[Stuckinda60s]

Once again, you want manifold vacuum, not ported. Set the timing at 12* at idle-with the vacuum hose plugged, then make sure you get the full 20* out of the distributor. Then, hook up the manifold vacuum and reset the idle speed and readjust the carb.

I know some use ported, but there're some very good reasons why Pontiac always used manifold. If you can drill out the idle passages and go through the carb to optimize it for the best idle by adding fuel, you can set the engine up for ported, but for most of us, that's not an option.

For those who don't think it works, a friend of mine was recently chasing some problems with a fresh 455 with the 274 XE cam and cleared them all up by going to manifold vacuum. It really woke the engine up. I've used manifold in every engine I've ever built and run on the street. I've tried ported and always gone back.

Low compression engines love timing. I've run more initial at times than I thought prudent, with manifold advance on top of it and still had no complaints out of the engine. I ran a 400 Pontiac in my GMC pickup with a Performer cam and manifold, Rhoads lifters, manifold vacuum, and a worked distributor and it still liked 16* initial. The truck had tremendous torque, and out-towed a lot bigger engines with ease, even though I ran a stick and higher gears and my friends ran 454-auto's and low gears.

My suggestion? Try it both ways. You can tell which is which on the carb by determining whether the vacuum tap is above or below the throttle blades. Ported will be above the blades. Just make certain you reset the idle and carb, whenever you change over.

[chiphead]

WOW. Does this engine really have tapered-seat plugs installed in gasket seat heads? Holy ravioli batman! Get those out of there!

Now I'm questioning everything. Quick timing curve, wrong plugs, etc... Who tuned this thing?

[tr709]

Unbelievable about those plugs, see what I mean about the shops down here?

[jakeshoe]

We can get the right plugs in it.

One thing I'll mention about timing and ported or manifold.

It IS combo dependent, so nothing is set in stone.

However my experience is that a performance engine typically works well with manifold vacuum.
Ported vacuum came about for emissions reasons. OEMs were using manifold vacuum on the factory musclecars until emissions laws forced them to go to ported to kill idle timing and improve HC emissions.

The typical V8 engine needs more (WAY more in some cases) idle timing than the 0-12* typically spec'd.

Usually 20*+ degrees and on some larger cube engines with large cams they seem to like 50* at idle.

Idle timing should be set for what the engine likes.
Put a vacuum guage and a tach on it and set the timing for where the engine idles the smoothest with the most vacuum. Then write the number down...

I do this with the vacuum unhooked just to baseline the idle timing because we'll need to know it later.

I then rev the engine to see how much timing comes in and get a rough chart of where it comes in at and where it stops.

That way I know what the total mechanical advance is. Write this down.

Then plug a vacuum pump onto the vacuum advance and see how much vacuum advance it pulls in, and approximate vacuum it does so.

Many of the smog era distributors have too much mechanical advance built into them. 20-24* of mechanical.

What you run into using the vacuum advance is that is may also have too much.
However the adjustable kit from Crane (if it's still available) allows you to limit the vacuum advance.

If you set base timing at say 16*, you have 20* of mechanical advance in the distributor, and 20* of vacuum advance, you will have 36* of timing at WOT, 56* at cruise, and 36* or slightly less at idle depending on the vacuum advance rate.

I usually limit the vacuum advance down to 8-12* and it works great. Puts you in the mid 20's range at idle with ideal WOT timing, and some advance at cruise to improve mileage.

You can also limit the mechanical.

Lots of ways to get there but the ideal is to get the idle timing up where the engine likes it but not get the total timing out of range for heavy throttle.

[ta man]

I like to set total timing first for full throttle power and try to have it all in by 3000 or so depending on application.Then I go after initial timing for a good idle with corresponding carb setup while keeping best total advance.This may require limiting mechanical advance.I also decide whether to use manifold vacuum as part of idle advance and cruise or use ported advance just for cruise.20 degrees advance with 50 degrees total is fine for maybe a low compression engine with a stockish style cam but I think with this engine you'll find it won't want that much timing.My "large cubic inch engine" with "large cam" only requires 9 degrees of advance at idle.It also idles at 800 rpm.

