Idle speed?

Jeff

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What should I set the high and low idle speeds to on a 1970 383 with an Edelbrock 1406 and an automatic transmission? This is the 4 barrel version of the 383. The manual has several idle speed specs, depending on what carb was on the car (i.e. 700/1700 and 750/1800). That made me think it was wholly dependent on the carb, but the Edelbrock 1406 manual does not have idle speed specs, which now leads me to think it depends on numerous factors.

This car sat for years and I am just trying to get it running decent. It has very low power at the moment (or a bad transmission). After reading up, it seems like setting idle speed is the first step in a lot of things.

Thx!
 
What should I set the high and low idle speeds to on a 1970 383 with an Edelbrock 1406 and an automatic transmission? This is the 4 barrel version of the 383. The manual has several idle speed specs, depending on what carb was on the car (i.e. 700/1700 and 750/1800). That made me think it was wholly dependent on the carb, but the Edelbrock 1406 manual does not have idle speed specs, which now leads me to think it depends on numerous factors.

This car sat for years and I am just trying to get it running decent. It has very low power at the moment (or a bad transmission). After reading up, it seems like setting idle speed is the first step in a lot of things.

Thx!


Either 700 of 750 RPM should work fine.

In checking for low power, start with checking the timing to be sure that it is accurately set. Then check the vacuum advance. You can do this by unhooking the vacuum lead to the distributor. The engine should slow down and then speed back up when the lead is re-attached. Next check the mechanical advance. Do this by unhooking the vacuum advance, attach a timing light and moderately rev up the engine, the timing should advance as the engine RPMs increase, if it does not, the mechanical advance is stuck and will have to be freed up. This happens frequently on cars that sit a lot. Was the timing jumping around a lot at steady RPMs? This could mean that the timing chain is bad and needs to be replaced. Next check the air cleaner to be sure that some critter has not built a nest and clogged it up. Check for obvious engine misfire issues such as a corroded distributor cap or points. Clean as required. Fouled plugs will also cause a misfire condition which will result in a loss of power. Old degraded fuel will also cause performance issues.
Another thing that happens on cars that sit around is that sometimes a bad master cylinder will trash a brake booster resulting in a large vacuum leak. Try blocking off the brake booster and see if the engine runs better with it unhooked. If it does, most likely the booster has an internal leak. Also check the PCV valve to be sure it is not stuck open.

The transmission is difficult to diagnose with a poorly running engine. Check for slippage and burnt foul smelling fluid. If appropriate, do a fluid change and a band adjustment with a filter change. Note if the transmission pan and filter are full of debris, the transmission is shot. If the transmission is ok, the band adjustment and fluid/filter change should take care of its issue if there is one.

Dave
 
lo idle, set as low as possible without the car dying. should be 700- ish could be as low as 650 ish and as high as 750ish.

try not to die -

- saylor
 
This is fantastic info! I needed a road map like that. Thanks!!
 
I set the idle at about 750 and adjusted the idle mixture screws. I then checked the timing at idle. It was advanced about 10 degrees. I set it to about 2.5 per the manual with the vacuum line disconnected. There is a little bit of jumping around on the timing mark at idle. It seems to be missing a bit. I forgot to check the vacuum advance, and it was too late to road test for improvement. I'll do that this weekend and proceed with the other things. I drained the old fuel and added fresh non-ethanol gas before I ever started messing with it.
 
I set the idle at about 750 and adjusted the idle mixture screws. I then checked the timing at idle. It was advanced about 10 degrees. I set it to about 2.5 per the manual with the vacuum line disconnected. There is a little bit of jumping around on the timing mark at idle. It seems to be missing a bit. I forgot to check the vacuum advance, and it was too late to road test for improvement. I'll do that this weekend and proceed with the other things. I drained the old fuel and added fresh non-ethanol gas before I ever started messing with it.

You can do a more complete check on the timing chain by doing the following:

1.) Jack up the car so you can get under it
2.) Remove the distributor cap
3.) Put a socket and breaker bar on the big nut that holds the Harmonic balancer on
4.) Have a helper rotate the crankshaft until the engine is at top dead center
5.) Now rotate the crankshaft back and forth, if there is more than 10-12 degrees of free play before the distributor shaft starts to move, the timing chain is shot and needs to be replaced.

Note that the 2.5 degrees of advance setting was an emission setting that did little for best performance. You can safely advance the timing another 4 to 5 degrees for best overall performance. If your engine pings under load, back off the timing a couple of degrees.

Note that a lot of cars that have been sitting for a long time also had something wrong with them which is why they were parked in the first place. Most Mopar timing chains are out of spec by the time the car has 80k to 120k on it use this as a guide for proceeding further on your chain. You might also want to run a compression check on all cylinders, if they are all showing low compression, that is a good indicator that the cam timing is retarded due to a loose timing chain.

