MikeyZee Posted September 15, 2008 Share Posted September 15, 2008 Hi All, My son has a 72 240z with a L24 and dual Weber DGVs. We have been having issues with these lately. I have rebuilt these carbs and after they were rebuilt they worked great for about 3 days. When we installed them after they were rebuilt we also put on a new filter and replaced all the soft fuel lines under the hood. The fuel filter appears to be a newer one so I didn't replace that one but I did add an electric one back by the tank. What will happen is that the front carb will just stop spraying gas at random. Maybe it will run for 2 hours maybe 3 days maybe 20 minutes. On Saturday the front carb decided to quit spraying gas. The temp was maybe mid 70s. We had the car towed to a friends house and swapped the front and rear carbs. ok....the one that quit still would not work on the rear but the front worked. The next day I took apart the top of the carb that failed the day prior. Blew out the fuel inlets and was able to get fuel spraying from it....yee haw! Both carbs were spraying. I made sure timing and idle were set (auto 1050 in p). I used the synchrometer and dialed in the carbs. After about 15 minutes the front carb stopped spraying. Hmmm? Maybe there is crud in the line that feeds that carb. I blew all the hard lines out with compressed air. The fuel in the line came out and about equal amounts of air from the front and rear feeds. Again I took the top off the troubled carb it was full of gas (it was on the first carb too). I sent some compressed air through it and again got it working for about 20 minutes. Then the front carb quit spraying again. It's always the carb I have in the front position. The screens in the carbs had nothing in them blocking flow either. I have also tried it without the electric pump with the same result. I have ordered a new mechanical fuel pump on order and plan to criss cross the lines that go to each carb......that is the next step. Has anyone had this issue? Any other troubleshooting advice? Maybe a fuel pressure reg/guage would help? Thanks for any help or advice! Quote Link to comment Share on other sites More sharing options...
Zmanco Posted September 16, 2008 Share Posted September 16, 2008 Hi Mike, Sounds like you guys had an adventure getting home after the Shine n Show Sorry to hear that. Can you be more specific about what you mean when you say it stopped spraying fuel? Are you talking about seeing fuel come out of the accelerator pump outlets when you move the throttle? Or is it something else? Since the problem seems to follow the carb when you swapped front and rear I'd focus on the troublesome carb and less on the fuel supply. As we had discussed earlier, it sounds like your fuel tank has rust/crud in it and perhaps a few small pieces made it past the filters/screens? That shouldn't happen, but the symptoms sure sound like it. You may need to tear that carb back down and soak it in cleaner again. Just some thoughts... Of course, you're going to have to deal with getting the tank cleaned up too otherwise I suspect this will be a recurring issue. Quote Link to comment Share on other sites More sharing options...
MikeyZee Posted September 16, 2008 Author Share Posted September 16, 2008 It was an adventure..... Yes, no fuel will spray out of the accelerator pump outlets on whichever carb is in front after about 15 mins after they are put back together. The issue does not follow the carb it follows the position of the carb.....always the front mounted carb eventually. The screens look clean and I can't really see any contamination in the carbs, filter, or screens......a very funky issue. It is a new filter and new screens along with the carb rebuilds, you would think some crud would be trapped in them but there is not. Like I said we have verified the lines have flow with compressed air and the float bowls have fuel in them. I am picking up a new fuel pump this afternoon that I ordered and I'll look for a preasure guage and regulator when I get to the parts store. Quote Link to comment Share on other sites More sharing options...
Zmanco Posted September 17, 2008 Share Posted September 17, 2008 I'm sorry, I missed that the problem stayed with whichever carb was in front. If you can get the problem to occur again, you might try opening the hood to cool things and see if the problem goes away. It's sounding like vapor lock only on the front carb, although I have a hard time believing that even as I type it. Quote Link to comment Share on other sites More sharing options...
MikeyZee Posted September 17, 2008 Author Share Posted September 17, 2008 I have tried letting it cool down and it seems to have no effect on it. The front carb will not start working. This is the most bizzar thing. I did pick up the new pump after work today. It is one that resembles the OEM pump. The one that was in there was a sealed pump and quite a bit smaller that the new one. Maybe it will have some effect on it. I forgot to pick up the fuel presure gauge today but I'll get one tomorrow. Michael should be back from his Mom's later this week so I think I'll wait till he gets back and have him put the new stuff on his car. I was also wondering if the fuel return is letting too much fuel back to the tank....I'm not real sure how that works. Thanks again for the ideas..... Quote Link to comment Share on other sites More sharing options...
Dayz Posted September 17, 2008 Share Posted September 17, 2008 I have had that kind of problem before. As stated above, clean your carb...you might have a little piece that makes it go bad (ei: rust) When that piece fall down in the bowl, it works and when it gets suck into the jet it blocks it until it goes down again and so on. Dismantle it, clean it and it will work. It is not so bad to rebuild it again! It is fun...a little puzzle! Dayz Quote Link to comment Share on other sites More sharing options...
cockerstar Posted September 17, 2008 Share Posted September 17, 2008 I would start things off by checking the fuel pressure at each carb and see if that reveals anything to us. Quote Link to comment Share on other sites More sharing options...
