i have a 1971 challenger slant 6 . i have an inline fuel filter (tried 2 different filter) right before the carb. runs fine at first the several times ive ran it, the filter fills up and the car runs fine. within 5 minutes the fuel lvl drops in the filter and you can see bubbles coming up into the filter from the fuel line coming from the brand new mechanical fuel pump. i replaced most of the hardline with hose and i double checked all clamps from just before the fuel pump to the carb and they are tight. it seems pretty evident that there is air being pumped instead of gas at some ratio so ive ruled out the carb and everything after. engine runs and fires thats not an issue. help?

 

more info- had the filter all the way full. air came again from the 'in' side of filter from the fuel line. turned it off and it still bubbled from that line for several minutes but the level of fuel in the filter didnt seem to drop all that much

 

It could also be a fuel pump problem. Sometimes they start going bad and losing their pumping ability as they warm up and that allows air to enter the system or else the fuel starts falling back and creating bubbles. Especially on a mechanical fuel pump. Check those things and see what you find.

Or It sounds like it could be a heat problem possibly? If you have some lines running to close to the exaust or headers or something of that nature then you could be boiling your fuel. but i would go with the fuel pump hypothesis first, but also just use some soap and water in a spray bottle and hit up the lines a few inches at a time and check for leaks.

hope this helps keep us posted

 

even though i just put this fuel pump on like 2 days ago? good advice thanks yeah i was thinking about the line being close to the exhaust cause they are really hot but i dont have many options to run it differently could i wrap it? what would the fix be for the lines? i dont see how soapy water could show me anything because if the line is sucking in air then bubbles woulnt form. if gas comes out ill see it wet and air shouldnt come out unless its already there in the line and if it is i can fix that part of the line but ill still have the air issue and not know the source. could you explain a little about that? thanks again for your advice!

 

I recommend highly that you trot over to this other joint, and download one of the shop manuals posted in this thread, then read the section on fuel pumps

http://www.forabodiesonly.com/mopar/...al%2C+download

DO NOT discount any possibility

Might be some debri plugging up the line, or even back in the pickup

Get / buy a pressure vacuum gauge, usually less than 20 bucks at any poor parts store.

Disconnect the pump inlet, and crank/ run the engine. It should pull over 10-12" vacuum.

Don't discount that the feedline from front to rear could have pinholes.

Hose is NOT a good thing to have for permanent use in an engine bay. Metal tube--just like the factory, is much safer, and so is a metal fuel filter.

Does this do this hot or cold?

You said "starts and runs so is not the issue."

What IS the issue? Surely the engine is down on power? Dies off/ surges at high speed/ up a hill?

 

I had a brand new pump and it was broke and it did this lol, it would prolly be better to move exhaust to me i hate foolin with fuel lines.

 

is your problem occuring at any level or when it is near empty. the reason i ask mine does the same thing when i get down to 1/8 tank or less. so i'm guessing that i am sucking a little air from the tank.

 

well unless you have a new or flushed tank i wouldnt run it that low cause you suck up all the crap at the botton of that tank but no my stuff is full. for ***** and giggles to shoot down the heat issue i ran 8 feet of fuel line all the way around the back and around and now no bubbles! amazing never thought it would do that! filters not filling up but hey i figured a couple psi fuel pump would have alittle trouble filling it up with that much line because of pressure build up and or ressistance. ill just run it from behind or over top ziped to the plugged egr hose and see what happens. works fine now no dying on turns or at idle no bubbles no issues so far. still need to run it on the highway. still alittle hickup when you stomp on the gas. thanks for everyones help

 

glad you found out that was the problem! keep us posted if anything changes