Mudge Posted December 16, 2002 Share Posted December 16, 2002 I'm floating around 15MPG so far, 2.4L P30 block with N42 heads, old 5 speed (15% OD), not sure what the rear ratio is yet. Dual weber downdrafts, dont know the jetting yet either. Quote Link to comment Share on other sites More sharing options...
fl327 Posted December 16, 2002 Share Posted December 16, 2002 my old dual su car with a four speed and 3.36 r180 got more than 22 mpg once we rebuilt the su's, and dropped in a 280zx electric ignition running 87 octane- cat pee. Quote Link to comment Share on other sites More sharing options...
Mudge Posted December 17, 2002 Author Share Posted December 17, 2002 This car has the GM HEI setup, probably needs to have the timing adjusted then! Quote Link to comment Share on other sites More sharing options...
Tim240z Posted December 17, 2002 Share Posted December 17, 2002 Mudge, I'm getting about the same on my 2.4 with dual webers. My jets are: Primary fuel: 140 Secondary fuel: 135 Primary emulsion tube: F50 Secondary emulsion tube: F6 Primary air: 160 Secondary air: 165 Pump jet: 50 Venturi; 3.5 Initially the primary and secondaries (both air and fuel) were reversed, but I thought it was running too lean, and since I am mostly on the primaries, I swapped them to richen it up. I know it's not jetted well because the driveability sucks, but am too busy with the V8 project to care. I am running the 280ZX electronic dizzy with timing at 10 BTDC. Tim Quote Link to comment Share on other sites More sharing options...
Mudge Posted December 17, 2002 Author Share Posted December 17, 2002 These carbs may need a rebuild then, as well as some tuning issues. I may end up throwing an LT1 in it before I get started, but who knows what the future holds Quote Link to comment Share on other sites More sharing options...
Tim240z Posted December 17, 2002 Share Posted December 17, 2002 Yeah, I'm starting to get tired of messing with them. I have an inlet manifold for a single downdraft weber. When I can find a 40dgv weber for a good price I will swap it out. That way at least I won't have the issue of trying to sync the carbs....ie...half the headaches. Tim Quote Link to comment Share on other sites More sharing options...
Z-Gad Posted December 17, 2002 Share Posted December 17, 2002 I installed new needles and nozzles 3 years ago, sync-ed the carbs and haven't touched them since (aside from richening the mixture slightly recently)I made a trip a few summers ago to Pa from Fl and got nearly 29mpg highway w/ the 2.8 liter, 5-speed and SU's. I get ~23-24 mpg in town as long as I keep my foot out of it. I did notice I had to richen the fuel mixture now that the cooler weather is here, so it is probably a bit less. It was 40 degrees down here this morning!!! Burrr!!! Quote Link to comment Share on other sites More sharing options...
Mudge Posted December 17, 2002 Author Share Posted December 17, 2002 Wow, thats great MPG, heck thats awesome. I still miss FI, nice MPG, fast startups, doh Hopefully it wont be too long for me to learn the carb stuff. Quote Link to comment Share on other sites More sharing options...
Guest Ian turbo240 Posted December 18, 2002 Share Posted December 18, 2002 I, too have seen 29MPG on an SU-carb'ed 240Z. The engine was a bone stock L24 w/E88 head, stock exhaust manifold, Monza exhaust, and Mallory Unilite dizzy. It's been so long, I don't know what the timing specs were, but the car would beat my friend's low 16 sec GTI 16V. I'm afraid that you will never get really great fuel economy with the Weber DGV's. No-one seems to understand that those were installed on Z-cars only to fix the problems they were having with the flat-top SU's. The DGV's are not a superior carb. They are easier to tune for emissions and have better drivability than the flat-top SU's. If you are using them on a 240Z, it is a mistake, IMHO. The earlier round-top SU's will outperform the DGV's on any level. The SU's require more maintanence, but the benefits are worth it. I challenge anyone to make more power with the DVG setup over a round-top SU setup. It just isn't going to happen. My advice (taken with a grain of salt, of course) is to get yourself a set of round-top SU's in good condition. You will be amazed at the increase in power, and the ease of tuning. Ian Quote Link to comment Share on other sites More sharing options...
