old cars and hot starts.

[lloyd3]

Does this ever happen to you? Pull into the gas station, shut her down, feed her 10-gallons of Premium, hop back in, light her up and then roar back out onto the acceleration lane to get back on highway. On warmer days everythings great until you really accelerate hard, bark second and then third, and then you get the heaves and power-loss in 4th gear. I'm guessing it's the fuel percolating in those hot Carter AVS secondaries.  I only notice this on very warm days (80 plus), and mostly at the gas station 5-miles from the house. Once it's been running for a while, no issue. It's only after I shut it down and then gas-up when it's hot.  I had a Super Bee that would do this too.  I always used to think that I had burned a set of points, but then it would smooth out and be fine. Any drop in ambient temperature would also cure it and I'd forget about it until the next time I gassed up at the end of a hot day.

[myk]

In my experience, the heat would affect the car as I turned the key, meaning I would get a slow crank from a heat-soaked starter or  hard start with the percolating fuel in the carb's bowls.  If you're able to start your car with no issues, then get it going on the road with no issues until you get to higher speeds, I would imagine that something else is going on.  The symptoms you're describing matched the issues I was having when my electric fuel pump was starting to crap-out...

[lloyd3]

MYK: This unit is a stocker (well, mostly, the return fuel-line isn't hooked up), so no electric pumps. It is almost certainly heat-related and is intermittant enough to where I've never fully solved it.  It never lasts and doesn't seem to happen under 70 degrees F.  Now, I'm way over-due for a tune-up (plugs, points, etc.) and perhaps a carb rebuild as well, but this is a recurring problem with this car (and, after 18-years, I'm sensing a pattern).

[twodko]

Do you have a heat bypass valley?

[Sublime/Sixpack]

I'd connect up the return line to start with.

[lloyd3]

twodko: Heat bypass valley? You've got me on that one. If you're asking if this is a stock intake manifold, it is. I know some of the aftermarket units eliminated several features of the standard intakes.

Sublime: Hook up the return line? I'd love too, but I fear that it has largely gone by the wayside.  Most of the cars I've seen over the many years I've played with them were also missing that system as well. For many (if not most) shadetree mechanics, the little factory filters with the return line fitting were hard to come by and the system was modified to use a standard filter, bypassing the obtuse little return line system. A common modification that occured very early in the lives of most of these cars (at least where I grew up). There might still be sections of it on the car, but it hasn't been used for  the last 18-years that I've owned it, and for likely much longer than that.  It has never been a performance issue before, to my knowledge.

[myk]

Twodko is refering to the valley pan gasket that may or may not block the heat crossover feature in some manifolds.

What I was referring to in my earlier post was fuel pump issues; it seems your car has no problems starting up but has trouble at higher speeds.  This could happen to either a mechanical or electric pump...

[Ghoste]

A carb insulator can help too.  Modern fuel and Carter style carbs you need to likely combine a few things to combat it.

[lloyd3]

All good ideas, thank you! I don't know what pan gasket was used when this engine was gone through the last time (~1991?). Carb insulators were all the rage 30-years ago, and I was never certain just how much they really changed things. This set-up has one that looks to be almost stock (maybe a little better). This, of course, lets the choke mechanism arm still work. The fuel pump was replaced maybe 8-years ago by me and has not showed any signs of problems since. I even had to replace the coil because of a similar issue many years ago. Yet another potential culpret!

[twodko]

The valley pan thingy is a Felpro kit that incident a new intake gasket set and a new metal
valley that blocks off the heat "pass through" designed to warm up the carb.
Myk and others know the correct terminology but I understand it was intended to
Help the fuel system function better in colder climates.

What happens without this heat bypass kit is after the engine is up to operating temperature
and you shut it off, the fuel in the carb and maybe the immediate fuel line boils off. The engine
is then a bitch to restart.

Did I run this down correctly guys?

[Dino]

Sounds about right. 

The valley pan does indeed block the crossovers intended to warm up the fuel on cold days.  If you drive in cold weather a lot, closing them off will pretty much render the choke useless but there's ways around it.  Even then it's still a good idea as the car will be much happier on warm days.  A spacer between carb and manifold also keeps the carb body cooler and the thicker spacer you can fit the better.  The valley pan really improved the situation on mine but it was the phenolic resin body on he thermoquad that really helped keep the fuel cooler.  I used to have to crank the car around 5-10 seconds after filling up as it simply boiled the fuel out of the bowl.  If you shut the car off and stayed in the seat for a minute, the fuel smell would become overwhelming and that's absolutely unacceptable.

A blocked crossover and spacer will definitely help but your situation is a bit different as you don't seem to have hot start issues but starvation issues.  The pump should not be an issue, either it works or it doesn't but do yourself a favor and get the pump push rod out.  If it's worn you would run into that issue.  It should measure 3.22" I believe.  Anything shorter than that and you need a new one.  Oh and I'd still replace the pump with a high volume Carter or Milodon.  Won't break the bank and will run better than the stock pump.

[lloyd3]

Thanks Guys, I appreciate that information. I suspect the crossover hasn't been blocked, and at god-knows how many miles, the pump arm might be a little suspect, but....I had it out today to run some errands and meet a friend for coffee and it ran fine (it was about 10 degrees cooler than yesterday and I didn't buy any gas).   

I did have some kid do a fly-by on my right, at a light (by driving straight through the turn-lane paint). He was going way too-fast (70mph?) and was way too-close in his white POS Japanese fart-can car (it might have been an early Civic, but it had been so mucked-with I really couldn't tell what it was).  It kind-of ruined my morning because it was way too-close. He missed me, the light pole, and certain death by mere inches.  I've got to learn to stay away from the suburbs. Rural cruzing is the far-better option here.

