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 Can't idle down with vac advance
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cortcomp
Coyote

USA
5335 Posts

Posted - 22 Jul 2012 :  2:11:09 PM  Show Profile  Visit cortcomp's Homepage  Reply with Quote
Hello all...

I've been starting to fine tune the 71 a bit now that i made it to the show i was aiming for this year. I want to use the vacuum advance on my new distributor but i've run into a problem.

When i set the initial timing about 12 deg, that seems to do decent for the car and what it likes driving around. I've put about 500ish miles on it so far. When i plug the vacuum advance into a ported vacuum source on the qjet, it idles fine, but the first time you give it gas and let off, it hangs the idle at about 1500 rpm and won't come down.

The car likes a lot more advance sitting still tuning if you're going by the old method to just advance the timing at idle until you get the highest rpm and then set the idle rpm where you want it at the carb. I broke it in that way and the cam was very smooth (XE284) but i read here that's not how to do it on bigger cams, and that the advance was just smoothing it out.

I'm thinking that once you hit the gas and the vacuum can advances, back at idle with vac advance is just a larger rpm. I tried braking while releasing the clutch slightly to see if getting the rpms down below 800 would get it back to hang there, and it doesn't seem to. Disconnecting the vac advance and all is back to normal. Start it up and it idles where i set it (750ish) and give it gas and it hangs up there again.

I can't rule out a carb problem, as i had cliff build the carb for a 428/XE262/9.3:1 compression and ended up putting it in a 462/XE284/9.3:1 compression. We chatted a few weeks ago and he said likely the only issues i would have were in the idle area, with it not getting enough (i think) idle fuel. I have the idle screws out 3 turns now i believe. You can screw it in until it stumbles and dies, past 3 turns doesn't seem to do anything for the idle or the vacuum gauge. Vacuum is about 8-10 inches, fluctuating between them at a rough idle. If you rev it up off idle vacuum stays very steady, so i don't think the new engine has any major issues.

Ideas?

Blued and Painted
Chief PONTIAC

USA
3405 Posts

Posted - 22 Jul 2012 :  5:01:17 PM  Show Profile  Reply with Quote
Your using the port, driver's side front of carb with no check valve? Your not using washer hose that can collapse and hold itself shut from the distributor side.
For street drivability i use manifold vacuum. You can use less throtle angle
I have not herd of your timing by ear procedure.


Bull Nose Formula/ 461/ Q-Jet/
TH400/ 3.08 8.5 / R44TS.

Edited by - Blued and Painted on 22 Jul 2012 5:03:57 PM
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bnorris_74
Crazy Horse

USA
1442 Posts

Posted - 22 Jul 2012 :  7:29:23 PM  Show Profile  Reply with Quote
I'd guess that he might have meant light on idle air but what do I know?

Have you checked the vac advance mechanism to make sure it moves freely? It should pull itself off advaance once the vacuum is gone. To me it sounds like yours doesn't have enough spring to return itself.
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cortcomp
Coyote

USA
5335 Posts

Posted - 22 Jul 2012 :  9:07:29 PM  Show Profile  Visit cortcomp's Homepage  Reply with Quote
It does return as, if you shut the car off, and restart it, the vacuum is back in and not advancing. Then you give it gas and it holds the higher rpm when you return throttle to idle. I would take that to mean that it's returning back to no vacuum. It's an entire new setup from summit. Using new actual vacuum line, and yes the drivers side front port (although there's several, this one i believe is not on the base plate but in the carb body?) Could it be that simple, wrong port?

He might have meant light on idle air but we talked quickly. We surmised that it wouldn't idle for crap if it was far off. I wonder if it's running lean in the mid range, as that's when the car really warms up, going down the road cruising, not puttering around town with no airflow.

