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Discussion Starter #21
The 2 steel lines are for the transmission cooler. They run to the radiator, or if so equipped, an auxiliary cooler. The screw on the modulator is for adjustment. Most modulators are sealed and not adjustable. The vacuum modulator delays the auto shifting of the trans. You can vary the shift point via the screw. If it's shifting well, I would not mess with it. As far as the originality of the floor paint, I will definitely defer to the Pontiac/body man experts.
And I think I might be missing here sth? This is a picture made from the underside of the factory a/c box. You can see a socket with, what seems to be a broken off hose, maybe part of the condenser drain?
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I had some problems similar to yours. I found that my vacuum advance was no good (you can test it easily by putting vacuum onto the hose leading to it, it should hold vacuum and pull in). It's an easy replacement. I also had an idle problem and, after rebuilding carb (also a 2 BBL Rochester like yours, by the way it's an easy job, you should try it next time), I found that it was the condenser. What an easy fix! And cheap, but get a good quality condenser. Be careful that all the connections are good inside the distributor.

I agree about the transmission modulator...if it's shifting OK, don't mess with it. Are you sure it's leaking?
 

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change to quality "blue streak" condenser and points they are 2 seperate parts

lots of issues for me at least with the quality of the 1 piece condenser points.... set up

or ask Mr Taylor what the delco points and condensers he uses ,,,

og might have the part number also ,,, I am not home till tomorow ,,,]

1007 ??

Scott T
 

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Discussion Starter #25
Hey guys,
I will try to make a full vacuum leak test, from the engine, down to the tranny. This time maybe with propane gas, saw some recommendations on Youtube for that? Maybe I could focus after it on the distributor electrical parts if the problem should still exist. I am also thinking if the carb could be still an issue, maybe the idle passages below the jets are somehow stucked (for remainder, the fuel tank has been cleaned out and some debree might have remained and now it’s stuck in the carb channels, altougth there are three filters on the way?). When I last opened the top of the carb to check the adjustments inside the bowl, floater etc. I noticed some „sand” like particles accumulating on the bottom of the fuel chamber. Is that normal? I replaced before the fuel inlet filter and the bigger one outside the carb with the additional condenser line.
For the distributor, I checked that „blue streak” condenser and points, as far I can tell they are made in the Netherlands, so it shouldn’t take long to get them. Having anything shipped from the US right now is a pain in the butt. Waiting for some things from Ames/Opgi now since 3 months... :)

Again, thanks for replying and have a good time with your presidential election debates :)
 

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Discussion Starter #26
Hey guys,

I finally checked my whole engine bay for vacuum leaks (did the propane test) and found not a single leak :(. The tranny's vacuum modulator was also tested. Furthermore, I unhooked everything from the carburetor (vac lines from distributor seperate) and no notable change in engine's rpm's was given. Reminding the fact, that changing the dwell was in the time line directly related to the sudden idle rpm increase makes me question if the higher octane fuel available in Europe (we got 95, 98 and 100) requires maybe lower dwell angle?

The OEM manual states that the engine dwell should be at 28-30° for 1966 in the US (guess again that this range was for fine adjustments, depending on what fuel and altitude you were travelling). From what I've heard the octane rating for gasoline was back then way lower then 85?
When the car was first filled up by me, I poured somewhat 20 liters of 95 octane, after flushing the whole tank I assume again 95 or 98 was filled in. Because of the knocking noise I thought maybe I should pour even higher octane (Shell got 100) and added some "lead" additive with anti knocking. At this point the engine dwell was still at 14°.
By changing it now to 30° the combustion is out of order and that's why I have this high idle rpm?
I couldn't find any information on the internet about the relation of gasoline octane rating and dwell angle.

In addition, if the rpm's are above ~850 + the idling passages in the carb are physically bypassed due to the change of vacuum flow inside the air horn and cluster, hence how am I supposed to lower the rpm's with the mixture screws?

