413 Lumpy idle

[Padre4art]

Looking for opinions about my 1964 NYer which has a lumpy idle especially when in gear. A little bouncy!

Off idle, runs great, strong. 0 to 60 in less than 8 seconds!

Engine has 104,000 miles; don’t know if ever rebuilt and not sure it would be worth the expense.

Compression test varies from 122 to 157 psi. Carb good, plugs good. No smoke or strange noises.

Thoughts?

Thanks

Art

 

[Welder guy]

Fill it up with premium gas and go for a good drive, anything else probably has ethanol in it and these cars don’t like the stuff. Let us know how it runs after that .

 

[Padre4art]

I was wondering about dumping in some Seafoam and going for a long drive. I do use non ethanol 93 octane. Thanks!

 

[Welder guy]

Well it won’t hurt anything it will smoke. Start there . Do you know if it has a stock cam or not ?

 

[Padre4art]

I would think so. I was thinking the low compression was causing the problem. Spec is 165.

 

[Slap Stick]

Check the oil pump drive gear and its bushing for play. Causes erratic timing which combined with a worn timing chain/gear can cause a lumpy idle when in gear.

 

[Padre4art]

How do you check that?

 

[CBODY67]

The compression test spec can vary with things like altitude, temp, whether the throttle was wedged open when the test was done, etc. Best guide is to look at how many cylinders register what pressure. Something like a 10% variation from low to high is fine, IIRC.

Unless somebody has done "something", it should be a 340 horsepower 413, which should idle pretty smooth, but probably not "glass smooth".

At that mileage, it probably needs a timing chain (not the reason for the roughness) and might well be on the way to one burnt valve (from our experiences with 383s). One way to check for that is to take a red shop rag and loosely place it over the end of the tailpipe with the engine idleing. IF the rag gets sucked into the pipe when the miss happens, that's an exhaust valve not sealing well. Have to look fast to see this, but it will be regular for whenever that cyl fires.

Additionally, at what hot base idle rpm is the carb set at? Might just need to re-balance the idle mixture and increase the hot base idle rpm maybe 25rpm or so.

IF you are brave, you can pull plug wires, one at a time, from the distributor cap or the spark plug itself. Watch the rpm drop on each cyl. No rpm drop? That's the weak cyl. Otherwise known as "cylinder balance test". Be sure to have an insulated pair of pliers designed to pull the plug boots with AND do not allow a bare body part to be near the fender! Proceed at your own risk!

I concur with the carb cleaner and "going for a one-tank highway drive". Personally, I'd use Berryman's B12 as I believe the Seafoam has some alcohol content in it. Key thing is to get it out and drive it long enough to burn out some of the residual carbon in the combustion chambers and cook any gremlins out of the motor oil.

Enjoy!
CBODY67

 

[Ripinator]

The compression test spec can vary with things like altitude, temp, whether the throttle was wedged open when the test was done, etc. Best guide is to look at how many cylinders register what pressure. Something like a 10% variation from low to high is fine, IIRC.

Unless somebody has done "something", it should be a 340 horsepower 413, which should idle pretty smooth, but probably not "glass smooth".

At that mileage, it probably needs a timing chain (not the reason for the roughness) and might well be on the way to one burnt valve (from our experiences with 383s). One way to check for that is to take a red shop rag and loosely place it over the end of the tailpipe with the engine idleing. IF the rag gets sucked into the pipe when the miss happens, that's an exhaust valve not sealing well. Have to look fast to see this, but it will be regular for whenever that cyl fires.

Additionally, at what hot base idle rpm is the carb set at? Might just need to re-balance the idle mixture and increase the hot base idle rpm maybe 25rpm or so.

IF you are brave, you can pull plug wires, one at a time, from the distributor cap or the spark plug itself. Watch the rpm drop on each cyl. No rpm drop? That's the weak cyl. Otherwise known as "cylinder balance test". Be sure to have an insulated pair of pliers designed to pull the plug boots with AND do not allow a bare body part to be near the fender! Proceed at your own risk!

I concur with the carb cleaner and "going for a one-tank highway drive". Personally, I'd use Berryman's B12 as I believe the Seafoam has some alcohol content in it. Key thing is to get it out and drive it long enough to burn out some of the residual carbon in the combustion chambers and cook any gremlins out of the motor oil.

Enjoy!
CBODY67

In addition to the foregoing, I would also check everywhere for a vacuum leak. . . EDIT: One more thing: check your power brake booster to be sure it is not leaking vacuum.

 

[CBODY67]

When the booster on our '66 Newport went out, it would run pretty much as it always did, until I'd stop. When the booster was leaking, with the brake pedal depressed, the engine would miss. Release the pedal and it would go back to normal.

Just some experiences,
CBODY67

 

[Gerald Morris]

Check the fast idle cam and screw too. If sticking, this can make a lumpy idle. I just doctored such 3 daze ago. Do the Rite of Idle Screws too. Got a good vac gauge?

Also, stick with Berryman for carb cleaning. B12 is The ****!

 

[Slap Stick]

How do you check that?

Remove the distributor cap and try to turn the rotor. Shouldn't be much play at all. Better yet, remove the distributor and with a long screwdriver insert the tip intonthe drive gear slot. Try to rotate the gear both ways and wiggle back and forth. Or remove it and look at the gear for wear. The bushing in the block can be worn, also. Wear will cause the gear to wobble, making for erratic timing. On the Magnum series engines it even throws off the fuel injector sync so it gets really weird.

 

[CBODY67]

Remove the distributor cap and try to turn the rotor. Shouldn't be much play at all. Better yet, remove the distributor and with a long screwdriver insert the tip intonthe drive gear slot. Try to rotate the gear both ways and wiggle back and forth. Or remove it and look at the gear for wear. The bushing in the block can be worn, also. Wear will cause the gear to wobble, making for erratic timing. On the Magnum series engines it even throws off the fuel injector sync so it gets really weird.