The timing by ear procedure i got from jim hands book, in the breaking in section. Was pretty far off for this setup.
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cortcomp
Coyote

USA
5335 Posts

Posted - 22 Jul 2012 :  9:08:27 PM  Show Profile  Visit cortcomp's Homepage  Reply with Quote
Also, i was thinking manifold vac and then dial initial back and set rpm and forget it, but seemingly no manifold vac port on this qjet except the choke pull off one. unless my manifold gasket is blocking it or something.
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Blued and Painted
Chief PONTIAC

USA
3405 Posts

Posted - 22 Jul 2012 :  9:53:14 PM  Show Profile  Reply with Quote
Sounds like you have the correct port. Have you put a guage on it?You may have to T off the brake booster for manifold vac.


Bull Nose Formula/ 461/ Q-Jet/
TH400/ 3.08 8.5 / R44TS.

Edited by - Blued and Painted on 22 Jul 2012 9:56:05 PM
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cortcomp
Coyote

USA
5335 Posts

Posted - 22 Jul 2012 :  10:15:32 PM  Show Profile  Visit cortcomp's Homepage  Reply with Quote
I used a gauge to look around to find manifold and no such luck. This one is def ported, as it has near 0 at idle and if you move the throttle at all it jumps up.
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cortcomp
Coyote

USA
5335 Posts

Posted - 22 Jul 2012 :  10:17:09 PM  Show Profile  Visit cortcomp's Homepage  Reply with Quote
I guess i could get it out of one of the random pipe plugs on the manifold too. Just never heard of ported advance hanging the throttle up like that.
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Blued and Painted
Chief PONTIAC

USA
3405 Posts

Posted - 22 Jul 2012 :  10:21:33 PM  Show Profile  Reply with Quote
Back to your pictures http://psp.aquacomp.net/topic.asp?TOPIC_ID=6013&SearchTerms=vacuum,can
The one on the base plate under the pulloff is for egr, no good. Test the others. You need a strong signal.
You may want to remove the intake and drill and tap there where it says eldabrock. Mabey grind of all the wording and go sleeper.


Bull Nose Formula/ 461/ Q-Jet/
TH400/ 3.08 8.5 / R44TS.
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Blued and Painted
Chief PONTIAC

USA
3405 Posts

Posted - 22 Jul 2012 :  10:27:48 PM  Show Profile  Reply with Quote
We could be a sleeper cell


Bull Nose Formula/ 461/ Q-Jet/
TH400/ 3.08 8.5 / R44TS.
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Phil
The Great White Buffalo

USA
7215 Posts

Posted - 22 Jul 2012 :  10:41:29 PM  Show Profile  Reply with Quote
So when you put a vacuum gauge on the ported nipple and hit the gas you see vacuum, as you should. BUT, I'm interested in what the vacuum gauge does when you release the throttle. Does it go back to zero? If so, it's your vacuum advance mechanism. If not, your throttle may be adjusted with too much "idle screw" and be right on the "edge" of ported/full vacuum.

Bowties are for Pee-wee Herman. "Chevy": even the name sounds cheap, but not as cheap as your Pontiac will be with an LS transplant.
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cortcomp
Coyote

USA
5335 Posts

Posted - 22 Jul 2012 :  11:00:35 PM  Show Profile  Visit cortcomp's Homepage  Reply with Quote
Phil: Yes, it goes back down.

I'll check the vac advance mech when i get a chance, maybe tomorrow. Operate it with the mighty vac and see if it sticks. Idle is about 850 right now, i've had it down to 650ish and it'll do it (making me think it's honestly not leaking air anywhere.) so maybe i'll adjust it down and see what it does if the advance isn't sticking.
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jeff
Buffalo

USA
93 Posts

Posted - 23 Jul 2012 :  6:32:31 PM  Show Profile  Reply with Quote
I had this exact problem with my engine. What I found was the primaries were open to far exposing the port and the cam made to little vacuum at idle to pull the advance in. When the throttle was opened vacuum went up high enough to pull the advance in and when returned to idle the engine had higher vacuum with the additional timing. Tee a vacuum gauge in and I'd bet you'll find your problem

73 Formula 72 T/A clone 406 #12 heads, Comp 280H, RPM intake,hooker comp. headers, Scorpion rockers 4spd. 3:42 gears
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jeff
Buffalo

USA
93 Posts

Posted - 23 Jul 2012 :  6:46:15 PM  Show Profile  Reply with Quote
Just read through all the posts. In the original you said that you had to shut the engine off and re start it to get it back to base idle, then in a later post you said the vacuum on that port drops back to near zero when you close the throttle? How much vacuum do you have at idle?

