'74 Dodge V8 360 Engine dying at idle


#1

So it’s a carburetor. Starts up cold first thing in the morning no problem whatsoever. Choke plate nice and closed, idle screw on the highest step on the ladder, good vacuum, and all of that.

Once the engine warms up, and the choke plate slowly opens up to let more air in, idle and vacuum decrease, and when I hit the gas and idle screw drops down off to the lowest step, the engine dies.

Please help. Where should I start?


#2

Increase the basic idle until the engine runs without stalling. On the Carter 2bbl the idle screw faces forward on the driver’s side at the base of the carburetor. Turning the idle screw clockwise increases the rpm.

But wasn’t the idle problem taken care of a couple of weeks ago?


#3

I had this same problem happen w/my 70’s Ford truck, and it turned out to be a vacuum leak. In my case there’s a vacuum operated door in the intake air path which is supposed to allow warm air in during the first few minutes, then close and allow fresh cold air in after that. That device had sprung a vacuum leak. Once I fixed that, the problem was gone. Use one of those vacuum pump/guage things, and check all the vaccuum hoses and vacuum operated devices for leaks.

Edit: The problem wasn’t the door not working so much as that there was unmetered air getting into the intake manifold through the leaky diaphram in the device. It didn’t show up during warm up as the mixture is enriched then, but as soon as the choke allows the mixture returns to normal, the extra air creates a lean condition and the engine stumbles and stalls.


#4

First find and eliminate any vacuum leaks…Second, set the points and check the timing. Third, on the front of the carb facing forward, down near the bottom, are two idle mixture screws. open them both 1/4-1/2 turn…It should idle fine now…


#5

TL;DR - In reverse, with foot on the brake, the vacuum fluctuates. What does this mean, and does this help the diagnosis?

To Red Knox: No, I thought I had fixed the idle problem, but it was a temporary emergency, get home in one trip only and strictly sort of band-aid, involving tape. But I drove it repeatedly like that. Basically keeping the idle on the highest step of the fast idle cam. The same as if I had my foot on the gas pedal at all times, in park, neutral, reverse, drive, etc. It was bad bad bad and the worst thing I could have done and I regret it terribly. Because doing that is what did my motor mounts in. It got the job done, which was kept the car running without dying at idle or getting into gear, but it was a violent shift into gear. My most shameful mechanical experience, next to easy bake ovening my Gi-Joe. Get out of there Gi-Joe! Suzie’s baking up Communist Manifestos!

I could kiss you George from San Jose. That makes so much sense it hurts. I swear the car runs fine on cold start up first thing in the morning, but as soon as it warms up, and I hit the gas, it dies. I pathetically tried to look for a vacuum leak, spraying brake cleaner around vacuum hoses. One tri-section trio/tee of hoses seemed to affect the engine’s idle so I’ll be replacing those old hoses. But I mean, that’s just a shot in the dark. There’s more, something else, something bigger I’m sure.

Oh! Key discovery today that I think will help greatly. On cold start up, before the engine had fully warmed up, I put it into reverse. The entire engine shifted and I did not like that. Doing that so many times was what broke the motor mounts I literally spilled blood, sweat, and tears replacing. Took days and almost 20 hours. A combination of the most rusted out 40 year old bolts in the world, not having the right tools, the most insane angles, and my having the strength of a small girl, did me in. But with the help of a ridiculous cheater bar, a torch, a go-through ratchet, and some wrenches, when I finally got that last bolt off, I was exuberant.

But anyway, while I was in reverse, with my foot on the brake, with the vacuum gauge connected, the needle fluctuated. I don’t know the correct term, but I believe it was hunting or surging. Please tell me what this means. It did the same fluctuating at another time, I forget the exact conditions. Ah! It’ll come back to me eventually, but maybe that was enough information there already. And again, a violent shift into reverse. Shook the whole engine. Didn’t like that and I’m pretty sure it shouldn’t do that.

It makes so much sense what you’re saying. And thank you for that edit, because I was getting the impression that I had a faulty part- that it was that door you were talking about. But it’s almost always something basic isn’t it - pirate, un-metered air. Hard to find a vacuum leak by spraying carb cleaner or using smoke, because the radiator fan blows straight across everything. Any other tips? Nonetheless, I will try. Oh! I’ll try putting a hose onto my propane tank, and poking that around. And I could smoke the lines with the engine and fan off of course, lol. I thank you again.


#6

1974 Dodge WHAT?


#7

It’s a 19 feet 1974 Dodge Tioga GT RV. Built on a Dodge B300 Sportsman Van chassis. 5.9L.


#8

I recall that Mopar used metered orifice EGR ports in the intake under the carburetor of early 70s engines. It would be worthwhile to remove the carburetor and look directly down into the intake to see if either of the orifices have been blown out or burned out.


#9

I have no idea what that is or what it looks like or what it even remotely does. Something with reducing NOx emissions? And I know there are certain symptoms that can point to a clogged up EGR valve or something rather. But doesn’t this just seem like a vacuum leak/pirate air situation, as simple as that may be? Because I have been down that road of throwing every other known random part at a problem, and I know where that road ends, and I do not want to go back down that horrible place. I am ready and willing to put on a brand up carburetor on that thing though, heh, but if it’s a vacuum leak, that probably won’t help. But again, I know nothing about carburetors.


