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car dies at idle sometimes


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'72 240z- triple 45 dcoe weber carbs

Hi, I have a problem with my idle. When the car is warmed up and sitting and idling it holds at about 500 rpm just fine, but sometimes when I drive it and come to a stop it'll slowly stumble to about 300 rpm and then die on me. I'm not too sure that's going on.

Help!

Thanks

Tyler

Edited by Esc8p2NeverLand
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Just a thought to share. I had a problem such as yours and found that I had a vacuum leak

at the brake booster. Each time I came to a stop my car would want to die. I replaced it and problem solved.

Edited by 2-4-T-Z-MAN
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I've had similar issues with loose ignition wires at the coil/resistor.

I've also had that happen with my recent dashpot sticking issues, but if the car drives fine then I doubt its anything to do with that.

When I had a battery in the car that couldn't hold a charge properly it also would die if left idling for a few minutes, probably due to voltage drop.

I guess the first thing to check is if it's ignition or fuel related...

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I'd go in with a can of carb cleaner and adress any areas that might show as a vacuum leak. With the engine running,the speed should increase as the carb cleaner gets drawn into the engine. You want to check hoses and mounting surfaces like between manifold and head....

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I'm new to z-cars so please forgive me if this is a normal thing for them- When driving at night and the car is at idle, the lights dim quite a bit, but when revved the lights brighten up again. Could this be a cause? Maybe bad battery or alternator?

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I'm new to z-cars so please forgive me if this is a normal thing for them- When driving at night and the car is at idle, the lights dim quite a bit, but when revved the lights brighten up again. Could this be a cause? Maybe bad battery or alternator?

Well it's not normal but it seems normal to early Z's. Problem is low output of alternator at idle, one cure is to replace with later model 60 amp interally regulated alternator, MSA has a kit available as well as zspecialties.

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I haven't had a chance to test vacuum leaks with carb cleaner, but I did a visual inspection and nothing seems out of place and in need of repair.

NOW I CAN'T GET THE DAMN THING TO IDLE. I have to set the idle high to about 1500 and it'll run for about 5 minutes then it'll just drop off and flat out die.

So frustrated!

I tried readjusting the throttle linkage. I took the arms off and tried them at three different spots. Originally it was hooked up to the middle hole on the lever.

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So after getting really frustrated, I just rechecked, retightened, retuned my carbs. I Pulled vacuum lines off, pushed them back on tightly and ziptied them. I redid the arms on the linkage. I retuned the idle mixture and idle. Here's what I got.

-Idle at 850 rpm. It drops to about 650-700 rpm with lights, fan, and radio on.

-Idle screw down 3/32 of a turn past touching

-Mixture screws set to 1 1/4 turn out all the way across

For reference the carbs are:

45 DCOE

36mm choke

155 Main Jets

170 Corrector Jets

55 F8 Idle Jets

F16 Emulsion tubes

On my previous tune last night where I microtuned with the ColorTune Tool for the mixture I got for the turns out

#1- 1 1/4

#2- 1/1/4

#3- 3/4

#4- 1/1/4

#5- 3/4

#6- 3/4

The car drove wonderfully, but I could not hold an idle at stop. Maybe due to incorrect jet sizing?

Let's hope the idle holds fine tomorrow!

Tyler

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So now something odd is happening with the idle. So when I start it up, I have to play with the gas for about 3 minutes until the temperature probe moves on the dash, then if I let go of the gas it'll stumble low to about 400 rpm and die.

On the other hand, if I pop the hood and manually give the throttle a little "blip" it'll go to about 850 rpm and idle great.

So I thought maybe I have to just give it a tap or two of the gas pedal to recreate the same thing. NO! It doesn't work. If I then proceed to pop the hood and "blip" it again it'll idle fine.

Any ideas?

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does it run better or worse with the air cleaner off? Try creating a lot of vacuum leak and see if it changes anything. Try jumpering the resistor to get full voltage spark.

If it runs fine with the air cleaner off and the vacuum lines open, then your mixture is off and fouling plugs. If it runs better with the resistor jumpered you have weak ignition.

When you turn the choke off make sure you push up on the nozzles, they tend to stick.

With old cars its likely a combination of things. Mine runs HORRIBLE with sooty plugs and will die.

You CAN clean up fouled plugs. Dont be silly and buy new plugs everytime a little bit of petrol splashes on them. Best way is a torch, burn off crud. You can also use sandpaper. I've even had success with carb cleaner and a rag wrapped around a thin screwdriver.

Edited by Z-Luke
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I cleaned the carbs with cleaner and reset the linkages. Seems to have helped some bit. A good amount of "brown" came out of them. No it'll hold idle fine, but I still get inconsistent idle rpm readings. At first it'll sit nicely at 700 rpm, but after driving it'll idle at 1000-1100. And then when I get into traffic it'll get back down to around 700-900 rpm.

Maybe I need to clean them some more.

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Sounds like a classic heat soak issue to me. No air moving though the engine bay at idle, means all the heat from the headers or manifold is possibly boiling the fuel in the float bowls. A header blanket or better heat shield may solve the issue.

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Sounds like a classic heat soak issue to me. No air moving though the engine bay at idle, means all the heat from the headers or manifold is possibly boiling the fuel in the float bowls. A header blanket or better heat shield may solve the issue.

It does have a heat shield (previous owner made it), but I'll try wrapping the header.

Thanks!

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