustment to not work?

[nsmall]

Can you adjust the distributor internally?  If not, buy the advanced limiter plate.  It's only $20 and buy a spring kit for $10.  I know we were talking about this on a different thread you started.

I contacted @Chryco Psycho  and he totally dialed in my car.  I sent him a little $$$ as he totally gets these cars and totally fixed me up and the dude lives in Panama and I know nothing about cars so I recommend touching base with him before you spend a bunch of money that you don't need to.  Just my opinion.

I think the company is called four seconds flat or FBO that sells a plate because your curve is way too crazy just like mine was.  I had the exact same problem but I was able to fix it for 30 bucks.

[Topcat]

Can you adjust the distributor internally?  If not, buy the advanced limiter plate.  It's only $20 and buy a spring kit for $10.  I know we were talking about this on a different thread you started.

I contacted @Chryco Psycho  and he totally dialed in my car.  I sent him a little $$$ as he totally gets these cars and totally fixed me up and the dude lives in Panama and I know nothing about cars so I recommend touching base with him before you spend a bunch of money that you don't need to.  Just my opinion.

I think the company is called four seconds flat or FBO that sells a plate because your curve is way too crazy just like mine was.  I had the exact same problem but I was able to fix it for 30 bucks.

Hit the nail on the head after I just sent him a PM saying similar, just like this.    

[kawahonda]

Thanks guys. I'm trying to keep the car on the road.  At least for another couple months until late fall is here and it's time to park and play with it.

What should I do to keep it going for another couple months?

Two options I see:

1) Plug advance and dont use it. Set initial at 16, which should lend me around 35 total.

Or

2) Tighten advancer screw back where it was (roughly)..won't be accurate, and set it back to 9 BTDC.

Then when the time comes, I can ship it out to someone and lose the 2-3 weeks required. I'm totally up for options when the time comes, but I do t want to lose a month of it parked quite yet. Give me an email and a reasonable price that I can send to and I'll touch base.

[Katfish]

For temporary fix, go back to 9 and keep the advance.
You always want vacuum advance on a street driven car.

[73_Cuda_4_Me]

As you have found out, adjusting the screw in the vacuum canister has no effect on amount of vacuum advance! It only changes the amount of vacuum necessary before it works. The amount of vacuum advance is hard coded by the length of the slotted area on the vacuum arm - shown in the picture below... this is the vac can from my 340, hard coded for 8.5 degrees dizzy advance (17 crank).

If you have a stronger cam in your 340, you may have to disable vacuum by either disconnecting it or tightening the spring screw so that it doesn't advance at any vacuum.

My cam likes 15-18 degrees initial, but with 30 degrees of mechanical advance, when I put it where it was happy at idle, it would ping under load (with 45-50 all in at 3000 with no vacuum!). I had to limit mechanical also... you can either get the limiter plate mentioned (4secondsflat.com), or build one like I did. Note that I shortened the slots on the inside edge of the slot, so that it raised the starting rpm of mechanical to about 1200 rpm... at 900 idle the stock springs start advancing, so my timing was bouncing around at idle. It doesn't anymore.

Last option is to set all-in at 36 degrees at 3,000 rpm, and wherever initial ends up, it ends up... set idle speed at that timing.

[73_Cuda_4_Me]

One more option is to set initial (with vacuum disconnected and plugged) at 3-5 degrees, then use manifold vacuum (not the timed port) for vacuum advance, and set vac spring so it pulls in at slightly less vacuum than you have at idle... cranking at startup will start advancing vacuum to where cam likes it, but under load at higher rpm, vacuum goes low, and timing goes back to mechanical limits... prevents the pinging...

If you have an automatic transmission, I'd disconnect the vacuum so you don't have to fight it when rpm drops putting it in drive, or anything else that loads the engine...



Also note that my mods are for ELECTRONIC IGNITION DISTRIBUTOR, so may be different from yours!

[Chryco Psycho]

To reduce the advance you need to turn the allen screw counterclockwise inside the canister , generally I don't use the vacuum advance anyway just mechanical , newer Dist have an adjuste on the mechanical also that will limit the mechanical advance curve , the other way to do this is weld the slot shown in the picture above or use the limiter plate sold by FBO

[kawahonda]

I thought I'd verify my dwell. I'd assume these numbers agree?