BrandenZ Posted May 15, 2012 Share Posted May 15, 2012 I've got an interesting and very intermittent issue that only seemingly happens during 1) racing / autox and 2) during hot days and 3) extremely long staging or hotlapping of the car Long story short, I get major hesitation and stumbling for a seemingly random period of time. If I get out of the throttle and let it idle for a bit, or in some cases let it coast for a long period of time (assume airflow helps), it clears right up and behaves perfectly. 1973 240z E88 / F54 Dual Webers Mechanical fuel pump JCI radiator So far have tried: Adding 2 more small fans, for a total of 3 fans covering almost the entire space of the JCI radiator, run off of a temperature switch that while racing is placed on the lowest setting (basically running constantly) Replacing the mechanical fuel pump Replacing the insulator between the pump and block Adding heat wrap around the lines running to the carbs Replacing the fuel filter Draining the entire tank (completely clean, both on the drain and at the filter afterwards) Checking fuel pressure (dead on at 4psi) Verifying returnline Running on 1/4 tank, 1/2 tank, full tank... Removing inspection covers while racing to increase airflow Leaning towards vaporlock as it seems to completely solve the problem if in-between runs I pop the hood and spray the fuel lines, radiator, pump, etc. down with water. Also find if I shut the car down on a hot day after a hard run and let it sit for a while, it takes _forever_ to get it started again. Open to any suggestions at this point. Not sure what else to do other than try to fab up a heat shield and reroute all of the fuel lines. Very frustrating because it happens exactly when I least want it to, and has basically managed to ruin probably 20% or more of my possible seattime over the past year. :-/ Quote Link to comment Share on other sites More sharing options...
Leon Posted May 15, 2012 Share Posted May 15, 2012 Make or get a heat shield, especially if your carbs are hot to the touch after a run. Make sure the fuel rail is well-insulated at its mounts. If the problem persists, then re-route the fuel lines within the engine bay. A good heat shield should be #1 on your list. Quote Link to comment Share on other sites More sharing options...
NewZed Posted May 15, 2012 Share Posted May 15, 2012 Isn't this why Nissan added the electric pump? Quote Link to comment Share on other sites More sharing options...
Leon Posted May 15, 2012 Share Posted May 15, 2012 Isn't this why Nissan added the electric pump? Possibly, but it's not a great solution. It'll help prevent cavitation of the mechanical pump, so the electric pump only solves the problem if the mechanical pump was experiencing cavitation. Otherwise, you'll have the same issues. Quote Link to comment Share on other sites More sharing options...
Perfect240z Posted May 15, 2012 Share Posted May 15, 2012 I'm pretty sure the 240z's had Vaporlock issues, head is a great idea from Leon. Def wrap your headers and of it helps the fuel lines as well. You should even see what your temp is at when the car starts acting funny. You may even want to get a vent on your hood or find another hood to install one on. Quote Link to comment Share on other sites More sharing options...
BrandenZ Posted May 15, 2012 Author Share Posted May 15, 2012 Maybe I should just run a 50-shot of nitrous... Thanks all -- I'll look into a heat shield / try to figure out a way to fab one up. Wrapping the headers is also a great idea, as they're right beside the intake manifold (and fuel lines too by proxy). Don't think I have the heart to replace or chop up the current hood, though! First time this ever started happening, water temp actually was up above normal. However, once I installed the additional fans, that resolved the issue. I assume that fixed the vaporlock problems as well, but I was wrong. Water temperature holds fine now, even when I have issues. I'm thinking about installing a 160 deg thermostat instead of the 180 that's in there now in an effort to bring radiant temps down (especially since the mechanical pump is bolted to the head), but will try some of the other suggestions first. Quote Link to comment Share on other sites More sharing options...
Tony D Posted May 20, 2012 Share Posted May 20, 2012 I'll get poo-poohed by the purists, but consider running a 160 thermostat. The underhood temperatures are CONSIDERABLY LOWER than if you runs 190 or 180 thermostat. Yeah, theoretically and practically you loose a percentage of power from thermal losses... But then again boiling fuel and having to get out of it for a while costs you power as well. Sounds like ypu're borderline, the 30F+ drop in underhood temperatures may do it for you. Quote Link to comment Share on other sites More sharing options...
nates240z Posted September 14, 2012 Share Posted September 14, 2012 Brandon z, need update did the 160 stat work on vapor lock? Thanks,Nate Quote Link to comment Share on other sites More sharing options...
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