Initially, when I got it on the road for the first time after the rebuild, it had a Holly 4160 600 cfm. Timing was set at 10-12 BTDC. vacuum was around 16 Hg. It idled fine with no problems. Even under throttle in park or neutral, it ran fine. However, after driving for 10-15 minutes, the car hesitated very noticeably when accelerating normally from a stop. It hesitated as well when accelerating from 20-30 mph. However, it seemed to run smoothly when cruising at highway speeds, albeit pretty richly.

I've since replaced the Holley with a rebuilt 1.08 autolite 4100 (C5ZF-E). Jets are 48 primaries, 58 secondaries, with a 7.5 power valve. I readjusted the timing to 14-16 to get a vacuum reading of 18-19 Hg. As I increased the timing past 16 Hg, the vacuum remained fairly constant, but the idle RPMs kept increasing. I was up to 30 BTDC ( based on a new balancer ) before I backed it back down to 14-16 where I first got maximum vacuum. Is this normal? Should timing be set on max vacuum or max idle RPMs?

I decided to be bold and take it to work this morning. All was fine until I exited the freeway and came to a stoplight ( 25 minutes of driving 55-60 mph). The car began sputtering/missing again while in gear. However, when placed in park/neutral, it ran just fine through all RPMs. No hint of a miss. It would only accelerate, albeit very badly, by a slight increase in throttle. Any more and it felt like the engine would die.

I'm new to this as this is my first ever attempt at automotive work, but am I correct in thinking that this would have something to do with vacuum, since it only seems to occur under load? Would a vacuum leak affect idle as well or just the scenarios I've listed?

I haven't yet checked the total advance, which I plan to do tonight to see if the vacuum and mechanical advance is operating correctly.

I did notice with the autolite, that the vacuum signal at the carb jumps immediately as soon as the throttle plate is opened off idle. ( I can't remember the exact number, but it was over 10 Hg ) I would have thought this to be more of a gradual/linear increase in signal as the throttle is opened more.

The only other factor I can potentially think of would be the distributor, as I rebuilt it and cleaned it up as well. Installed new points and condenser. At the time, the points were gapped to whatever the specs in the Shop Manual stated (can't remember them off hand). I remember being unsure of the mech advance springs when reassembling. I'm not sure that I've got the correct spring in each location. I'm sure this could potentially have some impact on the advance.

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Alex Denysenko
Co-Administrator and Moderator

NHRA/IHRA/SRA member and licensed Superstock driver
NHRA and IHRA SS/LA & SS/MA National Record Holder '00,'01,'02,'03,'04 &'05
First SS/MA in the TENS!
IHRA division 5 Superstock Champion
Fleet of FoMoCo products including 88 ASC McLaren Mustang #28

The Barry of BarrysGrrl

Thanks for the advice. I'll give it a whirl.

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Alex Denysenko
Co-Administrator and Moderator

NHRA/IHRA/SRA member and licensed Superstock driver
NHRA and IHRA SS/LA & SS/MA National Record Holder '00,'01,'02,'03,'04 &'05
First SS/MA in the TENS!
IHRA division 5 Superstock Champion
Fleet of FoMoCo products including 88 ASC McLaren Mustang #28

The Barry of BarrysGrrl

I remember from someone else's post that they had similar issues and the cause was the ground wire from the points to the breaker plate. I just noticed mine is in pretty shoddy shape. Could this be the culprit?

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Alex Denysenko
Co-Administrator and Moderator

NHRA/IHRA/SRA member and licensed Superstock driver
NHRA and IHRA SS/LA & SS/MA National Record Holder '00,'01,'02,'03,'04 &'05
First SS/MA in the TENS!
IHRA division 5 Superstock Champion
Fleet of FoMoCo products including 88 ASC McLaren Mustang #28

The Barry of BarrysGrrl

It will run great until there is a load or the coil gets warm and then it will miss like crazy. Either that or shut completely down.

Drove me bananas on a 302 '71 Comet. We thought it was water in the gas, points, etc.

Just a thought. Hope it helps.

