Greetings: Not long ago I purchased a '76 F-150 Custom. The seller told me the truck had been sitting in his garage for about 14 years, however it was in his driveway when I went to see it. It did run and I drove the truck back home (about 35 miles) and parked it in the driveway. The engine looks very clean and the seller did say it had been rebuilt before he'd parked it in the garage. However the engine did not run well and after arriving home I noticed gasoline leaking from the Holley Carb; I decided at that point that I needed to rebuild it, especially if it had been sitting all those years. Even the gas smelled strange.

I didn't do anything for a couple of days and noticed there was still a strong smell of gasoline under the hood so I looked in to see that gasoline was still leaking from the carb. I went back to the gas tank which is located in the rear of the truck and removed the gas cap. There was so much pressure in the tank it scared the daylights out of me. I tightened the cap back and a couple of hours later I noticed gas leaking from the carb again and once again went and removed the cap only to find tremendous pressure in the tank..

Since that time I have rebuilt the Holley Carb and am ready to try starting the truck. Before doing so I need to address this problem with the gas tank. I have left the cap lose so there is no pressure build up. I have looked along the frame on both sides of the vehicle and can find no vent canisters and do not see any lines from the tank except for the fuel line that runs up the frame on the drivers side. The tank looks original so I don't know if these '76s have vent lines or what system might be in use to equalize the pressure in the tank.

Any ideas would be a big help to me in getting this problem solved. I do not want to put an extreme amount of pressure to a fresh carb. The fuel pump looks to be fairly new..

Thanks for any info you have to share....

DW

 

On a truck with evap charcoal canisters etc. the gas cap is not vented on a truck without the evap system the gas cap is vented .. What fuel pump does the truck have ?

 

The fuel pump looks to be an OEM type found on a 360 cu. in. engine.

 

Additional info: When the carb was leaking gas it appeared as though the pressure in the tank was pushing gasoline through the fuel pump, into the carburetor, and leaking out through the accelerator pump on the carb.

 

It could be that the vent line to the charcoal canister is blocked, or that it's a non-evap vehicle that doesn't have a vent line, and someone put an unvented cap for an evap vehicle on it.

 

Quick solution: put a vented gas cap (for a non-evap vehicle) on it.

Long-term fix, if it has an evaporative emissions system is to find what's wrong and fix it right. Avoid any gassy smells, fuel you paid for evaporating away, etc.

 

Thanks for the information..... It does have a vented cap that lets air in but not out. I can find no signs of an evaporative emissions system. I am not sure if they had those in 1976.

 

They did, but it wasn't on every truck - depended on a bunch of factors including GVWR, where it was sold, etc. My '74 F-100 has it, but it's entirely plausible that your '76 F-150 doesn't.

 

vented cap

 

Agree a "vented" cap should help. The parts store variety I used on my '78 would let quite a bit of pressure or vacuum build up before venting. This seems to be common. Vacuum = vapor lock and pressure = leak so not desirable.

The fix is a small hole in the cap. ~1/16". Placed to vent to atmosphere. Tricky to find the right spot but once found will fix the problem.

 

I purchased a brand new cap.. the one without the evaporative emissions system. It was the more expensive cap. Doesn't look like the OEM cap but seems to have fixed the pressure problem. Yes, there is some pressure when opening the cap but it isn't like the old one that sounded like a jet engine when opening it.


Thanks very much for all the information. I really appreciate your responses...


DW

 

Glad it helped!