*Just for notice, the car did around 315 miles on new gasoline since I bought it, tough it wasn't raced yet on the highway. Before that the car stood a unknown time at the previous owner.

Again, thanks for helping me out! ;)

Greetings from Poland.
 

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There is not going to be a relationship between dwell and octane in the gas. Octane was a bit higher in the 60’s but not as much as everyone thinks ans they way they measured it was different.

An 850 idle is ok if your dwell is set at 30 and timing is correct, as your cam may not be original? Or the heads or piston stroke has changed. Lot’s of modified engines need a little more idle speed than the factory setting because of those changes.

Dwell is simply the the time in degrees of the distributor cam angle that the points are closed...when the points are closed the coil builds a charge, and it collapses once the points open and provides that 40,000 volts needed to fire the plugs. Keep it at 30 degrees as reducing it will give you a weak spark and poor running.

Dqell effects timing, and you may have way too much idle timing. If your vac can is pulling full manifold vac and more than 10 degrees then it is too much, your idle timing with a medium cam should be 20 to 26 in there,...like 12 from base and 10 degrees from vacumn can.....if you are pulling 12 from base and sixteen or 20 from vacumn can it will run up your idle.

When you changed dwell you changed your timing, so you need to work on the timing.
 

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Dwell Angle: It's the measurement of the length of time, in degrees of distributor rotation (not crankshaft rotation) that the points are closed. The primary windings in the ignition coil can only be 'charging'/saturating during the time the points are closed, therefore dwell angle directly relates to how much time the coil can be 'charging'. The longer it can saturate, the more energy is released (spark) whenever the points open and the magnetic field created in the primary windings "collapses" and induces a voltage in the secondary windings. From this we should be able to infer that as RPM goes up, this 'charge time' decreases, which is the reason that points/coil ignition systems produce a less powerful spark with increasing RPM.

If your "dwell angle" is too small (short), your spark will be "too weak" to light the fire especially at higher RPM. If the dwell angle is too large (long) then as long as they open at all you'll get a stronger spark, but you'll also get increased arcing when they do open which will significantly shorten their life.

"Back in the day" this was the reason that some performance distributors had two sets of points. Their timing was slightly offset from each other such that as long as at least one of them was closed, the coil was charging. The spark didn't happen until they were both open. This arrangement allowed for a longer dwell time (stronger spark) without burning up the points due to excessive arcing.

However, dwell angle even varying from one extreme to the other isn't going to be the cause of your problems. You either have enough spark energy to "light the fire" or you don't, and if you're engine is running - you're ok in that department. Just make sure you're not on the extreme end of the range that causes shortened point life.

Bear
 

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Discussion Starter #29
I see that,
so maybe I'll drop that one angle to 29° of dwell. Do you have any opinion about what octane rating I should use?
In relation to the cam and or other parts of the engine, the car has now approx. 36 k miles on the odometer (on the orig. title from the -90's the car had 35600 miles written). Both owners were woman from province villages around Kansas City - that and despite the good all around good shape of the car makes me believe that noone has tinkled with it, or furthermore pulled the engine or so.
I may be ofcourse mistaken but I assume it is all stock.
Manual says that while having the tranny in Drive and holding the brakes, the car should cycle at 600 rpm/s with the TH400, or 1030 rpm/s in Neutral with the adjusted dashpot at the throttle linkage.
If I pull the vac line of the distributor and plug the carb on warm engine (and the idle is at ~1.000 - can't lower it since it will cause jerking) the strobe shoots at exact 6+ BTDC, the idle drops the same time to around 850. Replugging the distributor the idle goes back to 1.000 and the timing rises above the 6+. I do not know what timing I should have with that 1.000 rpm/s or despite the 850, - maybe +7 or 8 BTDC?
I also checked the vacuum with a gauge (hooked it to the port where the vac for the dashpot and cabin go) and reading is almost steady (needle fluctuates only minor at 2-3 points) and shows around 18+ in of mercury (with the 1.000 rpm's!).
 

