rebuilt 301 vibrates at around 3k RPM or 40 mph

[Rusty Muffler]

Presuming you have the point dwell set at the correct value and point gap in similar, what does the dwell look like the rpm the roughness starts? If you unplug (capping the vac line unplugged) the vac advance, how might that affect it?

Might need to seek out an older repair shop which might have one of the ignition oscilloscope items to watch what the spark plug firing/ignition system is doing. That would quickly identify which cylinders are having issues or if all of them are contributing. As to what the ignition system is doing.

Just some thoughts,
CBODY67

Thanks CBODY. The problem is more in the 2k rpm and above and the dwell was off about 2 degrees at about 33 degrees. I adjusted it to 30 degrees at idle and it moved to 23 degrees at 2k rpm or above. The advance seems to be working as it drops about half of the advance timing off when disconnected. The timing light strobe light is steady on #1 at any rpm. Also the vacuum is in the green but has a high speed jidder. So compression is all even at 100, choking the carb did not help, the plugs look grey (maybe too lean?), none close to black. I have one of those gismos you hook at the spark plug that flashes and it shows the wires are good at any rpm.
Fuel?

 

[CBODY67]

Lean is chalky white. Good is white to beige. Never have seen gray. But he carb is for the engine, it's probably ok.

 

[furious70]

Sounds like you have vacuum advance hooked to manifold vacuum and not ported? Is that on purpose? Or were you not talking at idle?
Too much timing even at light throttle can cause lean surge/miss

 

[Rusty Muffler]

Sounds like you have vacuum advance hooked to manifold vacuum and not ported? Is that on purpose? Or were you not talking at idle?
Too much timing even at light throttle can cause lean surge/miss

It's ported at the base of the carb. I know this because I hooked the vacuum gauge to it and only shows vacuum at higher rpm's.

 

[furious70]

It's ported at the base of the carb. I know this because I hooked the vacuum gauge to it and only shows vacuum at higher rpm's.

What were you describing when you said the advance drops when you unplug it? Not idle?

 

[Rusty Muffler]

What were you describing when you said the advance drops when you unplug it? Not idle?

No, nothing happens at idle when I remove it. Only above idle does the timing advance more when I reconnect it.

 

[Rusty Muffler]

Just found out today that if I turn one of the idle mixture screws inwards the idle increases and stays the same even if the screw is all the way in? I'm used to having and engine idle real badly when doing this?
I also "heard" that when adjusting that you should go for the highest idle and stop. Carter 4 barrel.

 

[CBODY67]

Obviously, the idle mixture needs to be better-adjusted, BUT that has no bearing on what's happening at 1500-2000+rpm.

Lightly-seat each idle mixture screw, noting how many turns it takes to get there. Then, from the lightly-seated position, turn each one out 1.5 turns. Then start the engine and let it warm up until normal operating temp is achieved. Reset the idle speed screw if needed.

Once things are up to temps, with a dwell-tach installed, screw OUT one idle mixture screw to observe the rpm. Might need to turn in inward, sometimes, to get the highest idle rpm. Repeat fo rthe other idle mixture screw. Might need to go back and forth between them to get to the final mixture-optimized hot idle speed and then re-check when the idle speed is back to specs.

End result, when done, is that you can turn each screw IN to get a 25rpm speed drop, and then back to the highest base idle speed. EACH screw adjusted like that. That is "Lean Best Idle". A much more precise method than using a vac gauge, from my experiences, so leave the vac gauge on the shop counter! Also, at this setting, emissions out the tail pipe (hydrocarbon smell) will be diminished.

No vac gauge?? In reality, the "max vac" method can get to pretty much the same place as using a dwell tach, just that by its nature, the vac gauge does not have the same level of precision as a dwell tach does. When I figured that out, my vac gauge went to the bottom of the tool box and stayed there, except "for grins" to see where it might read.

When the car was built, a vac gauge was a decent-for-the-times tool as dwell tachs, or even tachometers themselves, were "high-tech" and expensive to purchase. More in the realm of genuine mechanic shops than the shadetree wrencher, by observation. Until about the mid-'60s, the factory tachs on Corvettes were cable-driven off of the distributor, for example, although the first electronic factory tachs appeared in the earlier 1960s. As the cable-drive tachs were considered to be more accurate, but worked like a speedometer worked.

Enjoy!
CBODY67

 

[Rusty Muffler]

Obviously, the idle mixture needs to be better-adjusted, BUT that has no bearing on what's happening at 1500-2000+rpm.

Lightly-seat each idle mixture screw, noting how many turns it takes to get there. Then, from the lightly-seated position, turn each one out 1.5 turns. Then start the engine and let it warm up until normal operating temp is achieved. Reset the idle speed screw if needed.

Once things are up to temps, with a dwell-tach installed, screw OUT one idle mixture screw to observe the rpm. Might need to turn in inward, sometimes, to get the highest idle rpm. Repeat fo rthe other idle mixture screw. Might need to go back and forth between them to get to the final mixture-optimized hot idle speed and then re-check when the idle speed is back to specs.

End result, when done, is that you can turn each screw IN to get a 25rpm speed drop, and then back to the highest base idle speed. EACH screw adjusted like that. That is "Lean Best Idle". A much more precise method than using a vac gauge, from my experiences, so leave the vac gauge on the shop counter! Also, at this setting, emissions out the tail pipe (hydrocarbon smell) will be diminished.

No vac gauge?? In reality, the "max vac" method can get to pretty much the same place as using a dwell tach, just that by its nature, the vac gauge does not have the same level of precision as a dwell tach does. When I figured that out, my vac gauge went to the bottom of the tool box and stayed there, except "for grins" to see where it might read.

When the car was built, a vac gauge was a decent-for-the-times tool as dwell tachs, or even tachometers themselves, were "high-tech" and expensive to purchase. More in the realm of genuine mechanic shops than the shadetree wrencher, by observation. Until about the mid-'60s, the factory tachs on Corvettes were cable-driven off of the distributor, for example, although the first electronic factory tachs appeared in the earlier 1960s. As the cable-drive tachs were considered to be more accurate, but worked like a speedometer worked.

Enjoy!
CBODY67

Thanks C body, I jumped the gun a little. The mixture screws are a little hard to get to and I think the angled screwdriver made me think it was bottoming out and it wasn't. I tried it again and it does as is expected, almost dies when within about a half a turn. I did the vacuum gauge method which is about the same as the rpm method and it pulls close to 20 on the gauge.

 

[Rusty Muffler]

Thanks C body, I jumped the gun a little. The mixture screws are a little hard to get to and I think the angled screwdriver made me think it was bottoming out and it wasn't. I tried it again and it does as is expected, almost dies when within about a half a turn. I did the vacuum gauge method which is about the same as the rpm method and it pulls close to 20 on the gauge.

Also CBody, how do you adjust your valves. Hot or cold? I cant move fast enough to do them all without the engine cooling a little bit so I do them cold adding 2 thousands to the hot measurements.

 

[CBODY67]

Perhaps do just one side at a time?