My car gets all pissed off at me sometimes......

[752dbl02]

..after its been driven normally (which in my case, includes some aggressive driving), parked, and then driven a short while later, it falls on its face at about 5k RPM. It almost seemse as if its running out of fuel..

I did ask one of the old school mechanics that I work with about it, and he said that it may be that the dist. isn't advancing the timing correctly all the time. Anyone ever heard of that happening? I have no idea what dizzy is on the car, as it is a '75 and it has a mech. adv dizzy, and to my knowledge, 74-76 had vaccum adv distributors. Correct me if I'm wrong here.

But a dist. going slowly bad would explain why the car sometimes seems to have a more defined powerband, and sometimes it seems a tad lackluster, but hell, the weather can do that too.

Car history wise, I just rebuilt the carb per CD's jetting RX, it has a brand new fuel pump and filter as well.

Any ideas??

TIA

Chris

[Guest Anonymous]

I have no idea what dizzy is on the car, as it is a '75 and it has a mech. adv dizzy, and to my knowledge, 74-76 had vaccum adv distributors. Correct me if I'm wrong here.

Any ideas??

TIA

Chris

After 34 years are you sure your distributor is original? It is not hard to lift the hood and closely examine the distributor to look for numbers on the side of the distributor body. Nor is it hard to remove the cap and figure out the nature of any vacuum retard or advance. The next step would be to check for movement and sloppiness in the plate holding the points and other loose points. And how about that rotor? Is it a rev limiter type?

Plugs that are the wrong heat range, Plugs that are improperly gapped, retarded ignition timing and even slightly retarded valve timing are among the many things that could cause or contribute to the poor high speed operation. Does the engine run hot at high speed? Maybe the radiator is marginal and occasionally is taxed beyond its limits?

The jetting prescription is no panacea for all 32/36 equipped engines. It is a baseline and a couple of size differences can make big difference. Smaller air correction jets? Larger mains? DIfferent emulsion tubes? How about that float level? Maybe you really are running out of gas!

If your engine hasn't been modified or severely worn, make sure it is tuned to specs and start from there.

Read the plugs, your tailpipe, the manuals and the archives.

hth

[Guest Anonymous]

As many times as this question arises on this board, there is the suggestion that you double check the linkage from your right foot to the carb throttle plates.

Remove the air filter.

With engine not running, have someone sit in driver seat and depress accelerator pedal to floor. You look directly down the mouth of carb and make sure that the throttle plates are fully opening!

I shouldn't have to remind you to make sure the choke (of any variety) is fully releasing when engine reaches operating temperature OR you may find your engine starved for air at high speeds.

[752dbl02]

I said that i know that the distributor isn't original. The 74-76 models came with vaccum advance distributors, and mine is a mech adv. What i ment by not knowing what type of distributor was that i dont know what it came off of, tii dist, or one of another aftermarket variety.

CD's jetting RX works great, and has for the past 4 months since i rebuilt the carb, including resetting the float gap. The car has run like a top ever since. The cap and rotor are fairly new, i replaced them about 8 months ago, and there is no serious wear on the contacts on the inside of the cap, so that is ruled out. Play in the retaining plate that holds the point doesn't sound likely, as it will run great one min and stumble the next, and it only happens every once in a while, and the same RPM. Loosness in that plate would cause it to run poorley more often. I may have not mentioned it before, but after it did this to me yesterday, i motored on a little bit down the road, punched it agian, and it ran fine.

The radiator being clogged or over worked wouldn't have any correlation with ignition issues, misgapped plugs wouldnt do this intermintently, and really and truely dont have that large of an impact. Like i said, i recently personally rebuilt the carb, so i know that the linkage is fine. Choke wise, its a water choke, so there isnt to much linkage there to fiddle with. Does it run hot at high speeds, yeah at 90mph it will kinda creep up on the temp gauge, but that is expected with the car almost topped out.

My main concern was wether the dist was advancing the timing properly throughout the powerband.

The mechanic that works at the shop that i work at pointed me in this direction, and i was just wondering if anyone had ever experienced this happening randomly on an otherwise great running car.

[Guest Anonymous]

I said that i know that the distributor isn't original. The 74-76 models came with vaccum advance distributors, and mine is a mech adv. What i ment by not knowing what type of distributor was that i dont know what it came off of, tii dist, or one of another aftermarket variety.