[Patronus]

First off, get rid of the points.
Second, get rid of the Carter.

[myk]

A blocked crossover and spacer will definitely help but your situation is a bit different as you don't seem to have hot start issues but starvation issues.  The pump should not be an issue, either it works or it doesn't but do yourself a favor and get the pump push rod out.  If it's worn you would run into that issue.  It should measure 3.22" I believe.  Anything shorter than that and you need a new one.  Oh and I'd still replace the pump with a high volume Carter or Milodon.  Won't break the bank and will run better than the stock pump.

THIS.  Again, the car reportedly has NO problems starting up and driving off; it encounters issues when it tries to go to higher speeds.  The fuel pump pushrod is a good idea too, and I was starting to think about the distributor advance, but again, none of this should be affected by the heat level of the engine and its components...

[lloyd3]

Patronus: This car is as originally equipted, 4428s Carter AVS carburetor and factory Prestolite (?) dual-point distributor. For as long as I have owned it, it has run almost trouble free. Performance has been more than adequate for my needs, and what's more, it is "correct". Highly modified cars are simply not as interesting to me, and when I look at the resale value of modified cars as compared to original cars, the market tends to prove my point. I had a similar issue about 8-years ago that required a replacement of the coil, as it was shorting internally as it warmed up. I'm guessing that I have a similar challenge here.

myk: Your diagnosis is spot-on, but i think you may have missed a few of the finer points. This issue only occurs when I've gassed-up on a hot day, with "hot" being 80 degrees Fahrenheit or more. The fuel system seems to be the more heat-affected component, but ignition can be impaired by heat as well.  I'll have to sort through both systems to try to solve this one.

[ACUDANUT]

First off, get rid of the points.
Second, get rid of the Carter.

X2

[HeavyFuel]

Maybe:

The fuel in your line near the engine, not the carb, is at a temp level where it is just about to boil.  When you pop the fuel tank cap, you release the small amount of pressure that has built up between the fuel pump and the tank.  The fuel in the line boils (vapor lock) due to the lowered boiling point caused by pressure loss.

Possibly, you are able to drive off for a short time because your engine is living off of the fuel in the bowls.   Then the vapor lock reaches the fuel pump. 

I think a vapor separator and a return fuel line might solve your problem.

[Dino]

Maybe:

The fuel in your line near the engine, not the carb, is at a temp level where it is just about to boil.  When you pop the fuel tank cap, you release the small amount of pressure that has built up between the fuel pump and the tank.  The fuel in the line boils (vapor lock) due to the lowered boiling point caused by pressure loss.

Possibly, you are able to drive off for a short time because your engine is living off of the fuel in the bowls.   Then the vapor lock reaches the fuel pump. 

I think a vapor separator and a return fuel line might solve your problem.

I have to agree.  You say you have a return line but not hooked up.  Clean it out and get a separator.  Remove the pump and check the pushrod. 

[lloyd3]

Gentlemen: What you're telling me makes sense. Ma Mopar, in her infinite wisdom, put that return system in place for a reason. Now all I've got to do is figure out what remains of it and how to put it back together, both at the front of the car and, at the tank. 

Not hard to fugure out why why all-original, numbers-matching cars command such high prices. It's because you don't have to undo all the ham-fisted things that have been done to them over the years.

[Cooter]

I don't care how 'correct' a car is, It was designed to be run on 100 plus octane fuel @.35/gal. I'd rather have one that ran to the best the factory couldn't/wouldn't allow.
today, there's resale, then there's bringing less cause it won't perform correctly on pump swill they call fuel.
all the original parts fit nicely into the trunk when sold.

Back 40 years ago, cast iron Intakes, 2" single exhaust, 4lb mech. Fuel pumps, points ignition, etc. Mighta worked ok.
today however, with aluminum intakes that look almost stock, as well as Pertronix, I can see no reason running these troublesome parts today, other than some paranoid psycho worried about all electronics being shut down by Gov.

[Patronus]

I just hope it doesn't end up a big black mark in the shoulder.

[Kern Dog]

MYK: This unit is a stocker (well, mostly, the return fuel-line isn't hooked up), so no electric pumps. It is almost certainly heat-related and is intermittant enough to where I've never fully solved it.  It never lasts and doesn't seem to happen under 70 degrees F.  Now, I'm way over-due for a tune-up (plugs, points, etc.) and perhaps a carb rebuild as well, but this is a recurring problem with this car (and, after 18-years, I'm sensing a pattern).

My understanding is that the cars didn't have what you call a return line, but instead a ventline to return vapors back to the tank.

I get this type of Vapor lock from time to time. It is worst in hot weather as you say. You can be running the car hard then shut it down for a moment or two. The fuel just sits in the lines and carburetor and actually starts to boil.
Several "fixes" for this. A wooden or plastic carb spacer works well as an insulator. An actual return line is great too...it keeps the fuel in motion instead of having it sit under pressure absorbing more and more heat.

[lloyd3]

Patronus: The real fire-breathers were the Pontiac Tri-power cars. I remember seeing plenty of those cratered by the side of the road. Most of the Mopars I've seen burned were the product of the timing chain being worn to the point of belching backfires and no air-cleaner.

Red 70 R/T:  As a practical matter, whatever you call it, the return/vapor line was likely an attempt by the Chrysler engineers to address the problem of big, hot engines that tended to boil the gasoline in the fuel-lines on hot days. Nontechnical people (& young kids like me, in the 70s and 80s) who worked on these cars just to keep them running, didn't realize that fact and disabled the system by using a non-factory fuel-filter replacement.  (No wonder why I remember my cars more fondly in the Spring and Fall!)  I'd guess that 95% of the cars remaining have this system disabled as well.