my car runs pretty good and the gas mileage is about 19 mpg in town, but i still have the same problem of it having to be set at 1400 rpm's just so it won't die when i put it in drive. the transmission seems to shift just fine. i took it out of town on a 130 mile trip and it did fine until i got to a stop sign then it almost died. when i got to where i was going i left the car running, and set the idle screw richer and it smoothed out. but now the idle screw was out about 4 1/2- 5 turns. it did the same thing on the way back. i'm guessing that i'm overlooking a vacuum leak that gets worse when the car has been driven hard. at this adjustment i lost about 2 mpg.. i checked for a vacuum leak using carb. cleaner last time, this time i'll use propane. the only place i can think of that i didn't check was the head gasket. well, if you guys can come up with some ideas, i sure could use the help. thanks.

well, i went out in 104 degrees and took off the new "flamethrower" coil and put the old one back on. only because i have read a lot of problems with this ignition system and aftermarket coils. i drove it to work and if anything it seemed to run better without it. i also got out my propane bottle and checked for a vacuum leak, but i think all i did was stink up the neighborhood. i couldn't find anything.

i've been driving this poor car with the idle set at 1400 rpm's and every time i put it into "drive" i cringe when i hear that "CLUNK". so out of desperation tomorrow i will try putting the car in reverse (with brake on), a/c on, and turning the distributor to see how far down i can get it to drop (rpm's) without it stalling. then i will see if i need to reset the idle screw and if it's driveable. if it is not, i am going to have to find a shop that works on /6's. i really don't know how much more abuse my poor transmission can take.

I don't know which carb you are running, but many carbs do have to have the idle screw turned out a number of turns.

But there are a number of factors that can affect your idle even if it runs fine at higher engine speed.

Usually if you don't have the torque to idle in gear, the idle circuit is too lean. At least if the idle is high.

The baseplate of the carb and the throttle blade position is supposed to be within a narrow range of adjustment. This is the first thing you need to check to start to decipher the problem.

The idle discharge port, (the port that the idle screws directly adjust) is right below the throttle blades during normal idle setting. Above the idle discharge port is the "off idle transfer slot"...this is a vertical slot that feeds fuel straight from the idle circuit channel that feeds the main idle discharge port.



This is a picture of a Quadrajet Carb, but you can clearly see the discharge port and the off idle transfer slot on the right side of the picture.


This collage you can ignore all the quadrants but the lower right...this is a close-up of the same baseplate above.

This configuration is going to be the same on almost all carbs ever produced, and 99% yours looks basically like this as well.

Anyway...the throttle blade when set correctly for any engine, will have about .020-.060" of the transfer slot showing to the manifold side of the throttle blade.

The way this works...when your throttle blade is closed, the fuel for idling comes thru your jet or another passage in the float boal into the idle circuit passage...the fuel then travels up this channel and is mixed with air(emulsified) to become a mixture somewhere in the main body thru a calibrated hole (or vacuum leak) into the fuel channel. This emulsification greatly increases the ability of the idle mixture to flow well into the engine without dropping to much fuel out of suspension and back into liquid in the intake manifold.

On with it...the mixture then travels down the idle channel to the off idle transfer slot...where only the lower .020-.060" sees a signal because the throttle blades uncover it to vacuum in the intake...but above the throttle blades is atmospheric pressure and no signal to pull fuel...so a little fuel will always be dribbling out of this lower part of the slot at idle...next, the mixture reaches the discharge port, where the mixture screw(s) adjust how much of the mixture(not just fuel) arrives in the manifold to combine with the dribbling part. The total quantity of "potential" fuel mixture that can be delivered is decided by a channel restriction somewhere up stream in the circuit, depending on the type of carb. The ratio of fuel to air is determined by the idle jet size vs the size of the air bleed...(and when I say jet, I mean a drilled orifice and not a screw in brass jet).

When you first hit the gas, the accel pump is to far upstream to keep from a off idle lean stumble. So as the throttle blades first move, they uncover the off idle transfer slot, and disharge extra fuel to cover the lean spot until the accel pump fuel and main venturi start to feed the system.

If any part of this system is out of adjustment, or clogged, or otherwise comprimised...you can get results like you have seen...or it could just be a bad vacuum leak.

However...to really solve your problem, the troubleshooting methodology would be to set the idle screw where it ran well, pull the carb and check to see the throttle blade position...if it is set too high(meaning alot of transfer slot showing, then it is a sign you are to lean, and by uncovering the transfer slot when loaded on the convertor, the extra fuel coming from the extra transfer slot showing will richen the mixture enough for it to stay running.