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Initial timing is >almost< of no significance. What really matters is total mechanical timing and the RPM where it occurs. What I consider "later model" (68 and later) Pontiacs with open chamber cylinder heads tend to "like" something in the general neighborhood of 35 degrees total, all in by about 2500 RPM or so. Earlier closed chamber heads can tend to like a little more than that. Both cases assume that the engine doesn't get into detonation (knocking/"rattling") under heavy load at low RPM. If you're running more or less stock cast iron heads on an otherwise un-modified engine, that can at times be a challenge and won't allow you to run optimum timing, due to the lower octane and lack of lead in today's pump gas.

That topic has been discussed on here multiple times, so you might avail yourself of the thread search tools to see if you can find those posts.

Timing is always adjusted with the vacuum can disconnected, hose plugged. Always. The purpose of the can is to add "extra" timing under light load, part throttle operations because it helps both fuel economy and engine cooling, but it has nothing at all to do with max power. The only reason to even look at timing with the can "active" is if you're curious to know how much it's capable of adding, but you never adjust timing with it connected.

Unless you know how much total >mechanical< advance you're getting, you're pretty much just spit-balling at things, trying to hit a bullseye target in a dark room. You're dealing with too many unknowns to have much success. I recommend using a light that's capable of measuring total advance. There are several on the market and some aren't all that expensive. The initial timing setting doesn't really tell you anything unless you know for certain how much "travel" there is in your distributor and the RPM where it's maxed out.

If you're getting "jerking" at less than 1000 rpm idle with the can disconnected and the hose plugged, and your timing is right, then your idle is probably too lean or you have an as of yet undiscovered vacuum leak (which causes a lean condition).

Try this:
Once you know for certain where your timing is at:
Completely close both idle mixture screws, being careful to count exactly the number of turns so that you can open them back to where they were.
Write down where they were, then set them back there.
Disconnect the can, plug the hose (or cap off the fitting at the carb), hook up your vacuum gauge.
Start it up, start backing down the idle RPM until it starts to get rough.
Note the RPM and the vacuum reading where that happens.
Try backing out/opening up the mixture screws and see if you can find a setting where the idle "cleans up" (use your vacuum gauge, tune for the highest reading you can get)
It's a dance. Dropping rpm decreases the vacuum signal which alters the air/fuel flow through the carb and can also lower timing (if the previous rpm was already starting to activate the mechanical advance mechanism) - so when you change something you also have to check and verify the other things too. At 1000rpm+ you may already be "getting into" the carb's transition slots due to the higher vacuum and higher air flow velocity. Dropping rpm decreases the signal and the flow, and can require you to add fuel "back in" via the idle screws.
Lather, rinse, repeat until you can get it down to a decent idle at around 750 RPM. -
If you're not able to achieve a decent 750 rpm idle, then either something is wrong (you've got a vacuum leak somewhere or some other problem), or that engine has a relatively nasty cam.

It's not rocket surgery :)

Bear
 

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Discussion Starter #31
Well,
I will take a deep look into this the next days and altough it is no rocket surgery there's litterally no mechanic in Cracow (one of the biggest cities in Poland) who would just jump right into those things. To be honest many times I have to explain a lot and the further I get the bigger the eyes of the mechanics become o_O The last known car carb expert passed away several years ago and now we got no one in the whole town :ROFLMAO:
One thing makes me really wonder about the carb because if I back up the acceleration screw on the linkage all the way back (the one that lays against the cam with the choke steps) so that the inner two throttle valves (I've got the two bore Rochester) are completly shut - the engine doesn't die. I always thought that there has to be a minumum pressure from the acc. screw (to slightly open throttle valves) to keep the engine alive or is this screw only for choke adjustment? Hell, I can even disconnect the whole acceleration rod/linkage coming from the cabin and nothing happens :unsure:

For the rattling as you mentioned, it occures only under load while accelerating on a warm engine, but, the intensity does not change with higher rpm's, it is just constant. I checked the heater valve on the right hand exhaust and it is assembled, nothing loose or broken, tough quite heavy rusted?!
 