Here's something which I found on my '70 DH43N when I bought it back in 1975 with about 83K miles on it. Just before it would get to the 1-2 WOT upshift point, it would act like it was running out of gas, for a second or two. After the shift, it was fine again. I did the normal base hot initial timing checks, even varied the timing a few degrees up and back, but put it back at spec. Made sure the point dwell was in spec, too. Checked the float levels in the AVS. No change. In my research, I came across a "high speed spark scatter" mention, of the actual distributor timing changing at higher rpms, due to oil pump loading/flow issues. More load, more timing change, it seems.

When I got the car, the dealer did an oil change as a normal deal on used cars. A normal, name brand of 10W-30 motor oil. So, I changed it to a Euro-brand of oil (C______), which many considered "motorcycle oil" at that time, in 10W-40. END of problem and it never resurfaced! In those days, considering that "wear issues" in the tower bushing of dist drive gear shaft, etc., were not real considerations in a normal-use motor. Yet the "spark scatter" issue might have been related to those things, in retrospect. Fuel pump pushrod wear was not an issue either, but that was well before anybody worried about the zddp content in motor oil, too.

Just some thoughts and experiences,
CBODY67

 

[Gerald Morris]

....
When I got the car, the dealer did an oil change as a normal deal on used cars. A normal, name brand of 10W-30 motor oil. So, I changed it to a Euro-brand of oil (C______), which many considered "motorcycle oil" at that time, in 10W-40. END of problem and it never resurfaced! In those days, considering that "wear issues" in the tower bushing of dist drive gear shaft, etc., were not real considerations in a normal-use motor. Yet the "spark scatter" issue might have been related to those things, in retrospect. Fuel pump pushrod wear was not an issue either, but that was well before anybody worried about the zddp content in motor oil, too.

Just some thoughts and experiences,
CBODY67

"Rick-O" sells a remedy for spark scatter which I use; a little steel collar to slip on the distributor shaft which keeps the tab firmly planted in the slot of the drive gear, down in the block. One CAN get that collar at a good hardware store, for less, IFF one knows JUST what to shop for.

for Mopar Distributor Collar Timing Stabilizer 340 440 383 Hemi Dodge Plymouth | eBay

He's asking just under $15 for this widget, and I recommend it. He sells the best stuff he can find, and his prices are fair. Best of all, the man has had his hands in Mopars a LONG time, loves and knows them.

 

[Slap Stick]

I disagree with "Rick-o" saying its not needed kn the Magnum series engines.
Even though they are crank triggered ignitions there is also the cam position sensor in the distributor. The distributor isnt used to set ignition timing but it does set injector timing. Also, if the rotor is in the wrong position in its rotation when it passes a plug wire the ignition timing is off. It fires early or late. Add to that the fact the dizzy tells the computer when to fire the injector for each cylinder in time with the spark it is doubly important the dizzy is stable. When the drive gear and or its bushing in the block is worn the timing becomes erratic. The proper fix is to change the drive gear and the bushing. But, replacing the bushing is a pain, as it takes a speacial tool to remove it in situ. Then it takes another tool to install it as after installation it need to be reamed to the proper size.
This collar is an ingenious and simple fix that anyone can do without special tools and IMO even more important on the Magnum engines for the reason stated.
Symptoms on the Magnums include lumpy idle in gear-the vehicle will bounce a bit, and at speed with the converter in lock up at light throttle-just enough to hold speed the vehicle will jerk a few times as if the ignition is being interrupted-and it is. It even will kick the transmission out of OD.
My 92 Dakota used to do it and I pulled my hair out chasing it until I turned the rotor by hand and found rotational play. Dont confuse this with timing chain slop which can have the same symptoms. A loose chain makes it even worse.
A new Melling pump shaft fixed it. One side of the gear was badly worn. Makes me womder what the gear on the cam looks like. It came with the shaft bushing but since I dont have the tools to change it I left it alone.
IMO this is another good reason to run high zinc content oil in roller lifter engines. It ain't just the lifters and cam lobes that need the protection.
BYW, keep the bushing in the dizzy lubed, too. There is one outside the dizzy where the shaft enters but it is bronze and can wear. The collar would eliminate that IMO. It is harder than the bronze and has a larger bearing surface.
Just my experience.
Mr. Morris, good Info for everyone.

 

[Gerald Morris]

I disagree with "Rick-o" saying its not needed kn the Magnum series engines.
....
Just my experience.
Mr. Morris, good Info for everyone.

Thank YOU for your informative, enlightening addendum! Not experiencing any EFI managed MoPar engines, these matters fall beyond my feeble reach. Running a Magnum on an A/LA-meant 747 has crossed my mind, and nigh all praise that motor for its power/mass ratio, but as a Simpleton with Ideology, I stick in the realm of pre-transistorized ignition/engine management. I wouldn't turn a good vehicle down so equipped for a suitably ridiculously low price I reckon.

Anyway, one CAN score a similar collar from Ace Hardware, made by Hillman. IDK who makes Rick-O's ware in this regard, though he tries to keep it U.S. made when he can get it so..... we're told.

 

[Slap Stick]

Thanks for the kind words.
I also prefer the simple stuff. Both my moorsickles have carbs, points and condensers. One of them I even converted to points. Why? At 4k miles one of the wonder boxes let out its smoke.
Also, speaking of points, Dont forget to keep the rubbing blocks lubed and check the centrifugal advance weights to ensure cleanliness and free movement. Give the fiber doohickey inside the dizzy shaft under the rotor a shot of lube now and then.