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Slight miss at any no load rpm

O

Old Frat

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Hi Guys, I'Mmmmmm Back
I finally got the 66 318 Poly running after some help from members.
Now I have a slight miss at any no load rpm The engine is pulling 20-25 inches vac. at idle, disconnecting a plug wire make no change in the rpm or vac. The engine starts and revs like it should.
I did replace the Cam and lifters with stock solid set up, I rechecked the lash and it is within specs. The cap and rotor look good and the wires read within specs. I also tried a different coil. The engine was rebuilt a couple of years ago but the shop installed an LA cam and lifters, the reason for my replacing the cam. I did check the compression when I first started, I don't remember what is was at that time.I have been told the wires, cap and rotor are new But they don't look new to me.
I know this may seem stupid but I have been out of working on gas burners for 30+ yrs, other than maintaining my own vehicles.
Any suggestions?
Frank
 
Have you pulled any plugs to check condition? Using correct heat range?
 
Did you just pull one plug wire? or each of them one at a time?
It's possible the problem cylinder is the one you tried.
 
Was the carb rebuilt ?? May need some fine tuning. I would replace the cap and rotor, if they don't look new. Has fuel filter and/or fuel tank been cleaned?? Perhaps the fuel type... no alcohol !!
 
Not that it has anything to do with your current problem but make sure your oil has a high zinc content. Today's conventional oil have no zinc since roller lifters don't require it along with environmental restrictions.
 
I’d try using an infrared heat gun aimed right at the ex manifolds at each ex port...... see if there’s one that’s noticeably different than the others.

I’d probably redo a compression test on all cylinders.
 
Could be a part throttle surge that usually means the carb is lean on the primary side.
 
What happens under load? Might be a fuel supply issue?
 
Just had a low rpm miss front fuel bowl was at the top of the sight glass. Adjusted to the middle took it away.
 
Today's oils have LESS zinc, not no zinc.
Replace the condenser.
 
Darter6 said:
Could be a part throttle surge that usually means the carb is lean on the primary side.
Click to expand...

This. open the idle circuit a little.

or it could be too much timing
 
PRHeads said:
I’d try using an infrared heat gun aimed right at the ex manifolds at each ex port...... see if there’s one that’s noticeably different than the others.

I’d probably redo a compression test on all cylinders.
Click to expand...
Thank you, I'LL probably do that tomorrow, Also running off a temp fuel tank/can, has a new fuel pump.
 
So you have a smooth idle, but a slight miss at light acceleration? One thing you can try is in a dark shop look for spark leaking from plug boots or anywhere the wires are close to metal. You can see if it is a lean misfire by misting some carb cleaner into carb as it is misfiring.
 
"T" into the fuel line by the carb and check the fuel pressure. Or / also check the entire fuel line. I has an issue like this once on my old truck, and the rubber hose was cracked at the tank pickup and the fuel pump was sucking air and just a bit of fuel that the engine world idle / sort of rev with no load.
When I got the '69 Coronet, the fuel line was cut up where an electric pump was installed, but the entire fuel line was rusted on the inside (and outside too.)
On yet another car the '76 Cordoba, the pickup inside the tank was clogged with a nasty black gunk. Not sure if the previous owner had someone put sugar in the tank? Some people told me it may have been from the MTBE from gasoline used back in the 1980s?

Now when I get a car, after checking the brakes, I check out the entire fuel system. Luckily for the '69 Coronet they reproduce everything, so new tank, stainless lines, and such. You mentioned a 1966, which model, Charger, Coronet? Anyhow, i think there is good reproduction part support for those cars too.
 
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