If your gas milage suffers, it points to your needing to lean the primary jet once you get the idle problem solved...and in 104 degrees that would seem reasonable to do.

All of this also needs to be considered for modifying the carb to run larger camshafts with less idle signal. When a large cam is run, the engine needs an easier way to get air because the signal is so weak, and you can't just open the throttle blade(s), because you would lose the off idle transfer slot function. Quadrajets, some other high perf carbs, have an idle air bypass hole from the factory, and the size of that hole determines where your throttle blade position will be for any given idle speed.

Same principle as drilling a hole in your throttle blades when a larger cam is installed...except there are more elegant solutions.

Hope this helps...if I knew what carb I might be more help

Gearhead

_________________
64 GTO...10.80's@122 on street radials
Destroked 455, Qjet, stock ign, 2400 stall

64 Valiant
Old 225, 4spd, 2.92-8.75, 2bbl, headers
dual 2.25"

Props to Gearhead!

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

Gearhead, thanks for the help! before i go any further, i really enjoyed reading your post on cams!! a little history: i bought the car about 3 months ago. 1974 scamp, /6 225 engine, 55k miles, all stock, 1945 carburetor. i have replaced: air filter, rebuilt carb., tried replacing carb. but re-man. carb. was junk and acted exactly the same way, replaced intake/exhaust gasket, all vacuum lines under the hood, new battery w/new cables, 985 plugs (set at 40), re-man. distributor, new plug wires. checked vacuum leaks with carb. cleaner and found none. plugs were white, drilled main jet, plugs now tan. had a flat spot, moved linkage to bottom (of three slots), now no flat spot. was weak at 70-85 mph. on hills, now will hold it's own or gain speed. all emissions still intacked. opened vacuum amplifier, diaphrams are old and stretched, the egr valve was completely plugged, cleaned, diaphram works good. tried tuning from 5*- tdc (no vacuum at carb. - distrib.) unless i hit throttle, then it moves fast, is now at 2.5*btc., temp. gauge reads at first mark most of the time and i believe it because heater is only warm and short lived. runs better and better after knocking carbon off (at high speeds) and with work done. went back to stock ignition (aftermarket coil w/ no ballast) afraid of too hot (no difference in performance anyway). ok... about carb.: will not go down to 750 rpm., i have to richen mixture to drop, then tune. choke is set at right about 1800 rpms (tempermental 1700-1900rpms. only) but she fires right up hot or cold, and choke opens quickly without electrical assist, drives good w/choke on. shifts fine: 2nd - about 30 mph., 3rd - 50 mph. part of my problem is believing that 2 ea. carbs would behave exactly the same. sometimes i wonder if it's an electrical problem. altenator has new brushes and puts out 60 amps., if at 1400 rpm., solid amp. metter reading, put in "drive" drops to about 800 rpms., amp. gauge drops and flickers, turn on blower to 1st setting (drops again, also drops another 100 rpms.). i will not use the 3rd setting because it may stall and amp. meter looks as though no charge. maybe it would help if i clean the plugs and just lt the car idle for a long time to read the plugs. anyway, thats about where i'm at... chasing my tail. thanks!

I don't think its an electrical problem. The marginal alternator output at idle is typical of Chrysler alternators- especially ones that have been "remanufactured" a time or two over the years and now have mis-matched rotors and stators. I wouldn't go chasing down blind alleys- my strong hunch is that this is ENGINE related, not electrical.

What does concern me is that the RPM drops so much when you turn up the fan blower- that's a VERY small load! For some reason, your engine is barely producing any torque at idle- EVERY symptom you describe ends up being a too-large drop in RPM with a small load applied, which means that the thing barely has enough torque to idle at all.

It certainly could be a mixture problem, but with it this extreme I would expect that it wouldn't idle SMOOTHLY if it were really that much too lean.

Lets run down a checklist again:

Are you setting the basic timing with the vacuum advance DISCONNECTED?

Are you setting the idle speed and mixture with the vacuum advance DISCONNECTED?

When you connect the vacuum advance, are you connecting it to PORTED vacuum on the carburetor? Here's a test for this: if you have the engine idling at, say, 800 RPM after checking your timing and setting your idle mixture and speed for the highest possible vacuum reading, you should NOT notice an increase in engine speed when you connect the vacuum advance to a ported vacuum source! If you do see a jump in engine speed, then either 1) you are connecting to a manifold vacuum source, not a ported source, or 2) for some reason your throttle blades are open too far, exposing not only the transfer slots as Gearhead described, but also the vacuum port. There are fixes for this involving drill bits, but lets not go there until we have to!