73 Formula 72 T/A clone 406 #12 heads, Comp 280H, RPM intake,hooker comp. headers, Scorpion rockers 4spd. 3:42 gears
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cortcomp
Coyote

USA
5335 Posts

Posted - 24 Jul 2012 :  10:03:25 AM  Show Profile  Visit cortcomp's Homepage  Reply with Quote
At idle off of manifold vacuum, i have about 9 inches give or take an inch. My gauge goes down to like 5 then it's hard to read, but i have another somewhere. But i'm pretty sure that port has SOME kind of vacuum at idle, like 1-2 inches. It seems to move the needle off 0 JUST slightly. even before i put the advance on it or do anything with the car but start it.

I could try a different port, they all seemed ported but i didn't check to see if they were exactly 0. Your problem sounds like mine, because this cam is so rough that you could REALLY advance that distributor and it'd smooth out while you're working on it. I just don't think you could drive it that way. But i do think you'd get more vacuum.

Right now initial timing is set at about 12, and i think max is like 30-32. I was trying to leave it a bit conservative. I think i understand what your problem was and i'll try to verify that this is the same. What was your solution, dial the primaries idle down?
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jeff
Buffalo

USA
93 Posts

Posted - 24 Jul 2012 :  12:25:01 PM  Show Profile  Reply with Quote
Yes I closed the primaries, but I am using a Holley and I think you have a Quadrajet? I opened my secondaries and drilled a small hole in each primary to get the air I needed. That cam will probably like as mutch base timing as you can give it. I have mine @ 16 with no starting or run on issues, advance is adjusted accordingly. I know very little about Quadrajets so I'm not going to be much help there. I would start by adding a lot base timing which should bring the idle up then turn the idle screw down just to see if it solves your problem.

73 Formula 72 T/A clone 406 #12 heads, Comp 280H, RPM intake,hooker comp. headers, Scorpion rockers 4spd. 3:42 gears
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cortcomp
Coyote

USA
5335 Posts

Posted - 24 Jul 2012 :  12:33:36 PM  Show Profile  Visit cortcomp's Homepage  Reply with Quote
I had it near 16 and it was ok, it was done at the last second before a road trip with no light. I thought i heard spark rattle but it turned out to be "just-put-together-motor-and-valves-might-be-too-loose-or-too-tight-or-exhaust-leak" rattle, as timing hasn't changed any of the minor noise i hear now and again under different loads and throttle positions.
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cortcomp
Coyote

USA
5335 Posts

Posted - 24 Jul 2012 :  1:24:11 PM  Show Profile  Visit cortcomp's Homepage  Reply with Quote
I will try setting the timing more and more forward until i get sparn knock and then coming back. As i recall, 16 was on the edge of hard hot starting.
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Blued and Painted
Chief PONTIAC

USA
3405 Posts

Posted - 24 Jul 2012 :  2:11:30 PM  Show Profile  Reply with Quote
Have you tried the advance curve mod in technical articles?


Bull Nose Formula/ 461/ Q-Jet/
TH400/ 3.08 8.5 / R44TS.

Edited by - Blued and Painted on 24 Jul 2012 2:13:24 PM
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cortcomp
Coyote

USA
5335 Posts

Posted - 24 Jul 2012 :  3:37:04 PM  Show Profile  Visit cortcomp's Homepage  Reply with Quote
I haven't touched the distributor yet as i wanted to get the car setup and tuned first. Also, i think if i read the directions properly, this distributor is setup to get most of the timing in pretty quickly. If i'm near 16 degrees initial, that puts me at a decent total. I'm thinking of going to 3.73 gears in this setup, which would make the dist about perfect for me. Won't change anything that might be off with the carb though.
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cortcomp
Coyote

USA
5335 Posts

Posted - 24 Jul 2012 :  4:53:35 PM  Show Profile  Visit cortcomp's Homepage  Reply with Quote
That did it! I used the same port (like 1/2" of vac at idle, and as soon as you crack it it's full manifold, so it seems to be proper ported.)

