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 What to do about Winter Fuel in hot temperatures? 
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Joined: Sun Jun 23, 2013 1:41 pm
Posts: 366
Location: Phila. Penn.
Not sure where to post this, but the carb is a Holley and the problem was it wouldn't take a load at interstate speeds when the air temperatures were 80 F yesterday afternoon. I know darn well this is the damn fuel because I've been through this before, worse actually, because this time it only seemed to be a problem when the carb was on the main circuits. It would gasp, lose power, and I could let it drop back to 50 and then feather it to 55 mph (2600ish rpm) and keep moving up the inclines.

According to the EPA website, summer fuel isn't mandated to be at the pumps until May 1.

So my question is what can I do in the meantime?
My guess is that the light end of the fuel isn't making it into the cylinder, so richer jetting probably isn't going to help.
Could I be wrong about that?
How about timing? If vacuum advance was reduced so it fired later, might there be more compression and density? enough to ignite the fuel?

Carb is open vented (no vapor recovery) 4150 vacuum secondary (3310-3) with annular primary boosters.

awful glad I didn't commit early to the Tracknite this Thursday.


Tue Apr 11, 2017 8:40 pm
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If the fuel line between the tank and engine mounted pump is near the exhaust system, or it gets near or above 100 degrees under the car, the fuel is boiling to vapor in the line ("vapor lock") and the pump can't pump vapor. If the engine mounted pump is getting hot, same deal, the vapor pressure is greater than the head pressure between the tank and pump.


Wed Apr 12, 2017 3:02 pm
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Joined: Sun Jun 23, 2013 1:41 pm
Posts: 366
Location: Phila. Penn.
Yes, that's a good possibility. It didn't show up at all last summer, even when the engine compartment got so heat soaked the nylon fuel fitting gaskets failed. But if it's vapor pressure and the winter RVP is higher, then it might be just that much difference to make it happen.

Most of the fuel here is what they call Complex Model RFG, but if I understand it correctly it still should meet 8.5 RVP in summer and is allowed 11.5 RVP Winter. Also that Refiners need to supply Summer blend by May 1, but Retailers have until June 1 to be switched over.

There is one location on the fuel supply line to the pump (engine mounted) that runs close to the headers.
It's covered in insulating fire sleeve, but I'll see what else I can do there.

If it is vapor lock in the pump feed, then am I correct that it should show no pressure on the outlet side once the bowl inlet opens?
If so, I'll dust off the fuel pressure gage and reinstall it.


Wed Apr 12, 2017 7:14 pm
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Joined: Sun Jun 23, 2013 1:41 pm
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Location: Phila. Penn.
Mattax wrote:
If it is vapor lock in the pump feed, then am I correct that it should show no pressure on the outlet side once the bowl inlet opens?


Following up on this. Is there a way to identify vapor lock if its in the output side of the pump?
Will the pressure gage go above normal and then drop when the fuel bowl float drops?


Thu Apr 13, 2017 6:00 pm
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Joined: Sun Jun 23, 2013 1:41 pm
Posts: 366
Location: Phila. Penn.
After looking over the fuel line, only the rubber hose to the pump is uninsulated. I can cover that, and add reflective over the hard line insulation.

While rummaging through my box of fuel lines etc, I dug out a kit that a Chrylser parts manager once suggested I pick up if I could.
IIRC he said it was a Chrysler fix for vapor lock. It's been years since I looked at, and thought it interesting enough to share.
Not sure its for vapor lock, but it could be.
It's a bypass around the fuel pump for tiny amounts of fuel, or more likely vapor.
Basically it consists of two Tees made of heavy walled 0.130" O.D. brass tubes with a cap on each. There is a pin hole in the cap that's maybe 1/2 the diameter of a #80 drill bit. Originally a translucent hose connected them as a bypass.
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Thu Apr 13, 2017 6:14 pm
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Ah Ha! That's the cure for hot engine shut off flooding, when the vapor pressure of the fuel trapped between the pump and carb overcomes the N&S and fuel overflows into the engine because the float level goes above the spill-over point. That was the authorized Mopar cure for the Long Ram 413 Chrysler 300 letter cars with air conditioning. The Long Ram had extra exhaust activity in heat riser pluming near the fuel pump to heat the manifold plenum under the carbs.

Mattax wrote:
Mattax wrote:
If it is vapor lock in the pump feed, then am I correct that it should show no pressure on the outlet side once the bowl inlet opens?


Following up on this. Is there a way to identify vapor lock if its in the output side of the pump?
Will the pressure gage go above normal and then drop when the fuel bowl float drops?


The pressure will go above normal and flooding is the result, because the N&S can't hold against the pressure. I am not surprised to see 15+ PSI when "winter blend" gets overheated.

Mattax wrote:
Yes, that's a good possibility. It didn't show up at all last summer, even when the engine compartment got so heat soaked the nylon fuel fitting gaskets failed. But if it's vapor pressure and the winter RVP is higher, then it might be just that much difference to make it happen.

Most of the fuel here is what they call Complex Model RFG, but if I understand it correctly it still should meet 8.5 RVP in summer and is allowed 11.5 RVP Winter. Also that Refiners need to supply Summer blend by May 1, but Retailers have until June 1 to be switched over.

