Points dist timing issues

[T0rch]

Hey guys. I've got a '69 Sierra grande with a 350 in it and still have the original points distributor. I've been fighting a rough, unhappy idle since I bought the truck. It idles like it has a really aggressive cam in it.

I rebuilt the carb and that helped a little, and I threw a timing light on it and tried to follow factory spec, timed initial at around 10° and 3000(ish) rpm at around 36°.

Problem is, the idle runs like sh*t unless I manually turn the distributor until it's at about 20° advance, at around which point it smooths right out. Anything past about 14° is a really hard start when it's warm, and I'm a little afraid total advance would be way up anyway. I've also noticed that the idle timing doesn't change whether the hose is connected to the vacuum advance or not... Should it? I feel like the vacuum advance should bring it from the initial 10° starting value up to around 20° or so at idle (high vacuum) to smooth out the idle.

I've also connected a vacuum gauge and it floats right between the low end of "normal" and the top end of "late ign timing" when at idle. 20° pushes it to the middle of the green "normal" range.

[67 chevelle]

Sounds like you need a vacume advance canister ,they go bad and are cheep and easy to replace , set the idle advance with the canister disconnected , you should be good to go

[Shady Rascal]

It sounds like your distributor vacuum is hooked to ported vacuum instead of manifold vacuum. At idle, ported vacuum is zero or very near zero.

Conversely, manifold vacuum is high at idle which will allow you to set your base timing correctly, then the advance will add more timing to smooth out your idle when you hook the vacuum line back up.

It's an age old debate about whether ported or manifold vacuum for the distributor is proper and manufacturers have set it up both ways over the years. What you're describing though, that it idles better with an extra 10 degrees of advance over spec, is a scenario where manifold vacuum is ideal. Set your base timing to spec, add in about 8 degrees of advance when you plug in your vacuum hose. Smooth idle and overall total timing is still good at higher RPM.

[geezer#99]

Your points gap is too wide or the points are worn out.
And you need a vac pot.

Likely easier to swap in a hei distributor. No problems with points then, a hotter spark, smoother idle, etc.

[T0rch]

It is hooked to manifold vacuum, i have checked with the vac gauge (edelbrock 1406, driver side port, shows vac at idle and the other doesn't). I guess the vac canister must be gone. It looks like the original canister. It *should* add advance at idle, correct?

I don't have a dwell meter to properly set points. I did it using a trick I found on the forum here by turning the Allen key counterclockwise until the engine dies, and then turning it back 180° and that is roughly 30° dwell, where it should be?

Isn't there a lot of rewiring involved in switching to HEI? If I need to buy new set of points, A new vac canister, and a dwell meter then maybe I should just get an HEI...

[Shady Rascal]

If you have your distributor hooked to full time manifold vacuum and your timing doesn't change by 8-10 degrees when you hook the line up, your vacuum can on the distributor is ruptured. Which is a vacuum leak, which further aggravates the poor idle.

As far as getting a new vacuum advance canister, Rockauto shows three different brands to choose from (Delco, Wells, and Standard) for about 8 dollars each (69 GMC w/a 350 engine). I'm sure things are different in Canukistan but surely the local parts stores won't whack you too badly when you ask the price.

Converting to HEI requires the distributor itself, new spark plug wires, and hooking up a new larger gauge 12v power wire to the distributor.

[Alex V.]

Since you're sure it's connected to manifold vacuum it sounds like the advance canister is bad. It's your call, but once they're right I have no problem with points ignition. Dwell meters aren't that expensive and IIRC my '67 owner's manual says to check the points every 12,000 mi. Though I do mine every thousand or so, just 'cause I'm always tweaking something else lately - jetting, timing, etc.

[geezer#99]

Easy to wire in a hei. Just need a 12 gauge wire to an unfused spade on your fuse box.
Only problem with an hei is the size. Tight fit back there.
Plus cost if you buy one new. Likely a couple hundred bucks for the hei and new plug wires.

On your carb drivers side is manifold vac, the other is ported.

