Won't stay running - help me figure this out!

[Snax]

Pulling my short hairs out here. I've been trying to figure out what is going on with the car all afternoon to no avail.

It has a Weber carb and it will not stay running.

Symptoms: Won't start without full throttle and will not rev initially. Releasing the throttle will allow it to die. Then for some reason it will miraculously start to run a bit, revving through the mid and upper range only to sputter and die at idle. And for no reason at all that I can see, it will then idle ok and rev normally for a minute or two before the sputtering behavior returns at idle or worse, requiring full throttle just to keep it revving at 1000 rpm.

I have checked, adjusted, and double checked my idle mixture and rpm set screws with little impact on this craziness. It will work one minute, then die the next. If I however manually cycle the acceleration pump while it is doing the rough idle, the extra fuel will keep it from dying.

The fuel filter is full of clean looking fuel and a reasonable amount seems to drain out the fuel line when I disconnect it at the carburetor. I thought my cheapo fuel pressure regulator may be malfunctioning so I removed it to run stock pressure. Nothing changed with that.

I'm now to the point of thinking that there is an intermittent air leak in the fuel supply line. But why would it be intermittent?

I'm baffled at this point and will probably end up dropping the tank unless anybody can suggest anywhere else to look. The fuel lines at the carb and at the filter all seem fine, so I can only guess that it is either the hose at the tank or something in the tank. Perhaps I will attempt to jerry-rig up a small remote fuel container up front to see if that provides a better supply.

Any thoughts?

[ARCHINSTL]

I'm sure this is of no help, as you've mentioned it before, but - why not just renew the lines from the firewall to the filter and thence to the pump and thence to the carb? Unless they are relatively new (with the carb), I'd try this first; they are certainly the easiest and cheapest. And then the PITA rear lines...
And something kinda far-fetched, but - if the steel line has any rust, you might try to draw a vac on it from the front after plugging at the rear - if no vac, then some perforations in the steel line.
How old is the pump? Could the filler cap have something to do with it?
I don't think anyone here with a Weber has experienced this before (as I have one, I'm interested).
Tom M.

[blade]

how is you fuel filter? how is your pump maby your pump is not pumping enought?

[takza]

Sounds like what an OEM carb will do when it has a vac leak? In fact my OEM carb has been doing some of this because I think I water into the tube in the primary opening when water flushing the engine.

[Snax]

I don't believe the pump to be malfunctioning, as it was just replaced a few months ago. I considered the possibility of a vacuum leak, but visual and tactile inspection of all of the rubber hoses didn't reveal anything.

My wife did however mention to me last night that her Mazda5 has been acting up in a similar way to a lesser degree. She mentioned that the problem started after she bought gas at the nearest gas station, the same gas station I have always used to fuel this car. I occassionally had wierd glitches like this, though never to this degree before, and never made any connection to the source of the fuel. She said there was a guy standing out on the sidewalk by it the other day with some sign about being ripped off with bad fuel etc.

So in a nutshell, I'm going to stop looking at the mechanical and pump the tank out - which is fortunately less than 1/4 full.

[4wdchico]

You could pull the drain plug on the tank and empty it that way.

[blade]

wow ishould have know i get thet all the time i fill up at the gas station here in my town i have since found out that there is water in the gas, not spoiled gas but watered gas. so maby the same thing has happened to your gas station? if it is the gas i would tell the people that own it just to let them know.

[Barto]

I run methyl hydrate in all of my carburated cars through winter. The weber that is in my truck will do all the same things that you are explaining when there is water in the gas.( found out the hard way that I had forgotten to put gas cap back on then drove for 5 hours through the worst rain ever). Also if it is anywhere near freezing my weber will ice over so fast, if no methyl hydrate is in the tank. It not only stop fuel line freezing but also removes the water. try pouring one of the small 3 1/2 oz. bottles in before you do anything, I bet it will make a difference.

Barto

[ARCHINSTL]

Boy, the (in some way) bad gas theory is something I'd not considered - quite possible, though - especially if someone was protesting in front of the station. If you see him again, I'd stop and ask. Maybe also call the local PD or TV station to see if anyone else has complained?
Tom M.

[Snax]

Thanks for the heads up on a drain plug 4wdchico! Never noticed or thought that there would be one!

I'll try the additive first - because I'm L A Z Y . .

Oh, I forgot to mention the part about the fog coming back out of the carburetor after it would stall. If I opened the butterflys, there would be a fog down in the carb and scant smell of gasoline. It's got to be water. I HOPE it's water. That would be easy.

[Snax]

Well unless there's more water than gasoline in the tank, that's probably not it. I dumped a full 12oz bottle of the Methyl alcohol treatment in to no avail.

The only other thing that I have not yet checked is for a plugged catalytic converter. Not sure if it would present the same symptoms, but I can't figure any other reason it might idle at only 1100 rpm with the throttle fully open unless it just can't get the spend gasses out.

Unfortunately it looks like the only way to really check that one is to remove the tailpipe section by cutting off the existing bolts.

[4wdchico]

You can use a vacuum gauge to test for a clogged ex system.

See scenario #14 on this link for more info: http://www.secondchancegarage.com/public/186.cfm

[Petros]

it sounds like you have fuel, the vapor is likely fuel vapor. It is normal to see fog in the carb right after you shut off the engine. Have you checked for spark? Sometimes a bad coil or igniter will parcially fail and only run at certain RMPs. You need to have an assistant crank the engine while you hold a spark plug wire approx. 1/2" away from a metal ground. You should have a strong yellowish blue spark that goes "snap!,snap!, snap!", if not you could have bad electrical component.

And to verify you have poor fuel delivery you could spray starter spray, or even raw fuel, down the carb. If it starts and runs, than dies, it may indeed be fuel delivery.

You have to verify it the problem is fuel delivery and not electrical.

BTW, the weber carb is known for not running properly if you do not have the correct fuel pressure. Too much will cause it to flood, you might have too much fuel supply. Go get a proper fuel pressure regulator for it before you do anything else. You can not know what to check if you have known problems to deal with anyway.

Good luck.

[takza]

Fuel filter?

[Snax]

I'm pretty sure it's not a fuel issue now. I didn't have any regular gasoline sitting around, but a splash of xylene (117 octane) down the throat of the carb did nothing to change it's behavior.

I'll double check the spark, but I think it's pretty clear now it has to be the converter. Ironic, but it's the first thing I thought of when it began to act up, but I gave up on checking it because of the rusted bolts holding it on. I have time to take a look at it today though, cutoff wheel at the ready.