Idle gets slower and slower . . .

[darth_linux]

The idle on my 66 Newport 383/2v gets slower and slower until it stalls. What do you think could cause this issue? Car ran fine when parked for the winter in November. Fuel in the tank and carb is non-ethanol 91 octane. Started it back up after sitting for three months, and now it doesn't really want to stay running.

thanks!

 

[Stoffauge]

I do have the same problem with my 383/4BBL . Even with hitting the gas its gets slower after some seconds until it stalls..... 95 Octane 5% Ethanol

 

[Boydsdodge]

Is this happening with engine fully warmed up?

 

[darth_linux]

Is this happening with engine fully warmed up?

No, it’s happening about half warmed up, choke partially open.

 

[MoPar~Man]

A vacuum is being created in your gas tank. Check for proper gas tank venting. Or maybe vapor lock happening between the fuel pump and carb (but it's winter so prob. not).

 

[Sixpactogo]

My first thought was fuel filter or sock in the tank mostly plugged up.

 

[david hill]

As MoPar~Man stated improper vented tank can cause your problem. A little Dirty Harry trick, loosen you gas cap and retry. Also look for collapsed rubber hoses between the fuel tank w/ it running.

 

[CBODY67]

Something like that was an issue on another car I have. With the engine running at idle, the speed would start to drop, as engine smoothness did not change. I could blip the throttle to get the speed back and it would be fine. New plugs, points, wires (which were all changed after I got it) did not help. Then it would do it running down the Interstate! Then, only with wild accel pedal pumping would it restart. I put a new fuel pump on it and it suddenly ran and sounded better than it ever had. This was on an engine which did not use a fuel pump pushrod.

A side issue might be alternator output, so clean the battery terminals and the posts, for good measure.

When the engine dies, how hard is it to re-start?

If this happens in the warm-up stage of things, what about choke plate hanging on the airhorn? Is the choke pull-off diaphram working and holding vacuum?

Just some thoughts,
CBODY67

 

[darth_linux]

My first thought was fuel filter or sock in the tank mostly plugged up.

The tank filter is brand new, but the filter at the pump is maybe a year or two old. I’ll look at replacing that.

 

[darth_linux]

Something like that was an issue on another car I have. With the engine running at idle, the speed would start to drop, as engine smoothness did not change. I could blip the throttle to get the speed back and it would be fine. New plugs, points, wires (which were all changed after I got it) did not help. Then it would do it running down the Interstate! Then, only with wild accel pedal pumping would it restart. I put a new fuel pump on it and it suddenly ran and sounded better than it ever had. This was on an engine which did not use a fuel pump pushrod.

A side issue might be alternator output, so clean the battery terminals and the posts, for good measure.

When the engine dies, how hard is it to re-start?

If this happens in the warm-up stage of things, what about choke plate hanging on the airhorn? Is the choke pull-off diaphram working and holding vacuum?

Just some thoughts,
CBODY67

The engine restarts easily. I’ll double check the battery terminals and take the air cleaner off so I can observe the choke plate during the warm-up process, as well as the choke pull-off diaphragm. Thanks for the tips.

 

[Big_John]

The idle on my 66 Newport 383/2v gets slower and slower until it stalls. What do you think could cause this issue? Car ran fine when parked for the winter in November. Fuel in the tank and carb is non-ethanol 91 octane. Started it back up after sitting for three months, and now it doesn't really want to stay running.

thanks!

Everybody is throwing out possible causes and not looking at what's going on.

The car has been sitting... Yea, 3 months isn't long, but it is older gas.

Next, it's when the choke is coming off and if it's working right, the idle speed is supposed to decrease as the choke opens. Doing a quick check, it looks like you are in the high 30's for temperature. Chances are really good that you haven't driven the car in that weather so the first thing I would wonder if the choke is set correctly... If the choke is right, maybe the idle is a little low.

Since the car apparently was OK when you parked it, if it were me, I wouldn't worry too much about it. Maybe... Maybe, give the idle screw (the one that rides on the choke cam) a little twist to up the idle and see what happens. Then see what it does when the warmer weather comes. Drive it a little, get some fresh gas etc.

