390 shakes at 1000 rpm – 1500 rpm – 2000 rpm, runs smoothly at 3000-3500 rpm.

[C6AE]

I didn't notice it, but have you put an dial indicator on the flywheel/crankshaft assy?
(I.E. is it concentric and square? I have had one engine where the crankshaft flange was not true. The man that balanced the rotating assy caught it. I remachined the flange in the lathe, it was out about .005" which is magnified at the flywheel rim!)

[oldiron.fe]

last easy things to try possible carbon tracks in dist cap often does wierd things try new one and different carb possible metering change / valve lift bad lobe/spring also can do strange things -good luck

[Clark Coe]

I didn't notice it, but have you put an dial indicator on the flywheel/crankshaft assy?
(I.E. is it concentric and square? I have had one engine where the crankshaft flange was not true. The man that balanced the rotating assy caught it. I remachined the flange in the lathe, it was out about .005" which is magnified at the flywheel rim!)

Using a dial indicator, I measured .008” of Flywheel Clutch Face Runout. This was measured at the very outside diameter of the McLeod flywheel. While .008” is not a great value, it is inside of the Ford specification of .010” maximum.

[Clark Coe]

Last November, I had total knee joint replacement on my right leg.  I am still recovering from that surgery (also recovering from twice-a-week, extensive, ongoing physical therapy).  As such, I can work in the garage until the swelling and pain forces me into the house for an ice pack.  But I continue to work on my 2000 rpm vibration.

So far, I have successfully identified the following items are NOT causing my 2000 rpm vibration.

Not the spark plugs. Plugs are clean and dry. One side of porcelain is white (front row), the other is dark tan (back row). Gasoline is 91 octane unleaded premium. Checked the gaps to .035” and reinstalled plugs….be sure to recheck the gaps if you drop them on the concrete floor.       Any problems here?   Some dark speckles?




Not the plug wires. Replaced wires with new, premium NAPA – Belden EDGE  BEL 7000142. The new NAPA 7mm wires all measured very low resistance, 4900 to 5500 ohms, I was impressed. The old, previous Motorcraft wires measured 15,000 ohms (plus/minus).


Not the rotor, but I replaced it anyway with a NAPA – Echlin ECH FA 157. Here is the original.



Not the Motorcraft distributor cap, but replaced it with a NAPA – Echlin ECH FA79 (brass terminals). Here is the original, clean as a whistle.



Not the old, factory coil. My Ford coil tested good to Ford specs, Primary = 1.5 ohms. Secondary = 7500 ohms. Not sure if orange color arc is good, but it would jump +3/8” inch. The spark color across .035” gap on an Autolite plug was a satisfactory blue/orange color.

[Clark Coe]

Yesterday afternoon, I installed a Pertronix II ignition module and the supporting Flame-Thrower II ignition coil. This did not make the 2000 rpm shake disappear, but the engine seems to start a little easier and settle to an 700 rpm idle sooner. Measured the voltage at the + terminal on the coil and got 11.98 VOLTS. Guess the resistor wire does not work, I was expecting 9 volts.


What to check next? At 2000 rpm, the ignition advance is 27 degrees, does that seem correct? At 2000 rpm, fuel is dribbling out of the primary boosters, looks kind of sloppy as it piddles out. Should the carburetor be metering the fuel from the boosters at this time?

The primary jets are #66. Would trying #68 jets be the correct direction?…richens the mixture a little bit for the single plane Streetmaster intake?

Thanks for everyone’s input and suggestions. Remember, it’s Valentine’s Day….hug your honey!   

Clark

[GerryP]

Speckling on the plugs is usually a sign of detonation.  But it depends upon what the specks are.  Sometimes, it's just carbon spotting.  Sometimes it's aluminum from the pistons.

If you are sitting still and the engine is turning a stable 2,000 rpm, no fuel should be coming from the boosters.  If you wang the throttle and the carb is right, you can usually get booster flow.  If you open the throttle by hand and the engine is running at 2k RPM, the throttle isn't open very far and you are operating on the idle and intermediate circuit.  Fuel coming out of the boosters could mean your fuel level is too high or you have a very tiny air bleed in the main metering.  Booster fuel comes from the main jets and the power valve.  But check your fuel level first.

