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1972 Nova
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Discussion Starter #1
Hey guys, I've been working on the Nova and driving it a little on our dirt road, and I'm having some issues. The main issue seems to be that the car is idling along at 20-25mph with my foot off the brake. I drove it up and down my road (maybe 1/2 mile total), and there was a little smoke coming out from the drum brakes!

I just hooked my tach up today to work on the idle. It was idling cold at 3000rpm, so I dropped that to about 2200 rpm, and that put my warm idle right around 900-1000 rpm (seems high, but I couldn't really adjust it any lower). I adjusted the fuel mixture screws to get 18-19 in/Hg, and it seemed that originally the screws were set way out (like 4-5 turns out), but they're now around 2-2.25 turns. This didn't help the issue of idling at speed. I did the adjustments with the air cleaner hose closed off and the vacuum gauge hooked to the vacuum advance hose from the carb.

Any clue what is going on? All original 1972 parts (2 barrel carb), other than headers/exhaust. It appears that the vacuum timing reducer by the carb was bypassed at some point, so I have the front PS vacuum port going to the distributor, rear PS vacuum port going to the air cleaner, rear DS vacuum going to the choke (are these all ported vacuum sources?). The plug on the rear of the manifold goes to the trans and inside the car, while the plug on the front DS under the carb is going to the charcoal canister (this hose is leaking, is that a source of a vacuum leak?).

I'll try to answer any questions. Thanks!
 

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IS the idle staying at 1000 rpm? What is it in gear with your foot on the brake?
 

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It never hurts to inspect the carb linkage return springs to make sure they are not weak either. Make sure the carb throttle returns hard all the way back to its resting idle position stop when you operate it by hand. It sound too simple, but sometimes the springs lose some of their tension.
 

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Mike - 74 Nova Baltimore, MD
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The main issue seems to be that the car is idling along at 20-25mph with my foot off the brake.
Can you give us a little more detail about the statement above.
Was the car at a stop with the engine running > you took your foot off the brake > and the car accelerated at idle speed of 1000 rpm to 25 mph without you touching the gas pedal?
OR... you were driving your car, and then took your foot off the gas pedal and let the car slow down by itself (no brakes) > and at 1000 rpm (idle) the car was moving 25 mph without you touching the gas pedal?
Do know what gear your transmission is in when the above scenario is taking place?

there was a little smoke coming out from the drum brakes!
You need to remove the wheel and pull the drum and check for proper brake shoe adjustment and also check that the wheel cylinder is not frozen. Be sure to also check for any signs of leaking fluids... since all of the braking system components that are under the drum should be completely dry.
 

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Discussion Starter #8
I actually did replace the return springs a couple months ago with a safety double spring. It was sticking a bit, but a blip of the throttle seated it again (it was sticking about 100-150 rpm). There car would still drive under idle power after the throttle was blipped.
 

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Discussion Starter #9
Can you give us a little more detail about the statement above.
Was the car at a stop with the engine running > you took your foot off the brake > and the car accelerated at idle speed of 1000 rpm to 25 mph without you touching the gas pedal?
OR... you were driving your car, and then took your foot off the gas pedal and let the car slow down by itself (no brakes) > and at 1000 rpm (idle) the car was moving 25 mph without you touching the gas pedal?
Do know what gear your transmission is in when the above scenario is taking place?


You need to remove the wheel and pull the drum and check for proper brake shoe adjustment and also check that the wheel cylinder is not frozen. Be sure to also check for any signs of leaking fluids... since all of the braking system components that are under the drum should be completely dry.
From a dead stop there car will pull against the brakes and accelerate to 25 mph. I do not know what gear it was in. Next time I'm out in it I can manually shift it and see.

The brakes were rebuilt in front, with turned drums and new shoes, springs, hoses, and wheel cylinders (all replaced last fall other than one cylinder, that was a couple years). Not saying they're adjusted right, but I turned the star adjuster until I just felt a tiny amount of drag. They were smoking (in my opinion) from trying to hold the car back (It's a dirt road, and trying to turn and stop took effort).
 

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Mike - 74 Nova Baltimore, MD
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From a dead stop there car will pull against the brakes and accelerate to 25 mph. I do not know what gear it was in. Next time I'm out in it I can manually shift it and see.
I assume you have an automatic trans.
Yes... The next time you are driving the car (and the engine is fully warmed up to operating temps + normal idle) and come to a complete stop, try manually shifting the trans into 1st gear and let off the brake... but do not touch the gas pedal. Note vehicle speed.

Now, put the trans back in drive and do the same procedures shown above. Try to notice if you feel the trans is shifting gears. Note vehicle speed.
 

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Discussion Starter #11
It's a stock TH350. I'll try messing with the idle to get it back down closer to the 600 rpm that the car calls for, then move the tach into the car and test that. Maybe I'll be able to get my temp gauge hooked up too, since I already said the stock sender in the head for an aftermarket sender.
 

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It's a stock TH350. I'll try messing with the idle to get it back down closer to the 600 rpm that the car calls for, then move the tach into the car and test that. Maybe I'll be able to get my temp gauge hooked up too, since I already said the stock sender in the head for an aftermarket sender.
it idles at 3000?
Don’t even get in the car till You get the Idle below 1000.
Starting that thing cold with that high idle will ruin your rod bearings and the crank if you keep doing that.
Jumping into gear is not good on the drivetrain parts either.
You know the engine revs high at idle, so dont start it till u figure out why
 

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Discussion Starter #13
Cold (choke) start was 3000 rpm before I turned it down to the factory 2200 rpm. When warm or kicked off the choke cam it's ~1000 rpm currently. I'm guessing the cold start is lower than 2200 now due to adjusting warm idle too.
 