Basically, i'm at 16-17 degrees initial, and about 35 degrees total mechanical, and seems to be all in about 3000ish. (I'm working with the hood tack and throttle by myself and blocking vac ports and holding gauges, etc, so every number in this post can be considered very close but off one or two in one direction or another).

This let me turn the idle down from about 900 to 650. It was low so i went for 700. It jumps to near 800 when completely warmed up (if you can trust the repop hood tachs.) Anyway, no more hanging idle! After test driving about 10 miles, here are the results:

Car SEEMS to take less throttle pedal for a given cruise rpm around town.

SEEMS SLIGHTLY less droney around 2000rpm

SEEMS way less chuggy around 1500rpm when you're maintaining a low speed in a high gear. (overdrive, 30mph, and you give it a little gas to get to 35mph without downshifting) i find it amazing you can do this AT ALL with this cam and setup.

After getting out of town, i found a quiet area where no one was, and did a fun run out. First was all wasted traction and some going, second was great, but over quickly and ended like 80 mph Third was fun but had to back off (third is my 1:1). It's a decent streetfighter now i think, but 3.73 gears would A) make 2nd and third even more fun, and make it a better ET i'm guessing and B) move my highway rpms up a couple hundred RPM so that i'm just out of the droning ar cruise speed (70-75mph might be like 2500ish rpm instead of 2000 rpm, and you barely notice the engine running at that speed. It just seems the resonance at 2K rpm with this car in any gear is the loudest. maybe i'm getting used to it)

Also, bonus, the car pulled a lot better at my partial throttle blips, and the extra 6-7 degrees timing made WOT more fun and solid pulling (after checking today, i was running around at 10 degrees after working on it the other day)

Double bonus, idling this car sits around 180 degrees (even idling around a parking lot in 114 degrees for 20 mins after highway driving) BUT cruising down the road, was 205 rock solid (210 with AC ON) EVEN if the car was dead cold, within about 5 miles, it was 200-205 (hard to tell, small gauge, electric). This whole test drive, 180 solid, didn't move.

I'm going to the restaurant tonight to fix some things, it's about a half hour drive so we'll see if the temps stay down. I was OK with 200-205 for the season, but was more expecting 180 with everything i had in the car. I had theorized that i was running lean in the mid range but maybe it was timing.

Side note, if you're like "cars don't eat enough of my money and time, and getting a divorce won't eat them fast enough either....what can i do?" ...jump in owning a restaurant. It's like a money vacuum.

Edited by - cortcomp on 24 Jul 2012 4:53:46 PM
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jeff
Buffalo

USA
93 Posts

Posted - 24 Jul 2012 :  5:40:10 PM  Show Profile  Reply with Quote
Glad you've got it fixed. What trans., gear ratio and tire diameter are you using? With my muncie 3:42 gears and a 27 in. tall tire I was @ 2,500 rpm @ 55 mph

73 Formula 72 T/A clone 406 #12 heads, Comp 280H, RPM intake,hooker comp. headers, Scorpion rockers 4spd. 3:42 gears
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cortcomp
Coyote

USA
5335 Posts

Posted - 24 Jul 2012 :  5:59:50 PM  Show Profile  Visit cortcomp's Homepage  Reply with Quote
3.45 gears in an olds 12 boly rear (8.5 gear if i recall). Tranny is 4spd np440 (its a gm chrysler a833 od, so 3rd is 1:1 and 4th is about .69 od.) Theres a decent gap between 1 and 2, so its like shifting 1 to 3 on a 5 speed. The torquey pontiac motors dont seem to mind, but its not the best racing trans at all. Tire is 225 70 15's.
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Blued and Painted
Chief PONTIAC

USA
3405 Posts

Posted - 24 Jul 2012 :  6:07:06 PM  Show Profile  Reply with Quote
I guessing you got the secondaries working.


