[minn-ta]

Hello,
I own a 1981 Trans Am with a 6.6 swap. If I don't drive it for a week, it has a terrible time trying to start. I usually need to use a syphon pump and pull the gas up to the carb after I disconnect the fuel line from the inline fuel filter just before the carb. One of the things that I did not do after the swap was to reconnect the fuel return line. Is this causing the issue?

Thanks,
Dave

[jwcfbd]

If I let mine sit for a long time it'll take a while to get the fuel flowing again but no need to pump it up. Your fuel pump could have a weak or torn diaphragm causing it not to get a good prime. I wouldn't think your vent line has anything to do with it.

[bluebandit]

Have you replaced the rubber sections of line from the tank forward? I once had a line that dry rotted and cracked, allowing it to pull just enough air to prevent the pump from pulling fuel.

[Kenth]

What is "a terrible time"?

Factory literature mentions 10-15 seconds on the starter to fill an empty carb that has been sitting for a week or more.

You may have to check the fuel line, from the nylon sock in tank all the way to the carb, and fuel filter in carb fuel inlet.
No extra filters between tank and fuel pump.
Fuel tank ventilation, correct fuel tank cap?

[steve25]

Post number 3 has it nailed .

A mechanical pump has a far far easier time pulling air than fuel!

Air weights in at .075 lbs per cubic ft,
Gas weights in at a minimum of 7 pounds per cubic ft.
So fuel weights over 93 times more then air!!

I also think that your pump is bad.

If it’s the original and even some older new replacements it was not designed for todays Ethanol cut fuel.

[Singleton]

Originally Posted by Kenth

Factory literature mentions 10-15 seconds on the starter to fill an empty carb that has been sitting for a week or more.

Would it be possible to post a pic of the literature or a link to it? Would be interesting to see.

[steve25]

What year was this carb filling info for, because a Q-jet will take a lot less time to fill than a AFB for example?
The AFB has over twice the fuel bowl volume by my estimate then a Q-jet does.

If I had to crank my motor for 10 to 15 seconds I would remove 4 if not all 8 plugs.

[Kenth]

Originally Posted by Singleton

Would it be possible to post a pic of the literature or a link to it? Would be interesting to see.

This info is from Jon Hardgrove at The Carburetor Shop:

"HARD STARTING, COLD
Difficult starting a vehicle that has been allowed to sit for a number of days (that will then start well the rest of the day) is often caused by modern fuel. Modern fuel begins to vaporize (evaporate) at a much lower temperature than fuel before the 1970’s. Once the engine is shut off, the fuel in the carburetor bowl begins to evaporate through the bowl vent. If there is no fuel in the carburetor, the engine will not start. Pumping the footfeed during this time simply prolongs the agony, as the accelerator pump will pump the fuel into the engine, but in amounts insufficient for starting. If you have this problem, try priming the carburetor by using an eyedropper and filling the carburetor bowl through the bowl vent prior to cranking the engine. If you do not wish to prime the engine, crank the engine for 15 to 20 seconds WITHOUT PUMPING. Then stop cranking, pump the footfeed 3 or 4 times, release it, and then reattempt to start the engine. Priming eliminates excessive wear on the starter. Another possible solution is the installation of an electric fuel pump. If an electric pump is installed, check local, state, and federal laws about wiring; and pick a pump with pressure not exceeding that of the original pump."

FWIW

[Kenth]

Originally Posted by steve25

What year was this carb filling info for, because a Q-jet will take a lot less time to fill than a AFB for example?
The AFB has over twice the fuel bowl volume by my estimate then a Q-jet does.

If I had to crank my motor for 10 to 15 seconds I would remove 4 if not all 8 plugs.

It was an example of how it can be for some, not all, so nothing to be afraid of or need to unscrew the spark plugs to start the engine (you are welcome to tell us how that would work).

[steve25]

Ken I did not say it would work,it was just used as a example to save the starter from a potential 15 seconds of loaded cranking .

The faster cranking speed from having some plug out would also get fuel up to the Carb faster.

[Kenth]

Might be a good idea if you´re able to pull the plugs and mount them in less than 15 seconds.

A better remedy would be mounting an electric fuel pump close to or in the fuel tank.

IMHO

[Singleton]

Originally Posted by Kenth

This info is from Jon Hardgrove at The Carburetor Shop:

Thanks, good info. I have read that before but was interested in the "factory" literature that was previously mentioned.

[minn-ta]

Thanks everyone. I'm planning to take a look at all you have suggested this weekend. Everything from the tank to the fuel pump are original (120k miles). The fuel pump is about 6 years old but I've only driven the car about 50 miles during that that. Could the diaphragm simply dry out and go bad?

[Ab69]

Could be leaking out the bottom of the carb from sitting too long. It happens to me. What I do is put about 4 table spoons of gas down the carb vent tube and about the same amount in the carb. I make sure the choke is closed. It fires up all the time.

[Kenth]

Originally Posted by Ab69

Could be leaking out the bottom of the carb from sitting too long.

This is an issue with 1968 and older Quadrajets.
For 1969 and later the issue was fixed by Rochester.

1968 or earlier brass plugs has to be replaced with threaded 1/2" UNF plugs.
Epoxi on leaking brass plugs will not last a week.

[GordonGeesey]

My car ALWAYS has trouble starting if I let it sit for a few weeks. All I do is remove the lid to the air cleaner and spray carb cleaner directly into the primary-side of the carb. A 3-second blast is all it takes. Reinstall the lid and the car instantly starts. The few seconds that the engine runs on the carb cleaner is usually enough to get the fuel bowl filled with gas, and the engine runs fine after that.

Added bonus: My carb gets cleaned every few weeks!