Idle speed suddenly slowed down...?

[Number21]

I have a 350 with an Edelbrock carb. Today I went for a short drive and as I was coasting to a stop, the truck died on me. It started again after a few tries and I drove right back home. It was running really rough and wouldn't idle without me holding down the throttle.

After I got home it started and idled again, but the idle speed is suddenly way lower than before, just barely enough to run.

Anybody have an idea what's going on here? I'll try playing with the idle speed screw tomarrow, but I don't understand why this happened?

[donut]

My q-jet recently did something very similar. Something went through the carb and held open the needle assembly, flooding it out. (Teflon tape from the PO.)

[68gmsee]

I wouldn't jump to adjust anything unless you suspect there was a bind originally or the choke linkage was out of adjustment.

In this case, if it has been running fine and all of a sudden it doesn't I wouldn't suspect the idle speed all of a sudden went out of adjustement.

As donut mentioned, suspect flooding or maybe fuel delivery -filters, bad fuel pump or clogged fuel lines are suspect.

It's possible a vacuum leak may be causing it to die but usually when I have had a slight leak it tends to increase the speed. Still it's worth looking at everything before doing adjustments.

[Number21]

I tried adjusting the idle screw, it made no difference at all. Checked for vacuum leaks, none that I can find. The fuel filter looks clean and the engine will rev up if I stomp on the throttle, that should rule out a fuel problem shouldn't it? (I have an electric fuel pump)

Could this have anything to do with my timing being set at 0 degrees? I know that needs to be changed but it WAS running fine...

[cableguy0]

Probably trash in the needle and seat causing it to flood. Do you smell fuel? Why would you set your timing at 0? Next question is did you tighten the distributor down all the way? Is you vacuum advance connected?

[Number21]

No, I don't smell any fuel. Long story about the timing, I was in the middle of playing with that. Yes the advance is connected.

[68gmsee]

When you say you adjusted the idle, do you mean the throttle idle setting or the carb idle/air adjustment screws?

If your truck was running fine before then I wouldn't suspect the timing issue unless the vacuum advance/mechanical advance has gone bad on you. You can easily check the vacuum advance with a vacuum pump on the end and making sure it moves and has no leaks. You can also use mouth suction if you have long enough hose you can install on the end of it. Remember that once you open the butterflies (stomp on the throttle) the vacuum advance does not come into play anymore. It's mostly for idle. Also, make sure the mechanical advance are free and not binding.

Suspect carb if everything checks out as mentioned above.

[Number21]

Originally Posted by 68gmsee

When you say you adjusted the idle, do you mean the throttle idle setting or the carb idle/air adjustment screws?

I adjusted the idle throttle setting. I guess I'll go take a closer look at the carb and see what I can find....

[donut]

On mine, when it stalled and I re-fired it, the exhaust puffed black.
Mine started after going 5 miles, fine before that. I could brake and gas to keep it going at a stoplight, pulled into a parking lot and checked it to make sure it wasn't a vacuum line or something I forgot. Choke side of carb was damp.
Got it home, pulled apart carb, I knew it was flooding at this point, and low and behold a strip of teflon tape on the seat, keeping the needle from seating. Something the PO had done, along with pulling the carb filter and running without one for quite a while.

[Marv D]

Do a search,, Both Google and here. you'll find tons of posts about edelbrock carbs,, and fuel presure.

If it dies when you hit the brakes, either the vacuum booster is completely ripped and leaking ,, or fuel is spilling into the carb. Float too high, or fuel pushing past the needle because you have more than 5.5psi of pressure.

but just my 2¢

[Number21]

Alright, now it's backfiring out of the carb. What does that tell you?

When it's not backfiring, there's a small hesitation just off idle, if I leave the throttle there it will die. If I rev it up it keeps running.

[68gmsee]

Originally Posted by Number21

Alright, now it's backfiring out of the carb. What does that tell you?

When it's not backfiring, there's a small hesitation just off idle, if I leave the throttle there it will die. If I rev it up it keeps running.

Have someone look at the exhaust to see if there's dark gray smoke coming out. It sure sounds like flooding symptoms.

[Number21]

Originally Posted by 68gmsee

Have someone look at the exhaust to see if there's dark gray smoke coming out. It sure sounds like flooding symptoms.

Nope, exhaust looks normal, mostly clear with a little white. (cold engine) Does flooding cause backfiring?

So I guess I need to remove the torx screws on top of the carb to open it up and see what's up?


Thanks for the help everyone.

[68gmsee]

Originally Posted by Number21

Nope, exhaust looks normal, mostly clear with a little white. (cold engine) Does flooding cause backfiring?......

In some cases, yes but you would see some dark smoke out of the exhaust. Actually a lot of things can cause backfiring through the carb. It may be ignition related- timing, defective ignition components, crossfiring (firing out of order), dist cap, old/defective spark plug or wires, timing adjustment and even burned valves.

In some cases it's best to back off and start at the beginning. Maybe start with ignition timing.

Make sure the timing mark on the balancer is correct by placing #1 piston at exact TDC on compression stroke. Harmonic balancer mark should line up with the "0" or TDC mark on the tab.

Set the timing to specs. If you have HEI advance it to 8,10 and maybe even 12 degrees. I'd start off with 10. Otherwise check the specs for you engine.

[Number21]

It works! Well, kinda. I advanced the timing a little bit and found one of my plug wires was loose. Took it out for a drive and no more stalling! It's pinging now though since I played with the timing, I'll have to drive it down to my shop to get a timing light on it.

One more question - is my fuel filter supposed to be full when the engine is running? It seems to only be about half full....

Thanks for the help!

[68gmsee]

Looks like you're heading in the right direction with it.

Fuel filter is fine. They never show full. I would get rid of it for a metal one, though. The plastic ones degrade with the heat and even the ethanol in the fuel and will eventually crack. Kind of like plastic containers left out in the sun. After some time they fall apart.