[jakeshoe]

Originally Posted by ta man

I like to set total timing first for full throttle power and try to have it all in by 3000 or so depending on application.Then I go after initial timing for a good idle with corresponding carb setup while keeping best total advance.This may require limiting mechanical advance.I also decide whether to use manifold vacuum as part of idle advance and cruise or use ported advance just for cruise.20 degrees advance with 50 degrees total is fine for maybe a low compression engine with a stockish style cam but I think with this engine you'll find it won't want that much timing.My "large cubic inch engine" with "large cam" only requires 9 degrees of advance at idle.It also idles at 800 rpm.

You can test of total timing first, either way you are recording it to determine how to recurve for best overall performance.

I've been tuning engines for quite a while and I've never seen ANY automotive engine that really "liked" only 9* of advance at idle, whether it be a stock grandma 307 Olds, or a 540 cubic inch BBC with a a cam in the 270*+ at .050 range.
Almost all will want 20* degrees at idle.
Even the late model computer controlled engines are usually sitting at 20* if you want the timing.

[James408]

Get you some 3.42/3.55 gears and see what it does. You may need a tad bit higher stall but see what the new gears will do first.

[goquick]

Gears isn't your issue.
I despise your pistons. For one thing the dish is as* backwards. Yeah I know thats how everyone wants to make them. But you will never have a good quench which is critical for anything performance wise without "ping". Those piston cause that "ping" in my opinion from the lack of a quench area near the spark plug.
I really think a degree wheel should be used on your cam. There is no excuse for this combo to not boil the little tires you have. I agree that better exhaust will help also, as I am thinking you are getting alot of reversion being that choked up. Get the long branch manifolds with the larger outlet and match your head pipes accordingly. Did you ask your builder how he degreed the cam?
Some still think putting the gears on and lining up the dots is straight up. If he didn't degree it with a wheel and write down the settings, he just slammed the timing gears and chain on it. It could be retarded or too far advanced and he has zero clue.

[tr709]

Working on getting the car Saturday over to board member jakeshoe's shop as it is about 30 minutes from the house. Plan is to get it tuned first and see where we are at and go from there. Strongly considering having Jake check the cam install.

When I contacted the builder about degreeing the cam, response was 'straight up', no mention of degree wheels or other details. If the cam turns out to be installed wrong that is pretty wild as when my motor was being built there was plenty expensive iron in that shop at the time like hemi's, 440's, 409's, 427's and a ford 347 stroker. Yikes!

I'll check back in with updates and hopefully some happy news and I could use some considering I have spent more on parts and labor for this motor than I did for buying the restored turbo formula!

[GAGuy]

tr709, your Formula is super nice, awesome color combo as well. I am guessing that very few Formulas had T-tops. Does the car still have the turbo motor? I know that those motors get bagged on all the time but they are cool engines non-the-less. I have an 81 Formula that was a WS6 car with a 305 4-speed. I swapped in a 1994 EFI LT1 6-speed combo. I origianlly wanted a 301 engined car but here in California the 305s were much more common. I wanted to put in a Pontiac motor but due to smog laws here I ended up with the later GM corporate motor to avoid hassles later on. I currently have Rally wheels on until I get the 15x8 snowflakes restored.

[mechanic17]

Well, he did say "street cruiser" in his initial post and his cam is not radical for a 428, so I'm still thinking ported vacuum. He'll want mileage, I'm guessing. Also, have often seen drivers that had an "off-line stumble" using manifold vacuum that was misdiagnosed as a bad carb. I don't build race cars where mileage is of no concern, and thought a lot of guys just did away with vacuum advance entirely for those. Maybe I was wrong about that.

[tr709]

vacuum is ported at the moment. I guess we will try both ways and see what works best.

GAGUY - Yup my formy still has the turbo motor in it, runs just fine. It as well is a WS6 car heavily optioned and everything works, incuding the 8-track. Ther a a few minor cosmetic issues I want to get taken care of once the 67 is sorted out.