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Discussion Starter #32 (Edited)
Today I tried to redo all the adjustments without having the distributor module connected and this is what I came to:

Timing at 6°BTDC, distributor vacuum clamped off, highest possible and "steady" vacuum between 13-16 in of mercury, idling between 70 - 97 x10 , full open choke throttle, fully closed throttle of both barrels (idling screw without contact at the choke plate). After reconnecting the distributor vacuum rpm's went instantly to 129 - 145 x10 :oops:
 

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A couple observations:
13-16 inches of vacuum seems to me a little bit low for a stock cam. I'd expect it to be closer to 20 or 22. As a point of reference, in the previous incarnation of the 461 in my GTO that had a solid lifter roller cam with 236/242 degrees of duration at 0.050 tappet lift still made 12"-14" of vacuum at idle, and it was definitely hotter than stock. That and what you've previously said about idle problems still makes me suspect that you've got a leak somewhere. Have you tried disconnecting the power brake booster? Examined that hose and all the other hoses and fittings for cracks? Watching your video, the vacuum source you're using for the distributor diaphragm is non-ported. That's not necessarily a problem, but it will start to add in some advance even at idle and that's going to tend to raise idle rpm some. Are you able to adjust idle down with it connected? With everything connected, what idle rpm can you achieve with the parking brake set and the car in drive? (Make sure the brake does hold the car - use some wheel chocks for additional safety - and don't be blipping the throttle!) Ask a (trustworthy) friend sit behind the wheel and hold it with the brakes.
Maybe disconnect and cap/plug every vacuum line you can find and see if that makes any difference.

Bear
 

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Discussion Starter #34
Will try to measure the exact vacuum readings after disconnecting every line and plugging the ports on seperate. What else could I check for leaks besides spraying around the carb stove and intake manifold + sparkplugs?!
 

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If the vacuum diaphragm in the power brake booster is leaking, you probably won't be able to directly check it. What you should see though if that's a problem would be an improvement with it disconnected and the fitting capped off. I think I remember seeing that you'd already checked around on the intake manifold and carb? Sometimes it's easier to just disconnect and cap "everything you can" and see if it gets better.
 

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Discussion Starter #36
Well if I plug everything, that is a) disconnect the trannys steel line and plug the port, b) power brake booster, c) dashpot and cabin line (they are on the same line), d) distributor can; I should eliminate any possible leaks from those devices.
If I see a significant change in the idle and or vac pressure after clamping off those external devices I should be able to track them sperately down by reconnecting them one by one.
Having this done I can only check the carb itself, intake manifold, pcv valve (both, the engine and manfiold port) and sparkplugs for any further vac leaks and do this with eg. carb cleaner or propane.

Do I see this right?

Just to be sure I understand this:
the „third” screw, located on the back of the carb is the idle speed screw, that regulates the choke what allows cold start and after warming up the screw should have full clearance from the choke cam (this half moon shaped plate with steps at which the screw lays again) as shown on my vid?
The carb regulation itself is only made by those two front screws aka „idle mixture screws”, one for each barrel?
Starting position would be 1,5 turns back out from the closed position, from where I would back out furthermore both screws, rotary, with possible same amount of turns until I achieve the max. vacuum on my gauge reading. Then making a half turn back inside to make sure I am not running rich?
 

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I excerpted all the pages from my '69 shop manual that address the setup for the Rochester 2GV 2bbl, which looks like what you have. I'll attach those pages to this reply.
On the idle mixture though, I'd recommend setting for best vacuum and leaving them there - don't turn them back in any. See if that changes things for you.

