duragg Posted October 1, 2006 Share Posted October 1, 2006 1973 240z with L24. Carb question, is this jetting wrong? Triple 40 DCOE-151 carbs. Mechanical and electric pump at 3 PSI Headers (wrapped and blanketed) to Cherry Bomb and out, nothing else. Rebuilt all 3 carbs with Weber kits, new needle valves and new floats. 30mm chokes. 50F9 idle jets. 115 Main Jet F11 Emulsion tube 200 Air corrector Idle needle screws 3 turns out! Carbs are sync'd perfectly with the $50 airflow meter. Occasional lean pop. Stumbles on throttle tip-in at speed. Plugs are very light in color, if not white. Idle mixture screws are 3 turns out to get smooth max rpm Power trails off after 5000 RPM Adjusted all valves to book spec. Fails Arizona emissions with high Hydrocarbons Loaded CO is like 1% and idle CO is similar. 36 degrees of total advance, no vacuum advance. Replaced entire ignition system. With the mixture screw 3 turns out and the plugs white I think its time for fatter jets. Any recommendations on target jet sizes? Tj Quote Link to comment Share on other sites More sharing options...
Dat260 Posted October 1, 2006 Share Posted October 1, 2006 Hi duragg, You should read all the pages of this link. I am sue you are going to find the solution to your question. It helped me alot understanding Webbers and how to troubleshoot them. Enjoy. http://forums.hybridz.org/showthread.php?t=93343 Quote Link to comment Share on other sites More sharing options...
duragg Posted October 1, 2006 Author Share Posted October 1, 2006 Thanks. In fact I have that thread printed out and carry it around in the car with me when I drive it.. TJ Quote Link to comment Share on other sites More sharing options...
Zmanco Posted October 2, 2006 Share Posted October 2, 2006 A few thoughts/questions: - The stock cam's power peaks around 5k, so the power falling off could be normal. - The 30 mm chokes will give you good driveability, but at the expense of top end. If you had accesss to a set of 32 chokes, it would be an interesting experiment to swap. You might find the trade-off worth it. - I would be surprised if you needed to go bigger than 50F9 idle jets, although three turns out and white plugs sure sounds like it. - Are you failing emissions at idle or high speed? If it's high speed, you might try going to a 50F12 or 50F6 even. That will lean out the higher revs (while you're still operating on idle circuit) w/o leaning out at idle. - You wrote: " Stumbles on throttle tip-in at speed." At what rpm and gear? You may need to go larger on the mains, or perhaps smaller on the air correctors. Or maybe you need to go smaller on the accel pump drain back jet. What size are you running right now? BTW, if you're going to try a different set of chokes, do that first. Although I haven't done that myself, I've been told that if you do change chokes, expect to change everything else No sense in buying any more jets until you know if you're going to keep your chokes. Quote Link to comment Share on other sites More sharing options...
Zmanco Posted October 2, 2006 Share Posted October 2, 2006 One more thing, what size fuel inlet needle/seat did you put in? I ask because when I rebuilt mine, I paid no attention. Turned out that the stock seats were 200 and the kit came with 150. The result was power dropping off at high revs. It was real pain to trouble shoot ... I looked in a lot of other places before it finally dawned on me to check. Quote Link to comment Share on other sites More sharing options...
SHO-Z Posted October 3, 2006 Share Posted October 3, 2006 My 260 also has a problem with high HC at idle and the AZ emissions. Under load it passes with flying colors! I have the down draft webers and have tried about everything. I think mine is a problem with the ignition at idle not being hot enough. I have found some advice on the web recommending putting in a multi spark unit to clean some of this up. I have the stock 260 ignition with all of the resistors and such so the voltage is around 9 volts to the coil. I just bought a 280zx distributor to upgrade the ignition and will be installing a multi spark unit and coil at that time. My next step if this does not work is a 2 stage cat. Keep me informed on your solution. Quote Link to comment Share on other sites More sharing options...
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