[jakeshoe]

Originally Posted by mechanic17

Well, he did say "street cruiser" in his initial post and his cam is not radical for a 428, so I'm still thinking ported vacuum. He'll want mileage, I'm guessing. Also, have often seen drivers that had an "off-line stumble" using manifold vacuum that was misdiagnosed as a bad carb. I don't build race cars where mileage is of no concern, and thought a lot of guys just did away with vacuum advance entirely for those. Maybe I was wrong about that.

It doesn't have to be a "race car" to use manifold vacuum for the vacuum advance.
As I stated earlier, look at the pre-emissions era cars and how they operated the vacuum advance. It was on manifold vacuum.

The entire reason for the really slow idle timing and ported vacuum advance was to clean up emissions at idle.
This is something I have considerable experience with, in the past I worked as a tech doing emissions repairs (ASE L1 certified on top of the Master Auto Tech, Master Engine Machinist, etc).
I have a thorough understanding of what the exhaust gases are, what they are caused by, and how to repair them.

Internal combustion engines are very inefficient at idle. This is why they work well with more timing advance, to compensate for the lack of efficiency.

However when you advance the timing and make the engine more efficient, you reduce exhaust gas temperatures. You want to keep exhaust gas temps elevated and introduce fresh air into the exhaust tract to finish burning the unburnt fuel, otherwise known as hydrocarbons. This was the strategy used by OEMs in the 60's-80's.
Slow timing at idle to keep exhaust temps up and introduce fresh air via a smog pump to complete the combustion process outside the chamber. The elevated exhaust temps also help a cat converter flash off and convert CO (carbon monoxide) to H20 and CO2.
The smog pump introduces oxygen into the exhaust because the exhaust is very O2 depleted and otherwise wouldn't complete the burn.

Modern engine controls (port EFI, O2S, etc) have made the combustion process efficient enough that these strategies are often no longer needed.

Early musclecars didn't have the off idle stumble you speak of when they used manifold vacuum advance...

The off idle stumble would more likely be caused by the carb idle transition slots being totally exposed due to excessive throttle blade opening to keep a good idle with retarded timing.

Race cars often eliminate the vacuum advance for two reasons, one is consistency.
It's another variable to deal with on a bracket car,
and two is the fact that at the end of the track, you may pull a slight vacuum possibly advancing timing, this is not what you want.

[jakeshoe]

The Firbird came in today.
I was expecting a gross mistune on the timing.
It has 15* of mech advance. It seems to like 18-20* of idle timing. This puts it at approx 35* of total timing. Very much in the ballpark.

Vacuum advance brings in 20* of timing. It is hooked up to ported and will likely stay there.

We'll probably unplug it for further testing but overall the timing looks very close. It's not an issue.

The secondaries weren't opening on the initial test drive. It is getting full movement of the throttle blades. They will open with the vacuum pot disconnected but the secondaries don't seem to pull like they should, possibly still not getting full air valve movement or fuel flow to the secondary side.

It does seem to feel like they open, and then it lays over a bit.

Next step is to get proper spark plugs in it and then we will diagnose from there.

[Stuckinda60s]

I figured the timing would be an issue, as well. Do the timing cover and the dampener match and have you verified TDC?

Those plugs being shrouded will probably act to delay combustion, giving the appearance of slow timing. The flame front would be slowed, especially in a low compression engine, and more-so if it doesn't have good quench. I wouldn't think it would make that much, but I could easily be wrong. You should definitely check to see what timing it likes after the plug change.

How much vacuum? Is the cam possibly retarded? What spring for the vac. diaphragm? If the engine isn't pinging when pulling, maybe the secondaries are too rich. Is it possible someone has worked on the carb and modified it? What power valve does it have? Are the primaries crisp? How does it pull on just the primaries, before tip in, and does it matter at what rpm you open the secondaries?

What about adjustable vac advance or filling the slot to limit it?

