Mark71

So I decided that it is time for a tune-up on my 71 Cutlass. I have the small block 350 and Q-Jet carb. The PO upgraded to a GM HEI unit and I am planning on rebuilding / replacing it soon. So my first step was to try and check the timing on my motor. So I setup the timing gun, removed the vac advance line from the front of the carb and plugged the port on the carb. Then I ran into something I've never really seen before.

The mark on the balancer is way before the metal gauge mounted above it. I had to set the advance on my timing gun to 20* BTDC in order to get the mark on the balancer anywhere near the gauge. Hard to describe and I can't really get a picture of it, but the mark is pretty far off in the direction of the passenger's side, so to speak.

This is where it got stranger. I put a vac on the vacuum advance canister and kept reading the timing - there was no change. In fact, I then pulled the vacuum cap off the carb port and measured it for vacuum and (surprise) no vacuum.

So this leads me to two issues:
1) Shouldn't there be vac on that carb port to cause the vacuum advance to function at low load and part-throttle condition?

2) My engine cannot be set at 20*+ BTDC base timing. It isn't set for a performance tune and I am not running race gas, so I'd be hearing all sorts of pinging, pre-ignition and the like, right? Am I crazy or something? I checked over and over to make sure I had the timing gun pickup on the right plug (number 1) and such things, but it seemed right.

Anyone have any ideas? I have to admit that the last time I timed an engine, I used a laptop... so I may be doing something really, really stupid unintentionally.

rustyroger

Don't trust the timing marks, you can accurately check true tdc by a number of methods.PM me if you need more information.
The distributor could be a tooth out or the plug wires may be set up wrongly. The cam could be a tooth out as well.
Timing being way out might also explain no vacuum on the carb.
Which engine do you have?, I'm assuming a small block Olds, be sure you use the correct tune up data for your particular engine, if it has been modified you will need to tune it specifically to your mods.

Hope this helps.

Roger.

svnt442

Well with HEI distributors that came from the factory in Olds engines the factory setting was 20° BTDC @ 1100RPM. Now if you're saying the mark is BELOW the timing tab as in towards the drivers side of the car then that would be ATDC and it wouldn't start.
Now 20° BTDC at idle is too much initial for sure so if that's the case it will need to be rectified anyway. If it's actually reading ATDC then you may have a spun balancer and that will need to be addressed asap.

roamer

Mark71, as for your engine "not" being able to run at 20degBTDC I will say that it is possible. I have a 73 Delta88 and with premium gas I have it set at about that mark. The big difference is that my distributor has a recurve kit in it where I have installed a bushings that will restrict the total amount of advance and therefore not cause any pinging problems. If this seems to be a bit out of the ordinary, I can tell you I did not do this without some research. Some of the older articles detail have to recurve the distributor. What I found was that these engines like a lot of initial advance. Your may want to check out what your total advance is at say 3000 rpm. If it's in the low 30's, then the previous owner may have done the same thing I have. If it's way up there at 40+degrees then the others are on the right track.

oldcutlass

You will not get any vacuum off the ported vacuum port @ idle! With the timing light on the #1 spark plug at what setting do you have set the light to see the balancer mark read zero??

Mark71

Definitely BTDC (towards the passenger's side of the car). It is a 71 SBO, but has been upgraded with an HEI out of a 74.

I don't think it has been recurved - the PO wasn't really a "car guy" and said he just knew that "points sucked" and had it converted to HEI. I'll try winding it up to 3K rpm and checking then.

You are 100% right. The ported vacuum opening in the carb is still covered at idle, right? So I was just not thinking clearly. Regardless, why do we have to always unplug the vac advance when timing these engines, especially when base timing is usually set at idle?

I had to push the timing light up to 20* BTDC before it got to the first tooth on the scale. I'd probably need 30* to get it to zero. To be fair, though, the gauge is kinda rusty and dirty, so I can't see exactly where zero is. I need to clean it up a bit.

