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rough idle

Steve, I didn't see anything that says single or dual plane? How far out are your idle mixture screws out?
 
cryplydog said:
Steve, I didn't see anything that says single or dual plane? How far out are your idle mixture screws out?
Click to expand...
I appreciate your help and im sorry it took so long to reply. Mom-in law is in the final days of her 94 and a half life. She is home with hospice and ive been running back and forth . Anyway having said that, im almost positive my intake is dual plane. The cam # is CL 21-223-4
Im suspect of the heads. These heads were rebuilt and off my old motor which had no millage. I wasn't happy with the lower end and so I had the original block rebuilt and the engine reassembled
When I had the heads rebuilt, I discovered one had a crack, the rebuilder located a good head and redid that one for me.
I don't know if they are mismatched or whatever and I need to check that.
The engine runs strong with no hesitation. I still have to take it out as I made those changes to the carb as it was running so rich it bothered my eyes when I was stoped at a light.
My complaint is rough idle and the RPM wasn't steady. It is running better now with decent vacuum and when I checked last the vac gauge needed was almost rock steady, just a very slight movement.
The roughness does not seem like a cam lope, something is off. Im getting a new compression gauge today and check that is next on my list, as soon as time allows--------thanks
 
steve from staten island said:
Im having a hard time getting my recently rebuilt 383 running properly. It idles rough, it does not hesitate. It was running way to rich and I finally had to install different jets and metering rods as per the tech support from Edelbrock.
The carb is a 1406 on a Weiand manifold. I have a Comp cam duration 268/280 Lift .477/48o.
I have a Firecore distributor. Im running about 34 degrees total advance.
A vacum gauge showed 14 inches and was vibrating slightly.
I was running Champion RJ12YC plugs, they were all black fouled and I installed Autolite 85
After I installed smaller jets and metering rods and readjusted the carb, the vacuum is now around 15-16 and the needle is steady.
However I feel it still is running to rough and it does not seem like a cam lope.
The heads were stock and the engine was originally a 2 barrel
Im thinking of doing a compression check. I have a compression gauge, the type that the gauge comes off and just the hose for easier use but im having great difficulty getting the hose started due to limited space, what do some of you use?
Any thoughts are appreciated, thanks
Click to expand...

What fuel pump and what is the running pressure?
 
steve from staten island said:
Stock pump,last I checked it was around 5 psi
Click to expand...

Gotcha. Probably not blowing fuel through the inlet seat. I've had a similar issue with a relatively new 1405 which went rich for no reason after sitting a bit.

Do the idle adjustment screws have an affect on the idle quality? If you turn one all in does it stumble and stall? All out, same thing? Mine did. Pulled out the pass side which did nothing and blew the passage out with compressed air and cleared some muck.

Also check to see how much your throttle plates are open at idle. If they are cracked too much you will be off the idle circuit and could be pulling in too much fuel.

Metering rods should be down at idle too. You can open the rod covers near the air horn and move it aside and screw down to watch them. Blip the throttle and they should pop up and back down.

Easy enough to pop the top and check float levels and for trash on the seat.
 
Is the electric choke properly adjusted/fully open when warmed up?
 
Steve , have you taken a propane torch (unlit of course) and directed the gas along top of intake where it meets the head, and around carb base to see if for some weird reason you have a hairline crack in the intake, or a leaky gasket?
I hate to see you rip into all kinds of things, only later to find out you had a near invisible air leak which was causing your problems all along not sure if you have power brakes, you may have a slight internal leak in booster. Just a couple of thoughts.
 
I spent quite a bit of time with my car today. Driving it around on a few errands, coming home and tweaking, back out for other errands, and back home for some tweaking. Focused on timing, idle mixture, and idle speed.
Vacuum is 15-16 inches at 900RPM idle with timing at 15BTDC. The guage does have some bounce, but it is a mild dip. I pulled each plug wire and do not find a dead cylinder. I just now pulled 7 spark plugs (all but number 6) and they are almost perfect on the brown side of black. No wet plugs.
I also filled up the car and still getting about 13.5MPG.
I think the rough idle is more cam related then anything else. This car has excellent power and overall runs better than any other B Body I have owned. It will chirp the tires in 1-2 shifts and I did a few brief blasts to 90MPH today and no smoke trails out the tailpipe. It's a bit long on cranking for hot re-starts, but otherwise starts easily cold, or warm.
One item to consider is I own a Grand Marquis. That 4.6l V8 is so silky smooth, so when I go from that car to my Road Runner I notice idle smoothness immediately.
Anyhow, if you have some updates on your end let us know what you found.
 
As someone mentioned earlier, how much of the transfer slot is showing? I set mine at a square and then adjust the timing to get that smooth idle.
Or you have a vacuum leak. Is the carb on snug? I was once messing with mine and I got distracted and put it on finger tight?
Good luck
 
IF too much of the idle transfer slots are exposed to manifold vacuum, due to idle speed set too high, they will feed fuel, rendering the idle mixture screws in effective, even in the almost closed position. The high idle speed can be related to the cam profile or a vacuum leak. IF reducing the idle speed does not correct the issue, you MAY need to drill 2 small holes (one in each primary butterfly valves) directly adjacent to the transfer slots, half the distance between the edge of the butterfly disc and the shaft. Perhaps starting at 3/32" diameter. This will allow the butterfly valve to close further negating (or reducing) the influence of the the transfer slots, allowing the mixture screws to control idle quality. Just my opinion of course.
BOB RENTON
 
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