Erratic idling

[Plymouth man]

I got this 77 newport with a 400 in it with erratic idling things I've done put new carburetor on new point distributor new coil new plugs and wires new timing set can't get the missing out of it just runs badly not smooth can anyone help

 

[darth_linux]

Does it have the “lean burn” setup? If so, Have you considered deleting that system?

 

[57fury440]

You have a distributor with points? Did you install it? I would think that a '77 Newport would have an electronic system on it. Was it originally a lean burn set up that was converted? First thing, I would check for a vacuum leak or leaks. Have you checked the compression yet? Does it get smoother when you drive it or is it just at idle? What carb. is on it?

 

[CBODY67]

With a new/different carburetor and a points (???) distributor, the only explanation I can think of is that it was previously an ELB engine that has been converted. With a points distributor, I suspect the ign system was changed. BTAIM

How many miles on the car or engine? Other than the ignition and carburetor, what else has been done to the motor?

Is the miss at idle or while driving, one or both? Which carburetor is on the engine now?

Has the EGR valve been eliminated with a block-off plate or a non-EGR aftermarket intake, or is it still in place and functioning?

Presuming all of the spark plug wires are going to the correct spark plugs?

Just some thoughts,
CBODY67

 

[65Port]

Any history on this car/motor? Sounds like you were trying to remedy something. What did the old plugs look like when you pulled them? If they have been tossed, can you pull a couple of the new ones to check the condition? Alternatively you can pull plug wires off (carefully!) the running engine to see which cylinder makes no difference in rpm/idle quality. Could be mechanical also. Check timing and vacuum yet? Any blue/black smoke?

 

[Plymouth man]

Black smoke some plugs are wet eliminated the lean burn carb is a 770cfm holley avenger but I had a carter avs on it and it did the same thing it misses going done road too until you get about half throttle can't find no vaccum leaks yes I installed the points distributor haven't checked egr didn't see one on it it does have a carburetor adapter from speard bore to square bore if you turn the distributor to much either way it will die I haven't checked compression yet the car shows 86000

 

[mrfury68]

It sounds like this car had the Lean Burn system deleted but the ignition system would have been the electronic ignition, not a points set up. When the Lean Burn set up was deleted it took a few other steps to get a good idle and drivability. Timing, idle, vacuum & air / fuel ratio needed to be adjusted as well. You need to research the work the previous owner did, and then process of elimination, just like any other trouble shooting. Good luck and keep us posted.

 

[CBODY67]

At that mileage, from experience on our 383s, at about 80K miles, #5 or #7 exhaust valve was "burnt" and needed replacing. An engine miss that did not feel like the classic fouled/dead spark plug engine miss. Carb changes would not affect it until the valve job is done to fix the issue.

When it happened on our '66 Newport 383 2bbl, it was a consistent rough idle, a bit worse on acceleration, which seemed to go away at highway speed, but going up a hill took much more throttle to maintain speed. More of a "comfort" disruption than a real operational disruption, but it was still there.

If you decided to do the diagnostics by pulling spark plug wires . . . do NOT have any body part that is near the car's metal/painted/chrome surfaces! ZAPS can happen. It can take longer but you can do the same thing by pulling a plug, restarting the engine, check for smoothness, plug the wire back in, cycle repeat. If you have a vac gauge, that can work, too, in this case. Whenever the weak cyl fires, the needle on the gauge will make a sudden and precise drop in vac level.

From my experiences,
CBODY67

 

[Plymouth man]

At that mileage, from experience on our 383s, at about 80K miles, #5 or #7 exhaust valve was "burnt" and needed replacing. An engine miss that did not feel like the classic fouled/dead spark plug engine miss. Carb changes would not affect it until the valve job is done to fix the issue.

When it happened on our '66 Newport 383 2bbl, it was a consistent rough idle, a bit worse on acceleration, which seemed to go away at highway speed, but going up a hill took much more throttle to maintain speed. More of a "comfort" disruption than a real operational disruption, but it was still there.

