Trans-am dumping fuel

[t/a 6.6]

I have a 78 Trans-Am and it just all of a sudden started getting real bad gas milage(even for a oldschool v8) I thought it was the carb, so I rebuilt it put a brass floot in it and everything, that helped a little I'm not sure what else could be wrong, any help would be greatly appriciated, cause I like to drive and need some gas mileage to do so

[MagicRat]

You replaced the needle and seat, too, right?

Is this a Quadra Jet?

For the moment, I would check the fuel pressure when the engine is at idle. You should have no more than 5 - 7 psi, tops. Any more will flood the carb.

Also, is your choke is fully open when warm; and does the engine reach a decent operating temp?

[crd14]

Check both mecanical and vacuum advance. Use a timing light and check base timing then disconnect the vacuum advance and rev the engine. Timing should advance. Reconnect the vacuum advance. If timing advances as soon as you connect the hose then it is connected to a manifold source and it's working fine. If you connect the hose and the timing doesn't change then rev the engine again and if the timing advances more quickly then it did with the hose disconnected then, again, it's working fine and your problem lies elsewhere. If you don't get these results repair as required.

[t/a 6.6]

thanks, I found the problem was when I rebuilt the carb, i actualy tore one of the fuel hoses, god the 70's suck, there are fuel and vacum lines everywhere. But on another note, I was woundering what is the easyiest way to improve gas millage on one of these old v8's, I know its laughable but a man gotta drive and right now thats hard to do, and with winter coming I have all the time in the world to work on the old bird

[crd14]

There are lots of things you can do but most of them will only make a small difference.

If your willing to spend money... Holley makes or use to make a throttle body fuel injection system. Even uses an O2 sensor for closed loop operation. That would give a reasonable improvement in mileage and a great improvement in drivability.

Make sure it's street legal before you proceed, I don't know where you live or the smog regulation you face.

Look here ---> http://www.holley.com/division/Holley.asp

[MrPbody]

Some of the most popular changes would be intake manifold (Edelbrock "Performer"), "torque" cam (or "RV"), headers (smaller tubes), flogging the car on a chassis dyno and making changes to the jetting and timing.

Is this a Pontiac or an Olds? That is, a 400 or 403? The 400 can be made very efficient, at the cost of high-end power. I suppose the Olds can do similar things. I had a '70 GTO with a 400 in it that made 22 MPG on the highway in '74. Of course, "right foot control" is the best thing for fuel economy... (:-

Higher ratio (lower numerically) rear axle can also help significantly. Manual transmission will generally provide better fuel economy than an auto, as well.

Like I said, lots of things can be done. The question to you is: Is it all worth the expense?

Lastly, CRD14, most Pontiac applications call for the vacuum to go to "ported" vacuum, not manifold vacuum as with a Chevy.

Jim

[crd14]

Originally Posted by MrPbody

Some of the most popular changes would be intake manifold (Edelbrock "Performer"), "torque" cam (or "RV"), headers (smaller tubes), flogging the car on a chassis dyno and making changes to the jetting and timing.

Is this a Pontiac or an Olds? That is, a 400 or 403? The 400 can be made very efficient, at the cost of high-end power. I suppose the Olds can do similar things. I had a '70 GTO with a 400 in it that made 22 MPG on the highway in '74. Of course, "right foot control" is the best thing for fuel economy... (:-

Higher ratio (lower numerically) rear axle can also help significantly. Manual transmission will generally provide better fuel economy than an auto, as well.

Like I said, lots of things can be done. The question to you is: Is it all worth the expense?

Lastly, CRD14, most Pontiac applications call for the vacuum to go to "ported" vacuum, not manifold vacuum as with a Chevy.

Jim

I agree Jim, all those thing can help. I suggested the throttle body FI because it would likely provide gains matching all those modifications you suggested would provide at a fraction of the cost and the work. It's the biggest bang for the buck and he did say that the fuel cost was a burden so I didn't think all those other mods were feasible. Actually the TBI is not likely feasible either.

Thanks for tip on the Pontiacs using ported vacuum source to the distributor. I try not to clutter my mind with to many facts and figures. If I can remember how to figure something out I don't have to rely on remembering facts.

In the end his best bet would be to tune what he has to the max and live with it but that wasn't the question.