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Rough Idle

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mgbjones

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Took a nice 50 mile ride in the car the other day. Went no more than 10 miles into the ride and stopped at a stop sign and the car would not idle for crap. It sounded like it was looping. Adjusted the idle to bring it up and it still did not idle properly.

The car has plenty of power on takeoff and cruise.

Once I go home I replace the fuel filter same condition.

Checked all of the wires going to the coil and HT lead, everything was secure and no broken or chafed wires.

Pulled each plug wire off while idling the engine did not show any faults.

Replaced the distributor cap and still idles rough. Engine will start almost first turn of the key when warm. With old or new cap.

I am thinking maybe condensor or coil going bad.

I am running a Weber 32/35, Mild street cam, 25D Distributor from Advance Dist.

Since then I took the carb top off and removed the jets, idle mixture screw and cleaned everything with carb cleaner. Started the car back up and it still ran rough. Adjusted the car and still running rough. Took off spark plug wires again and all were good except 3. When3 was taken off no change in idle. Pulled plugs and they all look while or lean. Adjusted mixture to richen and still rough idle. Checked dizzy and it was a little loose and could be turned by hand. Re-set timing at about 17 BDC still has rough idle and will not maintain good idle. It seems to want to go up and down.

Any ideas?
 
Don't know year but do you have points or electronic ignition? If points , might readjust. Could make rough idle if not quite right.
 
Last edited:
Have you checked all your vacuum lines?

And welcome to the BCF!

:cheers:
Mickey
 
Welcome to BCF!

This is your first post here, so we don't know the engine's history. Was it running fine up until that incident at the stop sign?

Seems if it runs well at speed and under load, it's probably not the coil.

Tom
 
It sounded like it was looping
Click to expand...

Are you sure it is not just your camshaft? Looping at idle with good acceleration and power suggests the camshaft to me. Normal. Maybe it isn't as "mild" as you think. My experience limited to an MGA, but bad coil would cause a misfire in my experience. Carb problem would also cause a misfire.
 
Thanks everyone for you responses. It is a 1966, running points, Weber Carb, Kent mild street cam.

I am going to purchase new Points, Condenser, plugs , Dizzy cap and rotor this afternoon. Pull the dizzy and install all new parts and start from scratch. I have not really done a major tune-up in about 5 years just installed fresh plugs.
 
It sounds to me like you found the problem without quite realizing it. If you pulled off the #3 wire and nothing changed, there's definitely a problem with that wire, or possibly the plug. So, before randomly changing a lot of parts, or trying to readjust things, fixing that problem should be first priority.

Plug wires can be bad without any obvious reason--it can be hard to see a bad connection at the cap or plug. Especially if you are using resistor wires, which are notorious for that kind of problem.

So, I'd replace that wire and go from there. You might have a weak condensor or something like that, as well, of course, but first priority is the things you know are bad.
 
Re: Rough Idle Resolved

Well pulled the dizzy today and replaced points, condenser, cap, rotor and plugs. Once I removed the points took a good look and found a hole right in the middle.

After putting everything back together, started the car set the timing, MOWOGMAN set the carb back up and now she is running like a champ.

So what causes a hole in the points, moisture??????

mgbjones said:
Took a nice 50 mile ride in the car the other day. Went no more than 10 miles into the ride and stopped at a stop sign and the car would not idle for crap. It sounded like it was looping. Adjusted the idle to bring it up and it still did not idle properly.

The car has plenty of power on takeoff and cruise.

Once I go home I replace the fuel filter same condition.

Checked all of the wires going to the coil and HT lead, everything was secure and no broken or chafed wires.

Pulled each plug wire off while idling the engine did not show any faults.

Replaced the distributor cap and still idles rough. Engine will start almost first turn of the key when warm. With old or new cap.

I am thinking maybe condensor or coil going bad.

I am running a Weber 32/35, Mild street cam, 25D Distributor from Advance Dist.

Since then I took the carb top off and removed the jets, idle mixture screw and cleaned everything with carb cleaner. Started the car back up and it still ran rough. Adjusted the car and still running rough. Took off spark plug wires again and all were good except 3. When3 was taken off no change in idle. Pulled plugs and they all look while or lean. Adjusted mixture to richen and still rough idle. Checked dizzy and it was a little loose and could be turned by hand. Re-set timing at about 17 BDC still has rough idle and will not maintain good idle. It seems to want to go up and down.

Any ideas?
Click to expand...
 
Re: Rough Idle Resolved

mgbjones said:
Well pulled the dizzy today and replaced points, condenser, cap, rotor and plugs. Once I removed the points took a good look and found a hole right in the middle.

After putting everything back together, started the car set the timing, MOWOGMAN set the carb back up and now she is running like a champ.

So what causes a hole in the points, moisture??????
Click to expand...

Glad you found the issue.

I seem to remember some points sets came with holes in them. Ventilation?

Or maybe the holes are in my head!
 
I remember them. I can not remember who made the ones I bought. I think I bought them in Pep Boys a few years back for my 54 Chevy pickup. I think they were just trying to make a set of points that didn't burn as fast. If you notice in the photo, those points weren't set properly, they had a twist in them and were only making contact on one side, something most folks never think about. PJ
 
Blue Streak sets were like that. Little tiny donuts. :jester:
 
Re: Rough Idle Resolved

Some points are made that way.They're called "ventilated points"--the idea is that air can move through the hole as they operate, to help keep them cool. I suppose it might actually do some good.

My guess is that you fixed the problem inadvertently--maybe it was a bad condensor after all. There certainly are lots of bad ones on the market. Or, maybe you have an intermittently bad connection somewhere and by moving it around, it's again solid--for now. There's still the question why pulling the #3 wire had no effect--that's the classic test to determine that a plug isn't firing.
 
My antique Ford tractor would burn the points after about 100 hrs of running. We use it to mow the fields in the areas where the big tractor couldn't go. I had to replace them twice a season. I solved the problem by putting a resister in the wire that goes from the coil to the distributor. I haven't had to replace the points in the past two years and the tractor runs perfect. PJ
 
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