Help Needed with Initial Timing

[colnago]

Okay, freshly-rebuilt 352. It's always had low vacuum, so I decided to play with timi g today. I found an article that suggested setting the timi g for max vacuum, rather than the timing marks. I figured, why not, all I'd lose is time. So it's now at 16hg, 550 idle RPM, and initial advance above 20, according to the timing marks. The needle is still bouncy, though.

What to do? I took it out for a spin, and had zero pigging. Do I keep advancing? Do I work on the carb? Normally, with a bouncy needle, I'd suspect the valves, but again this is a fresh rebuild. I figure the balancer must have rotated some, because I don't believe 20 degrees initial with no pinging.

Suggestions?

Joseph

[tnlprt]

Set your carb for the highest vacuum reading also

[Manny]

Okay, freshly-rebuilt 352. It's always had low vacuum, so I decided to play with timi g today. I found an article that suggested setting the timi g for max vacuum, rather than the timing marks. I figured, why not, all I'd lose is time. So it's now at 16hg, 550 idle RPM, and initial advance above 20, according to the timing marks. The needle is still bouncy, though.

What to do? I took it out for a spin, and had zero pigging. Do I keep advancing? Do I work on the carb? Normally, with a bouncy needle, I'd suspect the valves, but again this is a fresh rebuild. I figure the balancer must have rotated some, because I don't believe 20 degrees initial with no pinging.

Suggestions?

Joseph

Does it crank okay hot. Your approaching where its gonna start being hard to turn over. My base is normally 10-15. Then curve the vacuum and the mechanical to hold it a 32-35 total. All in by 3,000 rpm. I would adjust the carb out but would not set my base higher than 20 for sure. What cam and carb is in that one?

[colnago]

Cam is an Engine Pro 1776, mild RV grind. Their web site said that it provides a smooth idle, but other sites say that an RV cam can be a bit choppy. The carb is an Edelbrock 1405, on top of a Ford iron 4BBL intake. I see a lot of tweaking in my future ...

Joseph

[sargentrs]

I see a lot of tweaking in my future ...

Yep. I always like to time to max vacuum. Set the timing, tune the carb, set the idle, test run. Rinse and repeat multiple times until satisfied.

[colnago]

I've never tuned to max vacuum before. I figure it's only a different way of dialing In the timing, so I can't screw it up too much. I'll have to check the timing marks, and see if they've walked over the last 50 years. The C6 is shifting a lot nicer, most likely due to increased vacuum. I've got a hydraulic leak in the brake lines, so I don't know if they're any better or not.

When I check for total advance at 3,000 RPM, do I connect the distro can to vacuum? I assume so, since this is what I would have in the real world. I've never worked on total advance before, only idle.

Joseph

[DuckRyder]

I would have the vac advance off and plugged while checking total advance... You can tune that separately...

20 initial sounds pretty high, but it also depends on how much centrifugal and how fast...

Do you have a dial back timing light?

[colnago]

Do you have a dial back timing light?

Yes, I do.

Joseph

[Ren]

Yer vacuum gauge may be defective. Borrow another one. Or, test it on an engine you believe is running correctly.
I don't like dial back timing lights because the dial can easily get bumped.
I would think that with 20* initial timing, you would be getting pinging under load and kickback on the starter.
I got my damper rebuilt by Damper Dr. in Redding, Ca. I am still happy with the results.
I've never heard of an RV cam with a rough idle.

[colnago]

Okay, I played with the engine today. I did a "dowel test" to find TDC. As far as I can tell, it's pretty close. With that said, initial timing is 25 degrees BTDC ( ), and total timing is 38 degrees BTDC at 2500 RPM. Vacuum is 16hg, and lowers if I back the timing any further. Absolutely no pinging. Idle is set to 600RPM with a C6 tranny. Idle screws on the carb are out 1-1/2 full turns. The plug on #1 is sooty (too lean?). Two "bad" symptoms:

1. It idles smoothly, but maybe 10% of idles at stop lights are "ratty."

2. Maybe 10% of the 1 - 2 shifts don't happen unless I stop accerating. After that, life is good. The 2 - 3 shift is fine.

What to do?

Joseph

[Ren]

PCV valve? Defective vacuum solenoid or related plumbing going to transmission?

It sounds like there is a vacuum leak. Somewhere...

[colnago]

Hmmm, I hadn't considered a vacuum leak. Easy enough to check, but I probably won't have time until next weekend. Thanks for giving me something different to check. My problem is that I'm too locked into a mindset, so I need help thinking outside my box.

Joseph