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Cold (choke) start was 3000 rpm before I turned it down to the factory 2200 rpm. When warm or kicked off the choke cam it's ~1000 rpm currently. I'm guessing the cold start is lower than 2200 now due to adjusting warm idle too.
I have had a lot of chevys.
The fast idle solenoid should not work or be part of the mix until you turn on the air conditioning.
So a 350 should idle cold at 900-1000, warm, neutral. 550.
Ingear, 500.
With air on, it will be around 400. So to prevent it from dying, the fast idle solenoid kicks the idle up to 650 in neutral. The fast idle solenoid should pop up to extended position when the compressor clutch is energized.
 

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Discussion Starter #15
According to the decal on my radiator cover, fast idle is 2200 rpm, normal idle is 600 or so. From my reading, the 72 doesn't have a fast idle solenoid, only a low limit solenoid to drop the idle around 400 rpm once the car is shut off to prevent run-on.

This is the emissions sticker I have:
 

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Did u follow the instructions on the sticker?
Plug the tank vent and vacuum canister hoses with bolts or screws, then set timing, dwell and idle as indicated?
After that, reconnect hoses, it should work as advertised.
If it doesn’t, use pliers to squeeze all the vacuum hoses to find out which system has the problem allowing idle to soar.
Then troubleshoot that system.
my guess is you will have to trace the lines back to the tank under the car, and you might find the vent hoses will be all cracked, letting in sir to those hoses, preventing a good idle.
So after you get done up front, then fiddle around under the car, you will have adjustments to redo at the engine again.
Sometimes the tubes cannot be installed on the assembly line in one piece, and there might be a short piece of hose somewhere under the car that Connects the tubes has rotted out.
You just have to look.
Because you don’t have an engine computer to display codes, you have to be the computer and read the signs as the computer Would get sensor inputs.
first, check tailpipe for black soot
Second, check carb for choke operation and throttle stops, movement, interconnects, trans kickdown, etc.
Then check ignition, wires, coil connections, etc.
Then pull a plug on each side of the engine since Right and left intake runners feed opposite sides or multiples depending on design.
Check exhaust heat riser, then check belts to make sure water pump is turning up to speed, And not elevating temperature of intake that would effect the fuel’s ability to not vaporize in the intake runners near the heads.
 

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Discussion Starter #17
The TCS is not hooked up to the vacuum system, the charcoal canister is hooked up to the tank and valve cover, as well as the fitting on the front left under the carb (the other hose that is usually inline with the TCS and distributor is sealed at the TCS).

All emission hoses from the tank to the evap system in the trunk are new, as well as the line up to the charcoal canister (all 5/16" and 3/8" EEC/fuel rated, I don't have the hard line from the charcoal canister to the tank as it was deleted before I bought the car). The fuel lines were blown out, and the hose between the two runs is new. Gas tank sender/sump is new. Plugs and wires are new, as well as the fuel pump and filter at the carb.

The choke seems to be working, as it raises the idle when cold and kicks out when the throttle is blipped.

When I set the idle, I had the vacuum line for the air cleaner plugged, and the line to the distributor was disconnected from the vacuum advance and plugged into my vacuum pump/gauge. I did not touch any lines at the charcoal canister. I did not set dwell and timing (as I don't have the tools, and nothing seems to have been changed from factory with the distributor/ignition system).

I will be picking up the required hoses to replace vacuum lines tomorrow night most likely (long hours at work all through the summer), and I'm not sure when I can get time to mess with replacing those and looking at the tuning again. I will try turning the solenoid screw to see if I can turn the idle down more, as it seems to be resting on that if I remember correctly.
 

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Discussion Starter #19
I know, and I appreciate it. I'm just finding more stuff that I need to do (that I thought could wait) before even thinking of putting insurance on it (n)

I have not touched the distributor in any way, other than attaching new plug and coil wires to it.
 

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When u get a chance, u might want to pop the cap off and look at the advance weights. You have to remove the rotor. On the bottom of the rotor is a protruding square and protruding peg. They fit onto the dist. So u can’t put it on wrong.
It is possible for high humidity to rust those weights, then they get stuck on full mechanical advance.
You don’t always need a timing light.
On your timing tab, crank the engine to top dead center #1.
Then rotate crank to 5-7 degrees on the timing tab with a ratchet and 5/8” socket. You know you are going the tight way because u should be tightening the bolt.
Then pull the wire off of #1 spark plug. Put a spare plug or a 1/4” bolt into the wire end and position it about 3/8” away from the metal somewhere.
You can use a spring clamp to hold it or something heavy enough (ratchet, etc.)
Then loosen the distributor hold down, turn the key to on, but don’t go to start. Then retard the distributor and slowly advance the dist. Until the plug fires on #1 wire. Use a sharpie, make a mark on the manifold and dist. where the spark occurred. Then back off and do it again to make sure it repeats at same place. Lock the dist. Down, turn off key and put #1 plug wire back on.
Simple simple.
So when u do it like that,
No vacuum advance
No mechanical advance
Just pure actual timing with no variables.
 
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