Vapor locking?

[Darty03]

I seem to be having vapor lock and I cant figure it out. The fuel line coming off the fuel pump is in the 164*F range after a 10 minute drive with a few wot runs (wot until the carb bowls run out of fuel). I have tried wrapping the fuel line after the pump in a thermal sleeve and under the sleeve its still 160F. I have rerouted the fuel line from the pump to the inner fender and straight over to the carb to keep it as far from the motor as possible and no change. I realize the filter and some of the rubber hose up top is not covered in the sleeve, I just added the rubber hose to get the line away from the motor and I took the sleeve off the filter so I could see if it was empty. Any one have any ideas what could be going here?

I have replaced the fuel selector valve twice for the dual tanks and replaced the fuel pump with a high flow 110gph pump(no return like stock unfortunately) with no change. It does it for both the left and right tank. I have removed the charcoal canister and the vent line going to the tanks is just open.

[bd]

What have you done to insulate the supply line between the selector valve and the pump, especially in proximity to the headers and exhaust?  The factory fuel return line exists to cool the supply line and pump via a constant flow of fuel.  Eliminating the return line may have precipitated or exacerbated the symptoms. 

Perform static draw/delivery/pressure tests on the existing fuel pump to eliminate the pump and eccentric as the source of problems.  Then wrap or shroud the supply line in proximity to the exhaust and try again.

[Darty03]

The fuel line is at least 4 or more inches from the exhaust pipe aside from right where the header collector exits by the rear shackle mount. Its around 3 inches there but I have wrapped the fuel lines there in the same stuff I have on the fuel line in the picture above. The factory style pump I had one it was less than a year old and had the same symptoms, that is why I replaced it with this other one. This one does not have the return which I agree is probably making things worse. I will add a return asap. I checked the cam lobe with a camera when I swapped to this new pump. The pump pumps lots of fuel until things get hot.

[VileZambonie]

Sounds like you have a kinked hose or collapsed hose. Double check them all carefully and make sure you have the   hose properly routed from the valve. I've seen all too often the hoses improperly routed.

[bd]

Agreed.  If no issues are discovered with the hoses, tee a vacuum gauge into the pump inlet line and monitor the gauge as symptoms begin to appear - be sure to safely route and secure the vacuum hose to keep it from being entangled or burned.

[VileZambonie]

BTW, I would fix this correctly. Vapor lock shouldn't be occurring on the discharge side of the pump so the way you have the fuel line routed is not good. Not sure why I didn't see the picture before. You have the fuel lines dancing from the tanks to the engine to the body back to the engine. Keep the fuel lines relative to the frame and powertrain isolated from the body with the shortest distance.

Low pressure on the suction side coupled with excessive heat can cause the fuel to boil and loss of suction = vapor lock which I am willing to bet is not your issue. Fuel starvation is most commonly caused by a restriction.

[Rattler12]

All the above and remove your fuel filter from the engine bay and put it in the line somewhere along the frame closer to the tank
jm2c's

[Irish_Alley]

just want to add my 2 cents. but when it acts up do you see fuel in the filter? have you replaced your filer or checked for a primary filter in line after the fuel valve? or dont those edelbrocks have a fuel screen right at the inlet?

[Darty03]

Just an update, I ended up trying something a mechanic I know mentioned. I put a T fitting right at the carb and hooked the return up to it. So I now have the return plumbed in about an inch from the carb with no regulator or anything. It seems to have fixed the issue completely. The factory fuel pump with a return didnt keep the fuel after the pump circulating so it was getting to hot, adding a pump with no return of course didnt change that. Now that I have a high flow pump it seems to be able to keep up with the return plumbed in with no regulator. I guess the big aluminum radiator and electric fans along with the steel headers on the truck are just raising the under hood temps high enough to over heat the fuel in the lines. The truck never gets over 210ish at most when beating on it. I may need to look into more air flow under the hood.

To answer a few of the questions above.
Yes the fuel filter goes empty.
I know the fuel line is ran goofy, I ran it that way temporarily to get it away from the motor and heat. I will be running them so they look nice soon, I'm trying to keep the motor clean.
I did find the hose going from the selector valve to the hard line supplying the pump may have been collapsing some. It looked a little flat. Someone at some point cut the factory hard line back some so I now have about a foot and a half of rubber line there. I replaced that with a hard line and 2 short pieces of hose. It didn't seem to change anything so it must not have been the problem but did need to be fixed.

[bd]

Did you restrict the return line near the tee?  Running an unrestricted 1/4" return line will circulate enough hot fuel back to the tanks to elevate the fuel temperature in the tanks.  About 0.040" restriction should be suitable.

[blazer74]

You can also add a filter with a return line also.

[Darty03]

I did not restrict it since the pump was keeping up. I have some hard line I can slip in there and use that to restrict it. I have been driving it and beating on it for almost a week and it hasn't had an issue though. I will add a little bit of a restriction when I redo the fuel lines this weekend to look nice, they're still all over the place right now. Thank you all for the help!

[jeffrey.constance]

I have the same problem with an '86 C/20 with a 454.  The engine was replaced in 2012 with a jasper rebuild.  Has basically been doing it ever since during the warm months.  Just rebuilt the carb again( myself this time) added a phenolic spacer and a heat shield also and shielded the the pump to carb line with a foil and insulation covered contraption that looks a lot like electrical wire conduit with a thick coating of refrigerator insulation covered in foil...  helped somewhat but still starves out when you open the secondaries up unless the outside temps dip considerably ( not too likely in the south) but it has stopped stalling and refusing to crank for about 45 mins...  pump was new with rebuild flows great all the lines are in place... vapor, return etc.. running a 180 thermostat with a 4 row radiator and  factory 7 blade clutch and flex fan and usually temp never hits 200.   Not sure what route to take next... maybe new truck... lol


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[jeffrey.constance]

Oh yeah, less than 10k on rebuild installed fall of 2011...


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[blazer74]

Find some non ethanol gas and try a full tank. See if that helps.