DAW Posted September 17, 2008 Share Posted September 17, 2008 Are you using a stock steel fuel log (with the return line, like the original SU-style Hitachi side-drafts used)? If not, try that and make sure you have a patent return line back to the tank (it has a small orfice which regulates return/supply pressure). DAW Quote Link to comment Share on other sites More sharing options...
MikeyZee Posted September 17, 2008 Author Share Posted September 17, 2008 Each time I do clean it it does work for a little bit. I think I have done that about 4 times. No crud is in the bowls or screens. That was my thought first was that something was clogging the carb. The fuel lines are the factory metal lines and return lines. I did replace the soft lines under the hood from the hard lines that come in from the hard lines from the tank. I also replaced the soft supply lines at the tank as well. Quote Link to comment Share on other sites More sharing options...
Zmanco Posted September 17, 2008 Share Posted September 17, 2008 A few thoughts: 1) The next time the front carb "stops working", pull the hose off at the carb and crank the engine. Does fuel come out of the hose? If so, then the fuel supply is ok and the focus should shift to the carbs. 2) If you can, the next time the carb stops working pull its cover off and see if there is fuel in the float chamber. It sounds like right now you're using the absence of fuel coming out of the accelerator pump jets as an indicator that there is no fuel at all in the carb. While under normal conditions that would be a safe assumption, before we continue to assume that you should verify it. 3) Is there anything near the bottom of the front carb that might be preventing the accelerator pump linkage from moving freely? It's been a while since I looked at the DGV carbs, but IIRC there is a lever that is driven by the throttle shaft linkage that depresses the accelerator pump diaghram. Perhaps a heat shield or something else is preventing it from moving? (I think I'm reaching on this one, but hey, it's brainstorming...) Quote Link to comment Share on other sites More sharing options...
MikeyZee Posted September 17, 2008 Author Share Posted September 17, 2008 I have checked the float bowl and it does have fuel in it as I remember. The car will start and the front carb will get gas if I choke them. You can see that they are "wet". I have not actually pulled off the hose to the front carb but it seems that if the bowl has fuel in it and the line has fuel in it the carb should be working........It all "should be" lol Another thing that I have not tried is getting longer fuel lines going from the hard fuel lines right next to the valve covers and cris-crossing the supply lines. First I have to put the new pump in and the presure guage. There are no obstructions of the linkage on the carbs. Hmmm? wonder if the desk I'm banging my head against will dent before my forehead.... Quote Link to comment Share on other sites More sharing options...
MikeyZee Posted September 19, 2008 Author Share Posted September 19, 2008 1 PSI.......I think we have a problem! We put in the new pump and pressure gauge last night. This is with or without the Mr Gasket pump that is supposed to put out 2-5. Blockage in the tank or what? This weekend we will be taking out the electric pump and filter back at the tank. Any other suggestions about checking for restrictions? Thanks All! Quote Link to comment Share on other sites More sharing options...
Zmanco Posted September 19, 2008 Share Posted September 19, 2008 Where did you measure 1 psi? Was it at the hard line where it enters the engine compartment? Or at the outlet to the front carb? If it's the latter, I'd be curious to hear what it is where the hard line enters the engine compartment. Otherwise it's pretty simple. The hard line runs between the engine compartment and fuel tank. You probably have the electric fuel pump in line between the hard line and the tank. That's all there is. Quote Link to comment Share on other sites More sharing options...
MikeyZee Posted September 19, 2008 Author Share Posted September 19, 2008 The measurement was between the man fuel pump and the hard fuel line that runs around the valve cover. The electric fuel pump is in the rubber line between the tank and the hard line. I'll put the pressure gauge right after the hard line tonight and check it there too......good idea. So you can test the pressure before or after the pump....no difference? I could mount the gauge before or after the filter, right now I'm not real pleased how it's mounted. Could there be anything in the tank like a pickup screen that could be causing blockage? Is the spacer required on the manual fuel pump? Last night after we installed the pump the front carb started working but just doesn't seem as strong as the rear carb but it is still working at this point. Thanks again Daniel! Quote Link to comment Share on other sites More sharing options...
MikeyZee Posted September 22, 2008 Author Share Posted September 22, 2008 OK.....it was a busy weekend with no time to work on the Z. We found a few minutes to do some investigation and see what the fuel pressure problem could be. I found that the filter back by the tank in front of the electric fuel pump was clogged with a thick muddy like sludge. Looks like the tank will have to be cleaned and sealed. Now after removing the electric fuel pump and filter with just the factory style filter in it it is running 4-5 lbs. Both carbs are working very well. At one point the tank was ran dry, I am assuming that's when the filter was clogged with the sludge. At least we found the problem and I think we'll be able to get this taken care of. Thanks all for your input on this issue! Quote Link to comment Share on other sites More sharing options...
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