Willstar Posted July 6, 2009 Share Posted July 6, 2009 G'day, Last weekend i removed my old original carbs and intake manifold from my L24, which were running, but in need of attention. I took some genuine SUs off of a Skyline, which were running an L28 perfectly. Now mind my lack of carb knowledge but... Everything bolted up and plumbed up nicely, but now my L24 wont start. The only way i worked out to get it started is if i pull the ?pistons? at the bottom of the SUs downward (they hold down near the bottom) the car will start, sound smooth, but at too high a speed and too rich. Any help on what i need to adjust would be great. Thanks Will Quote Link to comment Share on other sites More sharing options...
Phlebmaster Posted July 6, 2009 Share Posted July 6, 2009 G'day, Last weekend i removed my old original carbs and intake manifold from my L24, which were running, but in need of attention. I took some genuine SUs off of a Skyline, which were running an L28 perfectly. Now mind my lack of carb knowledge but... Everything bolted up and plumbed up nicely, but now my L24 wont start. The only way i worked out to get it started is if i pull the ?pistons? at the bottom of the SUs downward (they hold down near the bottom) the car will start, sound smooth, but at too high a speed and too rich. Any help on what i need to adjust would be great. Thanks Will lol I had the same experience. You are on the right track, you will need to adjust your jet under the carbs. I started in all the way on both carbs, then backed out two full turns and tried that. Then it was just tuning by ear. You will be turning the big round thingy with the spring that the "pistons" come out of. lol Quote Link to comment Share on other sites More sharing options...
Willstar Posted July 7, 2009 Author Share Posted July 7, 2009 Thanks heaps, I will try that. One more question, on the original Hitachi SU carbs, when the choke cable is pulled, the pistons are pulled down slightly, where as the genuine SU carbs the choke cable doesnt seem to pull them down, but moves a different arm on each carb. Hopefully someone can understand me and let me know if this is correct. Thanks again Will Quote Link to comment Share on other sites More sharing options...
Phlebmaster Posted July 7, 2009 Share Posted July 7, 2009 Thanks heaps, I will try that. One more question, on the original Hitachi SU carbs, when the choke cable is pulled, the pistons are pulled down slightly, where as the genuine SU carbs the choke cable doesnt seem to pull them down, but moves a different arm on each carb. Hopefully someone can understand me and let me know if this is correct. Thanks again Will I learned this lesson too. You have to sort of "cock" the choke by setting the cables with the choke linkage slightly pulled, but not so much that it moves the jet down under the carbs. Play with it a little and you will see what I am talking about. You can set the choke so that you just have to pull slightly to activate the choke but it dissengages fully when you put the choke lever put in the warm position. Quote Link to comment Share on other sites More sharing options...
zedsn Posted July 7, 2009 Share Posted July 7, 2009 The lever that you see moving is supposed to move the jet downward during choke to basically add more fuel to the engine. I too removed the hitachi carbs and installed SU roundtops. Aaron is right about the mixture. For some reason you are probably running way too rich. Don't know how it got out of adjustment if the SU's came off a running car? You are supposed to balance the air between the 2 carbs before you attempt to adjust mixture. I got mine from JC Whitney but other places will carry the air balancer tool. Quote Link to comment Share on other sites More sharing options...
Willstar Posted July 7, 2009 Author Share Posted July 7, 2009 Thanks again, But when i pull the part that connects to the choke cable all the way up or down it wont move the jets up or down at all. Maybe i have hooked it up to the wrong spot. Quote Link to comment Share on other sites More sharing options...
xchaosx Posted July 7, 2009 Share Posted July 7, 2009 You should be able to at least start the car with the cable disengaged. These helped me a quite a bit when i was trying to get mine dialed in http://www.nicoclub.com/articles.php?id=186164 Quote Link to comment Share on other sites More sharing options...
