winfab Posted March 17, 2009 Share Posted March 17, 2009 Hey there. I recently purchased a 7/71 240Z, this being my first Datsun. Heres the situation. When i first received the car, it ran super rich. Fuel smell all the time, smoking from exhaust. Pulled plugs, they were BLACK. Picture of plugs below indicates about 40-60 minutes of actual running time on brand new plugs. Did a compression check, got 225-235 PSI across all 6 cylinders. Seems a little high to me, no? The engine, from what I can see/know, is a L24 block, E88 head combo. The head has obviously had some work done, since it is alot cleaner than the block, looks like its been hot tanked and possibly milled. The camshaft has E30 cast on it, looks stock. Changed the plugs. It fouls them literally in one week, not even driving the car down the road. Just starting it in the garage, moving it in/out, etc. Start and let it run maybe 5 minutes each time, plugs come out BLACK once again. If i start it, and give it gas slowly, the engine revs up quite nicely, aside from the rich smell and smoke filled garage. If i try to give it a sudden burst of throttle, the carbs seem to backfire, and fuel actually comes out of the carb intake. Also makes like a hissing or spraying sound, not like a BANG backfire as if the mixture was ignited. The SU carbs, early ones, have the stock N27 needles, move up and down without any problems, i have balanced them with a Unisyn, etc. The choke cables are not stuck, etc. , even disconnected them one time to make sure. Thought it may be a weak coil, ignition system, bought a Pertronix Ignitor and coil, FlameThrower 3.0 ohm. Noticed a difference after install, but did not solve this problem. There are a few marks on the crank pulley, one is highlighted with white paint, i would assume that its TDC? I took a pic of the pulley at this point, along with cam gear position and camshaft lobe position. When i do get it idling with little to no smoke coming from the exhaust, once i do try to drive it, its fine under 2500 RPM, but once I get around 3-3500 rpm, with anything over 50 percent throttle, it loses power and the smokescreen exiting the rear of the car is smoking out my neighbours down the street. If anyone has any insight, or things i should check, pics i should take for more info, please let me know. I like to think that I have good knowledge of how motors work, I have built over a dozen motors for other people, but they were all Honda/Acura motors so somewhat different than the L series. I have tried to explain this as best as i can. Sorry if I sound like an idiot at all in this post LOL. The previous owner was a young kid, and he didn't even touch the car, so I can't even ask him for any input. The motor work was done a few owners ago i think. Thanks in advance! Jay Quote Link to comment Share on other sites More sharing options...
tomtuna1978 Posted March 18, 2009 Share Posted March 18, 2009 Sounds like a fuel delivery prob. to me. Did u check your float levil in those su carbs ? take pics of the carbs and post em ! I'm shure someone else will chime in ! Quote Link to comment Share on other sites More sharing options...
TommyZ Posted March 18, 2009 Share Posted March 18, 2009 Dose it still have the stock mechanical fuel pump? Maby its getting too much fuel pressure? Quote Link to comment Share on other sites More sharing options...
tomtuna1978 Posted March 18, 2009 Share Posted March 18, 2009 also look at where your timing is and check your vacuume lines where they go and if there is a vacuume leak. Quote Link to comment Share on other sites More sharing options...
katman Posted March 19, 2009 Share Posted March 19, 2009 First, buy a factory service manual so you can tell what the TDC mark is on your crank pulley. The white mark may be something the PO painted on there to mark 12bdc or whatever. On a 71 there should be one nick that's slightly bigger than the others. It will be the leftmost as you look from the front. That's TDC. Each other mark is 5 degrees advanced from that. Second, go here http://www.ztherapy.com and buy the 240Z tune up video. If the timing is right, running too rich could just be jet position. Or, somebody has put the needle at the wrong height in the piston. Needles and/or jets could also be worn, but most likely its a matter of proper tune. Know that when everything is perfect, it will still smell like gas often. Carbs are just a semi metered fuel leak, and with 70's combustion chamber and metering tech we were never burning all the fuel we put in. Best of luck. Quote Link to comment Share on other sites More sharing options...
rejracer Posted March 20, 2009 Share Posted March 20, 2009 reach underneath the carbs, and put your finger on the jet (the piece that the rubber fuel line goes into from the bowl) and push up. If it moves your jets are binding up from being dirty/worn no lube on them. They do this on my old SU's and makes the car run pig rich. Quote Link to comment Share on other sites More sharing options...