There is one location on the fuel supply line to the pump (engine mounted) that runs close to the headers.
It's covered in insulating fire sleeve, but I'll see what else I can do there.

If it is vapor lock in the pump feed, then am I correct that it should show no pressure on the outlet side once the bowl inlet opens?
If so, I'll dust off the fuel pressure gage and reinstall it.


Yes, vapor lock on the between-tank-and-pump side of the pump results in no or almost no pressure. The pump isn't much good at pumping vapor and even if it were, the liquid fuel is pushed back to the tank by the vapor pressure in the line. If you could see inside the line it would be an empty vapor bubble.


Thu Apr 13, 2017 7:11 pm
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Joined: Mon Apr 08, 2013 10:21 pm
Posts: 122
For several years I've avoided the dreaded winter fuel vapor lock by utilizing a small bypass to circulate the fuel along with mixing ~ 20% 100LL Av gas. I got the bypass tip from Tuner several years ago. I ran a new 8 AN fuel line from my tank to the carb and plumbed a tee in the fuel line entry to the rear bowl to bypass fuel to the tank using the original fuel line. The bypass is a ~.040" "jet" threaded into the tee to meter the amount bypassed. RobbMC makes oem style fuel pickup/sending units for many stock tanks with an inlet and outlet to allow the return line,


Fri Apr 14, 2017 1:18 pm
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Joined: Sun Jun 23, 2013 1:41 pm
Posts: 366
Location: Phila. Penn.
Haven't had a chance to work on this much. Got by with cooler weather and some uh storage fuel similar to what Treyrags mentioned.

Tuner - Wouldn't that bypass also work to allow vapor to vent from the suction side to the pressure side when the pump supply side vapor pressure is higher than the fuel pressure on the output?

Treyrags - I like that idea. The pick up ass'y in the fuel tank already has a return - currently blocked off. Brake line would be big enough for such a small relief. Just a bunch of time under the car and hood figuring the routing... Time I haven't had. Wasn't even able to pull the car in to jack it up to place temperature indicating stickers along the line to identify the relative max temperatures.

However did have time to make a rough test of some of the insulating materials I bought and had around. Fired up the grill one evening and used a TC on the multimeter. Useful for a number of things, including setting up a second round test...

Test summary
Ambient temp. 70 F
Heat source was radiant from the gas flame's shield/ drip catch, plus the heated air.
The grill was run full heat with the lid closed until the lid thermostat showed 380 F (5 minutes),
The tc measured inside air temp 525, opened the grill and tc on the grilling surface showed 330 F.

Even with only one temperature measuring device and stop watch, putting the insulating materials on the grill showed a few things:
Shape and contact are very important.
All items in direct contact with the grill heated quickly due to conduction from the metal.
The wide flat ones (aluminum foil and Zircoflex) also blocked the hot air, so they heated even faster.
Heat was also tranfered by conduction to items lying directly on top of the flat surfaces.
Items that were too small to overhang got much hotter than those that stuck out over the grill housing.
In other words, the short pieces of insulation sitting on the foil and zircoflex got pretty hot inside compared to the long pieces. This was true of both the thick firesleeve and the aluminized fiberglass sleeve.

In the graphs below the first 10 minutes show how quickly the items respond when tossed on or over the grill.
At the same time, the air temperature just at or under the grilling surface shoots up because the air is trapped by 3/4 of the grill being blocked by the items.
After the first round of measurements, the heat was cut back to hold the grill surface temperature relatively steady.


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Fri May 05, 2017 2:57 pm
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Joined: Sun Jun 23, 2013 1:41 pm
Posts: 366
Location: Phila. Penn.
Here's the setup for those amused by grilling insulating materials.
I was rather impressed how well the aluminized fiberglass sleeve worked. Granted it was not subject to the conduction from the grill surface or temperatures of the air trapped below, but still did well. The zirco probably will hold up better in direct contact with a very hot exhaust surface.

My next test will be two or more pieces of steel tubing wrapped in firesleeve. One with reflectorized sleeve, the other with zircoflex, and another with zircoflex on thin stainless steel sheet partially wrapped around the tube. That's three. H'mm. We'll see how much material I have. The zirco on the stainless is the design I was planning to use. The stainless can slip over the existing insulation and will further reduce heat concentration. That's the concept anyway.
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File comment: Temperature at Minutes:Sec
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Annotated the picture to with first round of measurements. Notice the metal tube on the aluminum foil is hotter than the one across the grill. A demonstration of conduction in addition to blocked convection vs. radiation and normal convection.

Last note. Thermocouple is not a particularly good way to measure air temperatures. Further contact with surfaces was from pressure via the wire, not properly clamped. Finally, like most non-calibrated temperature measuring devices, accuracy is only so-so. So take all here with a grain of salt. I thought it was good enough to show relative differences or wouldn't have posted at all, but hardly the last word. More like a jumping off point.


Fri May 05, 2017 3:21 pm
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Joined: Mon Apr 08, 2013 10:21 pm
Posts: 122
Thanks for sharing


Sat May 06, 2017 12:37 pm
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