Bull Nose Formula/ 461/ Q-Jet/
TH400/ 3.08 8.5 / R44TS.
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cortcomp
Coyote

USA
5335 Posts

Posted - 24 Jul 2012 :  11:01:46 PM  Show Profile  Visit cortcomp's Homepage  Reply with Quote
Yes, took the carb off, everything looked good, center the gasket, tightened down and they were working. I can only assume that the carb or gasket were shifted slightly and catching on the edge.
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jeff
Buffalo

USA
93 Posts

Posted - 25 Jul 2012 :  07:08:46 AM  Show Profile  Reply with Quote
How difficult was the trany swap? Sounds like the cheapest way to go manual o.d.. I've got a couple of 833's but no o.d.'s. That low first gear has to be fun! Swapping the second gear set to 1:92 gears like the a non o.d. would make 1-2 a lot better.

73 Formula 72 T/A clone 406 #12 heads, Comp 280H, RPM intake,hooker comp. headers, Scorpion rockers 4spd. 3:42 gears
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cortcomp
Coyote

USA
5335 Posts

Posted - 25 Jul 2012 :  10:36:47 AM  Show Profile  Visit cortcomp's Homepage  Reply with Quote
It wasn't bad. You have to find the GM version of one, and there are two versions of those. One has the muncie bolt pattern. (i found a spare just to be safe). Basically, you have the bearing retainer turned down to fit the bell. One bolt you put back through the bell, and put a nut on the tranny side because of clearance issues, you can't get a bolt in from the tranny side. It has a TH350 yoke and normal tranny mount, so you got it bolted it. You can quickly mod a normal shift mounting plate to it, and then mount a normal hurst comp plus. Then you have to basically make your own shift rods, because they don't make a kit for that tranny, Shift hole lines up normal and all that up top. Use normal 10 spline clutch matched to the size of your flywheel, and normal fork, bearing, etc.

It has an integral light switch, so you can wire your reverse lights to that, or make sure your reverse lockout linkage was working. I bought a repop reverse lock out linkage kit from inline tube, and i only had to mod one rod as it was too long to get it to work. Also, i made my own swivel mount for the bracket that swivels off of one of the shift arm bolts. It's been working 600 miles so far.

When i made the linkage, I made it all with B7 fine thread rod, and heims joints. The clearances are close, but there is 0 slop. It's the most positive shifting old car i've driven. I used the universal linkage kits but they're sloppy and i despised driving the car. Also, on the fork, i made a better lower pushrod with a chrome acorn bolt on the end going into the fork and greased it well, and it's a lot smoother there.

With that low first gear, you can raise the rpms, even on the big cam, to about 1000-1300 and slide off the clutch, and it doesn't lurch or complain. I'll have to get a pic under the car, at a glance, you wouldn't know something wasn't a 4spd except the tranny is just a little bigger.
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cortcomp
Coyote

USA
5335 Posts

Posted - 25 Jul 2012 :  9:05:27 PM  Show Profile  Visit cortcomp's Homepage  Reply with Quote
Also wanted to report, after drive half hour each way, never topped 180/185 the whole way. Dropped 15-20 degrees just with timing!
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Phil
The Great White Buffalo

USA
7215 Posts

Posted - 25 Jul 2012 :  11:06:06 PM  Show Profile  Reply with Quote
Sounds like another satisfied customer.

Bowties are for Pee-wee Herman. "Chevy": even the name sounds cheap, but not as cheap as your Pontiac will be with an LS transplant.
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Total Jackass
Tribal Scout

0 Posts

Posted - 14 Jan 2014 :  04:45:17 AM  Show Profile  Reply with Quote
A. Because it saw a lolly pop!
http://www.kinddress.com/robe-de-bal.html

I'm a first class jerk and don't you forget it!
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Phil
The Great White Buffalo

USA
7215 Posts

Posted - 14 Jan 2014 :  6:32:28 PM  Show Profile  Reply with Quote
TTT

Bowties are for Pee-wee Herman. "Chevy": even the name sounds cheap, but not as cheap as your Pontiac will be with an LS transplant.
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