 

[413]

Go and drive the car, put some miles on it. Get it warm from driving, not idling. Run some fuel out, get some fresh fuel

 

[PurpleBeeper]

The idle on my 66 Newport 383/2v gets slower and slower until it stalls. What do you think could cause this issue? Car ran fine when parked for the winter in November. Fuel in the tank and carb is non-ethanol 91 octane. Started it back up after sitting for three months, and now it doesn't really want to stay running.

thanks!

Change the gas completely and put in a new fuel filter. Maybe look at the vacuum line on the distributor advance? Spray some carbuetor cleaner down the air bleeds of the carburetor (500 cfm Holley, right?) I'd start by changing the old gas. Even with stabilizers, it doesn't stay good nearly as long as people think

 

[MoPar~Man]

This is why I'm putting a drain plug in the new tank I just got from Van's tank sale. At the first hint of trouble, it's always "drain the old gas out" which is easier said than done. For those of us that have cars sitting for a few months or more at a time, being able to drain the tank just makes more sense than filling the tank and adding stabilizer (which is the general advice).

 

[darth_linux]

A vacuum is being created in your gas tank. Check for proper gas tank venting. Or maybe vapor lock happening between the fuel pump and carb (but it's winter so prob. not).

I removed the fuel filler cap while this was happening with no change, so I don't believe it to be a vacuum or vapor lock issue. Thanks for the tip.

 

[darth_linux]

Adding a little info to this thread just "for the record" in case someone else experiences this problem.

I pulled the plugs to give them a quick read and they were very black and sooty. I gave them a good clean with a wire brush and brake cleaner and reinstalled them.

I then pulled the air cleaner off, gave the choke plate shaft and throttle plate shaft a nice spritz of carb cleaner just to ensure there wasn't any gum/varnish making things stick. There didn't seem to be any . . . I also sprayed down the heat riser linkage and throttle linkages.

Leaving the air cleaner off, I checked operation of the choke plate. It was smooth but there is a point in travel where it's a bit tight or "springy" - I don't remember if it was like this after I rebuilt the carb last year, but it seems to be "normal" and part of how it actuates when you depress the gas pedal to the floor in order to engage the choke. Experts, please feel free to correct me if I'm wrong.

I then started the engine, and choke plate was fully closed. Upon start up, the choke pull-off opened the choke plate slightly, as expected. The engine began to warm up, running with what I think is that characteristic "lope" of a cold big block running on the choke. As it ran, it started to slow a bit. I'm not show if the choke plate is opening properly yet, so I gave the throttle a little blip, and the high-idle cam seemed to move from the high setting to the middle setting. The idle sped up again as the engine got more air. After a short time it started to slow again, so I blipped the throttle again and this time it went to the lowest cam, I think it was on just the regular idle screw at this point. The idle seemed a bit low, so I held the throttle open slightly and that helped, so I screwed the idle screw in about an 1/8th of a turn.

I think the real issue is just the fact that instead of getting a proper warm up with the carburetor linkages getting a normal workout from driving, the car is just sitting in the driveway, idling. So, that being said, I'm going to just go drive the car for 40 or 50 miles and put it through it's paces. I did take it to the gas station and put 20 gallons of ethanol free 91 octane in the tank, so a long drive will certainly burn off any of the gas that was put in the tank back in October. (I can't see how gas could be too bad after just 3 months.)

Anyway, to summarize, there might be a slight issue with the choke operation causing the car to run rich, but I think it's just a matter of it being a bit tight and sticky after sitting for three months, and a good long drive should get things back to the way they were.

 

[MoPar~Man]

Is there a thermostat mounted on the intake manifold on the passenger side beside the carb? In a pocket in the manifold? With a rod coming from it up to the carb? If so, then it needs to be adjusted. It's moving the high-speed cam to a slower speed before it should. There's a way to adjust the rotation of the bimetalic coil (the coil is the thermostat).

 

[darth_linux]

Is there a thermostat mounted on the intake manifold on the passenger side beside the carb? In a pocket in the manifold? With a rod coming from it up to the carb? If so, then it needs to be adjusted. It's moving the high-speed cam to a slower speed before it should. There's a way to adjust the rotation of the bimetalic coil (the coil is the thermostat).

I’ll check out the adjustment, thanks.