Csomme Posted May 24, 2011 Share Posted May 24, 2011 First off I've built many 240sx's, rebuilt many motors, tuned many cars, used to work on racecars, etc. I would consider myself to be very knowledgeable in the mechanical department, but DAMN I'm stumped, and I have never dealt with these motors before, but it seems pretty straight forward. L26, E88 head, Round top SU's, stock exhaust, etc. Well when I first got the car, I retuned the carbs, and the car ran great for 200 miles, then the plugs fouled. They were black a sooty, a sign of running rich, so I retuned the carbs AGAIN, and they were pretty close to spot on, then took it to a local Datsun guy who used to race these cars who made sure that the Carbs were working top notch. He made a few adjustments, but they were pretty close. 200 miles later, fouled plugs again, same thing. I had yet to check the timing, so I put a timing light on it and it was at perfect TDC on the timing marker. Which I believe is the 2nd notch from the top, so I advanced it.(I think, I can't find any information on advancing/retarding in reference to the timing marker thingy) to the 2nd mark from the bottom, so I'm guessing that's around 15* BTDC advanced. I retuned the carbs immediately afterwards, and now it still feels slow, and sounds like it's missing a little under full throttle. So I'm just asking for some feedback on what this could be, what I could be doing wrong? What I should be doing? Etc, Criticism is incouraged! Poke holes in my story, poke holes in my mechanics, I really don't care, I can handle it, I would just like some insight. Quote Link to comment Share on other sites More sharing options...
DCZ Posted May 24, 2011 Share Posted May 24, 2011 If you clean/buff the timing plate you might be able to see the markings. Working from memory, I think the next to the last mark in the direction of rotation is 0 degrees, with each tooth being 5 degrees, so you can measure from about 20 degrees BTDC to 5 degrees ATDC. Someone shout out if I'm wrong! What type/heat range of plugs are you using? Most people have good results with the stock NGK. Quote Link to comment Share on other sites More sharing options...
Tony D Posted May 24, 2011 Share Posted May 24, 2011 What three plugs are fouled? Quote Link to comment Share on other sites More sharing options...
Csomme Posted May 25, 2011 Author Share Posted May 25, 2011 No 3 plugs are fouled, it's all of them untill the car doesn't run. Quote Link to comment Share on other sites More sharing options...
30 ounce Posted May 25, 2011 Share Posted May 25, 2011 Check that the rotor & cap are in good shape. Make sure you have the correct gap between the star wheel and trigger (forgot what they are called!!) under the rotor.(unless you have points!) Then make sure the coil is in good shape. I'd just replace it, they're pretty cheap. And the wires too. I think you have a spark problem unless your floats are cavetating or not seating properly. Quote Link to comment Share on other sites More sharing options...
Csomme Posted May 25, 2011 Author Share Posted May 25, 2011 I've recently replaced the plugs, plug wires, cap, rotor, coil, etc. haha, I'm so at a loss here. Quote Link to comment Share on other sites More sharing options...
z-ya Posted May 25, 2011 Share Posted May 25, 2011 I've recently replaced the plugs, plug wires, cap, rotor, coil, etc. haha, I'm so at a loss here. What plugs are you running? What do you have them gapped to? Quote Link to comment Share on other sites More sharing options...
Tony D Posted May 25, 2011 Share Posted May 25, 2011 No 3 plugs are fouled, it's all of them untill the car doesn't run. Then your carbs 'are not tuned right'... On the off chance you have some super-cold heat range plugs I would inquire which plugs you are using, but you have far too much fuel for your needs if the plugs are fouling....unless this is wet fouling from oil... You say 'fouled black sooty'. No compression results... This engine is NO different than any other internal combustion engine out there, there are no magic bullets when it comes to tuning. What would you think the problem would be in any of the 'other' engines you have experience with? You surmise fuel, I would agree. 200 miles of running---too cold a heat range plug? Fouling is not an issue with timing lead, and it would be an extreme stretch for anything spark related. Fouling is deposition on the plug, and that means fuel or foreign deposits---so heat range, fuel, or bypass oil from somewhere. No mention of blue smoke or burning oil smell in any posts...so we are back to fuel. You say 'tuned the carbs' but you won't see any appreciable driveability or visible smoke until you are well into the 10's for AFR, and the car will drive fine. Running lean best, or rich best on your tuning? I suggest you try "Lean Best" for a change and see if it improves. Quote Link to comment Share on other sites More sharing options...
Csomme Posted May 25, 2011 Author Share Posted May 25, 2011 Yeah, I am running stock NGK plugs gapped to .028. I mean, it has to be fuel, I pull the plugs, black and sooty means rich condition, they smell like fuel, it doesn't smoke at all.... And exactly Tony, I would surmise fuel in any other motor, but I have had multiple people tune these carbs and each one has extensive experience with SU's and Z's. I guess maybe just try to go even leaner than before and see what happens. Thanks for the input guys, I will keep updating this thread until I get this figured out. Quote Link to comment Share on other sites More sharing options...
Tony D Posted May 26, 2011 Share Posted May 26, 2011 "Stock NGK Bpr6ES"??? 7's 8's ? If you don't tune to lean misfire and back down 1 turn, likely you are well into the 11's for AFR. You will not see black smoke out the tailpipe until DEEP into the 10's or high 9's for AFR. I can't count how many SU's I have seen 'tuned to run great' puffing black out the tailpipe. That's not tuned right, but hey the torque curve is FAT and they drive nice like that! Quote Link to comment Share on other sites More sharing options...
z-ya Posted May 26, 2011 Share Posted May 26, 2011 Yeah, I am running stock NGK plugs gapped to .028. I mean, it has to be fuel, I pull the plugs, black and sooty means rich condition, they smell like fuel, it doesn't smoke at all.... And exactly Tony, I would surmise fuel in any other motor, but I have had multiple people tune these carbs and each one has extensive experience with SU's and Z's. I guess maybe just try to go even leaner than before and see what happens. Thanks for the input guys, I will keep updating this thread until I get this figured out. 0.028" is too small a gap for such a low compression motor. Try running a 0.040" gap. You should be using BPR6ES-11(projected tip) or BR6ES-11. Quote Link to comment Share on other sites More sharing options...
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