fuel pressure upon startup
Thread Starter
Le Mans Master
Joined: Jan 2001
Posts: 6,938
Likes: 1
From: San Diego CA
fuel pressure upon startup
I'm curious as to exactly why you need to pump the aceelerator upon cold startup versus no pumping when the engine is warm. Now given there should be fuel in the lines regardless of when it was last started and cranking over develops fuel pressure instantaniously, plus there is alot of fuel in the fuel bowels there should be no difference. This problem doesn't concern me, i.e. I'm not about to fix anything but I'm curious as to why I have to pump and crank (cold) while when warm I can reach from outside the Vette into the interior and click/ boom she fires right up.
Melting Slicks
Joined: Feb 2003
Posts: 3,053
Likes: 4
St. Jude Donor '03,'11
a cold engine needs a much richer mixture. Pumping the accelerator dumps gas in the manifold to richen the mixture up to compensate for a choke that doesn't close enough.
i do the same thing to mine. The colder the weather the more i have to pump, but YOU wouldn't know about that.
actually fuel injection systems do the same thing when cold, give a little extra squirt from the injectors to get it going.
i do the same thing to mine. The colder the weather the more i have to pump, but YOU wouldn't know about that.
actually fuel injection systems do the same thing when cold, give a little extra squirt from the injectors to get it going.
Team Owner
Joined: Jul 1999
Posts: 65,492
Likes: 230
From: Orange Park Florida
Turtle is right, Cali, being as you in San Diego apparently, yo don't notice, as you seldom see balow 60 if that....
us who see overnight lows of below 40 have a fit with carbs....another reason why DPFI is so neat....
GENE
us who see overnight lows of below 40 have a fit with carbs....another reason why DPFI is so neat....
GENE
Race Director
Joined: Aug 2000
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Originally Posted by paul67
Sets the choke.
Senior Member since 1492
Joined: Aug 2000
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From: Just because I'm paranoid doesn't mean people aren't out to get me...
St. Jude Donor '09
After sitting a few weeks idle, my engine needs about 5-6 pumps just to get going. The dies, then I pump about 3 more times and she's going. Much like my '67 F'bird.
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Race Director
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From: Foxfield CO 1970 Convertible
Originally Posted by Brettmc
Pumping the go pedal shoots gas from the accel pump into the intake for that richer mix a cold engine needs to start.
Brett
Brett
The gas evaporates from the manifold after a long time, like overnight, even if the bowl and lines are full. Pumping the pedal gives the manifold a shot of fresh gas. It also sets the choke if you still have is like most folks do...
Last edited by Z-man; Nov 28, 2004 at 08:52 PM.
Melting Slicks
Joined: Feb 2003
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Likes: 4
St. Jude Donor '03,'11
Originally Posted by Double Aught
If you had a manual choke, would pumping the carb still be necessary?
Burning Brakes
Joined: Nov 2004
Posts: 1,028
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From: San Antonio Texas
i have the same problem with mine (79 L82 with aluminum manifold, aluminum heads and headers). in addition, after pumping to start a cold engine (fully choked Q-jet with manual choke), i MUST run the engine at 1500 rpm or more for usually 15 to 30 seconds (more, the colder the outside temp) before it will hold an idle without dying. even then i may have to give it a few additional "mini pumps" to keep it going. then must be run in high idle (1300 rpm) for 5 to 10 minutes before it can be put in drive (turbo 350) with stalling and dying. is this normal with headers and no heat risers or manifold/carb heat??? is there any way to overcome this (inexpensively)?? thanks for the input.
Thread Starter
Le Mans Master
Joined: Jan 2001
Posts: 6,938
Likes: 1
From: San Diego CA
Well LARS specifically said NOT to get a choke and I have to hold the idle for a minute till it runs on it's own. I could have just as easily got a choke version of the Barry Grant 750DP but he said not to so for now I sit in the car.....I'm getting the choke.
