Engine acts like it's starved for fuel - solved vacuum leak

[ClayJ]

This morning my Bronco started acting up on me. I'm running a 302 with a quadrajet carb and electronic ignition.

Normally I have to pump the gas a few times will starting. The colder it is, the longer I have to pump to get it to start, then a bit of light acceleration for 10 to 20 seconds until it will maintain idle.

This morning it took allot of pumping and never did settle into an idle. If I wasn't pumping the gas, it would immediately die. I figured it might just be extra cold, so I backed out of the garage and headed down the road. The first stop sign and it died instantly, then every stop sign and stop light after that it died the instant I took my foot off the gas and pushed in the clutch. It acted like it was starving for gas.

So I nursed it to work and home again tonight. I pulled my inline fuel filter and my quadrajet internal fuel filter and replaced them with new ones. No change.

I'll check my timing and maybe spray a bit of carb cleaner through the car, but that's tough when it won't stay running. I couldn't see any obvious vacuum leaks but I'll throw the vacuum guage on and see if anything looks obvious.

Any other ideas?

[Viperwolf1]

It was very cold last night. Sounds like you don't have a working choke. Might try backing out the idle mixture screws just a little for the cold temps.

[Jesus_man]

Dump a bottle of HEET in the tank too. Could be water in the fuel.

[Booger]

How did it run once you got going? Sounds like it might be a choke issue as Viper said. It wouldn't hurt to dump in a bottle of Heet or other gas line antifreeze.

[Kinder]

I'm not a Q-jet guy, but maybe the idle circuit is clogged with something.

[ClayJ]

It's been a hectic couple of days so I just rode the motorcycle to work. Boy that's cold in the mornings.

The engine acts the same cold or hot. Tough to keep running, dies instantly if the RPM drops below about 1.5k. I kept expecting it to get better as it warmed, but it never did.

Playing with the idle mixture screws as Viper suggested made no difference. I verified the choke was closing. I pulled the air filter to be sure it wasn't starving for air. I put a pressure gauge on the fuel and it looked fine.

I took it for another run around the block and noticed some coughs and fits that I might have missed before (I turned the radio down). While driving, if I hit the throttle hard, I get something almost like a backfire.

I'm starting to wonder if it isn't ignition rather than fuel. I run a H.E.I. distributor from B.C.Broncos. Last year the pickup went bad and I chased various fixes for days before changing it. Maybe I'll try looking at that again tonight. Viperwolf helped me out allot that last time. If it's the same thing again I might have to seriously contemplate switching the ignition system entirely.

http://classicbroncos.com/forums/showth ... p?t=171670

[Shawns Fords]

Another thing it could be if it is not your ignition is a vacuum leak.

[ClayJ]

I checked the internals of the distributor. Nothing obviously wrong.

I'll check the vacuum when I get a chance.

[ZOSO]

did the timing advance or retard? I'd look there and vacuum leaks too.

[ClayJ]

I tracked down the problem with my Bronco (Quadrajet carb). It was a vacuum leak. One of the vacuum ports from the carb was wide open. I know I had purchased one of those various size plug kits when I first rebuilt the Bronco and plugged this port. But there was nothing on it now.

It probably dried up, cracked and fell off. It's a port that's nearly impossible to see. I only found it by running the bronco for a bit, then carefully looking around the carb and spotted a slight amount of mist that appeared to be coming from near the adapter plate. I tracked it back and found the unplugged port. This was the 4th time I had gone looking for vacuum leaks.

[Jesus_man]

Nice work Clay! And you are not that much more familiar with your rig!