#10

If the EGR ports are blown they are a vacuum leak. If you remove the carburetor and look into the intake it will be somewhat obvious if either of the ports is damaged. They are just small metered orifices that are in the floor of the intake where they allow exhaust to be drawn from the crossover.


#11

Interesting. I think I’ll take my carb and take a look at that. I gotta remember that I could possibly have an exhaust leak as well. There are yards of exhaust tape over a pipe down there. I don’t even want to know. We’ll see how it goes.

Something awesome I found. Homemade smoke machine to find vacuum leaks: http://www.thesamba.com/vw/forum/viewtopic.php?t=461116

Put a rag on fire, put it in the can, connected the compressed air line to it, and viola. Amazing. Except I don’t have an air compressor. Neighbors do though. Hmm…


#12

Surging is a common symptom of unmetered air getting into the intake manifold. Another cause of surging is that the idle speed has been adjusted (using the idle speed screw or the mixture screws) to fix some other problem, which shouldn’t be fixed that way. In other words if the intake manifold gasket it leaking, don’t fix the problem by adjuting the mixture screws, fix the gasket instead.

Finding a vacuum leak is pretty straightforward if it is occuring in the vacuum controlled devices. It takes some time, but finding what is leaking is really pretty simple. Absolutely no air is supposed to get into the intake manifold through the vacuum lines. The intake manifold supplies the vacuum, but no air should flow. Like if you block off one end of a straw with your finger, then suck on it, you create a vacuum force you can feel pulling on your finger, but no air flows through the straw. If the vacuum system is working properly, that is what should be happening. A force is created, but no air flows.

So if you hook a hand-held vacuum pump up to the vacuum line (or lines) where the intake manifold normally supplies the vacuum to the entire set of vacuum controlled devices, and pump it up (down actually), it should hold vacuum at that negative pressure for several minutes or more. If it doesn’t, if the guage returns toward 0, then you know you have a leak. All you have to do then is use the same technique to find, one by one, which device is leaking.

There may be a few vacuum devices which are on the other side of a thermally controlled vacuum switch. The above method won’t find leaks in these devices, as the engine has to be at operating temp before the vacuum switch opens and vacuum is applied to them. On those, you have to test each one individually.

Also, if you poke around you’ll probably find another source of vacuum coming before the throttle plate. That port controls vacuum operated devices which are supposed to activate during rapid acceleration only. Those devices could leak too, and should be tested separately, as above.

Leaks around gaskets, like the intake manifold gasket, I don’t have much experience w/diagnosing those kind of leaks, but experts here, and you seem to know about this too, say spraying starter fluid in the area of suspicious gaskets can aid in the diagnosis of these kinds of leaks. I guess the idea is that the starter fluid will be sucked into the intake manifold if there is a leak, and the engine will briefly idle better.

Best of luck.


#13

An abrupt dying at idle on a carbureted engine could be a vacuum leak as mentioned or possibly an idle circuit plugged up in the carburetor.

Sometimes the latter can be fixed by removing idle mixture screws, spraying a healthy shot of aerosol carb cleaner into the holes, and then hitting it with compressed air.


#14

So I took off the carburetor and found a massive hole on top of the engine, right on the edge of the left valve cover. Could that have caused a vacuum leak? I cut out a thin piece of aluminum can, placed it over the hole, cover it with a copious amount of exhaust sealant, and then torched it. It hardened.

Pictures: http://imgur.com/a/AP6ZU
Spark plugs, just to satisfy curiosity: http://i.imgur.com/DTc41QC.jpg

I took off the carburetor and sprayed carburetor cleaner in every single passage and oriface. Put a wire through the two mixture screws in the back a bit.

I reconnected the carburetor, and now the engine won’t start. It would start on cold start with a cold engine every single time before. Gas was leaking out of one of the fuel lines. I replaced that line, and it stopped leaking, but seemed like it was stopped up. It hadn’t done that before. I sprayed carburetor cleaner in the choke while cranking, and the engine would start and die. I had just replaced the spark plugs as well, and the old spark plugs looked like death. Never seen such horrible spark plugs. But because the carb cleaner started the engine, I knew the problem was a fuel issue.

A neighbor came up to me and told me that I needed to reset the floats or something. Also the throttle pedal and linkage aren’t working like they were before. No spring - it’s not bouncing back. I have to manually hold and move it. I may have forgotten to reattach a spring! I will check tomorrow.

I’m at a complete loss.

Is this getting close?: http://www.vintagemusclecarparts.com/pages/needleandseat1.html

Before, I would hit the gas pedal, and gas would come out of the two cattle prods in the carburetor, but after taking the carb out, cleaning it, and putting it back in, well now the gas pedal isn’t working properly like I already mentioned, and gas doesn’t come out of the cattle prods like before.