Dave
 
The vacuum advance works. Have to put further tuning on hold until I fix an exhaust leak. I'm huffing too much CO, even with rear of the car out of the garage and fans on.
 
Still working on the exhaust leak so I can't tune under the hood, but I took it for a couple of short drives today and got a little more info. The engine was cutting out under load (going up a hill). It didn't die completely but cut out repeatedly. Maybe that is the mechanical advance? I barely made it up the hill. On the second short drive, a fairly loud whirring noise began soon after we started. It sounded like it was coming from deep inside the dash or in the transmission area. It varied by RPM but was otherwise constant. This happened once before on a test drive. This time the car was fully warmed up. The first time it happened the car was not fully warmed up.
 
Still working on the exhaust leak so I can't tune under the hood, but I took it for a couple of short drives today and got a little more info. The engine was cutting out under load (going up a hill). It didn't die completely but cut out repeatedly. Maybe that is the mechanical advance? I barely made it up the hill. On the second short drive, a fairly loud whirring noise began soon after we started. It sounded like it was coming from deep inside the dash or in the transmission area. It varied by RPM but was otherwise constant. This happened once before on a test drive. This time the car was fully warmed up. The first time it happened the car was not fully warmed up.

Would suggest the obvious stuff. An engine can miss under load for several reasons, weak spark is the most common. Check your points , cap and rotor for corrosion and clean or replace as needed. Be sure the points have the proper gap and that the plugs are clean and properly gaped. Next check the fuel filter to be sure that it is not clogged with crud as fuel starvation can also cause the engine to miss under load. Check all of the above to see if that solves your problem. The loud whirring noise could be a lot of things, check your alternator for bearing noise, remove the belt and spin the alternator by hand to see if it has bearing noise, do the same with the water pump. Check the fluid level in the power steering pump, if it is low, it can make a lot of interesting noises.

Dave
 
I was going to replace my fuel filter so I took a close look at my fuel line routing today. I think it is a mess. See picture below. I already know that the electric fuel pump should be relocated to near the tank and plan to do that. When I do, should I replace some of this hose with steel lines so it is more like the stock setup? It looks like the fuel filter was originally under the alternator and hard to get to. For now, is it OK to just replace the filter or this setup glaringly unsafe? I also noticed that the original fuel pump is still in place. Is that SOP when putting in an electric pump?

2017-09-10 12.07.45e.jpg
 
I was going to replace my fuel filter so I took a close look at my fuel line routing today. I think it is a mess. See picture below. I already know that the electric fuel pump should be relocated to near the tank and plan to do that. When I do, should I replace some of this hose with steel lines so it is more like the stock setup? It looks like the fuel filter was originally under the alternator and hard to get to. For now, is it OK to just replace the filter or this setup glaringly unsafe? I also noticed that the original fuel pump is still in place. Is that SOP when putting in an electric pump?

View attachment 142476


I can't really tell what type of electric fuel pump you are running from the photo. Most electric fuel pumps are the bellows type which do not live very long when mounted that far from the tank, the bellows is designed to push fuel not pull it. This far from the tank the bellows will rupture and the pump will be dead. The normal location for the fuel filter was behind the alternator which made it a pain to service. You fuel line routing should be fine as long as the extra length is not causing vapor locking problems. The stock fuel pump should have been removed when the electric one was installed along with its operating rod and the hole covered with a delete plate. This was what they call a quick and dirty fix to get the car running. The edelbrock carb that you are running would be more than adequately supplied with fuel by a stock fuel pump and that is what I would suggest you revert to. The are usually more reliable than the electric ones. If that is what you decide to do, try to find a Mopar, AC Delco or TRW fuel pump as they are still USA made and hold up a lot better than the after-market Chinese knockoffs. Also check to be sure some idiot did not draw power for the fuel pump from the coil circuit. That is a resistance circuit and it would be overloaded by the addition of an electric fuel pump, not to mention the fact that the fuel pump would not be getting full voltage to operate properly and the overload condition would produce low voltage to the coil and cause misfire problems.

Dave
 
The edelbrock carb that you are running would be more than adequately supplied with fuel by a stock fuel pump and that is what I would suggest you revert to.
I really like that suggestion and will do it. The electric fuel pump is powered by a wire going to an accessory section of the fuse box.
 
Replaced air and fuel filters and checked spark plug wires to cap and plug connections. All looked good but one that had white powdery corrosion at wire/cap connection. That one seemed loose at plug too. Cleaned it up. Looked under cap and was nice and clean but didn't pull rotor or check points.
Tried to drive to exhaust shop today for exhaust leak but had to abandon trip. It goes fine, but sluggish for about a mile and then starts sputtering and dies and won't restart for 10-15 mins. First die was around a corner so thought carb. Second die was on small hill at 30 mph. Current one was smaller hill at about 30. Hopefully can make it home on next restart. Cursing hills around here.
 