What size is your carb?  A 66 jet would be fine for a 600CFM carb.  That's too small for something like a 750CFM.  And a single plane always takes more jet than out of the box.  If out of the box was a 66 jet, then you need around six sizes larger, or around a 72.  You might have a lean surge going on there.

[Blueoval77]

Bah that fuel "Dribbling" out can cause a myriad of things depending on how much there is . Ive had a few act common from that over the years....Didnt someone mention before about swapping a known good carb just to see if there was any change ?

[machoneman]

Bah that fuel "Dribbling" out can cause a myriad of things depending on how much there is . Ive had a few act common from that over the years....Didnt someone mention before about swapping a known good carb just to see if there was any change ?

Yes, I did. Beg, borrow or steal a known good carb.....................

[chris401]

You asked what to check next, did you check the running compression that was suggested earlier? Look in your compression gauge instructions.

[Blueoval77]

Sounds unrelated but for whatever reason the two barrel Holleys on the small Ministock engines I have fooled with over the years were prone to that dribbling deal at part throttle and I cant remember now what I did to stop it but it was very very annoying...
Maybe if I bang my head against the wall the answer will fall out.... There was a logical answer for it...

[Clark Coe]

Depending on which TV station we listen too, tonight's low temperature forecast for eastern Nebraska is -27F to -30F. High temperature forecast for tomorrow is ZERO. Because of the cold weather today, the Omaha area electrical power company was doing controlled brownouts to regulate power consumption. Didn't happen to my house, at least not yet.

So until the outside temperature increases by a bunch, I am keeping the garage door down and not completing any more running tests on my 390. Not messing with anything related to gasoline in the garage. Later in the week, I am going to check the fuel levels in the carburetor bowls and clean/blow out the air bleeds. But not inside my heated/attached garage.

Thank you to everyone for you suggestions and insights.

Clark

[My427stang]

Clark, sorry I couldn't get to you.  Been swamped and cold weather slowed me down as we look for homes outside of town. 

A couple of things.

1 - Compression check is smart, doesn't hurt to know what you are seeing even if it is good
2 - Do you have any valve train noise when the shake starts?
3 - Have you looked at the advance curve as it comes in?  Might be hard to do with one person, but it should be consistent with RPM, if it jumps, maybe the advance weights are sticking and its retarded then releases.  You could add 10 degrees initial after it starts (can't really drive it that way, but if it changes it tells you something.  No load it'll be fine)
4 - Could you record a movie of the exhaust when it's in the shake?
5 - When it is hot, and the choke is open, if you cup your hands over the carb, does it rev up slightly before it chokes? (Don't use the choke plate, use your hands, watch your jacket and hoodie for the fan etc)

After that,  likely smart to bolt on either a 600 I have or a 3310 and see what it does.  I am working out my schedule, sorry I vanished, we can likely get together soon if you don't figure it out

[shady]

Was the Torino that you pulled the engine from crashed? If not, did you drive it b4 pulling it, noticing any vibration? You had this vibration from day one of the rebuild? I had a 289 that I went through with this. Pulled it from a crashed Mustang that was hit hard and low in the front. I just put up with it until one day a rod nut vibrated loose and it puked it's cookies. I too had changed transmission, clutch & flywheel to no avail.

[oldiron.fe]

   unlead gas hard to read plugs- yours may look lean  check w/known carb/fuel psi-be positive !! timing-spark plug heat range or new set -if available o2 sensor - total fresh fuel - I like ngk plugs-bp fuel     after all the items have checked out you may need to get inside engine vs chasing all things you have worked at  esp. if internal before hard damage happens-worked at ford dealer early 70s seen factory .030 piston on one cyl!! balance issue!! if internal and done you can enjoy rather than long term issue good luck

[Dr Mabuse]

   .030 piston on one cyl!! balance issue!!

Ford over size replacement pistons are the same weight as standard. OEM warranty repairs allowed individual cylinder boring and piston replacements.