akuma-z Posted August 9, 2009 Share Posted August 9, 2009 I just recently finished a motor swap on my 240z and I have noticed that my car will no longer start if the gas tank is full. I never had this problem before the swap. The old motor was the original L24, the new motor is a 3.1L stroker with SU carbs. I am using an electric fuel pump. I first noticed that I had a problem the first time I went to the gas station and topped off the tank. After filling up I could not get the car to start so I just assumed that it was vapor lock from the car sitting while filling up, but I no longer think that is the case. I was able to get the car home, but I noticed that if I let up on the throttle the motor would die. I also noticed that the farther I drove the better the car would run. The next time I needed to get gas I filled up the tank and once again the motor would not start. I was able to siphon out some of the gas from the tank and it started right up. It almost seems like if the gas level is higher than the bottom of the fuel fill tube the car will not start. I assume this could be due to the tank not venting properly. For now I have just been filling the tank up to 1/2 full and I have not had any problems but I would like to actually fix this issue so I dont have to worry about getting stuck at a gas station again having to siphon out gas if I put in too much gas. Quote Link to comment Share on other sites More sharing options...
akuma-z Posted August 19, 2009 Author Share Posted August 19, 2009 I think I have found something very wrong with the way my carbs are connected to the fuel lines, but I am not sure. Today I replaced my fuel pump and filled up the tank so I could start troubleshooting my fuel issues. I have verified that I am getting good fuel pressure up to the carbs. If you look at the picture there is a second smaller line that is currently connected to the fuel return line. I do not believe this is correct, but I do not know what this line should be connected to or what purpose this line serves. Since it appears that my current setup does not appear to have a proper fuel return line would I be better off using an original fuel rail since I have one laying around in the garage? Where should the smaller line pictured be connected? Quote Link to comment Share on other sites More sharing options...
ArizonaZ Posted August 19, 2009 Share Posted August 19, 2009 The "connected to return line" are just vents for the float bowls, normally they are just connected to the air filter Quote Link to comment Share on other sites More sharing options...
akuma-z Posted August 20, 2009 Author Share Posted August 20, 2009 Today I fixed the fuel line routing. I am now using the stock fuel rail from my old L24 motor with a functioning return line and the vents on the bowls are no longer blocked. The motor will start with a full tank of gas now, but it is very rough and I have to press the throttle to keep it from killing itself. The motor will always start, idle and run well when the tank is low but I cannot explain why I start having problems when the tank is full. I suppose I will start tearing apart the carbs to see if there is anything wrong since I have checked everything I can think of fuel wise. Quote Link to comment Share on other sites More sharing options...
akuma-z Posted August 21, 2009 Author Share Posted August 21, 2009 I advanced the ignition timing a bit and the motor runs on its own now, but it is still pretty rough. I think I may be running too rich or not firing on all six cylinders because I can see what appears to be unburned fuel spitting out of the exhaust. I made a video this morning and if you look you can see the fuel spitting out of the exhaust onto the ground. http://www.youtube.com/watch?v=YksDfpZoPfU Quote Link to comment Share on other sites More sharing options...
zedman240 Posted August 21, 2009 Share Posted August 21, 2009 Check your float levels then have them balanced; they may be out of adjustment. Do that first before you start pulling everything else apart. Quote Link to comment Share on other sites More sharing options...
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