Vapor Lock/Fuel Perc:Fuel Line "Re-Route"?

[Two Lane]

1971 225c.i. Slant/6 40-thousand miles, Automatic
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Typical common slant/6 problem...fuel line percolation, vapor lock, hard re-starting, etc.

It's a total bummer sitting 30-45 minutes to re-start after warm shut-off.

Have done the "extended tip plug mod", added a Pertronix II module w/a MSD-6. No metal ring-gaskets on plugs. Fresh carb.

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Have seen the fuel line re-routed from fuel pump over the valve cover & on to the carb, in order to avoid the exhaust manifold heat.

The same fellow used A/C line insulation as a cover for the re-routed fuel hose.

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QUESTIONS:

What cured your vapor lock, fuel perc, & hard re-starts on your slant/6?

Any other "mods" to do? One fellow said he improved his engine's re-start probs with a valve lash re-set. Another said the stock location fuel filter
contributed to the prob, acting as a little coffee pot.

------------------Any pics of your cures?------------------

Thank you tremendously, as this beautiful car, wonderful in all other respects, simply can not be driven often or reliably as-is.

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[67Dart273]

I'm a HUGE believer in vapor return systems, so much so, that I added one to my '67. It has not "extra" vent lines, as it's made prior to "smog" stuff, but I ended up adding a return to the front face of the tank. Turned out to be relatively easy

Used a sheet metal awl to punch a hole in the front face of the tank, on the driver's side next to the pickup/ sender. Worked the hole carefully larger until it is a friction fit for a 1/4" tube. Installed the tube in the hole.

Pulled the vent out of the trunk floor, and extended the vent AND the new tube out with scrap fuel line tubing to behind the car.

Plumbed the (drained) tank pickup feed tube to my CO2 bottle off my mig, and allowed CO2 to flow. Actually LIT the gases forced out of the two rear lines, until the CO2 flushed fumes out of the tank. Allowed the CO2 to flow a few more minutes, then hi-temp silver brazed the tube in place.

I previously junked a 70's Duster, and used the carbon can line out of that car for a return line in my 67.

Use a 33040/ 33041 Wix filter. These are 5/16 -3/8" respectively fittings, and have a built in 1/4" return orifice fitting. You simply plumb it to the return line and away you go.

 

[805moparkid]

ok 273 made some good ideas!

some things to check for is the thick 3/8- 1/2" wood or plastic spacer under the carb...

also depending on the set up adding a electric pump to boost fuel pressure can keep the fuel from boiling...

 

[slantsixdan]

Do the Fuel line mod and put in a heat shield (see here; pictures here). Make sure the manifold heat control valve is free to turn.

Install a vapour-bleed fuel filter (NAPA Gold 3040, for example) and run the ¼" vapour line (proper fuel line hose and/or metal pipe, please, not just generic rubber tubing) all the way back to the rear of the car. Because you are working on a '71, you needn't go through the hassle and (manageable) danger of attaching a new tube to the fuel tank itself. You can add the vapour line fitting to the top of the vapour separator in the trunk of the car; see here for detail on how the '71 (+'70 California) evaporative emission control system works. While you are reading up on it, take note that it is aggravating the problem you're experiencing, because fuel vapours accumulate in the crankcase after engine shutdown and flow freely into the intake tract (making the mixture too rich) as soon as you sit down and start cranking. You can eliminate this part of the problem by moving vapour storage from the crankcase to a '72+ type charcoal canister with a purge valve as described here. No changes would be needed at the back of the car to add the canister, just plumb it in as described and install an easily available '72-up crankcase breather (without the extra hose fittings).

Other notes:

• You say it's got a "fresh carb". Uh-oh, what does that mean? If you got a "remanufactured" unit from the parts store, I surely hope you kept your 40k-mile original; "remanufactured" carbs are almost always unworkable junk.

• An electric fuel pump, IMO, will cause more problems than it solves -- discussion here and here.

• Make sure you are using the correct starting technique. For a hot engine, hold the accelerator about 1/3 of the way down (do not pump it!) while cranking, and hold it there for a second after the engine catches.

• Your car will run a great deal better if you set the initial timing at 5°*BTDC instead of the factory 0° (TDC) spec. And if yours happens to be a California car, check for a widget with a wire running to it placed in the vacuum hose from the carb to the distributor. Bypass it by running a hose directly from carb to distributor.