winfab Posted March 20, 2009 Author Share Posted March 20, 2009 Yes i have been through the SU tuning procedures. I found multiple websites with great writeups, and followed them to the T. Also followed the instructions in my haynes manual, no go. Last night when i was messing around with it, i had both fuel mixture knobs turned all the way IN, checked inside the carbs to see the placement of the jet, they were flush with the carb body. The chokes are not stuck. I neglected to add that i have replaced the floats, pivot pins, and float gaskets. Dampening fluid (ATF) is full to the line, float level OK, floats set to 14mm. Got it running good again last night, new set of plugs gapped to .044, not too much smoke or fuel smell. Took it for a drive around the block, ran rich, but drove ok at light to part throttle. Gave it a good shot of throttle, revved up to about 4500ish there was only a slight hesitation, so I backed off. 10 minutes later in the garage, my eyes were burning from the fuel in the exhaust, and the idle was lumpy again. Pulled a plug, black already. When i check the number 1 cylinder plug and compare it to the rest of them, the number 1 plug actually is cleaner than the rest. More of a tan/black mix, like you would see on a slightly rich situation. So if the marks on the crank pulley are correct, then I am almost right at TDC. However, the cam gear picture I have added shows its position with the crank pulley at near TDC. Shouldn't the cam gear be at the number 1 position? Quote Link to comment Share on other sites More sharing options...
winfab Posted March 20, 2009 Author Share Posted March 20, 2009 The next thing I will make sure of, is that I am on the compression TDC, and see where the cam gear is lined up. Ill check the manual tonight, and get familiar with the cam timing procedure, then report back with my findings. So in a perfect case scenario, crank at TDC, cam gear lined up like -v and camshaft lobes for Cylinder 1 should be at 10 and 2 (both valves closed)? I will be building a 3.1 stroker over the summer/fall, all I want to do is get this car driveable so i can hit a few shows this summer. At least with the stroker I will know that everything is done correctly because i will be the only one working on it. Theres nothing worse than getting into someone elses build ARGHH... On a side note, what are the fuel requirements of the stroker? Do I have to go with a triple setup or are the SU's/SM needles combo enough? Anybody just keep it FI and run a Megasquirt or something? Thanks for all the help so far. Jay Quote Link to comment Share on other sites More sharing options...
winfab Posted March 20, 2009 Author Share Posted March 20, 2009 Heres what i found out about the valve lash, and timing. Checked the valves, they were WAY too tight. Couldn't even get a .002 feeler gauge in some of them! Adjusted them to .008 and .010 as per manual. The cam gear was lined up like "_V" as it should be. I have attached a few more pics. Still runs super rich, now worse since the plugs are most likely black and will need changing again. Even with the adjustment knobs turned all the way in (lean) the fuel is still filling my garage, and burning my eyes it is sooooo rich. Quote Link to comment Share on other sites More sharing options...
winfab Posted March 20, 2009 Author Share Posted March 20, 2009 Dose it still have the stock mechanical fuel pump? Maby its getting too much fuel pressure? Yes, stock mech fuel pump. I noticed as well, when the car was running last night, that the fuel level in the fuel filter (pass. side inner fender) only had about 1/2 inch of fuel in it at all times. There is a line, about half way up the filter, is that where the fuel level should be? Quote Link to comment Share on other sites More sharing options...
DCZ Posted March 20, 2009 Share Posted March 20, 2009 Did you see this reply on zcar.com? (quote) It sounds like you are doing everything right so this is a bit of a mystery. When you screw your fuel adjusting nuts all the way up, you should cut off enough fuel that the engine will not run. Are your needles set so that the needle shoulder is flush with the bottom of the piston and not the groove in the piston? You may have worn or mis-matched jets in the carbs that are letting fuel pass the needle at full lean. One thing you can try is this: 1) loosen the set screw on the needle in the carb so that it can slide in and out but not so loose it will fall out and pull the needle so that the shoulder is well above the piston bottom. 2) Screw mixture nut all the way up (lean). 3) Carefully place the piston back in the carb so that the needle slides into the jet. This should push the needle back into the piston but only so far that it is still sealing the jet. 4) Remove piston and tighten set screw to lock the needle in that postion. You might find that the shoulder of the needle is slightly raised from the bottom of the piston. This should allow you to cut the fuel completely at full lean adjustment. (/quote) Katman mentioned something similar above. You should not be able to have the car run if the mixture nuts are screwed all the way up. I don't think you have a problem with your fuel filter, mine used to be like that (I don't have a clear filter any more). Quote Link to comment Share on other sites More sharing options...
winfab Posted March 21, 2009 Author Share Posted March 21, 2009 Yeah thats my post LOL.. Going to try that now. Quote Link to comment Share on other sites More sharing options...
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