If you decided to do the diagnostics by pulling spark plug wires . . . do NOT have any body part that is near the car's metal/painted/chrome surfaces! ZAPS can happen. It can take longer but you can do the same thing by pulling a plug, restarting the engine, check for smoothness, plug the wire back in, cycle repeat. If you have a vac gauge, that can work, too, in this case. Whenever the weak cyl fires, the needle on the gauge will make a sudden and precise drop in vac level.

From my experiences,
CBODY67

At that mileage, from experience on our 383s, at about 80K miles, #5 or #7 exhaust valve was "burnt" and needed replacing. An engine miss that did not feel like the classic fouled/dead spark plug engine miss. Carb changes would not affect it until the valve job is done to fix the issue.

When it happened on our '66 Newport 383 2bbl, it was a consistent rough idle, a bit worse on acceleration, which seemed to go away at highway speed, but going up a hill took much more throttle to maintain speed. More of a "comfort" disruption than a real operational disruption, but it was still there.

If you decided to do the diagnostics by pulling spark plug wires . . . do NOT have any body part that is near the car's metal/painted/chrome surfaces! ZAPS can happen. It can take longer but you can do the same thing by pulling a plug, restarting the engine, check for smoothness, plug the wire back in, cycle repeat. If you have a vac gauge, that can work, too, in this case. Whenever the weak cyl fires, the needle on the gauge will make a sudden and precise drop in vac level.

From my experiences,
CBODY67

Thanks cbody67 I will try that and a compression test I was hoping it was ignition but looks like it may be mechanical

 

[Plymouth man]

At that mileage, from experience on our 383s, at about 80K miles, #5 or #7 exhaust valve was "burnt" and needed replacing. An engine miss that did not feel like the classic fouled/dead spark plug engine miss. Carb changes would not affect it until the valve job is done to fix the issue.

When it happened on our '66 Newport 383 2bbl, it was a consistent rough idle, a bit worse on acceleration, which seemed to go away at highway speed, but going up a hill took much more throttle to maintain speed. More of a "comfort" disruption than a real operational disruption, but it was still there.

If you decided to do the diagnostics by pulling spark plug wires . . . do NOT have any body part that is near the car's metal/painted/chrome surfaces! ZAPS can happen. It can take longer but you can do the same thing by pulling a plug, restarting the engine, check for smoothness, plug the wire back in, cycle repeat. If you have a vac gauge, that can work, too, in this case. Whenever the weak cyl fires, the needle on the gauge will make a sudden and precise drop in vac level.

From my experiences,
CBODY67

Tried to use timing light in car today and it run best at 35 or 40 degrees before TDC and the light kept bouncing 10 to 20 degrees back and forth what would do that? The car will miss erratic still it will go dead when you put it in drive or put a load on it you have to get the rpms up to keep it running going down the road

 

[57fury440]

Timing chain.

 

[Big_John]

Tried to use timing light in car today and it run best at 35 or 40 degrees before TDC and the light kept bouncing 10 to 20 degrees back and forth what would do that? The car will miss erratic still it will go dead when you put it in drive or put a load on it you have to get the rpms up to keep it running going down the road

The erratic timing could be the chain, but the 35-40 BTDC is another problem.

First thing to check is if you are on the correct #1 plug wire. If so, the outer ring on the balancer has slipped and the balancer will need to be rebuilt or replaced. So we're on the same page, #1 is driver side.

 

[Plymouth man]

Has a new timing set no.1 on distributor is at front of engine right behind the clip on distributor cap and runs to the 1st plug on drivers side engine is a 400 big block

 

[57fury440]

If you have a new timing chain and sprockets, then you should not be at 35-40 degrees BTDC. Look at the balancer like Big_John said.

 

[Plymouth man]

Where can I find a new external balance harmonic balancer

 

[halifaxhops]

Set the engine to TDC make sure it is on number one then check the balancer. Might not need one. Usually in a points system timing jumping around like that is a bad distributor ground. Double check that also new points from the store? Can have really weak spring tension that will do weird stuff. Also the timing light you used is it a dial back?

 

[furious70]

I agree with
Verify TDC timing on the balancer
If you've correctly done the r&r on the timing chain then the bouncing timing must be in that dizzy. Verify gap and dwell.