 

[RustyRatRod]

If you want a sure fire way to verify the problem, clamp a bunch of clothespins on the fuel line. They'll absorb the heat and stop it. IF that's what it is. Sounds corny but it works.

 

[slantsixdan]

If you want a sure fire way to verify the problem, clamp a bunch of clothespins on the fuel line. They'll absorb the heat and stop it. IF that's what it is. Sounds corny but it works.

Nope. Myth. Old one. Never been true, never will be. Clothespins are wood or plastic, neither of which conducts ("absorbs") much of any heat. Sometimes the clothespins would space the steel fuel pipe away from hot engine parts, which reduced the problem and led to people "explaining" it by stating their faulty interpretation of what they thought they were seeing.

(You can get metal clothespins, but there are better uses for them -- or so I'm told -- and that'd be a very expensive way to fix the problem. :shock

 

[cudamark]

First determine which is the problem, vapor lock or percolation. If it's percolation, holding the throttle wide open while cranking the engine, will clear it and the engine will start. If it's vapor lock, there won't be any fuel in the carb, line, and/or filter depending on where the heat source is. In my experience, I've never had a vapor lock on a slant 6 but I can see where it's possible if the fuel lines are routed too close to the manifold. I have had many, many cars with percolation problems. Adding a carb spacer usually helps but you may have to add a heat shield like Mopar designed for the late 70's cars.

 

[RustyRatRod]

Nope. Myth. Old one. Never been true, never will be. Clothespins are wood or plastic, neither of which conducts ("absorbs") much of any heat. Sometimes the clothespins would space the steel fuel pipe away from hot engine parts, which reduced the problem and led to people "explaining" it by stating their faulty interpretation of what they thought they were seeing.

(You can get metal clothespins, but there are better uses for them -- or so I'm told -- and that'd be a very expensive way to fix the problem. :shock

Dan, I appreciate your input, but I have actually done this before and it DOES work. Done it several times in fact. I didn't say it was a fix. I said it was a diagnosis tool.

 

[slantsixdan]

Dan, I appreciate your input, but I have actually done this before and it DOES work.

In this universe, wood and plastic do not conduct ("absorb") heat. They're both insulators, not conductors. If spacing the fuel pipe away from hot engine parts with clothespins works in any particular situation, groovy. But it's not because the clothespins are "absorbing" any heat. When what you think you are seeing is not possible, it's better to figure out what you're actually seeing than to argue that the laws of physics don't apply to your car.

 

[805moparkid]

In this universe, wood and plastic do not conduct ("absorb") heat. They're both insulators, not conductors. If spacing the fuel pipe away from hot engine parts with clothespins works in any particular situation, groovy. But it's not because the clothespins are "absorbing" any heat. When what you think you are seeing is not possible, it's better to figure out what you're actually seeing than to argue that the laws of physics don't apply to your car.

everything absorbs heat on some level dan... i rock will absord heat and eventually explode lol...

im sure the cloths pins tricks work untill they to are "saturated" with heat and then the problem may arise again...

now i have never tried it so im not backing either one but to say it (any material other than "conductive materials") wont absorb heat isn't true...

 

[RustyRatRod]

In this universe, wood and plastic do not conduct ("absorb") heat. They're both insulators, not conductors. If spacing the fuel pipe away from hot engine parts with clothespins works in any particular situation, groovy. But it's not because the clothespins are "absorbing" any heat. When what you think you are seeing is not possible, it's better to figure out what you're actually seeing than to argue that the laws of physics don't apply to your car.

Not arguing the laws of physics Dan. You're doing that. I don't care what the physics say....I've done it. Stop and think about what you're saying. If that's so, then why do people bother to insulate their fuel lines with insulation? Simple. Because it keeps heat from gettin TO the fuel line. Same thing. That's why it works. Because the wood insulates the fuel line temporarily allowing you to isolate whether or not there really is vapor lock. In the end.....insulate.....absorb....what the **** ever. It WORKS.

 

[green1]

this is funny, clothes pins insulate; are the piled on like a bumble swarm?

 

[RustyRatRod]

this is funny, clothes pins insulate; are the piled on like a bumble swarm?

Yeah actually. I put as many as will fit in a given space exposed to heat.