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hey guys so i just recently got my 75 280Z up and running, and actually drove it around some, needless to say, i'm stoked. the only problem is that the engine backfires any time i try to give it more than a little gas. if i press on the gas slightly, to allow the rpm's to creep up, it's fine, but any time i step on the gas with any real force, the engine sputters, backfires, and loses power. I've checked all my vacuum hoses, and there are no leaks. any idea what the problem could be? thanks in advance, Zach

Alrighty lets get to it. car: 10/1972 240z with an L24 and an E88. completely stock engine. I have recently been able to get my car to move under its own power, but it seems that problems keep coming about. Yesterday while taking her out for another test drive she drove fine for about 1/8th of a mile then she started to sputter, i gunned it and once i got past 3kish rpms the car pulled like I was hoping this car would be capable of. but as i started a to do some normal driving, 2k rpm cruising and 3krpm shifting the car started to sputter, lean pop, and backfire again and again. brought her back into the drive way and started testing there. she revved fine and it seems that whatever the problem was it was gone. and then after i let it idle for awhile it came back. so i came back here and started looking at what to do. This is what I have done in hopes to stop the problem. cleaned both of the carbs, replaced gaskets where needed checked float - 10.31mm checked timing - 0deg set valve clearance - with engine warm .012 exhaust .010 intake checked carb air balance - unisyn at idle checked carb fuel - tried colortune on cyl. 1 and 5, but it kept acting up and resorted to the SU carb tuning tech on classiczcar checked timing again - 0deg, and jumps to 20+ when at high rev. then I let the car sit for a night because it was getting cold and damp. double checked all of my info and found that: the timing should be at 7-10 deg not 0, i should balance the carbs at 3k rpm not idle, and colortune at 3k rpm on cyl 2 and 5. started the car up this morning, in hopes that it would all be sorted out with the inproper set up, but it obviously wasn't. here is a vid of the first start up that pop at the end is both backfire and a lean pop. awesome. So I started to re-tune everything. timing now set to 8ish deg synced the carbs with unisyn, backed down all of the screws equally and set idle to 650-700 rpm. turned off the car, and then pulled the #2 plug looks normal, and they are less than 20 miles old. stuck the colour tune on and here is what it is at idle and then i set the idle to 3k and tuned it. movie doesnt show it well, but color that I achieved, bunsen blue with hints of orange. turned off the car and pulled #5 plug tuned the rear carb at the same rpm and finally got the same color that I got in the front. then I checked to see if my needles and nozzles were binding. the rear piston is a bit harder to pull up than the front, so I am planning on dunmping the ATF and using some 10w30. To see how the carbs were actually balanced I used the lifting pin to see how the engine ran on only 1 carb. from what I have read about the pins, the carbs look to be too rich, but according to the colourtune they are at their best. So meh. Then I checked to see how the car revved through the power band. All of the jumping around is me playing with the throttle. It seems that all of my problems were solved! So I took a photo of my temp gauge to show you all what "normal temp" is on the car, to see if that is what everyone else sees. and while i was doing that the car started to act up again. so i checked to see if both carbs were actually working, twice. and showed you the difference in nozzle richness. So yeah... I have no idea what is wrong. please someone give me some advice. The only thing that I think it could be are the needles and/or nozzles, but why would it only happen after the car was warmed up, or under load?

Hello all, I have been searching and tuning and searching some more and I'm throwing in the towel and asking for help. I have a stock 73 240 with the exceptions of a lightened flywheel (5lbs taken off), roundtopps, a turbo oil pump, and just recently a zx dizzy upgrade. I rebuilt my l24 600 miles ago and have been tinkering with tuning carbs and ignition timing and it just doesn’t seem right. I just replaced the oil today from the 30w break-in oil to 10w-30 valvoline vr1. Compression test showed 150psi in all cylinders. Ignition timing is set to about 10.5. I am a newb and this was my first engine rebuild. Alright done with the introduction now to my symptoms: 1) When accelerating hard at higher rpms (4000+) the power seems erratic like it’s there and then it’s gone, back and forth. Not to an extreme degree, but it seems to vary at revs within 100+/- of each other just going by seat of the pants. 2) It isn’t a lean pop as far as I can tell, but if I hold rpms (in neutral) at about 4000 and then let off there is a backfire or 2 on the way down that I believe is through the exhaust. 3) While I was tuning carbs I was going to rev after idling for a few seconds and as soon as I started to open the throttle both carbs backfired white smoke (I haven't been able to replicate this event) 4) When tuning the carbs with the front disabled I can’t seem to get the car to die even with the adjustor fully leaned on the back (bad jets?) 5) When I let the engine brake the car it backfires, I am unsure if it is through the exhaust or the carbs. 6) With the new dizzy the idle has smoothed, but still seems a little rough 7) On the initial break-in trip the car had normal oil pressure, but on the 80 mile trip home I lost the pressure and it has been non existent since, I replaced the sensor. I know all connections are good because the sensor sends the needle all the way up and then down again when the key is turned to on. I am unsure if the oil pump is truly a turbo pump because it was an eBay purchase. I have pulled the valve cover to make sure that oil was still circulating Also, I don’t have much to compare to, but the power seems to be lacking I don’t know what a slipping clutch feels like, but could the erratic power be contributed to that? On my to do list tomorrow is re-checking valves, plugs, float settings, and ordering a video from Ztherapy. For the video do you recommend “ZTV09 Just SU's ” or “ZTV01 240Z-280X TuneUp” Thanks for the help in advance and I’m sorry if this has been posted before, but I cant find it. Also I once found a great write up on what caused backfire where once and I cant find it, if anyone can help with that it would be appreciated too Thanks again, roger