jacob80 Posted June 18, 2008 Share Posted June 18, 2008 Hey guys, we have a set of 45s from motorsport and we cannot seem to get the idle set. We have messed with the idle speed screw and mixture screw, get a decent idle but when we go to rev it up slowly, it starves immediatly and then goes up. What is causing this? It only starves about 100-200rpm above idle when you put on the throttle slowly. It seems fine when you pump it fast, what is going on? If you guys could diagnose this or give your tuning procedure for this, that would be helpful. Thanks!!! Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted June 18, 2008 Share Posted June 18, 2008 There is a really informative book for tuning Webers. I pretty much memorized it back in the day when I ran Webers. I have since forgotten the details but there are separate jets for slow throttle opening and fast throttle opening. Slow opening uses progression holes in the bore that are exposed to vacuum as the butterfly opens. Those holes are fed through a separate jet in the bowl ( I think) Foggy memory. Fast throttle opening accel enrichment is performed with a spring plunger and a piston that squirts fuel into the bores under spring force when the throttle plates snap open quickly. There are a ton of variables with jets, emulsion tubes, accel springs.... First make sure all the proper jets are installed. Then set all your idle mixture screws the same number of turns in or out. Make sure your throttle plates are all very closely synchronized and are at the proper angle in the bores. (not exposing progression holes to vacuum at idle). 9 out of 10 times, old or dried out carbs need to be cleaned and flushed. Soak them in a carb cleaner and blow air through ALL the ports. Make sure the floats are not sunk, and the float valves operate, and that the accel plunger is not bound up. Oh...and don't rule out a vacuum leak in the gaskets or manifold. Buy the Weber tuning book! It also has suggested jet sizes for the L motors. http://www.webernorthamerica.com/pdffiles/45DCOE152.pdf http://www.redlineweber.com/html/Tech/Table_of_contents.htm The golden egg: http://www.redlineweber.com/html/Tech/dcoe_adjustment_layout_typical_i.htm Dave Quote Link to comment Share on other sites More sharing options...
jacob80 Posted June 18, 2008 Author Share Posted June 18, 2008 Ok, the webers are brand spankin new, we ordered them from motorsport and they were "ready jetted" for L series motors I believe. I also read somwhere that the butterfly should be open just enough for the progression hole closest to the engine to be covered by the butterfly. Is this true, or should I follow the steps in the last link provided? There are no vacuum leaks I believe, it is a brand new intake and gasket. Is there no real tuning solution for them starving at very slow acceleration? Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted June 18, 2008 Share Posted June 18, 2008 Set them up according to the last link. Also, idling them a bit on the rich side, I found, helped to make the transition off-idle to be smoother. (on my Alfa Romeo engine). I suspect that the following might be your issue: "This is all based on the important fact that your speed screws (idle speed) are not open more than ½ turn if they are then that is also an indication that you have a lean Idle circuit. You are cheating by opening the throttle plates and exposing additional progression holes in the transition." Basically, you DO NOT WANT fuel coming from the progression holes at idle. A lot of times, people tend to open the throttle plates too far to make the engine idle and they expose the progression holes. Having done this, the progression holes are not there when you need them while opening the throttle slowly. Good luck and remember to have fun. Webers are fun once you really learn how they work. They sound great and breath really well. It takes some patience but you will become an expert with some quality time and a screwdriver. I used to synch them with a length of fuel line. Stick it in the venturi and listen to the suction sound. Make all of them sound the same. Another trick was to pull the plug wires off, one by one, and observe the idle speed change. It should be equal for each plug. Quote Link to comment Share on other sites More sharing options...
jacob80 Posted June 19, 2008 Author Share Posted June 19, 2008 Is it possible that I am overcarbed for a 73 L24 with stock E88 head? Would 40s behave better? Quote Link to comment Share on other sites More sharing options...
jerryb Posted June 19, 2008 Share Posted June 19, 2008 40s may be better but that depend on what you have done to the engine..cam and etc. I would rather undersize than oversize....its keeps air velocity up and the engine running well. What chokes are you running? If you have 45s on a stock like engine.....it may be a tough tune! unless you are running high race revs 40s should be all you need. One thing about webers....small changes are better than big....MIkunis are a lot more forgiving! cygnusx1 has a lot of good advice...that book is tops! Quote Link to comment Share on other sites More sharing options...
jacob80 Posted June 19, 2008 Author Share Posted June 19, 2008 40s may be better but that depend on what you have done to the engine..cam and etc. I would rather undersize than oversize....its keeps air velocity up and the engine running well. What chokes are you running? If you have 45s on a stock like engine.....it may be a tough tune! unless you are running high race revs 40s should be all you need. One thing about webers....small changes are better than big....MIkunis are a lot more forgiving! cygnusx1 has a lot of good advice...that book is tops! The engine/head setup is all stock...for now. We plan on putting on our E31 head with Stage 2 MSA cam and an N42 block. So the 40s would behave better with the stock setup we have now, correct? Not sure if it matters, but we have the cannon manifold and MSA 6-1 header. Quote Link to comment Share on other sites More sharing options...
