Outlander

I have a 86 305 G code Trans Am that I have put a lot of work into. Basicaly it comes down to this; I only get about 175 miles out of a tank. The car was a wiring nightmare under the hood, all smog has been removed and a q-jet from a 75 was installed with a vacummed advanced distributor. Fine, I understand that a lot of people do that, though there must be a vaccum leak as there is no vaccum to it. The brake vaccum works just fine though) thus no advance. My mechanic friend that the vaccum should not make that much of a diff. Im going to try the 2 base gaskets and see if that helps with that. I did replace the carb and a full tune up but the mileage is still cruddy, the car does run better though. I cant find a fuel leak, but sometimes under the hood I smell gas, cant find it, dont see any drip marks. When I put petal down the car does take off for about 30 ft. then its like the fuel just shuts off, the car sputters, and then powers up again. Any ideas?

Vader

What part number QuadraJet? Jets? Primary metering rods?

As for the vacuum advance, it CAN make a big difference in cruising MPG. The vacuum supply for the advance unit is usually Port H at the LF corner of the carb, and may be routed through a TVS. Make sure the TVS is working or bypass it. Test for vacuum at this port (directly with a gauge) as you blipo th throttle just above idle. It should rise when the throttle is opened.

85cmroz28

You need to track down that vaccum leak. You said you got a tune up, but your car cannot be truly in tune if you're not getting any vaccum advance to your distributor. Replace the carb to manifold gasket, replace any old, cracked vaccum hoses, and make sure all of the vaccum hoses are routed correctly. Also, make sure any unused vaccum ports are capped off.

Lo-tec

Your fuel pump isn't up to par. It's time to replace it. Your gas smell could be fuel leaking out of the pee hole in the pump.

fulo

O.K. this happened to me when I was making the transition from electronic Carb to Mechanical.

Make sure that the problem is not in the base of the carburetor. I had one carb that for some reason had some vacuum port internatlly blocked. You could not see it at first glance. Also, make sure that the base plate of the carb is the one that come with it. THere are tons of Q-jet variations... literally.

I assume you test the vacuum advance of the Distributor. Why not try another vacuum source? Just for kicks.

Hope this helps.

Outlander

Well I took out my fuel pump, the rod was ever so slightly bent, but just enough to not let the rod move fully. The return line was not clamped down at both ends (prob this is the gas smell) and I did replace the carb manifold gasket, tried the 2 gasket trick. Car does run a lot better, I can floor it now with no loss of power, but still no vacuum from the H port, and there is no TVS. Sorry I didnt write the numbers down. Im thinking maybe it is blocked off as some the other vacuum hoses are working. I did have to change the linkage and butterfly for my application, I also had to put on the choke from my old carb, and I did have to remove a plug and add a inlet to the carb, I think it was for the heating/AC system. Could it be that there is a block inside the H port? I got the carb off Ebay, the application numbers were very close and looked almost a match.

82camaro

Are you checking vacuum at idle or when the throttle is open? It may be hooked to a ported vacuum source (which has no vacuum at idle)

Outlander

Thanks guys for all the help. My mechanic, Mr. "Why the hell do you do it that way?" friend who helped with the vacuum hoses hooked 2 up wrong. He was working off the thought that this was a newer carb, and not a older one. He hooked the advance up to the snorkle line and blocked off the H port. Somebody posted pics of both carbs and the CC carb line came off from that general area to the TVS, but on my carb it it on the other side. Runs even better now. Now I think its time to upgrade my HEI distrubutor to something a little better than the old GM one I have.