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Offline ToniJ1960

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gas smell and stumble off idle
« on: March 15, 2015, 06:21:27 PM »
 Ok while Im working on these dents I did a little mini tune up on my 78 2.3L.

 Sometimes when Im driving I smells gas,but if I stop and raise the hood nothing in there. No smells.

 I had just adjusted the mixture and made it as lean as I can, idled it down real low to see if I could it to stay running like that.

 I rebuilt the top of the carb less than a year ago.

 So, I dont think its running rich or a ruptured power valve diaphragm like we all know these cars get. I can kill it with the idle screw in too far.
 Its not `loading up` at idle so I dont feel its dumping gas over the bowl.

 Maybe its a hole in the gas filler neck? How do I check for this? Are they difficult to replace?

 It also has a stumble off idle is it because of being too lean maybe? It doesnt do it every single time I rev it in neutral one out of three or four times.Im thinking its fuel or timing related.

 Im hearing a little surging too I might need to check the carb mounting bolts again theyre known for getting loose.I just cant remember or they 8mm or 10mm and six point or 8 point?

Offline Wittsend

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Re: gas smell and stumble off idle
« Reply #1 on: March 16, 2015, 11:11:34 AM »
For the gas smell, lay off the burritos.

For the stumble, lay off the booze.

Seriously, search down the fuel line not only under the hood, but under the whole car. Often the smell can come from leaking filler tube seals, fuel sender seals, fuel line to gas tank connections etc.  Other times a solid fuel line may have been broken to facilitate a part removal. Patched with rubber hose and clamps there might be a leak source also.

An engine at idle takes less fuel than one in use. Try resetting the mixture and see if that removes the stumble. If the idle is cranked down there is a slight possibility that the accelerator pump is not functioning until the linkage makes a certain amount of movement. One thing I have learned over the years is to make a notaction of an original setting BEFORE making adjustments. Then, if needed you can get back to the base setting.

Offline ToniJ1960

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Re: gas smell and stumble off idle
« Reply #2 on: March 16, 2015, 11:25:02 AM »
 I think the mixture is probably the first thing to try. I usually set it with a vacuum gauge. In fact Im wondering if thats the best way to set the timing too.

 The gas smell isnt me :) but it seems weird its so noticeable when Im moving at a decent speed you would thik if its underneath the outside of the car the air going back over it would carry it away? I would even think  it might still be able to be smelled under the hood if its sitting and idling and leaking underneath.

 The filler neck or the seal are stilll where Im thinking.

Offline Pintosopher

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Re: gas smell and stumble off idle
« Reply #3 on: March 16, 2015, 12:08:25 PM »
Given that the smell isn't generated by humans (  ;D)  Think how much a low pressure area under the car could draw fumes into the cabin. Leaking filler neck would be easily checked, but I would pull the entire tank and check the hoses for the vent and sending unit that exit the tank to the hard lines to the engine compartment. These are almost never replaced when they should be and if you are running the originals with ethanol additive fuels, you have a disaster waiting to happen. Replace these hoses with Gates "Barricade" hose for carbureted vehicles. 

Also check for pinhole leaks in the top of the tank where rust gets to rotting the tank from the inside out. Ethanol is your car's greatest enemy , because it creates corrosion when it draws moisture from the air. If your drive you car infrequently, it only gets worse for the  fuel system.  This is why newer cars use plastic fuel tanks and use polymer plastic fuel hoses with special Viton or fluoroelastome r rubber products in the system.
 
 Keep looking until you find the leaks, then tune it up.

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Offline amc49

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Re: gas smell and stumble off idle
« Reply #4 on: March 16, 2015, 05:24:50 PM »
The idle mixture screw not only sets the idle at dead stop, it also affects the fuel setting just off idle as well, or the first few degrees of throttle rotation. Leaning it out also has some leaning effect on transfer slot fuel which is the transition between idle and the car moving at lower speeds. Too lean at idle dead stop will be too lean at just off idle as well. The stumble there.

Setting timing by idle vacuum alone is an excellent way to tear up an engine from too much advance, the engine spends more time and load higher than that. Timing gets set for overall use, not just idle.