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Car almost dies after spirited driving


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My 2002 has a 292 cam, 9.5:1 pistons, new DGES 38/38, electric fuel pump and 123 distributor with a Ti curve. After some spirited driving, say zipping up a hill, when I come to a stop the car idles at 900 and then starts to dive to almost 0. If I tap on the gas the idle will pick up again, and all is good in the world. 

This morning I cleared the idle jets and set the float level to 40mm closed, 51mm open. This flies in the face of the common 35mm closed, 50mm open, but according to the attached chart it's the correct setting. I run a vacuum advance to my 123 distributor. I warmed the car up and re-calibrated the carb with about 3/4 turn in on idle adjustment and a 900rpm idle with about a 1/2 turn in on the speed screw. I am running size 50 idle jets. I also checked for vacuum leaks with carb cleaner, but didn't notice anything. 

I am new to jetting carburetors, so I wondered if it was just some fuel / air mismatch I should investigate. Otherwise the car feels great, has solid throttle response and is quick off the line.  



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Never been a fan of electric pumps up front as I think they are better at pushing fuel than pulling fuel. That said, it may just be a loose hose clamp somewhere between the pump and the tank. This will allow a small air leak when the pump is running which reduces the volume of fuel pumped. I assume that you have also replaced all of the hose within your stewardship so that you know that there are no leaks or swollen hoses. 


I note that you appear to be using the steel return line for some reason. These have been known to get pinched shut (or partially shut) against the body. Maybe check the full length of this visually and if it was freshly used by your mechanic then it could have been standing open for years. Maybe a blow through with an airline after disconnecting the hoses at each end?

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What is the typical power source for these in the trunk? 


I just had mine "silenced" with a rubber stopper after hearing it click click click, and would hate to hear it chirping again. 


Also in terms of fuel venting, the return line is plugged at the rubber tip in the engine bay, connected to the return line and attached to the tank in the trunk. 

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I tightened all the clamps I could find and went to O'Reilys. On my way back from the store I noticed it wanted to die at idle in stop and go. It was intermittent doing it at one light, but not the next. The tach would be at 900 rpms, and just slowly fall down to zero. I had to blip the gas a few times to keep her running. I pulled over and tried tuning the carb one more time. I have a hard time getting the car to actually run with a 1/2 turn on the idle-speed screw. I have to turn it about 3/4 - 1 full turn, then adjust from there. Both idle mix screws are about 1 turn out. I turned on the fan, lights, fog lights, etc. and set the idle speed to 900. It seemed to stop for the time being, but only the next few blocks to my house. Could an idle speed screw too far advanced cause this issue? A vacuum leak? I just replaced the vacuum hose from my 38/38 to my 123 distributor, thinking that was the issue originally. 

I also got out of the car, and gave the throttle linkage a good few bursts, then held it there for a while as I watched the fuel filter. It stayed a consistent 1/2 full. But I also never got the stumble. 

I went ahead and swapped the used but new hose running from the fuel sender to the plastic line. I noticed there was a 1 inch plastic "sleeve" inside the fuel line where it connected to the fuel sender. I am using 5/16" fuel line, and it seemed like it needed the sleeve to fit tightly on the sender unit, but fit fine on the plastic line leading into the cabin. I also notice - as this has been the case for as long as I've owned the car, despite swapping the sender o-ring, the sender puts of creeping gas fumes that just lightly wet my tank. They seem to come and go. 

Edited by silasmoon
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what about vapor lock?  You know, when it gets hot and vaporizes fuel in the line, and the bubble prevents actual fuel from reaching the engine.  This would be more of a problem on hotter days, and usually occurs when you slow down and decrease air flow over and around the engine.    


How thick of a gasket do you have between the carb and intake manifold?  Is the fuel line fully protected from any heat sources?  Any other cooling issues with car?

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11 hours ago, silasmoon said:

I noticed there was a 1 inch plastic "sleeve" inside the fuel line where it connected to the fuel sender.


If that plastic sleeve/adapter is cracked... it will leak.  Recent thread talked about how you can simply cut 1 1/2" from the white plastic supply line leading into the cabin and use that as a replacement piece.  I've done this and it works like a champ.  There's plenty of white supply line in the trunk to spare...


Have you pulled the plugs to check for color? I'm thinking instead of running out of fuel, perhaps the choke butterflies are closed ?  Plugs would be black and sooty, or wet with fuel.


Easy check.... Let it die in your driveway and turn off the key to kill the electric pump, get out and pull the filter off the carb and see if the choke plates are closed.  Then you could pull the top off the carb and see where the fuel level is?  No fuel in the bowl? That's your problem.



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Is the float level in the carb to specs?  


Next time it dies like that, if you're able, pull the top of the carb and see if the float chamber is empty.  If so, you may have a misadjusted or sticking float or malfunctioning needle valve.  If it's full, I'd start to suspect clogged idle jets.



Edited by mike
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Float level was just set yesterday according to Weber's spec, it had been way off out of box, and so far it hasn't made a difference. 


Started it up cold, fired right up and the choke came on (electric). About 5 minutes in it died, but I was in traffic. I drove around for 30 minutes up and down some neighborhood streets and main streets. Nothing. Car ran great. Always idles at 1,000. 


So I hauled ass up a nearby mountain road, hitting about 5,500 RPMs. I came to a stop at the top and turned around slowly. Cruised down the back normally. Came to a red light, it idles fine, then shot up and empty inclined road at 6,000 RPMs. It died at the next light. I then hit another stretch at the light going down hill at 6,000 RPMs and got it to die again. I immediately pulled over but the fuel pump was on for another 15 seconds. The fuel filter was full, but it was raining. I did manage to pull the plug from cylinder 1. It was brown with a bit of soot on the ring. 


I cruised home slowly and modestly for another 15 minutes, with only slight dips in the RPMs at rest (700 to 900).  I checked the plug one more time in my garage, and to my eye it looked wetter and a bit darker. 


Attached are the plug shots. The first check and the second check. The second check are the blue cloth photos. 







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I'm still leaning towards an over-rich condition. Your last picture shows a very wet plug.   You say that giving some throttle will clear it up... if the pump isn't delivering fuel, giving it throttle won't deliver any more because there wouldn't be any to give. 


That electric fuel pump... what pressure is it delivering? Your Weber only wants about 2-3 psi...any more than that and it will push fuel past the needle valve and flood the car. Might need to put a regulator in line between the pump and carb.


On another note.  Where is your timing set?  Did you just stab the 123 at TDC and leave it, or did you set it with an advancing light?  ...just curious, perhaps you don't have enough advance at lower rpms to light things off?




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