I am not seeing massive pinging, pre-ignition or the like. There are no serious driveability issues at all (let's hope it stays that way). It is a little slow on throttle response and I think the secondaries don't open up until very late, but neither of those should cause a timing issue. I doubt the engine can really be at 20*+ base timing without causing serious problems under load...

svnt442

Like I said in my previous post Oldsmobile used a different mechanical curve in the HEI than they did in the points type. With the points type the initial was anywhere between 6° and 10° BTDC @ 1100 RPM with the vacuum pulled and capped. With HEI it's 20° BTDC @ 1100 rpm with the vacuum pulled and capped. You do not check timing at idle and that is why you pull the line.

oldcutlass

The reason it is plugged is to be on the safe side and not introduce stray vacuum to static timing. I have to ask, you have the light connected to the front spark plug on the drivers side right??

Mark71

Thank you for asking this! I keep having that same thought pop in to my head... Did I have it on the right plug?? Yes, I am "pretty sure" it was the right one. Driver's side, front of engine (towards the balancer), first plug wire. I am going to take some pictures tonight when I work on it some more.

Some guys don't seem to agree on this. First, it seems some folks think the timing should be roughly the same with points or HEI, though I do see your point of how that could change things...

Second, if I don't set / check timing at idle, what RPM should I be using? The reason I ask is that except for the high-step idle (before the choke opens up fully), I don't know what other RPM range should be used... From my shop manual (I know, I need a manual to set timing ), it seems that warm, normal idle is what I would use to check/set base timing.

svnt442

It goes like this. Chevy didn't change the advance curve when they switched over to HEI from points, but Oldsmobile did. With Olds the total timing stayed the same, but they changed both the initial and the mechanical.
So with an Olds points distributor you'll have 10° initial @ 1100 RPM with 24° of mechanical to give you a total mechanical timing of 34°. The vacuum canister will add more to that under part throttle conditions to improve fuel economy, but that amount will depend on how much is set into the can.

Olds HEI distributors will have 20° initial @ 1100 RPM and 14° of mechanical to achieve the same 34° of total advance. This is supposed to be for easier starting and designed around the emission controls of the day.

Mark71

Woah! Thank you much for the detailed info. I have been looking at the underhood emissions sticker which suggests 6* BTDC at idle! Things are starting to make a lot more sense now. One question I do still have though is whether or not my 1971 engine with a 1974+ HEI setup needs a completely different curve...?

I am going to try and find TDC with a piston stop and use some timing tape to figure out what's going on exactly. I'll post my results once I have some. Thanks again!

jpc647

subscribing to this thread. I'll be doing this in the next coming days with the same setup.

Mark71

Sorry to revive this thread, but I wanted to chime back in now that I have more information.

I used a piston stop to determine TDC on 71 Olds 350 with HEI conversion (also - now with headers, because I finally got that job done! ). It turns out that the balancer has not slipped and in fact, that the line is "about right". I added some timing tape from Summit to ensure that I could get as exact as possible. Here's what I came up with:

Initial timing, idle (700 RPM) - 20* BTDC
All in without vac advance (3000 RPM) - 35* (approx)
All in with vac advance (3000 RPM) - 45+* (wow)

I also ran a vac gauge on the car. It was running about 16 in. Hg with "a little" flutter down to 15.4 or so. So that shows the vacuum to be a little low, but relatively stable. From my research, that could indicate timing which is not advanced enough.

Can I try to increase the advance on this? I've never set timing on this car. Anything I need to know? What's the risk that I detonate the engine trying to set the timing at idle or 1100 RPM? I know it sounds stupid, but I was amazed when I found out it is running 20* and that's "normal"...

Thanks,
Mark

bigD

this is interesting! i just recently put a curve kit in the points distributor in granny and yesterday i checked the timing at 800 rpms it showed about 20 degrees. i put the gold springs in... never gave any thought to them having an effect at idle... but she runs like a top, good throttle response and it starts great when up to tempurature...

Mark71

Sweet! I am glad it worked out for you - and that I am not the only one going through it.

I ordered a Pertronix rebuild kit for my HEI setup. I am going to try and put it in this weekend. I'll start with 20* and the strongest springs and move "upwards" from there.

