Muskrat Posted February 21, 2005 Share Posted February 21, 2005 To begin, I have a '72 240z that I've swapped a 2.8 motor into. Its got a N47 head, flattop pistons, header, and I'm running un-rebuilt roundtop SUs with an electric fuel pump and clearflow fuel filter on the factory gas tank and lines. I also converted to an electronic 280zx ignition. The coil, wires, and plugs are all less than a month old. This setup was running flawlessly for several months, burning a little bit of oil (a few cracked valve seals, nothing major), but otherwise pulling fine. As of about a week ago the motor had between 140-150 compression on all cylinders with the throttle closed. The problem started around two weeks ago, and about a week after running a big can of fuel system cleaner through the motor (probably unrelated, but I dont want to leave something out). At the time, the problem was limited to the motor leaning out after a long gear pull. It's been progressively getting worse over the past two weeks, and now the motor idles very rough at 500rpm (previously a nice healthy 900), and will pull for short bursts before stumbling and misfiring badly. Oddly enough, until today (problem is now even worse) I could use about 20% throttle to get me to work and back, and the car would cruise relatively smooth. Now, the car will barely move under its own power. After pulling the spark plugs, I saw that except for the cylinder that's burning oil, all of the plug grounds were WHITE. Not yellow with white flecks, but for the most part, uniformly white. I've tried my best to eliminate potential causes for this worsening condition. The fuel pump was replaced yesterday, the fuel filter is clean with no debris in it, I checked fuel flow at both the inlet to the fuel rail, and the outlet. Both had a pretty good amount of flow. I have no way to check fuel pressure at the moment, but the car ran fine before with the same model pump I replaced it with, so I doubt thats the issue. Most of the ignition components are new or less than a month old, and the vacuum advance on the distributor is connected and working. An odd thing I think I should note, I drained the fuel bowls to check for any trash (didn't find any) but I did notice a rather small amount of fuel coming out of both bowls compared to the flood from when I drained them to swap them from the 2.4 to the 2.8. It almost seems to me that the fuel bowls aren't filling up fast enough to support anything more than cruising and light throttle. So: I figure I'm looking at a fuel system issue somewhere along the lines, probably in the carbs. I do, however, have a hard time believing that both carbs would fail in the exact same manner at the same rate. So I'm stumped, hoping someone out there has had this exact problem and can tell me what needs to happen to make it right again. This is my daily driver, and at the moment, it doesn't run at all. Quote Link to comment Share on other sites More sharing options...
Tim240z Posted February 21, 2005 Share Posted February 21, 2005 Have you checked for vacuum leaks, esp around the throttle shafts? Do the spray trick around the shafts while its running and see if the idle changes. Quote Link to comment Share on other sites More sharing options...
Muskrat Posted February 21, 2005 Author Share Posted February 21, 2005 Oh, I know the throttle shafts have a vacuum leak, but I'm relatively certain that's not the problem, as I've been running the carbs as they sit now for 2 years. Quote Link to comment Share on other sites More sharing options...
SHO-Z Posted February 22, 2005 Share Posted February 22, 2005 You need to check the floats in the carbs and all of the jets. You probably loosened up a bunch of shellac in the carbs and have them all clogged up. I picked up a set of triple SK racing carbs that were sitting around for some time. After soaking them in carb cleaner for some time the shellac still was like hard plastic in the bottom of the bowls that I had to scrape out. From your original post I would say your carbs are all clogged up. Quote Link to comment Share on other sites More sharing options...
Muskrat Posted February 22, 2005 Author Share Posted February 22, 2005 Well, its looking like the problem is twofold. I'm no longer getting spark, which I'll try to troubleshoot tonight. This doesn't explain my previous lean problem though... I'll have a look at the floats like you said Sho-Z. Thanks for the tip. Quote Link to comment Share on other sites More sharing options...
Muskrat Posted February 24, 2005 Author Share Posted February 24, 2005 Fixed. I love compound problems. The positive trigger wire for the ignition module was faulty, and the section of wire the previous owner had crimped in to replace the ballast resister was corroded beyond belief. As for the carbs, there was some gunk on the floats, and some more gunk on the pistons themselves, making them stick badly. Cleaned everything up, and fired the car at around 2am and took a victory lap around the block. My neighbors hate me. Quote Link to comment Share on other sites More sharing options...
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