RedNeckZ Posted June 19, 2008 Share Posted June 19, 2008 :burnout:The carbs you have are not bad for the L24 engine. I have been running it on mine for over 7 years. Before I moved up to a L28 block. you need two items that need to be looked at. First is the cam, is it stock or modifidy? With those carbs, you will need a good 3/4 cam and header to make them run right. Second, you will need to know what size main venturis, you have on the inside of the carbs. If I remember right it right it should be between 30mm to 37mm in size. The smaller in size the better off idle it is. My current setup has the 37mm size in it for more power in the high range. My jet setup for Colorado was as follows: Emulsion Tube - F16 Auxiliary Venturis - 4.5mm Air corrector jets - 200 Idle jets - 45F9 Main jets - 115 Pump jets - 45 Needle valve - 1.75mm My cam at the time was a Sig Erson cam grind number #290AS or #735321 (good racing cam, hard idle on street). My cam is now Schneider Racin cam grind number270-80F (good street cam for the carbs). Remember that Datsun carbs like to run on the rich side. Good Luck, Rich. Quote Link to comment Share on other sites More sharing options...
jacob80 Posted June 20, 2008 Author Share Posted June 20, 2008 Once again, THE ENGINE IS COMPLETELY STOCK INTERNALLY. The engine is setup like this: Stock '73 L24 Triple 45 DCOEs MSA 6-1 header Mallory unilite distributor We have gone ahead and ordered a set of 40 DCOEs to see if they'll behave better for our specific application. What do you guys think? Quote Link to comment Share on other sites More sharing options...
jerryb Posted June 20, 2008 Share Posted June 20, 2008 I believe you have done the right thing ordering the 40s....while the 45 will work, the 40s will work better. BUT...get a cam and exhaust to optimize the setup. Honestly, running 45 on a stock to mild engine is way overkill. My 3.1 L ran 40s and was quicker than most that ran 45s. Once again, THE ENGINE IS COMPLETELY STOCK INTERNALLY. The engine is setup like this: Stock '73 L24 Triple 45 DCOEs MSA 6-1 header Mallory unilite distributor We have gone ahead and ordered a set of 40 DCOEs to see if they'll behave better for our specific application. What do you guys think? Quote Link to comment Share on other sites More sharing options...
jacob80 Posted June 20, 2008 Author Share Posted June 20, 2008 I believe you have done the right thing ordering the 40s....while the 45 will work, the 40s will work better. BUT...get a cam and exhaust to optimize the setup. Honestly, running 45 on a stock to mild engine is way overkill. My 3.1 L ran 40s and was quicker than most that ran 45s. Ok, we have the 6-1 header and MSA premium exhaust system (2.5"). Hopefully they will work out well. And finally, once these carbs arrive, is this the procedure to go by?: http://www.redlineweber.com/html/Tech/dcoe_adjustment_layout_typical_i.htm Thanks!! Quote Link to comment Share on other sites More sharing options...
jerryb Posted June 20, 2008 Share Posted June 20, 2008 Yes that is the basic procedure! The jets and the emulsion tube should be "optimized" to a generric 240Z...... but to get the most of your carbs you should have extra jets. It takes a bit of playing but when you get it right ...YOU WILL KNOW IT! It tool me hours of jet changing and adjustments...but then Im a bit anal.... patience is the most imortant thing. I ran run after run into many late nights to get it right. Hell in the end I ran 40s with 32mm chokes with instant throttle reponse right up to 7000 rpm. Ok, we have the 6-1 header and MSA premium exhaust system (2.5"). Hopefully they will work out well. And finally, once these carbs arrive, is this the procedure to go by?: http://www.redlineweber.com/html/Tech/dcoe_adjustment_layout_typical_i.htm Thanks!! Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted June 20, 2008 Share Posted June 20, 2008 So true....half the fun of owning Webers is the test drive every time you turn a screw 1/4 turn. Quote Link to comment Share on other sites More sharing options...
jerryb Posted June 20, 2008 Share Posted June 20, 2008 Thank you ...Im not alone! Saying that Im learning FI with my Power FC...different worls all together. So true....half the fun of owning Webers is the test drive every time you turn a screw 1/4 turn. Quote Link to comment Share on other sites More sharing options...
jacob80 Posted June 20, 2008 Author Share Posted June 20, 2008 Alright, well, hopefully they'll work out. Thanks for all the help! Quote Link to comment Share on other sites More sharing options...
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