Mike C Posted December 18, 2002 Share Posted December 18, 2002 I average about 20 mpg with mine. That's in town for the most part and hammering it at every light! My motor is weak, however, and even with the 5 speed it doesn't get as good mpg as my last 240 with the 4 speed and a strong motor that averaged about 22 around town. Quote Link to comment Share on other sites More sharing options...
Sleek Z Posted December 18, 2002 Share Posted December 18, 2002 Having owned and driven more than 6 registered, early Z cars at one time plus nearly 100 others over time, not to mention several thousand customers that drive theirs daily, I can confirm that what others have said about averaging in both the low and high 20's is common. I'd guess that most of mine ran in the 21-23 mpg range, but have experienced 28-32 mpg on trips. Occassionally a car or two will dip down into the mid-teens. My guess is that most of them suffered from low compression, worn carb components and improperly set timing & ignition. Quote Link to comment Share on other sites More sharing options...
Mudge Posted December 23, 2002 Author Share Posted December 23, 2002 Well, after working on the timing not only is low end WAY better, but the idle screws are close to correct also, and the mileage is WAY WAY up, somewhere in the 20s. Previously it was a real bear getting it to operate without using the choke, and I had the idle screws out about 6 turns to get it idling very fairly at all, so it was just stinking pig rich. Quote Link to comment Share on other sites More sharing options...
Guest norm[T12SDSUD] Posted December 24, 2002 Share Posted December 24, 2002 I run the crap out of my Dual SU equipped 2.9L stroker and I average 22-24 mpg in daily driving. later,norm Quote Link to comment Share on other sites More sharing options...
Moridin Posted January 14, 2003 Share Posted January 14, 2003 I think I'm getting around 10 to 12. Its hard to tell. This is with Triple Mikuni's on the small 2.4L. Of course, I'm having problems with it. By the MPG and massive carbon in the tailpipe, it would seem way too rich. On the other hand, it hesitates big time until I wind it up. Planting my foot in it at low RPM sends it gasping for breath. Anyways, just my 2 cents. Quote Link to comment Share on other sites More sharing options...
Ray Posted January 14, 2003 Share Posted January 14, 2003 My white 72 240 with a 280zx long block and weber downdrafts woud consistantly get 24-28 on the highway and I never saw less than 18 in town. Look at your distributor and double check the jets in the webers. Mine were way fat when I got it.. dont know why... BTW this was with a late model 5 speed and a 3.54 rear end. Good luck... Quote Link to comment Share on other sites More sharing options...
Mudge Posted January 16, 2003 Author Share Posted January 16, 2003 Ray, if you remember the jetting your using now that would be GREAT to know I have an F54 sitting around to be rebuilt eventually, so it would help put me in the ballpark. In the meanwhile I'm reading up on them trying to figure it out. Quote Link to comment Share on other sites More sharing options...
Moridin Posted February 16, 2003 Share Posted February 16, 2003 I have that optical distributor. I guess the car had an MSD box, before my friend (guy who I bought the car from) fried that and some part in the distrutor. I wonder when he put the new dist. piece back in, he messed up the timing curve. When I get the tranny again, I'll have to see if it stumbles now more than it used to. Quote Link to comment Share on other sites More sharing options...
zolorin Posted June 1, 2003 Share Posted June 1, 2003 I get 18-20 city milage and 22-26 highway on the roundtops and 3.9 diff with early 5speed (L24) I recently installed the electronic ignition and my average millage improved from 19 mpg to 21 mpg and I do like to let the petrol burn. A bit rich mixture since our weather is hot in the day and quite cool in the night and I optimized for evenings/winter 8) Quote Link to comment Share on other sites More sharing options...
zolorin Posted June 13, 2003 Share Posted June 13, 2003 for me I have experience 19-21mpg mixed driving and up to 26mpg on a highway long trips. I have 3.9 rear end with early 5speed and points. I am planning to go to florida on my Z and I will long my gas milage to find best V-cruise. and oh yes I need to change the oil in my carbs to 20W since I was running experimental oil. Quote Link to comment Share on other sites More sharing options...
Nismo280zEd Posted May 2, 2005 Share Posted May 2, 2005 I hate to bring up this old thread but I think we could add some usefull info to it. With my triples i'm getn' 9.4 mpg in town... 11 with the regulator on 3psi. My new jets come in tuesday... smaller air correction jets and bigger idles. hopefully my tail pipe won't be so black. -Ed Quote Link to comment Share on other sites More sharing options...
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