Hi guys I have finally replaced all necessary parts on my engine in the attempt to get it to run right. The distributor has been rebuilt and cleaned up with a new VC208 vacuum advance can installed on it. I have replaced the I/E manifold gasket with the carbon fiber unit from Australia. Engine runs fair however I am sure that it is not good as it could be. My harmonic balancer has slipped on its ring so I have really no idea where I am at timing wise. I have fixed all of my vacuum leaks and at idle it draws 0" inches of vacuumat carb base. I also have the carburetor butterflies close so that there is no vacuum applied to the distributor port at idle.(thank you SSD for the education) However I am not a guru so I don't know what to do first. I was advised that 1974 engines were set notoriously lean and to try to richen the carburetor to raise my low idle speed without resorting to opening up the butterflies? It is currently idling around 525 rpm when hot. I don't know in what order I should be doing these things; the items I think that need to be adjusted- idle mixture, the timing, and the vacuum advance. By the way this is in a large heavy car that will be used for intermediate towing. Thank you so much .

I know that feeling. Have you checked for timing chain slop? Pop off the distributor cap and, using the belt and fan blade, manually rotate the engine in one direction until you see the distributor rotor begin to turn, then see how far you can manually rotate it the other direction before the distributor rotor starts turning. If there is any perceptible lag (keep an eye on the timing mark to get an amount-or-degrees-of-movement idea of how much lag there is), the T-chain is slack and needs replacement.

Are your EGR and OSAC systems still operational on this '74, or have you disabled/bypassed them?

Is your thermostatic air cleaner hooked up and working correctly?

Is your manifold heat control "heat riser" valve working correctly?
You need to fix that. Replace the damper. They're available new.
Not sure what you mean by this. A more or less stock engine in proper operating condition, idling at sea level, will pull about 20 to 21 inches.
No. There is only one correct idle mixture setting. Carburetor operation and repair manuals and links to training movies and carb repair/modification threads are posted here for free download.
Way too slow. 750 to 800 is your target.

Tune-up parts and technique suggestions in this thread.

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Too many people who were born on third base actually believe they've hit a triple.

ok Dan thanks for a good start !

1) the timing chain is surprisingly tight w/ little if any decernnable movement in the dist. rotor.

2) EGR is Bypassed and OSAC is completely removed.

3) thermostatic air cleaner works like a charm and the manifold heat control valve is loose and operating correctly.

4) as far as the harmonic balancer, do you have any recommendations what brand to get as new ? are they decent quality and accurate ?

5) Im sorry. I should have clarified at hot idle it pulls 19" of vacuum and is jittery. I meant to say the it now has 0" of vacuum at the distributor spark advance port like it is suppose to to. I had the hot idle screws holding the butterflies from fully closeing at idle.

I guess what I'm asking is since I need to raise the idle speed by 200 rpm what do I do first ? if I just crank in the curb idle screws then I can achieve my curb idle speed, but I will be opening up the butterflies enough to bring the vacuum advance in at idle. Should I play around with the mixture screws to see if I can pick up my 200 rpm there to keep the butterflies closed ?? - I hope this makes sense to you guys..

Sounds to me, that your vacuum advance line is hooked up to the wrong port on the carburetor. One of those manuals that Dan has suggested will show the correct port for your carburetor.

There should be no increase in timing advance when the idle is adjusted to the proper 750 rpm.

Kesteb - My vacuum advance line is connected to the right carb port. The initial problem is that the curb idle speed screw was holding the butterfly open slightly thus admitting vaccuum to the dist. I have now remedied that except I need to raise my idle speed without opening up the butterfly. That's why I'm asking about idle misture screws ....

If your idle is too low and if you screw in the curb idle screw and start giving the dizzy advance then your timing might be too retarded?! Mine is supposed to be factory set at 12* btdc And idle at 600rpm +/- 50rpms. I have it at about 650 and it runs great. Probably could do a little more fine tuning with the mixture on mine though as it still is a tad rich.

Cody

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Old truck: 82 D150 225, 2bbl, dutra duals, 2.5" straight pipe to dual 2.5" tail pipes. Mud tires, 4spd, old forest service truck.
Current truck: 98.5 Ram 2500 ccsb, sport, 24v cummins, 5spd, 4.5" lift, 35's, 5" straight pipe.

Advance the base timing.

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Too many people who were born on third base actually believe they've hit a triple.

The Australian-made ones are quite good, yes. Expect to pay about $120ish. See here and here for two such dampers up for immediate sale.
19" isn't bad. Jittery suggests you might be due for a valve adjustment.
Don't insist on the throttle plate being fully closed at idle. That's not a valid criterion for determining whether things are adjusted correctly. You may have to crack the throttle plates slightly to meet your idle speed and base ignition timing targets. You should be shooting for 750 to 800 rpm hot idle in Park with the high beam headlights on, and a base timing of about 5° BTDC with the vacuum advance hose disconnected from the carburetor and its carburetor nipple plugged -- all of this to be achieved with minimal or zero vacuum at the spark advance nipple on the carb.

