Spark plug diagnosis

[forestb]

I am assuming that I should cap off my vacuum advance when doing this?

[geezer#99]

Originally Posted by forestb

Okay thanks. Is there an amount of advance that I should not go over when doing this?

You won’t be checking the timing as you set the idle and move the distributor.
You’ll check it after you’ve got things set.

Leave the vac pot hooked up if it’s plugged onto manifold vac port on the carb.

[forestb]

Instead of chaining the truck to a pole will it work to lift the rear off the ground and then prop the break peddle down with a pole?

[geezer#99]

I shouldn’t have mentioned chaining my truck to a tree!
I only did that because there was no other way to get my idle rpm low enough to accurately set my carb and timing.
You don’t need to do that if you can turn your idle down below the point where your mechanical timing starts kicking in.

[forestb]

Forgive me if this is a stupid question but how do I know when my mechanical timing starts kicking in?

[tdangle]

Easy, with the engine idling (not in gear) lower the speed as much as you can. Note the timing it's currently at. Now slowly raise the engine speed watching the RPM and keeping the timing light watching the timing. As soon as it starts to advance that the where your timing starts advancing. Using a dial back timing light you can map out your total advance and when it happens. Don't forget to disconnect the vacuum advance with doing this as you want to see true initial and mechanical advance. At idle you can hook up the vacuum advance to manifold vacuum and measure the total vacuum advance you get. If you have a hand vacuum pump you can also see when it starts and total amount. Have fun.

[AcampoDave]

I don't have a dial back timing light, but i did get one of these https://www.summitracing.com/parts/s...BoChAAQAvD_BwE from my local parts store and used it with my regular timing light along with my tach to view when and how much initial, mechanical and vacum advance my distributor was putting out. It worked great and I picked up a few stray ponies by getting it all dialed in.

[forestb]

So I tried to lower my rpm and adjust my timing to make up for it. When I got lower than 700 rpm by adjusting my timing idle screw, I was not able to increase my rpm by advancing my timing. So I could not get the rpm adjustment screw down any lower than that. I did make a few observations.

1) my timing is set to around 15 degrees advance at 1000 rpm with the vacuum advance unplugged and in park.

2) at 700 rpm it is around 14 degrees when in park and rpm adjusted using the idle screw.

3) with my vacuum advance disconnect I have around 15 pounds of vacuum.

4) when I plug my vacuum advance in (when in park) my rpm goes from 1000 rpm to 1300 rpm

5) when I plug my vacuum advance in (when in park) my vacuum increases from 15 pounds to 20 pounds

6) when I adjust my mixture screws with my vacuum advance disconnect and the ports plugged I was able to adjust my vacuum but it took several full turn to make any kind of difference.

[geezer#99]

We now know a few things.
You can get it to idle at 700 rpm.
You have 14 degrees initial.
Your mechanical timing doesn’t start kicking in until 950-1000 rpm.
Your vac pot is good (not blown).

At 700 rpm in park will it keep running when you put it in drive?

[forestb]

I don’t try. I will try tomorrow

[geezer#99]

Also when at 700 rpm check for vacuum on your ported port on the carb.

[forestb]

Ported port?

[geezer#99]

Yup!
The one directly above your drivers side mix screw.

[forestb]

Thanks. Please pardon my ignorance

[geezer#99]

Hopefully you read this.

If it’s at 700 in park and won’t idle in gear and you need to increase the idle to keep it running (say 800 rpm or whatever it needs to be) then let us know what the vac reading is on the ported port.

[forestb]

Yes you caught me in time. Keep in mind that the ported port is where my vacuum advance is connected to. So I had to disconnect my vacuum advance to do this. I set the idle to 700 rpm in park and the vacuum read 12 pounds. I shifted into reverse and the rpms dropped to 600 and the vacuum dropped to 8 pounds.

[geezer#99]

That says a bunch.
You know it will idle in gear at 600 rpm.
Showing any vacuum On that port says you’re idleing on the power circuit. Need to fix that.
Leave your vac gauge hooked to the ported port, hook up your vac advance to the manifold vacuum port ( blue cap just left of drivers side mix screw), start your motor, warm it up and turn the idle back down to 700. Put it in gear and tell us what your vacuum reading is.

[forestb]

11 pounds at 700 rpm (park)
7 pounds at 550 rpm (drive)

[geezer#99]

Did you hook up your vac pot to the manifold vac port?

[forestb]

Here’s how the vacuum pot is hooked up.

[forestb]

Right side up with arrows

[forestb]

Could it be that the vacuum pot needs adjustment? Using the screw?

[geezer#99]

I thought so!
That’s not the vacuum pot on the distributor.
That’s the choke pull off pot. Don’t worry about it. Leave it alone.
Looks like you have the manifold vac port (where the blue cap was) hooked with the hose that goes back to the distributor. In that pic.
Leave it there.
Show me your vac gauge and where it’s hooked to.

[forestb]

It’s the one with the zip tie

[geezer#99]

Now, leave all as it is.
Leave vacuum gauge hooked where it is.
Leave distributor vac pot hooked up where it is.
Check your timing at 700 rpm in park.
Let me know what number you get.