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Replaced air and fuel filters and spark plug wires to cap and plug connections. All looked good but one that had white powdery corrosion at wire/cap connection. That one seemed loose at plug too. Cleaned it up. Looked under cap and was nice and clean but didn't pull rotor or check points.
Tried to drive to exhaust shop today for exhaust leak but had to abandon trip. It goes fine, but sluggish for about a mile and then starts sputtering and dies and won't restart for 10-15 mins. First die was around a corner so thought carb. Second die was on small hill at 30 mph. Current one was smaller hill at about 30. Hopefully can make it home on next restart. Cursing hills around here.

It sounds like your engine is starving for fuel. If you have a fuel pressure, check your pump output by disconnecting the fuel line. Put the disconnected fuel line into a capture container, it should spew lots of fuel. If you have not yet changed the fuel pump, I suspect that it is probably failing. Any distributor cap that has white corrosion on the plug sockets should be replaced.

Dave
 
Sounds like fuel issue. I know people swear by electric fuel pumps but I am one who swears at electric fuel pumps. You my just have crud or pin holes in pick up in tank.
My suggestion would be to get rid of electric fuel pump and put it back on reliable diapham mechanical but that's your call.
 
I'm absolutely going to do that. I found a good source yesterday. I pumped out old fuel with current pump when first got car, but will test again. Still stuck, still cursing, but thanks for the quick responses.
 
I'm absolutely going to do that. I found a good source yesterday. I pumped out old fuel with current pump when first got car, but will test again. Still stuck, still cursing, but thanks for the quick responses.
I would pull pick up/sending unit out to have a look then work forward.
 
I made it another mile! Now the car is just a couple blocks from home and I am typing on the home computer. This time it just died going straight on pretty flat ground. It does sound like it is running out of fuel. It seems like through the restart attempts I am getting fuel into the carb so it eventually starts and runs for a short time, and then the pump can't keep up or something else causes the fuel to cut out. It's parked in a better place and I think I can get it home on the next restart so I'm not swearing as much now. My wife has been a champ this morning, following me around all over hell and back. She only told me to sell the damn thing once.
 
Get some starting fluid, when it dies spray some in and see if it restarts then you know for sure fuel issue.
 
If not done already, check the short piece of fuel line AT the tank. If the car's that old, it might well have the original hose on it, which was well prior to ethanol-blend fuel. Just normal age issues, plus the ethanol'd fuel might have caused a delamination of the inner layer of rubber, in the wrong direction of fuel flow.

Idle speed? Somewhere around 650 with the a/c running. Key test is to get a smooth engagement into "D" from "N". "R" will always be a little firmer engagement as the line pressure doesn't have an "accumulator" in that fluid circuit in the valve body, as the "D" circuits do. Or is it higher line pressure by itself? One of the two.

Going into gear, it should just happen smoothly with no jerks or roughness.

Timing? The factory spec is 2.5 degrees BTDC for an idle emissions reason, but the total advance at that setting is still what it used to be, on the original distributor. On my '66 Newport (closed chamber factory heads), the setting was 12.5 degrees, but the same total advance (initial and total centrifugal in the distributor). I could set the idle speed by advancing the distributor, but not on my '70 Monaco 383 4bbl (open chamber heads). From the stock setting, more advance didn't change idle speed very much at all. Once you get it running reliably and can drive it a ways, then you can advance the timing to the point you get trace rattle on mild acceleration, then tick it back a degree or two. In theory, IF the engine is an original 4bbl motor (check VIN digit), then you can probably expect to use at least "mid-grade" or "premium" octane fuels, but this can be variable.

Some like electric fuel pumps and they have their place, but the factory pumps on Chryslers worked fine. The fuel filter DID mount between a short piece of fuel pipe coming out of the fuel pump, then the filter was pretty vertical, then a metal line went to the carb from there. At least with earlier fuels, it worked pretty good.

With an electric pump, you need ONLY the stock fuel pressure pump (5.5psi or so) to not overpower the needle and seat in the carb and not have any pressure issues with the normal rubber fuel lines.

As the vehicle has been sitting for a good while, you will probably need to remove the tank for a good rinse and check for rust. Might be necessary to add a fuel filter prior to the pump to catch any rust particles before they get to the fuel pump, plus the filter between the pump and engine. At least until you're confident the lines are all clean and such. A marine fuel filter, with different fittings on the end, can be found at WalMart, for example. A clear center section with a mesh filter element that can be disassembled and cleaned, if needed.

CBODY67
 
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