Re: coil connector. AutoZone has them listed.

Gary: I thought that maybe a Proform HEI from Summit might be good but when I checked the reviews they were very spotty as to quality and durability. I haven't heard anything bad about D.U.I. but they are a bit pricey. I'll probably just stay with Duraspark.

I have also heard quite a bit of badmouthing about Mr. Gasket, so I will probably go with Crane for the advance kit, provided the distributor does not need complete replacement. If it does, I'll probably go with Re in"Car"nation for a re-curved unit.

 

Glad to hear that DUI isn't bad as that's what Dad's truck will have. Tim Meyer is making distributor housings from aluminum and installing DUI electronics in them. It does use an HEI module, but uses an external coil. So, it looks stock but just w/o the DS-II module.

 

Whisler, I don't remember what all you have done but have you tried to fatten up the carb?
Not just the idle mix but the main jets.
I could not get a MC 2100 carb to run right so I replaced it with a Holley 500 cfm 2300 v2 carb. It is half a v4, uses all v4 parts to tune it and made the motor run great.
Dave ----

 

I moved from 53 main jets to 55 jets already, but I do have a set of 57s and 59s that I haven't tried yet. Easy enough to try the 57s and see if there is any change.

 

I'm with Dave on this one. (Not sure how Dave would feel about that...)

I'm still wondering about fuel delivery issues. If not the carb itself, perhaps the volume from the fuel pump is marginal, and has a deficit under high demand.

Here's one thought to muddy the waters: When the truck acts up, is it immediately when you stomp on the gas? That is the instance of highest demand on the ignition system, so that's when I'd expect to see the stumble. An internal carb problem, such as jetting or a bad accel pump, might act the same way.

However, if there's a slight time delay between stepping on the gas and the stumble, that would point towards a fuel delivery problem TO the carb. That would be the carb float chamber being depleted faster than the pump could refill it. That's why I suggested teeing in a fuel pressure gauge at the carb inlet for troubleshooting. Yep, I know, a lot of work, but you're in Twilight Zone territory.

I keep circling back to that because I'd expect your tach to be jumping around if there was a problem on the primary side of the ignition. You've already replaced all components on the secondary side with no change, so that can be ruled out.

The longshot is still AC ripple from the alternator. Not very likely, but it can be ruled out in just a couple of minutes. Who knows how the coil or DuraSpark module would behave under heavy load if expecting clean DC but actually getting dirty, choppy AC. I'm giving away my age here, but I've fixed many 727 autopilots by fixing AC ripple bleeding through into a circuit designed for clean DC.

 

KR - Are you sure it isn't the timing chain?

Seriously though, the bizarre thing is that it'll miss while in the driveway, presumably out of gear. I can't imagine that the fuel pump can't keep up with no load on the engine.

As for the AFR being lean, it misses under heavy load, which means the power valve is wide open.

But, I agree that the tach would be bouncing if there was a primary problem. However, if the primary and secondary are good but the distributor shaft is chattering all over the place then the tach would read correctly but the spark would be coming at weird times.

 

My crackpot theory on that is a weak return spring for the arm on the fuel pump. At low RPM, also a time of low demand, the pump can keep up. At high RPM, the arm would float if the spring action was weak. That would reduce fuel delivery to the carb at high RPM, but possibly pass the pressure/volume tests done at cranking RPM. That's my story and I'm sticking to it. Or maybe a fuel line is partially collapsed and restricting flow under high demand. Or maybe, oh look, SQUIRREL!!!

I'm waiting with bated breath to hear exactly when the engine acts up. I'm also looking up crow recipes in case a new distributor is the fix. I'm leaning towards Cajun style...

 

Lol! I now have a chance to use a line a friend used to say: I'm waiting with bait on my breath as well.

I guess the pump could be bad, but isn't there enough gas in the carb to get past a few rev's in the driveway?

Anyway, this is a conundrum and I'm curious what the culprit will be. I know that I've guessed so many things I'll surely have been right once. Now, if I just knew when,.....

 

just the fit and bulkiness of the hei. Plus I'm going to rebuild the upper half and put new intake, cam, and heads. So why not if it's possible. They make other brands that areally more cost effective than msd.

 

Kr, I feel with my hands........that's what I tell my wife


I guess it could be a bad dist. but being everything has been replaced but the dist. I just don't see it being bad.


I also think if the dist. was bad and was the cause of the miss it would have to show up on a tech. Why? Because the dist. is sending the signal to the box to fire the coil and the coil using that signal to cause the miss it would have to show up on a tach.


I think it is now a fuel issue after the plug/wire change and why I said run bigger jets. It can also be something inside the carb that even going with bigger jets will not fix.
Even with a carb rebuild if a passage inside the carb has a chunk of junk that moves under high demand and blocks the path of fuel and runs lean causing the miss.
Is there a FR meter on this to check when it happens? I am thinking no.
Fuel PSI gauge taped to the windshield for a few test runs is the next best thing.


After my time with the MC 2100 carb I could not get to run right I am not a big fan of them so I would look to replace it but that's me.
Dave ----

 

Ooh! Ooh! Ooh! Mr. Kotter! I know this one!

It's another long shot, but what if the tach itself was the problem? Not very likely, but not impossible. It's connected on the primary side of the ignition. Since we're approaching straw grasp territory, it's as good a gamble as anything else. Disconnect the tach for a test run and see if there's any change.

 

You know the tach is not that far of a reach. I had one that would not let the motor start, car was new to me and was trying to get it to start.
Dave ----

 

But, what if it isn't truly a miss? What if the timing is changing so significantly that the engine is running roughly, but all cylinders are firing?

 

I am pretty sure that I have said this a few times but just in case I am wrong (who me?), this is not a dead miss, more like a stumble or loss of power momentarily. Very hard to explain.
The closest I can come as a comparison is a temporary cross-firing; but I have checked wire routing and separated the usual suspects. The fact that it only does it at about 2800 RPM under a hard uphill pull or 3800 with no load is the clunker. I can accelerate pretty hard to 3500 RPM on level ground with no issues, but that is not really WOT like the hill climb.

Checking for a faulty distributor is next up. Gary's suggestion of bad bushings seems feasible. Or perhaps something wonky with the advance weights or springs. I only have 22 degrees of total mechanical advance at 2500 RPM, so if I lose all vacuum advance on the hill climb, wouldn't the engine fall on its face with only 22-23 degrees of advance under a heavy load? That seems like a long way from 34-36 degrees optimal advance. But what I know about ignition systems is not a great deal (says Mr. Obvious).

 

34-36 degrees is only optimal for certain loads and RPM. That's why the mechanical/centrifugal advance comes in as a curve vs all at once.

Think of it this way: The time it takes for the flame to spread across the cylinder is fixed at a given load on the engine. So the faster the engine turns the earlier the spark needs to happen to get the push down on the piston to happen at the same point on the stroke.

As for the vacuum advance, if you have the throttle fairly well open your manifold vacuum will be somewhere between 6" and 2". But the vacuum advance starts coming in around 10", so you won't have any vacuum advance when you have a lot of throttle on it. So, for the hill climb the vacuum advance is out of the picture. And if you are just slowly revving it up in the driveway you'll have close to full vacuum advance. But, since it has the problem in both cases it isn't the cpvacuum advance.