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Too many people who were born on third base actually believe they've hit a triple.

Have you checked and confirmed that the valve lash is set correctly?
The engine will idle rough if the lash is set tight or unevenly.
Checking / adjusting the valve lash is the first thing I do when tuning a SL6.
DD

If this is true, then you won't see any vacuum advance at 750rpm.

The idle adjustment screw is supposed to open the throttle blades. That is how idle is set. The idle mixture screws adjust the air/fuel mixture in the idle circuit. Turning them out may increase the idle speed, if they do, then you adjust the idle back down with the idle adjustment screw.

Advancing the base timing may increase the idle speed, once again you adjust it back down with the idle adjustment screw.

I think you need to get those books that Dan is always recommending. You seem to have a fundamental misunderstanding on how the all the various components work together.

Doc - the valves were adjusted three years ago but the engine hasn't seen more than 1000 miles since then (sadly) Could they still get out of adjustment while sitting ?

Kesteb - there is no doubt i have a fundamental miserstanding of tuning. But i'm trying to learn. it just seems like there is alot of components that come together between fuel and ignition to get a motor to run right.

Dan - i followed your advice and had to crack those throttle plated open slightly to get the engine to idle correctly. i opened the butterfly up slightly and the idle picked up to 650 rpm. then i advanced the ignition timing and it picked up to 720 right now. i locked it in. i am only getting 1" of vacuum to the distributor right now so i have it running decently with minimal vacuum at port for distributor.

So the idle speed screw would be the last and final adjustment to get the rpm's where they should be at after the ignition timing and idle mixture are set properely ? am i correct in my thinking ?

shouldn't he carburetor idle by itself on the idle circuit (with the butterfly closed ) and not rely on the butterfly's be open slightly to idle correctly ?


thanks for being patient with me guys.

Getting your idle speed and mixture correct involves adjusting three parameters: (1) your curb idle speed set with the idle speed screw on the carb; (2) your base timing, set by disconnecting and plugging the vacuum advance line and turning the distributor; and (3) adjusting your curb idle fuel/air mixture using the fuel mixture screw(s) on the carburetor.

With everything set correctly, you should have no vacuum at idle at the distributor advance port.

To set the idle speed and timing and adjust the mixture, first find out the correct idle speed and base timing for your year and emissions package. This is usually found on a green and white sticker under the hood (at least it is in the States. I don't know how it is done in the land of Oz). Now, follow the following procedure:

(1) Disconnect and plug the vacuum advance hose going to the distributor.

(2) Set your curb idle speed to the factory specification using the idle speed screw.

(3) Set your base idle timing to the factory specification.

(4) Check your curb idle speed. If it has advanced or retarded from where it should be, reset it using the curb idle screw.

(5) Check your base timing, adjust as necessary. Because the distributor advance or retards timing based on engine speed, a large increase in idle RPM might cause the timing to be advanced from where you set it before.

(6) Check your curb idle speed again, adjust as necessary. Changing the base timing also changes the idle speed. Advancing timing increases idle speed (unless you advance it too far) and retarding timing decreases idle speed.

(7) After curb idle speed and base timing have been set, THEN adjust the curb idle mixture. If adjusting the mixture increases or decreases idle speed, adjust the idle speed using the idle speed screw as necessary.

(8) Once idle speed and mixture have been set, check your base timing again. Adjust as necessary.

(9) Verify curb idle speed still correct.

(10) You are done.

It takes some time to adjust everything right, but isn't that hard to do. just be patient and be willing to go back and double check things you have already set.

It also is worth rechecking the valve lash with the engine HOT and running. It is quick and easy to do, and you might be surprised at their state of adjustment.

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Casually looking for a Clifford hyperpak intake for cheap.

Were they adjusted correctly?
More or less yes; you will sometimes have to go back and forth between the mixture and speed screw to get it dialled in.

[quote[shouldn't he carburetor idle by itself on the idle circuit (with the butterfly closed ) and not rely on the butterfly's be open slightly to idle correctly ?[/quote]

Some carburetors have a closed-throttle idle system of one sort or another. Others do not. Most of the ones we encounter on slant-6s do not, and so the throttle plate(s) must be cracked slightly to provide correct idle speed.

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Too many people who were born on third base actually believe they've hit a triple.

a good starting point with your carb is a full turn on idle screw and a full turn on mixture screw, i have never seen a idle setting with throttle plates seated in the bores,

You will when you look more closely at more carburetors. Also see pp. 380-381 of the Petersen book.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.