[jakeshoe]

The engine seems to idle well, it pulls 16 lbs of vacuum at idle. I don't think the cam is way out of time but it COULD be advanced causing a good idle and power to fall with rpm.

We may limit vacuum advance but we'll test it without vacuum advance first to see what if anything it does.

IIRC this is around a 9-1 compression engine, while not a racing engine, 9-1 isn't "low". It's very acceptable for a street cruiser.
I've played the "let's see how much compression we can run on pump gas" game and it's not worth the hassle to run 10-1 or above on a true street pump gas engine. The power difference is negligible.
I've had 8-1 454 BBC combos that would rip up the road and run on 87 octane. 7.90s in the 1/8th spinning badly on Radial T/A's.

I agree with Tony it just doesn't feel like it should. It seems responsive revving it with no load, it's a Q-jet carb so no power valves, etc.

The secondaries weren't coming on at all at first, I got them working for temporary testing. Noticeable that they do come on but they never seem to really open fully.

[Cliff R]

Jake, the secondaries are mechanical, make sure the linkage is adjusted for full opening of the throttle plates.

The secondary airflap is held closed by vacuum/link from the pull-off. It should not simply "whip" open by visual inspection matting the accellerator without a load on the engine.

The airflaps open with engine demand, and if the linkage allows the airflaps to fully open (test this with the engine off by simply pushing down on them) during a static test, they are fully opening when you test.

The opening rate is fully adjustable, via the adjustment spring on the secondary airflap shaft. When set correctly, you should not "feel" any transistion, just strong power clear thru the rpm range......Cliff

[jakeshoe]

Originally Posted by Cliff R

Jake, the secondaries are mechanical, make sure the linkage is adjusted for full opening of the throttle plates.

The secondary airflap is held closed by vacuum/link from the pull-off. It should not simply "whip" open by visual inspection matting the accellerator without a load on the engine.

The airflaps open with engine demand, and if the linkage allows the airflaps to fully open (test this with the engine off by simply pushing down on them) during a static test, they are fully opening when you test.

The opening rate is fully adjustable, via the adjustment spring on the secondary airflap shaft. When set correctly, you should not "feel" any transistion, just strong power clear thru the rpm range......Cliff

Cliff,
Read my post above, we already checked the linkage.

I'm not checking the secondaries with no load on the engine and yes believe it or not I understand they shouldn't "whip" open.

I've been doing this long enough to know how a Q-jet should operate and also how to tell if the secondaries are opening.
They were NOT opening. PERIOD.

You know how a Q-jet sounds when the secondaries are open. It's not there. Neither is the power that should be there.

The airflap opens freely by hand with the engine not running.

The vacuum diaphragm on the pull off actuates at 1 lb vaccuum and is fully pulled with 2 lbs. We unhooked it to see if we could get secondary operation without it because that seems like a low number to me.
We could get SOME secondary operation with it unhooked but it seemed to come on and then go away.

Possibly a fuel delivery issue.
Do you install the stock filter in the Q-jet?

[Cliff R]

OK, so you checked the linkage for full opening of the MECHANICAL throttle plates, and the "airflap opens freely by hand with the engine not running", then the secondaries are working. Maybe the engine doesn't have enough ars to pull open the airflap?

I've seen this a few times. The worst one we ever had in here had the timing off two teeth. The engine builder advanced the 9 degree timing set two keyways, the used the standard "dot to dot" to line up the sprockets, instead of counting back two teeth to the left from the new keyway. The engine actually started, idled and ran fine, but would NOT do anything when you matted the accellerator. It acted like the secondaries were not working at all......Cliff

[jakeshoe]

It may be an engine issue yet.
I'm not condemning the carb, I'm just noting that the secondaries are obviously not coming on and it's not the mechanical linkage adjustment.

The first thing I did was check timing when it came in.
I wrote down the timing points, and all that seems in order.

Carb seems to idle well, carb seems crisp, but no secondary action.

It "FEELS" like a fuel delivery issue, good initial response and then it continues to accelerate just not with any authority.