Engine miss

[C Body Bob]

Ok I had some time today to work on my 66 300. With the vacuum Advance hooked up it stumbles & shakes badly when I begin to give it throttle. Diconect the Advance & it is smooth but accelerates very slow. I put a vacuum tester on it & removed the dizzy cap. It starts to move the Advance plate at 12 inches & stops moving at 17. Didn’t notice anything unusual about the movement. Everything looks surprisingly clean. Engine is a 383 low deck. Believe to be original. It still has points. The carb is a Edelbrock. The port at the carb pulls no vacuum at idle. I forgot to check at throttle. The other port has about 20 inches at idle. So I’m sure I’m using the correct port.

 

[Kapt]

Still has points you say? How are they?

 

[Davea Lux]

A misfire under load is usually indicative of weak spark, if you have a voltmeter handy, check the resistance on the points and check the gap, clean off any corrosion on the cap and rotor. While you have the voltmeter out, check the voltage to the coil. If the car sat for a long time, the condenser may have failed from moisture intrusion, if it is shorted, that can also explain the misfire under load. Also check the plug gap and clean the plugs as necessary. The other potential issue might be if you have old degraded gasoline in the fuel tank, they will always run like crap on bad gas. Probably be a good idea to get the detached heater hose away from the manifold so it does not catch fire.

Try this stuff and report back.

Dave

 

[stubs300]

Not knowing the love or neglect that the car's received over it's life. It might not be a bad idea to put that dist. and give it a good going through with a fine tooth comb, clean a lube everything inside, new springs, etc.? How's the cap & rotor? How old are the plugs & wires? If your gas is gunky, then replace filters too. Good Luck

 

[C Body Bob]

Still has points you say? How are they?

Yes points. Have not looked at them

 

[Newport 66]

Bad plug wire(s)?

 

[C Body Bob]

View attachment 235623 View attachment 235624 Ok I had some time today to work on my 66 300. With the vacuum Advance hooked up it stumbles & shakes badly when I begin to give it throttle. Diconect the Advance & it is smooth but accelerates very slow. I put a vacuum tester on it & removed the dizzy cap. It starts to move the Advance plate at 12 inches & stops moving at 17. Didn’t notice anything unusual about the movement. Everything looks surprisingly clean. Engine is a 383 low deck. Believe to be original. It still has points. The carb is a Edelbrock. The port at the carb pulls no vacuum at idle. I forgot to check at throttle. The other port has about 20 inches at idle. So I’m sure I’m using the correct port.

How do I check

A misfire under load is usually indicative of weak spark, if you have a voltmeter handy, check the resistance on the points and check the gap, clean off any corrosion on the cap and rotor. While you have the voltmeter out, check the voltage to the coil. If the car sat for a long time, the condenser may have failed from moisture intrusion, if it is shorted, that can also explain the misfire under load. Also check the plug gap and clean the plugs as necessary. The other potential issue might be if you have old degraded gasoline in the fuel tank, they will always run like crap on bad gas. Probably be a good idea to get the detached heater hose away from the manifold so it does not catch fire.

Try this stuff and report back.

Dave

how do I check the points ?
I know how to set them. Don’t know how to test them
I’ll double check the cap.
Yes car has sat for years. Occasionally start it.
Gas tank was cleaned out last year & resealed by Member Wollfen. Has fresh gas in it. 1/4 tank.
Have not checked plugs or wires. Today was the first time I have touched the car in a while. Was hoping to drive it some this winter so I’m trying to get it ready. Heater hose is fine. That’s an old pic.

 

[C Body Bob]

Not knowing the love or neglect that the car's received over it's life. It might not be a bad idea to put that dist. and give it a good going through with a fine tooth comb, clean a lube everything inside, new springs, etc.? How's the cap & rotor? How old are the plugs & wires? If your gas is gunky, then replace filters too. Good Luck

Today was the first time I’ve messed with the tune of the car. I do need to check all that stuff. It runs ok on the road just sluggish

 

[C Body Bob]

Bad plug wire(s)?

I will check them.

 

[Davea Lux]

How do I check

how do I check the points ?
I know how to set them. Don’t know how to test them
I’ll double check the cap.
Yes car has sat for years. Occasionally start it.
Gas tank was cleaned out last year & resealed by Member Wollfen. Has fresh gas in it. 1/4 tank.
Have not checked plugs or wires. Today was the first time I have touched the car in a while. Was hoping to drive it some this winter so I’m trying to get it ready. Heater hose is fine. That’s an old pic.

Rotate the engine until the points are in the closed position, unhook the distributor lead from the coil, attach one lead from the volt meter set on resistance to the detached distributor lead and the other to a good ground. With good points you should show low amounts of resistance. Cars that set for long periods of time often have corroded points which I suspect is your problem with this car.

Dave

 

[Davea Lux]

Rotate the engine until the points are in the closed position, unhook the distributor lead from the coil, attach one lead from the volt meter set on resistance to the detached distributor lead and the other to a good ground. With good points you should show low amounts of resistance. Cars that set for long periods of time often have corroded points which I suspect is your problem with this car. Be sure to unhook the condenser lead as well from the point set and tighten the screw back up to test.

Dave

 

[65sporty]

After you check the points, dist cap, spark plugs, etc... Be sure to check your base timing.

 

[C Body Bob]

After you check the points, dist cap, spark plugs, etc... Be sure to check your base timing.

Checked base timing already. It’s good.

 

[cantflip]

Heater hose is fine. That’s an old pic.

Oh good... I thought this was a test to see who spotted the disconnected plug wire... or is that one really looped around the suspension to get where it belongs?

 

[C Body Bob]

Oh good... I thought this was a test to see who spotted the disconnected plug wire... or is that one really looped around the suspension to get where it belongs?
View attachment 235973

No these damn aftermarket wire for BBM’s are too long by a mile. My D440 truck has the same problem. And those are expensive MSD wires

 

[C Body Bob]

Like I stated the car runs smooth untill I hook up the vacuum Advance. Then it’s like I took two plug wires off.

 

[commando1]

Like I stated the car runs smooth untill I hook up the vacuum Advance. Then it’s like I took two plug wires off.

Then don't hook up the vacuum advance.
K. I. S. S.

 

[C Body Bob]

Then don't hook up the vacuum advance.
K. I. S. S.

Haha. It’s sluggish then.

 

[CBODY67]

The vacuum advance has to be there for part-throttle response and fuel economy.

What do the dwell readings look like when you hook up the vacuum advance AND is it hooked to ported vacuum? AND were the points set prior to setting the base timing?

Just curious,
CBODY67

 

[Gerald Morris]

You can visually inspect the points w a jewelers' loop or magnifying glass if you don't care to remove them. A light touch w an emery board nail file can resuscitate points just slightly damaged or corroded. Otherwise, I'd replace all the ignition stuff, as I do ever so often. I'm about due to check my points, condenser, plugs and wires. I normally tune up for winter and summer anyway.