Also worth noting, I took off about five screws from off the top of the carburetor, thought, “Yeah… I probably shouldn’t be doing this.” and then put them back in.


#15

For a TL;DR short summary of the previous post just above this one: I think I found a large vacuum leak that I think I fixed. But in taking off and messing with the carburetor, now the engine won’t start. A neighbor told me that I had to set the float or something? The carburetor is not getting fuel like before, and fuel is not coming out of the boosters when I hit the gas pedal.


#16

weeell, I ve been rooting for you man. is taking the truck to a mechanic an option?


#17

Oh, what’s the fun in that. I live for the struggle and pain and heartbreak, because it makes the victory that much more sweeter. If our life here on earth is hell, and marred with unspeakable trauma and pain, it’ll make heaven that much more beautiful. No one enjoys freedom more than a man that’s been imprisoned. And my, how we take it for granted. I can get in my car, (well, not this one) and drive anywhere I want. I have hands and feet and vision to see beautiful things and ears to hear unspeakably beautiful music. Life is a gift that we squander on senseless and worthless things. There is no greater joy than in helping others.

Well I don’t know where that came from. Uhhh, anyway, I found this fantastic post from a classic Mustang forum:

“Take a small amount of gas and pour it down the air tube. It will travel to the front fuel bowl and if its only been 6 months since you have run the car it won’t take too much to return to normal operation. You should look at the accelerator pump and make sure its not leaking gas as sometimes the diaphrams will shrink and leak gas onto the manifold. “FIre hazzard” So be careful when starting a motor and don’t let the leaking gas get to a spark. Make sure you place your air cleaner lid back on before cranking the motor in case of backfire. Keep a extinguisher close by also. If the power valve is blown you will notice the motor will idle low and when you try and rev it up it wll run wild and not idle. My guess the inlet valve in your carb is stuck holding the front float bowl up closing the fuel off from comming in. Once you have fuel back in the bowl it will probably loosen the gum from the valve. Wouldn’t hurt to spray a little carb cleaner down the air tube where you prime it also. Let the car run at idle at first so the fuel will catch up to normal pressure. In past times I have found a dry rotten hose that connects the tank to the line near the axle housing allowing air in to the line preventing pressure and gas flow. Check this before you go to the trouble of priming the carb. It may be all thats wrong. Not enough pressure to maintain flow.”

I think I need to prime the carburetor, like a lawnmower, lol. How? I plan on pouring gas all over the carburetor. I will have a fire extinguisher ready, lol. No but seriously, I ought to find the proper way to do this.

I think this may be it:

"parts you’ll need :

1] large empty bottle with a squeeze tube end like a gear oil bottle

2] fuel line or surgical tubing the same size as the fuel bowl vents , probably 1-1/2 foot of length is all that’s needed

procedure :

locate and remove fuel bowl sight plugs and set them aside

locate primary and or secondary fuel bowl vent tubes

install tubing over either of the two vent tubes

pour fuel into clean and empty gear oil bottle and re-install squeeze bottle top

next attach tubing onto the tip of the bottle and squeeze the bottle allowing fuel to enter the bowls

continue filling bowls until fuel begins to come out of sight plugs

re-install sight plug and gasket and repeat procedure for the other fuel bowl"

I still don’t know where to add the fuel. Here’s a picture of my carburetor:


#18

Unless you opened the carburetor and altered the float setting leave it alone for now. The burned out hole is in the intake manifold at the exhaust crossover. It would appear that your manifold is shot. You need to remove the intake and inspect it closely top and bottom. The manifold was leaking hot exhaust under the carburetor and heating the fuel in the bowl and at the same time dumping exhaust into the intake. You must drain all the coolant before loosening any intake bolts. Post photos of the intake when it is off and cleaned.


#19

Red Knox, I want to you thank you. Are you saying that I think you’re saying? That I’m going to need to replace the intake manifold? Lol, awesome. Scared but at the same time excited and eager to do it. Should be fun. So I’ll try and remove it and take pictures and report back.

I don’t quite understand the manifold leaking hot exhaust under the carburetor and heating the fuel in the bowl, but can I just say, no wonder my fuel economy has been amazing with the heated gasoline molecules! Lol jk. (Reference: 100+mpg carburetors: http://www.abovetopsecret.com/forum/thread802712/pg1)

So I suppose there’s probably more holes in the intake manifold possibly, causing the vacuum leaks that are causing my engine to die at idle? That’s my guess so far.

Oh, I was able to get the engine started again! I sprayed some carb cleaner down what I think is the vent hole, and when I went to KOEO, the electric fuel pump started going, and I could hear the carburetor filling up. Best sound ever. Then it fired right up! It was awesome. Maybe something was lodged and got loose and finally the fuel was able to fill up the carburetor, I don’t know.

So maybe that was the pirate air getting in? Excess exhaust gases getting into the intake? Thus, too much air, and dying at idle?


#20

Under all that dirt in your photo I think you have found the vented area for the cross-over. Plugging this vent will serve no benefit.

I the photo below look at the horse shoe shaped opening above the cross-over passage, note that it is above the gasket. Disregard the arrows, I found this photo in a search.