Who Can Diagnose THIS Total Mystery? Win A Prize?

[sgwilson904]

I'm new, inexperienced and at my wits end trying to resolve an issue that's about ready to make me walk away from my Model A, a '29 pickup. Even the best and brightest in our club (Gawd bless 'em for their patience with me) are shaking their heads.

The problem: The engine starts right up, runs cool like top all around town and will cruise at 45 mph cruise for miles until suddenly, with no warning, it starts to pop, sputter, lose all power and eventually just won't go. After it sits and cools for 10 minutes or so, it'll start right up, go on down the road and it should but then the problem is back, usually a little sooner than before.

What we've tried: First, we thought it was a carburetor problem, perhaps crap in the tank, fuel line or in the carb itself. We drained the tank, saw it had been coated and no sign of anything but a few flakes at the bottom and in the clear glass filter at the firewall. With those cleared out (gas bulb is now crystal clear) we also replaced the filter screens at the tank, shut-off valve, and at the filter. Again, it started right up and ran...for a short trip and started the same problem again.

At this point, we decided the problem must be electrical. We re-set the timing (even though it always started with one turn-over) and replaced the condenser. That SEEMED to fix it...but not for long.

At this point, we're thinking the time it took to replace the condenser allowed a cool-down that led to a temporary fix. So next, we replaced the coil AND the condenser. Same result.

When we noticed the wire between the coil and distributor seemed just a little lose, we replaced that, too, and assured secure connections at both ends. This time, she ran 110 miles on a club tour (mostly at 45 cruise speed) with 0 problem until....10 miles from home, the problem was back!

Other observations: There seems to be no real trigger for when this is about to happen.

When it starts misbehaving this way, twisting the choke rod to add fuel to the carb seems to have little effect. Pulling the choke rod out about two-thirds of the way (flooding it with gas) will cause it to sputter a little less and limp a little farther.

Following one of these "attacks," when you then shut off the engine, you can count to about 4 or 5 and there is frequently a single huge, loud backfire (always great for making a dramatic arrival!).

Engine temp is steady (and relatively low at about 170) but once the problem starts, things can (but not always) heat up. (The vehicle has a new radiator that works fine.)

At first, it seemed to happen after five minutes of sustained cruise followed by sitting at a traffic light for 2 minutes and then trying to start moving again...but that has not been a consistent pattern and seems to have gone away lately.

Early on, we thought the dreaded "vapor lock" was a problem because we've been dealing with this since it was 90+ degrees in the Florida summer. Now, it's 70 and we have the same problem and, as I say, the engine isn't overheated when the problem kicks in now.

Somewhere there's somebody who has had this same problem or knows how to fix it. I can't imagine what to try next...and I surely can't keep holding up tours and taking this thing on the road when I have no confidence I can make it there and back, short distance or long.

Maybe we should make it a contest and I could send a nice little prize to the first one who can solve this mystery? <grin> And if that doesn't work, maybe we'll have a drawing and the winner can take this headache off my hands! (Did I mention I'm now on my last nerve with this?)

This newbie sincerely appreciates ANY help/suggestions/thoughts and ideas.