After verifying all of the above, if you still have the problem:

What are your valve lash settings? If the lash is too tight and the valves are being held open slightly, I'd expect this kind of behavior (but again I'd expect other problems, like burned valves!)

Do you know if your camshaft timing is correct? Have you put a new timing chain and gears on this engine? A severely retarded cam can produce behavior like this- it will kill the low speed torque, but the engine will come alive like gangbusters at higher RPM. And before you ask, YES it is possible to have the spark timing perfect, and still have the cam timing wrong. Changing the cam timing will change the spark timing, but you can always correct the spark timing back to normal by adjusting the distributor.

Anyway, those are things that spring to mind right off the top of my head.

_________________

440 Magnum: sorry, it took me so long to get back to you. i had to go to work again...4th time this week already and it's getting old. anyway, i read what you wrote and i was thinking about my valves. when i got the car, they were all real loose, so i adjusted them to 10-20. then i noticed that the clacking had went away but three cylinders were running a little lean, so i adjusted those three at 11-22. but sense then i have drove the car on the freeway 130 miles to and from twice at about 85 mph.. i have noticed a big difference in power after those trips. i have not reajusted the valves sense, and i know i knocked off a lot of carbon. would that make the valves loose or tighter? i figure loose. anyway, Saturday i will adjust them again and check the timing after i do. what difference would plugging the vacuum line to the distributor make if there's no vacuum? i have a 1945 carb. and i thought the only place to put a vacuum gauge was where it connects to the distributor, is that right? by the way the car ran great tonight! seems like the more i drive it the better it runs. thanks!

Knocking off carbon shouldn't affect the valve clearances at all. But they still could be a little too tight, especially when hot.

If the dist. vacuum line is REALLY connected to ported vacuum, and not to manifold vacuum, plugging it shouldn't make a difference. But if its connected to manifold vacuum, you'd have a vacuum leak with it disconnected.

Measuring vacuum at the distributor should show NO vacuum at idle, because ported vacuum should be blocked at idle by the throttle blades. OTOH, manifold vacuum will be the HIGHEST at idle.

Its really important to set up the timing with NO vaccum advance, hence the suggestion to un-plug it while doing the settings. And its also important to connect to ported vacuum when you do hook it up.

_________________

ok, that makes sense. i think all this would be much easier if i could use my digital camera and just show you and others what i'm talking about. but, i'm not real good with computers and sending pictures seems like a real pain. heck, i can't even figure out how to use the emoticons. so, i take it that i'm unplugging the right vacuum line? to be honest, all the others are either way too big, or their is one that is even smaller but if i remember right it goes to the radiator. i will see if my friend knows how to send pictures, if he does he can show me. i did plug the vacuum line when i tuned it last time, but i will tune it again after i adjust the valves. thanks again, for your help!

You can email me a picture and I could post it for you...to post pictures easily you have to set up a bit of infrastructure. In my case, I have a hidden directory on my web site, and a simple program that creates a page and stores the pictures as quickly as I can get them into the computer.

If you try though, make sure your camera is set to 640x480 or maybe one size larger, else the file size is huge and hard to deal with...

Karl

_________________
64 GTO...10.80's@122 on street radials
Destroked 455, Qjet, stock ign, 2400 stall

64 Valiant
Old 225, 4spd, 2.92-8.75, 2bbl, headers
dual 2.25"

hello Karl, thanks for the help! i will try that soon as i get settled down (hopefully tonight). i've been giving what 440 Magnum said a lot of thought and the only weakness i have experienced with my car is at idle. so hopefully after my errands, i will get to readjust the valves and tune her up again to see if that helps any. thanks!

Gearhead, i sent you a pm. please let me know if you received it. thanks.

Heres your pictures...I haven't chimed in on this thread again because 440 has been giving you good info to go on...

The vacuum advance should be to the ported source of vacuum.

If you send me a closeup of the driver and pass side of carb I can label the ports for you...



Here is the passenger side:



I can't see from these pictures well enough what is connected where.

And...I'm so used to cars with every non essential thing removed that your engine compartment actually looks complicated!!! LOL !

Gearhead

_________________
64 GTO...10.80's@122 on street radials
Destroked 455, Qjet, stock ign, 2400 stall

64 Valiant
Old 225, 4spd, 2.92-8.75, 2bbl, headers
dual 2.25"

I second that...I was comparing to my 62 and saying "WOAH"

MJ