Ed

Anyway, once I got it home, I checked the points and they are just fine. Also, the bowls are still full, so I don't think fuel supply is a problem. Tonight, I'll put the old carb back on that I know worked in order to try to isolate the problem, ignition or carb. If the other carb doesn't improve the problem, I'll try a new coil and hope to hit paydirt.

By the way, the shop manual lists a way to test the coil by checking the resistance across the primary circuit. Would this give any indication if the secondary circuit is faulty?

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Alex Denysenko
Co-Administrator and Moderator

NHRA/IHRA/SRA member and licensed Superstock driver
NHRA and IHRA SS/LA & SS/MA National Record Holder '00,'01,'02,'03,'04 &'05
First SS/MA in the TENS!
IHRA division 5 Superstock Champion
Fleet of FoMoCo products including 88 ASC McLaren Mustang #28

The Barry of BarrysGrrl

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William
I'm too busy workin', to get rich.

68 Coupe
Stock 289
C4
Edelbrock 600/RPM Intake
Pertronix Ignitor/Flamethrower Coil
Thorley's with Cherry Bomb's
2.79's out back(for now)
15"x7" AR ASTRO's(needin' new 225 60's)

First, I pulled off the new carb and was going to install the old carb that I new worked and noticed a significant amount of fuel in the intake. I pulled the plugs and all eight were soaked. I flushed the manifold and cylinders with compressed air and let them sit overnight to hopefully dry out. Next morning, installed the old Holley and plugs and tried again. Still could not get it to fire.

Next, I checked the points. They were new points, originally gapped at .016. Now, they read .014, but still within specs.

I then checked the coil. I first checked the voltage to the coil and it was in spec, so my resistor wire is fine. I then checked for spark by opening the points manually and holding the coil wire to close to the block. I got an intermittent spark. I noticed that I got spark if I waited a while between opening the points. However, when I cycled the points quickly, I wouldn't get a spark. I then assumed it was a faulty coil. Replaced it and still no luck.

Next, I checked that I was getting spark to each plug by using a timing light on each plug wire to see if the light would cycle and it did. I then checked each plug individually by hooking it directly to the coil wire and grounding the plug. I then opened the points to see if the plug would fire and they all did.

I check the dist. cap as well and terminals look good and the cap has no cracks that I could find. I also haven't noticed any arcing at the dist or cross firing.

Finally, reverified that my timing was correct. I found TDC by ticking the starter until I felt compression on #1 and the piston was at it's highest level. The rotor pointed just past (going counter-clock) the #1 wire ( a little advanced ). This also confirmed that my balancer read correctly as well.

The only thing I haven't checked was the operation of the valves that Alex recommended. I assumed since all of the plugs initially were wet, that I least all of the intakes were operating.

As I knew, the Holley that was on the car when I bought it was running rich. The new plugs that I installed (Autolite 45s) after the rebuild were pretty sooty. Could this rich condition have fouled the plugs such that they will not fire under compression? What would a strong spart look like? When I checked the spark of each plug, it would dance all around the tip. It never would arc in the same spot consistently. Plus, it was a little yellow in color. I still have the Bosch plugs that came in the car when I bought it. I tried one of them and it seemed to be more blue in color.

Also, I noticed that I'm down to less than 1/8 of a tank of gas. I still have fuel (I've checked the pump output), but could the fuel be bad or have water in it. Does, the fuel pickup take fuel from the top or bottom of the tank. If the top, this could make sense, because since I've purchased the car, this if the first time I've had under 1/4 of a tank.

Cleaned the plugs, burned the excess gas off the plugs, blew them out with compressed air, nothing.

I ended up dropping the gas tank and cleaning it out as well as the lines. Replaced whatever gas was in tank with new stuff just to rule out gas as the culprit. Replaced the plugs with new Autolites as well. Gave it a shot and still no go.

Finally, got the bright idea to replace the condenser and Voila. She fired right up. ( Well not really. I had to repair a vacuum leak at the carb base gasket I introduced by swapping the carbs so many times. )

I guess I learned my lesson that just because something's "new", doesn't mean it's exempt from trouble shooting. In case anyone's interested, I found a good article on point's type ignition systems and how they work.

Ignition