RetroRanger

watching this thread my 72 mostly stock 350 has the 4 wire HEI.

when I bought the car intial timing was 8 degrees with ~20 degrees showing at 3k rpms (no vac advance).

I recurved the dist (moroso kit)and found the lightest springs had me advancing at idle (maybe this is why the OP sees 20 at idle ???) I switched to 1 light 1 mid spring and 12 degress initial and now get ~30 degrees at 3k rpms (no vac advance)

The low end (below ~2200 rpms) is sluggish still but way better than as bought condition. I think it should have more umpphh

My vac advance is ported I forgot to check the total advance at 3k rpms (intial + mech + vac) Ill do that this weekend

whats in the pertronix rebuild kit ?

rustyroger

In these days of computer controlled ignition and fuelling it's easy to forget advance mechanisms wear just like any moving part, I have come across cars with the advance springs so tired the distributor would go to maximum advance any speed above tickover.
Something to bear in mind when tuning our old engines.

Roger.

bigD

the pertronix rebuild kit has a higher performance coil & module as well as cap, rotor and a recurve kit.

at the very least i'm gonna have to get a timing tape for my balancer and then do as you did ranger and mix & match springs to get the desired effect. i might put the heavy springs back in until i figure out what i've got going on here... the car acts fine and i detect no detonation but my hearing isn't what it used to be...

this is turning out to be a rather interesting thread, hopefully we can all gain some knowledge from it...

Mark71

The timing tape REALLY helps read the timing and a buddy of mine gave me a tip that really helps keeping it on there. Put some clear nail polish or clear silicone caulk on the ends of the tape and spread it over the edges onto the very clean balancer. It'll stick better that way.

I don't get it... I tried putting mine down to that range (the original sticker says 6*) and the engine runs like crap. I mean, noticeably bad. It is much happier north of 15. I have it at 20 again and have no pinging, but I haven't installed the rebuild kit just yet. I am going to try advancing a bit more after I get the rebuild kit in there.

For the moment, I am going with svnt442's advice on this one...
Does anyone know if 45* BTDC all in with vac advance is ok? It doesn't seem to ping or have issues, so...

Thanks!

svnt442

Remember that the vac adv only functions under light throttle so when you stab it only the mechanical advance works. The high amount of advance is advantageous for cruising fuel efficiency.

RetroRanger

haha my car ran like crap too thats when I started looking at the timing...others reccomended 12-14 intial so thats what I went with (12)

well it ran ok just had no power

From reading 45-50 all in w vac advance is the goal.

I didnt try moving as far as 20 degrees intial but maybe I will give it a go this weekend.

when recurving I left the vac advance disconnected and drove around w only mech advance to check for pinging absolutely none on 87 at 12 degrees so I could likely stand a little more

Mark71

Hehe... Maybe that the issue. I've only been putting 92 in mine, but it doesn't see many miles either, so I can still afford to do that.

RetroRanger

ok so heres what happened

I started w 12 degrees ini, and 25 degrees at 3k w no vac.

first I checked w vac advance at 3k and saw ~51 degrees

I went to 15 ini and 3k w vac showed 54 degrees at 4k I saw ~56 degrees The 56 degrees total was more than I expected not sure if the extra 2 degrees are mechanical or vac (from 3k to 4k readings) I guessed mech but IDK

I drove it saturday and sunday and was pretty happy w it I thought maybe I could hear some slight unwanted engine noise if I was cruising about 45-50 and there was a slight downhill other than that no issues in the several WOT and cruise tests that I ran

after that I reset my idle mixture and idle speed and put the car away for the winter

I think it could stand a little more intial (with a little less vacuum advance) if I had an adjustable vacuum advance

So maybe next spring ill bump it a little more but for now its running pretty good (now that I have to put it away haha)

RetroRanger

its interesting how different your set up is than mine
ini - 15
mech 15
vac 26
ttl 56

I used my buds timing light w adjustable degrees, It seemed reasonably accurate at the zero setting on the light I saw my original 12 degrees BTC then I set it to 12 on the light and the mark was right at the zero mark on the pointer...at the higher rpms I had to dial the mark into 0 pointer then read the dial after

my vacuum was steady right at 18 at ~800rpm idle