Gettin Funky with gas

[Chevy305]

So I noticed that everytime I fill up my tank with the usual 93 octane, my truck sudden gains pep. Like it opens up. Then about a day later it loses some of its get up and go that it gained with the gas. Why does this happen?

My fuel filter is no more than 2 months old, gas tank/sender unit about 2 years old. It doesn't matter what station I go to, but usually I go to the local Hess station.

 

[Chevy305]

Ttt

 

[bigjak]

Maybe your fuel tank vent is plugged up. When you put in the fuel, your releasing the vacuum, then after a while of driving, the vacuum builds back up.

 

[sled_dog]

I have no answer other than to ask, why are you running 93 in a 305? Are you one of those "I make more power and get better mileage on 93" people?

 

[blazindorito]

What year is the engine and is it carb or ? What it could be is that the gas is clogging the injectors or nozzles after it has been sitting. If your engine does not require higher octane gas then it doesn't need it. If your truck only runs on regular unleaded then thats all you need.

 

[resurrected_jimmy]

What year is the engine and is it carb or ? What it could be is that the gas is clogging the injectors or nozzles after it has been sitting. If your engine does not require higher octane gas then it doesn't need it. If your truck only runs on regular unleaded then thats all you need.

http://truckworld.tenmagazines.com/mygallery.ten?id=9814

here is his truck info, its a collection of things, unless he knows exactly how his fuel system is set up we are grasping at straws

 

[Chevy305]

http://truckworld.tenmagazines.com/mygallery.ten?id=9814

here is his truck info, its a collection of things, unless he knows exactly how his fuel system is set up we are grasping at straws

I have no answer other than to ask, why are you running 93 in a 305? Are you one of those "I make more power and get better mileage on 93" people?

My 305 is a L69 from a Firebird so it has a compression of around 9.5 and I have always been under the impression that it needs a higher octane. The timing is adjusted properly. I never did try to run anything lower and I don't think I get more power or any mileage gains purely from running on 93 octane. (mileage is kinda a mute point with my truck)

My truck has the stock fuel system and a single feed 4bbl Holley carb (model is 4160)

Maybe your fuel tank vent is plugged up. When you put in the fuel, your releasing the vacuum, then after a while of driving, the vacuum builds back up.

Where is the vent located, and how do I unclog it?

 

[Chevy305]

ttt

 

[resurrected_jimmy]

Maybe your fuel tank vent is plugged up. When you put in the fuel, your releasing the vacuum, then after a while of driving, the vacuum builds back up.

If this is the case you should be able to unscrew the gas cap for a couple of days to test this theory.

 

[Chevy305]

I did that today and I got the extra get up and go I was talking about.

Is the vent tube the smaller hose that is next to the filler neck on the gas tank?

 

[dyeager535]

Vent tube runs to the front of the truck, to the EVAP cannister. Prior to EVAP, most if not all just used a vented gas cap, which seem to be impossible to find.

The one you are talking about is just to vent the tank when you fill it up.

 

[Chevy305]

Vent tube runs to the front of the truck, to the EVAP cannister. Prior to EVAP, most if not all just used a vented gas cap, which seem to be impossible to find.

The one you are talking about is just to vent the tank when you fill it up.

Yeah, all emissions equiptment were removed by the previous owner. So I don't think I have an evap cannister. My gas tank has 3 lines that all run directly to the fuel pump, then 1 line continues to the carb. Could replacing my gas cap fix the problem? or maybe the fuel pump?

Sorry I am a little clueless about this issue.

 

[Chevy305]

ttt

 

[dyeager535]

Well what happened to the vent line?

If plugged off to remove the emissions stuff, then you either have to run a vented gas cap, OR vent the line some other way.

All gas caps are actually vented, but the only ones I've seen for sale at parts stores are the later high pressure ones, which don't work with unvented tanks.