greygears Posted July 8, 2009 Share Posted July 8, 2009 Here’s how I set up the chokes. First, remove the air cleaner completely, so that the carburetors are exposed. Detach both choke cables and move them out of the way. Pull up on the lever that the choke cable was attached to on the carburetor and watch the nozzle (A.K.A. jet) on the bottom of the carburetor. It should pull down as you pull up on the lever. Also notice there is a dogleg shaped lever rod that opens the throttle linkage a little when the lever is pulled. More on this later. If you cannot move the nozzle, It has most likely glued its self in place with varnish. Not unusual if it has sat for a while. Check both carbs. If either one is stuck, You’ll halve to pull the nozzle out and clean things up. Unscrew the plunger out of the top of the Dome. Pull the dome and piston out of the carb body, soak the Nozzle in carburetor cleaner and unscrew the large round nut on the bottom of the carb as far as you can. Disconnect the lever arm that moves the nozzle up and down by removing the small screw in the base of the nozzle. This screw is usually to tight to brake loose with a small Phillips screw driver, if so, crack the screw loose with a small pare of needle nose Vice Grip pliers. Disconnect the small black hose between the float bowl and the nozzle. Be careful with this hose, new ones are hard to find, and nothing else works. Using a wooden dowel, and a wooden dowel only, tap, not beat, the nozzle with a light hammer, until it moves a little. Unscrew the nut as far as you can, and soak the Nozzle again, and tap some more. Repeat the process until the nut and spring come loose, and the nozzle comes out. This may take some time, Be patient, you will win. Use lots of carburetor cleaner, run the nozzle up and down in its bore until its smooth and free. Put every thing back together again. Now when you pull up on the lever, the nozzle moves up and down freely. Using a dial micrometer, (a cheap plastic one will work) set the depth of the nozzle in its bore to about .130" (3.3mm). This is a good starting point for your fuel mixture. The shoulder on the needle in the piston should be flush with the bottom of the piston. Use a straight edge to check it. If it is not flush, there is a setscrew in the side of the piston that locks the needle in place. Loosen the screw and move the needle in place with your fingers only. If you can’t move the needle with your fingers, don’t try anything else, you’ll just ruin the needle. You can’t hardly find those anymore either. If you can’t move the needle with your fingers, it’s most likely some fool has over tightened the setscrew and crushed the needle in place. Very common. Just snug up the setscrew and put the piston back in, and start looking for a good needle. Fill the piston damper with 20W oil. Every body has there own secret oil to put in the piston damper, but only 20W oil works correctly. Put the dome back on and make sure the piston moves up and down freely. If so, screw the plunger back in the top of the dome, and set up the other carburetor the same. Now, make sure your choke lever in the cab moves freely, and then push it all the way forward. At the carburetors, put the choke cables in place and move the lever on the carb up to take the slop out of the linkage and tighten the cable setscrew. Do the same on both carbs. Pull the choke lever about half way back and start the engine. It should be running about 1500 RPM or so, move the choke lever to get the engine speed around that number. Using some tool to measure the airflow through the carbs (I use a Uni-syn) Adjust the airflow through the carbs until both draw the same amount, by bending the dog leg shaped lever rod close to the carburetor body, that moves the throttle linkage when you pull the choke lever. You can bend this lever rod with a pare of common pliers and a twist. Grab the rod near the bend and bend the rod slightly to change the airflow. Open up the dogleg for less airflow, close up the dogleg for more airflow. Your chokes are now set up. Quote Link to comment Share on other sites More sharing options...
Phlebmaster Posted July 8, 2009 Share Posted July 8, 2009 Wow! Nice information! My eyes are crossed now though..lol Is there anyway to break up those steps so they are easier to follow? Example: Step1:...... Step2:..... and so on. Thanks! Quote Link to comment Share on other sites More sharing options...
Willstar Posted July 8, 2009 Author Share Posted July 8, 2009 Thanks everyone! Heaps of information. I figured out where i was going wrong last night though. Phlebmaster was right, i needed to cock the choke levers until just before they pull the jets down, then set them. The round tops have a much more complex choke lever system than the standard flat tops. Again, thanks everyone. My Z is puuurrrrrrring! Cheers Will Quote Link to comment Share on other sites More sharing options...
