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rough idle

steve from staten island

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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
 
I think you are on the right track. You should be able to get the hose on each cylinder.
You likely know this but as a reminder remove all the plugs.
Throttle wide open crank til you see about 4 needle bounces on the gauge.
Another idea would be to get a set of heavy rubber gloves and do the old pull one plug wire at a time and note how the idle changes.
Assuming you did a "proper" cam break in and had oil with zinc?
Let's hope you didn't lose a cam lobe.
What was done on the heads?
 
Did you pull the autolites to see how they look since rejetting and adjusting? Just curious. Hopefully they are the correct heat range for your setup.
 
Thanks Don. I have a snap on cylinder shorting meter. Every cylinder I short out the RPM drops so I do feel its running on all cylinders.
I used the break in oil that the rebuilder told me to and yes it had the zinc.
Now the breaking in of the cam was a concern. I did exactly as told but the car stalled after around 15 minutes of running. I have no valve train noise, no hesitation or hoping through carb
 
You could try some 14's or what I did was go with NGK iridium. Runs very smooth with those so far.
 
What is your idle speed?
Do you have the stock converter, you may need a higher stall speed with that cam in a 383?
Not a balance problem I hope...
 
383 with 906 heads and that cam is what I have in my Superbee and I had the same problem back in 2012 when I had the engine rebuilt. With
this setup and probably in the low 9.1-9.3 compression you should be able to bump up the initial to 14-16 degrees and 38 total mechanical and with vacuum advance hooked up should be up around 54-56 degrees.
 
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What is your idle speed?
Do you have the stock converter, you may need a higher stall speed with that cam in a 383?
Not a balance problem I hope...
Thanks for the help Don....the engine was balanced. The converter is stock
I have to do a compression check. I ordered another tester with smaller hoses so hopefully I can get them in spark plug holes,,,will try from under car....if I have to take the manifolds off, so be it.
 
383 with 906 heads and that cam is what I have in my Superbee and I had the same problem back in 2012 when I had the engine rebuilt. With
this setup and probably in the low 9.1-9.3 compression you should be able to bump up the initial to 14-16 degrees and 38 total
timing.
Good point.:thumbsup:
You may need to change your advance curve to get 20 degrees initial.
Try 20 as a test see if it starts hard it likely won't, just be careful to avoid predetonation.
906 heads can take a lot of advance.
 
Steve, what is the part# on that cam?,,,,,,,,,,, I looked in my cat-log and see a xe268h, it shoul do the trick but I think it's got plenty of duration for your combo. Good luck
 
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I may caught at lot of crap for this but have always set timing to were the starter will turn the engine when hot and go from there on the rest. To much time and they just will not start when hot unless you want to delay spark till it is turning over. You should be fine setting timing between 10 and 12*.
 
I'm watching this thread as I am in the same situation. Unknown build; seller told me 'not too extreme cam', but he himself really didn't know.
Like Steve I tuned my 1406 with the Edlebrock kit. Tailpipe AFR shows high 13 at idle, low 14 during cruise, and 12.5, or so WOT. My idle is 800 in park with about 15 inches of vacuum. Timing is initial 14. Spark plugs are the black side of brown, but not wet, or really rich looking.
This car has excellent tip in and lots of power. I get an occasional ping at WOT running 91 pump gas.
My idle is all over the place on the smoothness scale. At one stop it will be smooth as silk and at another stop it will be rough. My Mopar friends said to try Berrymans in a half tank of gas, and it might be phycological, but this weekend it did seem to reduce idle roughness. They also claim I have "a bit too much cam", and I tend to agree, but not going to touch it as it has excellent power and fairly good fuel economy.
Anyhow, like to see the comments and advice here. Thanks for the help.
 
Before everyone suggests an engine rebuild....have you check that a float or needle are not sticking in the carb?
 
Before everyone suggests an engine rebuild....have you check that a float or needle are not sticking in the carb?
That is a good one. Surprised no one had suggested it on Steves freshly rebuilt 383.
 
I may caught at lot of crap for this but have always set timing to were the starter will turn the engine when hot and go from there on the rest. To much time and they just will not start when hot unless you want to delay spark till it is turning over. You should be fine setting timing between 10 and 12*.
Agreed...I'd be curious to know where the timing is set now, and how much total mechanical advance he has. I put an FBO limiter plate in mine, set initial at 16° and use the 18° slots for 34 all in. Runs excellent and stays cool.
 
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