Chances are that you "sucked in" the intake gasket.

 

I recieved the tool I needed to check the intake vacuum, it is Mityvac Model MV800, cost $53 free shipping, it is a brake bleeder tool too.

OK, here we go, vac test result in needle fluctuating around 17hg, the manual says it is the carb running either lean or rich. Normal vac is between 16-22. Ford shop manual says a good engine vac is above 17.

Before that I reinstalled my old Petronix ign module (was new installed 2004), replaced the new coil I installed one month ago with another new one, I believe they are both China or Taiwan made. resistance is almost zero.

Done compression test on all 6 Cyl, the lowest is #2 (155 psi), the highest is 165, they are all within limit as per shop manual (150-200).

Engine idles smoother this time, when drive tested feels some power gain, easy acceleration. I say that new coil I put is the clue.

Engine timed to spec, idle is 500 RPM, adjust the mixture screw inward 1/2 turn, everything looks fine.

Maybe a valve job will refresh the engine, bring the vacuum to normal config, I ordered one flamethrower coil from LMC, I hope that will boost engine performance a little.

Wish this was interesting for you all, I appreciate your ideas, correct me if I stated something wrong.

 

What is your elevation? The higher the elevation, the naturally lower the engine vacuum will be. For example, the same engine that reads 20hg at sea level can read 17hg at 5000 feet.

17 is a pretty good vacuum, but the needle fluctuating isn't. Your needle should be as stable as a rock at idle.

You have great compression numbers. I wouldn't worry about that.

Your idle RPMs sound low. I know when my engine starts to get around 500 RPMs, the vacuum drops, and the engine runs rougher. Stock RPMs is around 650 or so. 700 is a good number to shoot for. See if that alone stabilizes your vacuum.



Try timing your engine and adjusting your idle mixture with the vacuum gauge.

1. Disconnect the vacuum advance and cap off the vacuum line so it doesn't leak.
2. Loosen the distributor.
3. Rotate the distributor to advance the timing until the needle on the vacuum gauge maxes out and won't increase anymore.
4. Retard the timing until the vacuum lowers to around 1.5hg less than the highest vacuum you were able to achieve. So, if you were able to get it up to 20hg, lower it to around 18 - 18 1/2.
5. Reconnect the vacuum advance and reset your idle RPMs.


For your idle mixture, adjust the idle mixture screw until you get the HIGHEST vacuum reading possible. If the RPMs change a lot, reset them and then adjust the idle mixture screw again. Repeat resetting the idle and adjusting the idle mixture screw until no more adjustments can be made and the vacuum is as high as it can go.

 

ftrk66,

This may be basic knowledge, but clarifying what AbandonedBronco said... on our beloved 300/4.9L engine, one rotates the distributor clockwise to retard and counter clockwise to advance the timing.

 

Mine will idle at 500 fairly smoothly but I set it for around 650...vacuum will then be nearly 19 hg.

What AB said about elevation. I can gain a full 1+ hg at Lewiston, ID (about 900' elevation) or sea level like around Seattle. Where I live the elevation is 1900'+ to 2400'+ just depending on where I'm at in the Spokane area.

 

AB:
My elevation is sea level.
For the 500 RPM idle, I have the YFA Carter 1 brl carb and that was not for the 66 year model it is for the late 70's and early 80's. Guess I looked at the wrong chart, did I?.

1986F150six: Thank you for this valuable info.

Harte3: thank you for sharing the info,
Spokane is where I bought my 300 at RAMR back in 2002.

 

Something else to check would be the voltage of the Coil "hot wire". The stock coil hot wire could be a resistor wire. So the coil isn't getting 12V.

Just something else to check.

 

RAM is no longer in business. I bought a long block from them when the original engine in my truck was ruined when the fuel pump sprung a leak to the inside of the engine and I didn't catch it in time. RAM didn't have the best of reputations but the engine I bought from them was fine at 148,000 miles when I swapped it for the modified one I had built by Motor Works.

 

I advanced the distributor to the max, reading was 18 and the needle fluctuates but lesser this time ( one degree +/-), retarded the timing to the best vac reading (around 17), engine sound a little smoother.

Did not do the idle mixture advise as AB mentioned, but later I will. Did not check the voltage at the coil, I will check that later too.

For my satisfaction I will drive the truck 100KM (60 miles), that will ensure if the engine working fine.

 

Yes, when you max out the vacuum reading by advancing the distributor, the needle should start to fluctuate. Then, smooth back out when you retard the timing to the desired setting.

I'd definitely recommend re-doing your idle mixture, especially after re-doing the timing. It'll only take you about two minutes. Preferably before you go on a long drive.

 

The volts at the coil hot wire is 6 volts, I guess that is normal, but some said it should be 12.

Else, I drove the truck nearly 30 miles, nothing abnormal power is noticeable, idling is fine, just need to go in a long trip not less than 100 miles.
Hope the truck keeps in shape.

 

For electronic ignition you want 12V at the coil. The stock points set up had either a ballast resistor or some kind of resistor wire.

 

DSII setup also has the resistor wire in the loom; full battery voltage to the coil at START, drops to around 7 in RUN.





This might help, too:

Duraspark II conversion

 

My ignition is a conventional non resistorized type for the 1966 year model, the only electronic part I have installed is the module inside the distributor(condinsor and points removed).

Thank you for your help.

 

My ignition is a conventional non resistorized type for the 1966 year model, the only electronic part I have installed is the module inside the distributor(condinsor and points removed).

Thank you for your help.