Bear
 

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Discussion Starter #38 (Edited)
Thank you for the pages, from what I know I have a Rochester 2 Jet 2G carburetor. I have adjusted some time ago all the linkage and float level according to my factory manual (the pages are identical to yours:).
Unfortunately none of this operations helped, I always end with the same setting: Carb’s idle speed screw can be backed out fully and even if I disconnect the acc. rod coming from the cabin, thus relieving the throttle lever fully the engine runs „by himself” on ~1100 rpm’s and the mixture screws doesn’t really change much (probably because rpm’s too high). Before the carb was rebuild, there was the same issue with the rpm’s but back then faulty was a gasket under the carb with a big vacuum leak on the backside (spraying carb cleaner on that spot Immediately killed the engine). Now something much more dodgy must have occured. Can’t get a clue on that one :(,... and it all happened after I raised that dwell from 14 to 30 degrees...
What eventually comes to my mind now is that when I put on the aircleaner, thus lowering the vacuum noise I can hear a clear clicking noise like every half second, might be electrical, it is very gentle. Was thinking first that maybe some short cut found it’s way on one of the sparkplugs but I definitely changed all wires and rechecked tightness of all connections. Might the distributor just give this noise under normal working condtions?

Ps. I did not change yet the points and condenser since the dwell reading is very stable (+/- 0.1 degrees, so it should be pretty healthy?) and besides that shipping from US is now with Covid very cumbersome.
 

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You have a problem if you were to disconnect the carb from the pedal linkage and close the throttle butterflies and the engine doesn't stall out. Try that.

Have you tried that? Is it 1.) possible that you gas pedal linkage is holding the carb throttle open? 2.) that your throttle valves in the carb were not centered in their bores when the carb was rebuilt and now will not close completely and thus shut all incoming air/fuel and allows the engine to continue to run? You can check by pulling the carb off, closing the throttle valves and shining a flashlight up through the bottom as you look down inside. You should see no light.

That on/off clicking you hear, if at the back/firewall, could simply be the voltage regulator points opening and closing - or possibly the Alt.

Ignore the highest vacuum reading for now. Can you adjust the idle mixture screws to get a smooth idle? Try that. I typically seat the idle mixture screws, then back out 2 1/2 turns and go from there. Back them out first, one side at a time, and see if it will run better. Then run the screw in until the engine begins to run rough, then stop. Back it out again until engine runs smooth and stop - idle mixture set. The do the other side.

Your idle will jump up, as well as your initial timing when you reconnect your vacuum line to the distributor. Once it increases, then you should be able to adjust your idle speed found on the side of the carb on the 'low" notch of the fast idle cam and choke wide open.

Don't know how old your engine is, but it is possible the timing chain/gears are worn and sloppy, or even the harmonic balancer outer inertia ring has slipped and is inaccurate. 6 degrees BTDC could be completely wrong. With vacuum disconnected, adjust the distributor by ear and see if the engine smooths out. So going by factory specs on a worn/old engine may not work.
 

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Wait... you're saying that if you back the idle screw all the way out it STILL runs? That should not happen. My first suspicion is like Jim's, that whoever had the carb apart last may have removed the throttle plates to clean everything and then didn't get the throttle plates reinstalled correctly. There are two things to check there. One is relatively easy: remove the carb and see if they're completely closing. You can use a light as he suggested to verify. The other thing that might be wrong is they may have been reinstalled upside down/backwards. The leading and trailing edges of the plates have a slight bevel on them so that they will seal flush against the throttle bores when they shut. If those edges are 'backwards' then they won't seal very well and can leak air. Getting the plates centered in the bores is relatively easy: just loosen the screws so that they can move, hold the throttle shut - that will force them to align themselves in the throttle bore, then tighten the screws down while holding the throttle shut. To check the bevel, open the throttle all the way so that the edges of the plates are visible. You should be able to see the bevel(s) on the edge(s) of the plates. They should be situated so that when shut, the whole edge of the plate is "flat" against the throttle bore. If they're not oriented correctly, remove the screws, and "turn them over" so that they are, then re-center in the bores as previously described.

The engine should not be able to run with the idle speed screw backed all the way out.

Bear
 
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