Moridin Posted November 7, 2002 Share Posted November 7, 2002 Sorry to post this here. Sometimes, the carb section is a little slow. I just want to spread my question to a wider knowledge base. I'm pretty sure they are 40mm, I will check again tomorrow morning. Basically, I'm an idiot when it comes to carbs. Well, then again, I'm an idiot when it comes to cars too. I'm learning though. That's what this forum is all about. Anyways, I'm pretty sure the car is running extremely rich. Bogs really bad at low RPMs at low speed. It was like this before I put new air filters on. I may not have helped it, because I took the air horns off to put the K&N setup on. I may try to find some shorter horns. I would like to develop a ram air intake, but that is for another time. Anyways, I just had the head completely redone, so nothing should be wrong in the valve department. The exhaust is slighty black and exceptionally cool, but it also has a greasy/liquidy feeling to it when you put your hand behind it. From what I've read on a few other boards, these are conditions for a rich running car. Now, the real question, if its running really rich I'm going to have to rejet the carb then, right? I was thinking of taking it to Rebello, because I don't have that much time (I want to have the car ready to take to LA on a trip in a few weeks, but I can't live with the car eating up this much gas. Can't afford it either). I would like to go down to the drag strip and make a bunch of passes, but I don't have the money for a ton of sets of jets. Now, this is where the idiot part comes in. Are there only one set of jets involved with fuel, or are there mains, secondaries, etc...? I'm probably one of the few to ever say that fuel injection is easier for me to understand. Now, I have a 73 240Z with what I believe to be the orginal L24 (Is there any way to check on this?) It does have the original head (N42? I don't know all the casting numbers yet. Guy from Rebello said it looked to be a late 72/73 head. Anyways, I am also running headers and a larger exhaust. Not sure about what the current jets are (Any way to check that?). What goes with installing new jets if that's the problem? Do you have to take apart the whole carb? Sorry if this seems elementary to you gurus. I'm trying to learn though. Oh, when circuits come up in reference to a carb, what does that mean? Is that the system in which the fuel travels, or other systems? Basically, the questions that may be somewhat hidden in the earlier parts of my post are: 1) Is it running rich? I'm pretty sure of it. 2) What jets should I run with L24? What if it is an L28? 3) How much does a whole new set of jets cost? 4) Will I have to buy more than a few sets? Thanks a lot, Ryan I really appreciate everyone putting up with all my crap. I know a lot of it must be simple to most you, so I understand if you get frustrated. Anyways, thanks for all the kindness so far. Quote Link to comment Share on other sites More sharing options...
Mike C Posted November 7, 2002 Share Posted November 7, 2002 This is a pretty complicated question. I would recommend you buy a book on (I assume Weber carbs?) You can get a combined book for Webers and Del'Lortos or a Weber only book.(I bought both when I got my triples.) I would imagine there is a Mikuni book as well. For $20 you can get jetting recommendations and diagrams, idle speed and mixture adjustment instruction. www.classicmotorbooks.com or my local Barnes & Noble had the Weber only book. Quote Link to comment Share on other sites More sharing options...
Dan Baldwin Posted November 7, 2002 Share Posted November 7, 2002 The dyno would be a much better place than the drag strip to figure out what's going on with your mixture, and how that affects torque/power. Does the engine bog when you step on the gas? You may have too much accelerator pump volume. I'd encourage you to take one of your carbs apart and play around with it to see how the accelerator pump works. My OER Racing carbs have a screw on top that limits accelerator pump travel, allowing adjustment of how much fuel goes in through the pump circuit. The idle screws at the base of the carbs control the fuel going in at idle, and to a lesser degree during part-throttle operation, so there's another place to adjust. The MAIN jets are underneath the removable cover on top of the carbs, along with the smaller idle jet(s)/holder. You didn't say what kind of carbs you have (Weber, Dellorto, Mikuni, SK). There are differences, but there's always a MAIN AIR jet on top of the jet holder/emulsion tube, and a MAIN FUEL jet at the bottom. These determine what the mixture will be at more open throttle positions at mid to higher rpm. Bigger fuel jet => richer mixture. Bigger air jet => leaner mixture, particularly at higher rpm. There's lots of info on the web on these carbs. Search around and read up a bit. You don't have to be a genius to get them working properly, but it would help if you knew about the major systems (idle, accelerator pump, main) and how to adjust them. Disassembling a carb with an exploded diagram like this: http://www.teglerizer.com/dcoe/dcoe45_tour.htm handy would be a big help. Quote Link to comment Share on other sites More sharing options...
Guest Xtinc Posted November 8, 2002 Share Posted November 8, 2002 If you're running triple weber 40mm DCOE's then you can use these simple instructions to get you in the ballpark. weber adjustment Quote Link to comment Share on other sites More sharing options...
Moridin Posted November 8, 2002 Author Share Posted November 8, 2002 I apologize, I got so caught up writing up my problems, I forgot to mention that they are triple Mikuni's. I'm still pretty sure they are 40mm. Thanks for all the help so far. Oh, it does bog when the gas peddle is depressed at low speed and low RPMs. Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted November 8, 2002 Share Posted November 8, 2002 Ok,take a deep breath,relax it's not that bad.It,s easy to check what size main jets you have. If you have webers; just un-screw the small wingnut and remove the little round cover.The main jets are the two big ones, un-screw them and pull them out.The actual main jet is on the bottom, tappered with six sides.With an L24 the main jets should be 130ish.If you have Mikuini/Solex then remove the two screws on the basically rectangular jet cover.The procedure is the same. Hey, about those removed air horns, can I talk you into selling them to me??? Quote Link to comment Share on other sites More sharing options...
Moridin Posted November 8, 2002 Author Share Posted November 8, 2002 I don't know about selling them just yet. If I can find a set of shorties I might. I may just have to cut the inner bracket on the K&N housing to fit the horns in there. I wouldn't know if they'd do much good anyways, because there is so little room between to opening of the horn and the plate on the filter. Quote Link to comment Share on other sites More sharing options...
Dan Baldwin Posted November 8, 2002 Share Posted November 8, 2002 I think you should try to reduce your accelerator pump volume before worrying with main jets. When you step on the gas, the accelerator pump dumps raw fuel into the runners, if you're bogging when you step on the gas, I think you're getting too much additional fuel. The accelerator pumps are, I believe, on the bottom of the carbs, and should be adjustable. Fiddle fiddle fiddle. Get the idle screws and accelerator pump adjusted so the car runs OK, then go to the dyno and see what your A/F ratio is throughout the rev range, and change jets based on that. Ultimately you will want air horns for them. Not having them makes the carbs' throats' effective diameter a lot less than 40mm. Would be good to have the air horns before going to the dyno. Quote Link to comment Share on other sites More sharing options...
Mike C Posted November 8, 2002 Share Posted November 8, 2002 99% of the time a low speed bog when you stomp the throttle is TOO LITTLE accelerator pump shot, not too much. There is just a lot of air introduced at one time and a significant shot of fuel is needed to make up for that. Quote Link to comment Share on other sites More sharing options...
Guest Xtinc Posted November 9, 2002 Share Posted November 9, 2002 Speaking of air horns, I found a decent price at $10 each for 1 1/2" horns. How do you think these will work under 3 1/2" closed top filters? Click Quote Link to comment Share on other sites More sharing options...
Moridin Posted November 9, 2002 Author Share Posted November 9, 2002 I will have to see about those air horns. Thanks for the help so far. I was also wondering if the 9MPG that I'm getting is any real indication of anything specifically wrong. Thanks though. Quote Link to comment Share on other sites More sharing options...
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