Surging under load after hot restart

Hi,

I've been having trouble lately with a strange problem:

My 1937 Zephyr starts and idles great. So I'm driving for maybe 30 Minutes, no problem. When I stop and turn ignition off, wait a couple of minutes (e.g. getting some go-juice) the car behaves different: It surges and stutters under load in 2nd and 3rd gear, idle is fine, cruising at constant speed up to 45 mph is fine. This condition stays. When I start it up the next day or so, it's fine again. This is a constant problem, and it doesn't matter too much, how long the first drive is (15 Minutes already generates the problem).

So I guess it's heating up problem, but what could it be?

I have checked fuel delivery, changed carb. Playing with the choke doesn't change the condition. One of the carbs is brandnew (One of speedway motors 9 super 7 thingies), the other one is stock Holley.

Anyone ever had such a problem? I'm out of ideas by now...

Thanks in advance for any suggestions!

Kay in Germany.

Kay,

My first guess would be that your car is experiencing vapor lock, in which the fuel lines have absorbed enough heat to start vaporizing the gas within. When that happens, the fuel pump encounters these "bubbles" of vaporized gas and for a brief period can't pump. The solution I have used is to put an electric fuel pump just forward of the gas tank on my 1932 Plymouth. That solved the problem.

Sounds like you may want to take a look at the distributor. The points may be sticking open? I have encounted this condition where the points were fairly tight on their pivot and the spring leaf a little weak. At low speeds they would be fine but as the rpms increased the points would tend to stay open. The point contacts may also need to be cleaned and set?

Yet another possibility is that the gas tank is not venting properly. That might explain why after a period of time the enine restarts and then runs for a short period and the problem returns. The gas cap may be the problem? You might try driving the car with the cap removed to see if this makes a difference.

Hi again,

THANK YOU SOO MUCH FOR THE IDEAS!

It looks like eduzit is right on! I think it was the in line fuel filter that made a little too much vacuum. I moved it from before the fuel pump to between fuel pump and carb. Let's see, if that's the fix. I will let you know!

So thanks again for these great infos!

Kay.

So after the winter, I got back to the problem. It was still there. Now I did a valve lash adjusting job (valves where too tight!) and that helped a lot! It seems, I lost compression when the engine warmed up. I also reset the distributor and now the problem is nearly gone. Nearly means: If the car has been running for way more than 30 minutes I still get a little hesitation when accelerating from ca. 50mph, but I can live with it, since driving that fast isn't what the car is meant for...

So there still has to be a minor problem with the whole system. The coil resistance differs between the two: one is 5 kOhm the other 8 kOhm? Its a 6 Volt original.

Thanks again for all your inputs on this.

it is vaporlock..period. I installed an electric pump at the tank and use it only for these occasional circumstances..

good luck otherwise..I have new fuel lines, clean tank..diff distribs and carbs.. The temp of a car and pump on a hot day is over 100 degrees

I am sorry, I have not modified my car at all, I think the skill is to make em run like Henry did...but the reality is that I have stopped on a 99 degree day after

a 75 mph drive on the freeway only to restart and drive 20 ft and buck, stall stammer...u can flutter the choke and maybe get lucky..

but the low press pump is the simple.. safe..way to go..also helps restart after long period of dis-use

The Hot Rodders have an old saying, "Suck through steel screen, pump through paper".

Beautiful car! Great color! I can see why you would want to drive that a lot, probably a lot of fun!! Paul

Little has been mentioned of the coil. I would suggest that you send the coil to Skip Haney in Fla and have it rebuilt. A failing coil will show the same symptoms as vapor lock. I had a Lincoln with a bad coil that would pick the most inconvenient times and places to stall out and not start. After Skip did his magic I never had any more problems. If you think that the problem is in the ignition, send him the distributor also to have the points replaced and timed.