Phlebmaster Posted July 8, 2009 Share Posted July 8, 2009 Thanks everyone! Heaps of information. I figured out where i was going wrong last night though. Phlebmaster was right, i needed to cock the choke levers until just before they pull the jets down, then set them. The round tops have a much more complex choke lever system than the standard flat tops. Again, thanks everyone. My Z is puuurrrrrrring! Cheers Will Very nice! Glad you got her running, you will like those round tops better than the flat tops I think. I know I noticed a difference in performance. Quote Link to comment Share on other sites More sharing options...
greygears Posted July 9, 2009 Share Posted July 9, 2009 Glad to hear you got your Z running with a simple cable adjustment! A lot of people throw away the flat top carbs. I don’t know why, with a little trickery they can be made to run just a strong as any of the earlier carburetors. And I think the choke system is better on the flat tops. Quote Link to comment Share on other sites More sharing options...
Willstar Posted October 8, 2009 Author Share Posted October 8, 2009 How critical is the adjustment on the floats of Hitachi Carbs??? Quote Link to comment Share on other sites More sharing options...
MAG58 Posted October 8, 2009 Share Posted October 8, 2009 How critical is the adjustment on the floats of Hitachi Carbs??? Well given the corollary that Hitachi's will run like crap regardless of what's done to them, I would say not important at all. But seriously, It's just as important as other carbs and can lead to all the same issues, way lean, way rich, flooding out, etc. etc. depending on how high or low it's set. Quote Link to comment Share on other sites More sharing options...
Willstar Posted October 8, 2009 Author Share Posted October 8, 2009 But how sensitive? The guide that i have says set it to 10.31mm (0.401 inch) for 1970-71 "4 hole suction chamber" carbs How close do i have to be? mm perfect? or close enough is good enough? Quote Link to comment Share on other sites More sharing options...
Willstar Posted October 11, 2009 Author Share Posted October 11, 2009 Ok, now I've set both floats to 10.31mm and now it's running way to rich. Does anyone know what to set the 240z carb floats to? Any help would be awesome! Quote Link to comment Share on other sites More sharing options...
Apex944 Posted October 11, 2009 Share Posted October 11, 2009 Ok, now I've set both floats to 10.31mm and now it's running way to rich.Does anyone know what to set the 240z carb floats to? Any help would be awesome! Hey there, I had the same issue's with my Z when I first got it back in June. Ztherapy has a video on how to setup and tune the SU carbs which is extremely helpful. http://Ztherapy.com According to him, the floats should be set basically even with the ridge that you see when holding the float upside down. By ridge I am referring to the lip that you bolt onto the lower half of the float bowl. Have you tried adjusting the mixture screws on the bottom of the carbs? Like someone said a few posts up start out by screwing them all the way into the carb (leanest) and then turn them out 2 full turns and start from there. Also be sure that you have oil in the carbs as well as no oil will cause issue's as well as to thick or too thin of an oil. From what i've seen on here most use 10w-30 or 20w-50 oil in the carbs for normal engines. Not sure what you have and have not done and what you do and don't know, just trying to cover as much as possible to help out. Quote Link to comment Share on other sites More sharing options...
Willstar Posted October 11, 2009 Author Share Posted October 11, 2009 Thanks Apex, Thats a big help. Yep, got everything there ticked off except for the position of the floats. Do you mean the top of the float should be parallel with the bowl cap? At the moment, set to 10.3mm, mine are a long way away from parrallel. Quote Link to comment Share on other sites More sharing options...
Apex944 Posted October 12, 2009 Share Posted October 12, 2009 Thanks Apex, Thats a big help. Yep, got everything there ticked off except for the position of the floats. Do you mean the top of the float should be parallel with the bowl cap? At the moment, set to 10.3mm, mine are a long way away from parrallel. Yes, that's the way mine are set right now and it runs pretty good. Quote Link to comment Share on other sites More sharing options...
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