CD's jetting RX works great, and has for the past 4 months since i rebuilt the carb, including resetting the float gap. The car has run like a top ever since. The cap and rotor are fairly new, i replaced them about 8 months ago, and there is no serious wear on the contacts on the inside of the cap, so that is ruled out. Play in the retaining plate that holds the point doesn't sound likely, as it will run great one min and stumble the next, and it only happens every once in a while, and the same RPM. Loosness in that plate would cause it to run poorley more often. I may have not mentioned it before, but after it did this to me yesterday, i motored on a little bit down the road, punched it agian, and it ran fine.

The radiator being clogged or over worked wouldn't have any correlation with ignition issues, misgapped plugs wouldnt do this intermintently, and really and truely dont have that large of an impact. Like i said, i recently personally rebuilt the carb, so i know that the linkage is fine. Choke wise, its a water choke, so there isnt to much linkage there to fiddle with. Does it run hot at high speeds, yeah at 90mph it will kinda creep up on the temp gauge, but that is expected with the car almost topped out.

My main concern was wether the dist was advancing the timing properly throughout the powerband.

The mechanic that works at the shop that i work at pointed me in this direction, and i was just wondering if anyone had ever experienced this happening randomly on an otherwise great running car.

You did not state the distributor was a replacement. You said it was mechanical and all of the Bosch distributors are driven by centrifugal advance weights and/or vacuum advance and retard systems. Since you did not identify the distributor as being from a tii or an 002 or 008, someone might interpret your post to mean you have a stock distributor which has an inoperative vacuum advance/retard mechanism. You also stated you "just" rebuilt the carburetor, not that you performed this 4 months ago.

You may have your reasons for targeting the distributor, and maybe you are correct.

Is the distributor hold-down clamp tight? Or just snug? It is possible that the distributor has some longitudinal movement so that the position of the distributor and the timing changes with vibration or some other influence. As remote as it may sound, I discovered this with someone else's car. The caked-with grease distributor seemed secure and at low speeds things seemed steady and everything was contained by the well secured plug wires. Even if your distributor is secure, is your timing set to spec? Do you hear any pinging under load? If not, and you do not have a timing light, advance the distributor to the point of pinging as described elsewhere in the archives. Maybe your timing is retarded enough to permit what seems like decent performance except when things are occasionally pushed hard.

Perhaps unnecessary, it is not that hard to partially disassemble the distributor to expose the centrifugal advance assembly. Maybe the weights are sticking, maybe the springs are stretched or maybe only one of the springs are connected. You can avoid any disassembly if you know what to look for. If you had a vacuum advance setup you would have noticed the points plate actually moves. It is the advance or retard pot that actuates it. Since you are using a pure mechanical advance this is a non issue.

If you have a timing light and a tach you could double check the distributor's operation at all rpm and maybe duplicate the problem. Most of the J4 distributors reach full advance well before 5000 rpm (more like 3500) so the fact that you only encounter the problem nearer redline makes me think the problem is other than the distributor's advance mechanism. At anything near red line a sloppy distributor may be more obvious than at lower speeds, but like I said before, if you get a rock steady timing mark and there is advance with speed consistent with the curves plotted by PatAllen in another post, you can connect the dots. This does not discount a loose coil wire a weak coil, a loose or bad condenser or plug gaps that are overstressing the coil.

The fact that your problem is sporadic suggests something is loose - or the engine is being starved of air or fuel. A loose choke plate doesn't make a lot of sense, but it is possible. But so are a lot of things like your carb is dirty (even though you cleaned it, it is only as clean as the gas and air flowing through it and that includes backfiring and crankcase fumes) or you have a coil that is on its way out (sometimes described as mimicking a bad fuel pump). Plugged air filter or restricted exhaust.

Even if you thing your float levels are correct, it may be that it is borderline correct and you are still suffering a slight amount of fuel starvation at maximum fuel consumption time. Does this happen during hard cornering per chance? You were asked if your engine was running hot, maybe its running so hot that the heat is being convected to the intake manifold and the fuel in the carb bowl. Maybe the heat is just enough to cause a bit of boil off? Stop or slow down and things momentarily cool off enough for the problem to disappear? You mentioned the weather having an effect on the engine's performance. If things are running hot, a lot of the heat warms both the carb and the air going into the carb. There is a reason for cold air intakes and while they are not too effective, maybe you just have too much heat and it is leaning out your mixture? Reading your plugs would help with this diagnosis.

Valves adjusted correctly? Maybe the lash is a little too loose. Above .008 will get you a smooth idle but high end breathing is slightly restricted. This would not explain the sporadic nature of your problem.

Only the tii was without a vacuum advance (until 1974 US Models) If you search through the archives you will find that some automatics had vacuum retards and the later years (manual and auto) had both vacuum advance and retard systems that were designed with emissions in mind.

Good luck in DeKalb or Fulton!