Pop the distributor cap off and hook a hose to the vac pot and use some lung power to pull the arm on the pot. I've seen them pop off the plate inside. The end of the arm is bent into a 90 degree angle and sits in a hole in the plate.
Easy thing to check.

If you keep the points and need a dwell meter, just pm me your address and I'll send mine over.

[Stocker]

I adjusted points in several vehicles over many years and never used a dwell meter, just set the gap with a feeler gauge. Not the best way perhaps but it always worked.

That said, I would switch to HEI. Yeah, there's not a lot of room, but it fits. Installing it with the cap removed makes it easier. New hot wire and larger plug wires have been mentioned, and the plugs (same as stock) need re-gapped to .045".

There are several how-to threads on the site, and I ran across this a long time ago: http://rmcavoy.freeshell.org/HEI.html

[Mike C]

Could also be the balancer has slipped on the inertia ring making the mark not in the correct location. There were some motors that actually had the tab in a different spot for a different balancer.

[ChuckLee]

Originally Posted by Shady Rascal

If you have your distributor hooked to full time manifold vacuum and your timing doesn't change by 8-10 degrees when you hook the line up, your vacuum can on the distributor is ruptured. Which is a vacuum leak, which further aggravates the poor idle.

As far as getting a new vacuum advance canister, Rockauto shows three different brands to choose from (Delco, Wells, and Standard) for about 8 dollars each (69 GMC w/a 350 engine). I'm sure things are different in Canukistan but surely the local parts stores won't whack you too badly when you ask the price.

Converting to HEI requires the distributor itself, new spark plug wires, and hooking up a new larger gauge 12v power wire to the distributor.

Canukistan.....wow

[mike16]

sometimes the timing marks on the balancer are not correct for the indicator thingie on the timing chain cover.

[T0rch]

Well a buddy just gave me his old gm HEI distributor and plug wires after upgrading to an MSD billet thing, but it looks like the vacuum advance on it is shot as well, since I can just blow air through it. I guess since I've got it now I might as well fix up the HEI rather than the points distributor.

[Swar]

I went with an MSD distributor with the digital ignition box and never looked back.
Been running strong for almost 10 years now. Noticed the difference the second it fired up.
And that was after an HEI.

[67 chevelle]

Originally Posted by T0rch

Well a buddy just gave me his old gm HEI distributor and plug wires after upgrading to an MSD billet thing, but it looks like the vacuum advance on it is shot as well, since I can just blow air through it. I guess since I've got it now I might as well fix up the HEI rather than the points distributor.

Your better off doing that , get a vacuum can "cheep" , easy install , run a new wire into the same plug on the firewall fuse block where the white cloth wire is , discard the white wire , its a resistor and will not work with hei

[T0rch]

Just as an update, I dropped the HEI dizzy in and got a new vacuum can for it. Even with the old, worn-out cap and rotor, it runs like a new truck. Lots of power, very smooth, no more rough idle. Feels like a later model EFI truck. Way more power and acceleration. Can't recommend this enough, and it was a really easy swap just like everybody said it would be.

The only difficulty I had was the spade connector that goes into the firewall fuse block had to be spliced onto the new wire because the spade connectors at the auto parts store didn't fit all the way through the hole into the contact. So I have about 1/8 of an inch of the fusible wire left, which I don't think should be an issue for the moment - but does anyone have a source for the GM long spade connectors so I can eliminate the old wire completely?

[davepl]

Originally Posted by Shady Rascal

It sounds like your distributor vacuum is hooked to ported vacuum instead of manifold vacuum. At idle, ported vacuum is zero or very near zero.

Which is how it was designed, and how it should be run.

If you need a ton of initial advance, give it initial advance and limit the mechanical. Don't connect vacuum advance to manifold vacuum.

Odds are the throttle blades are open too far. I'd wager the fuel mixture screws do nothing.

If the cam is big enough, you wind up drilling holes in the throttle blades to get enough air moving without uncovering the transfer slots.

I'm not an expert on giant cams - maybe in that case it makes sense to run vacuum advance off manifold, but never in a normal application.

[mike16]

I alays put a vaccuum advance from a 75 corvette in there.