Poor performance after engine rebuild

[Nikkortim]

I’ve been reading several posts about poor gas mileage, and have a similar problem.

A friend has rebuilt a ’80 350 and replaced it for the 350 in my ’85 Silverado.

He used the intake manifold and Q-Jet, and HEI distributor from my ’85.

The engine would not start until we bypassed the ESC by jumping two wires together, (thanks guys).

While driving it home in rural South Dakota I could see the fuel fall very fast, and it used a quarter tank in 25 miles, but the bad part came when I was going up a hill. I was losing speed and gave a bit more gas, then it start running bad, and shuttering, and my wife said it blew out some smoke , (about the time I punched it). I had the pedal almost all the way to the floor and could barely maintain 55 mph.

It stalled when I got to a stop sign, and I had to push the pedal all the way in to restart it. When I got to my next stop I down shifted and brought the revs up. To my surprise it began running smooth again so once I got into town it stayed running all the way home.

Since it sat for almost 4 years I’m going to say I have an issue with the carb even though my friend says he “knows” the Q-Jet. I also have the “Choke” light coming on in the dash, but I don’t know if this is because he did not connect it or the choke stayed closed. I’m not 100% certain about how it was timed. I am not certain if what we did to the distributor is the correct thing to do, or if I should replace it with a MSD HEI.

I also have a not related issue of a hissing (vacuum) sound when I depress the brake pedal. I have been told it is vacuum boost for the brakes, yet they work ok. Would this vacuum issue also be related to any vacuum issue with the timing or operation of the Q-Jet?

As long I have a good block and new exhaust now I guess all the other items I might need to work on should not be that hard for me now, I just need a bit cash and time.

I open for suggestions. Thanks in advance.

[grinch4om]

your choke light and the dieing may be related. on the back of the block behind the distributor, there is a connector that uses oil pressure to close the switch which sends power to the electric choke. I had the same problem when I put the big block in my truck. loop the connector or plug it in, I looped mine, if memory serves me, it is a round connector, two wires to it

[kenm78]

I would check my ignition timing once more. If you are not using this as a performance application the HEI ignition will work fine save your money. I would check that choke light issue out. Was the truck bogging down really bad like it was flooding??? Before you go ripping your carburator apart or changing it out get a can of carb cleaner and spray while the engine is running at idle along the intake were it mates to the cylinder heads and at the carburator base listen for a increase or decrease in engine RPM that should help pinpoint any vacume leaks related to carb and intake. As for the hissing while pressing the brakes have your wife or a helper press the brakes and spay some soapy water around the brake booster check valve and around the edges of the brake booster where it is assembled together look at the ovious problems before you go swapping parts. Just my 2 cents worth..

[Nikkortim]

Thanks for the info so far.

The Vacuum hissing IS related to the engine running. It did seem to run a bit rough and stall when I pressed on the brakes, and my wife just told me today that it blew out smoke every time I press on the brakes. So it must be messing with the vacuum with the rest of the truck.

I understand I need focus one item at a time any input will be helpful.

[edman87]

I would also say timing and vacuum leak issues. Also may have a plugged cat. Find your vacuum leak first, then check you timing.

[Nikkortim]

Negative on the plugged cat. The smog stuff has been bypassed and the pump removed, (it's South Dakota what can I say), and a new exhuast has been installed.

BTW, new plugs, wires, rotor and cap. To my knowledge not much, if anything, was done to the Q-Jet.

[magnethead]

The smoke is unburned carbon. So, your engine is going to the rich side when a load is put on the vacuum system.
also, check if your choke is functioning properly- is yours an electric choke or well choke? If well, check that vertical rod that goes to the stat housing, mine came off and that thing would flop to full closed whenever it pleased.