Timing and Idle Question

Quick question about adjusting the timing, and I haven't seen this mentioned anywhere. First off, the vacuum advance on my distributor is ported off the rear HS4 for my 18gk engine. Also had the distributor recurved by Jeff @ Advanced Distributors.

I've read the procedure's here, and it seems there are two ways of going about setting the timing. One is to set the timing at idle with vacuum advanced disconnected and plugged (for me, Jeff said to start at 14 btdc), the other is set it at 32 btdc with the vacuum advance disconnected at 3500 rpm.

So here's my question, setting timing via the first method at idle, first I have my idle set at 1000rpm with everything hooked up as normal. When I disconnect and plug the vacuum advance, the idle drops to 600 rpm. Now am I supposed to set the timing at this "lower" idle setting of 600rpm? Or should I temporarily bump the idle to 1000 with the vacuum advanced disconnected and plugged?-which then when I reattach the vacuum the idle will probably jump up to 1600 rpm or so.

Jeff's 12-14 BTDC should be good. This ought to result is something around 32-36 at 3500-4000 so the two procedures should be about the same.

but a drop of 400 rpm disconnecting the vac advance at idle raises my eyebrows. And I wonder. you ARE connecting the vac adv to the carb not to the manifold...yes?

I think that what I'd do is--assuming the car runs ok at 600 (mine does, with HS4s and jeffDist and Pertronix)--time it at 12. And hook everything back up and see what the reading is now. Note it, and drive the car. how does it run?

How are the carbs set? (what mpg do you get is a quick check).

Mac,

Yes, the 400 rpm drop is what is raising my eyebrow too! I went out and double checked, just to make sure I wasn't losing my mind, and it is ported off the rear carb. If I remember, when I hooked the advance back up the the idle both increased and timing increased too. I'll go out and time the engine to get exact numbers.

The carbs are set pretty close, the #1 cylinder is tan and the rest are a little grey, so it probably is a little rich.

I went out and checked the timing, here's what I'm getting:

1. Vacuum disconnected, at 600 rpm idle timing is 10 degrees.
2. Vacuum connected, idle rises to 1000 rpm, timing advances to ~25 degrees.
3. Vacuum disconnected, 3500 rpm timing is at ~31-32 degrees.
4. Vacuum connected, 3500 rpm, timing is ~45 degrees.

Thoughts?

Ryan,
Its pretty clear that the port you're using is manifold vacuum. If the timing advances at idle with the vacuum line attached, then its getting manifold vacuum. Can you post a picture of the vacuum line and where it hooks up?

The rpms are rising by 400 because you're advancing thetiming 15 degrees. That's normal too! If you use ported vacuum, the rpm and timing will not change at idle!

Here is a picture of the port location:

Is it possible that your throttle butterfly is installed wrong? Its getting vacuum at idle and shouldn't be, or there would be NO advance. Do you have a MityVac tester? If so, hook it to the port and see what you get for a reading. It should be zero at idle and climb from there.

The timing settings you have aren't bad, its just working with manifold vacuum (somehow.)

It looks like your carbs are freshly rebuilt. May I ask who did them? Hopefully this will be an easy one to sort out!

Jeff, had a guy named Mike Brown out of Rouge River, OR rebuild the head, rocker assembly, change needles, and port the carb at the same time. I honestly don't remember if he rebuilt them completely, if he didn't then Lawrie Alexander in Sacramento rebuilt them 2-3 years ago.

Don't have a mity-vac tester handy either. I'll get in touch with Mike Brown also to see if he has any input also.

Probably a great idea! If nothing else, just continue to run it as-is. It should still work great. If you don't find a resolution to the ported/manifold situation, I can recurve it for use with manifold vacuum and you'll be set!