Guest Zachb55 Posted December 26, 2003 Share Posted December 26, 2003 i need to tune my SUs i think. my timing is a little funky right now, it seems to change around a bit, like it will idle at one position for the distributor then it will get flaky and i'll need to advance or slow it a little bit to get it idling right again. but i can get it to stay good long enough to tune the carbs, which im thinking are way out of wack. what i need to know is what are the main tuning points? i have a brass wheel thingie at the bottom of the big black piston thing where the gas comes in at, i would assume this has a bit to do with tuning the mixture yet it doesnt seem to follow the rules of my manual, like it doesnt screw in or out, it just spins and it has divots in it to hold it in the general spot that it is, do you guys have something like this? mine are early SUs on an L28 block, or atleast thats what i think, my manual's carbs look a bit different, and i have nothing left of the emissions crap except the bit tube interconnecting the two manifolds... well im sorry for all the random babble, i just need someone to point these little things out for me. also, would you suggest i just buy a colortune and a flowmeter to make this easier or can it be done without those things? thanks guys, hope that was somewhat understandable... -Zach Quote Link to comment Share on other sites More sharing options...
Guest Nic-Rebel450CA Posted December 26, 2003 Share Posted December 26, 2003 There is a good adjustment walkthrough on http://www.ztherapy.com If you have any questions after that, let me know. I had my SU's tuned very well. Quote Link to comment Share on other sites More sharing options...
datsunlover Posted December 26, 2003 Share Posted December 26, 2003 If your dizzy is jumping around and not keeping the engine timed properly, I think it would be very difficult to tune the carbs proberly.. I think I'd address the timming/ignition quirks first, then tune the carbs... just my $.02 Quote Link to comment Share on other sites More sharing options...
Guest bastaad525 Posted January 2, 2004 Share Posted January 2, 2004 If your dizzy is jumping around and not keeping the engine timed properly, I think it would be very difficult to tune the carbs proberly.. I think I'd address the timming/ignition quirks first, then tune the carbs... just my $.02 agreed... elliminate your known problems before trying to tune carbs you think may be out of whack, even if they are you'll never know if you have them right if the timing wont stay still. Luckily, on a 240 you should have very little trouble eliminating the timing problem. First off, if you really like the car and dont mind outlaying some cash, and you or a previous owner havent already done so, get rid of the points distributor. Cheapest way is to get a dizzy out of a 280zx. You can pick up good used ones for $50-75. Or get a rebuilt one. I'd bet money this would solve your problem right there, I guarantee your car will run better, especially at higher revs. Once you take care of that tuning your SU's should be a snap. First thing I'd do though is check them for vacuum leaks... as this is another one of those problems that a)is very common on old 240's with factory stock carbs, and will pretty much negate any attempts you make to tune them properly. You can do this by spraying some carb cleaner around the carb bodies, particularly the ends of the throttle shafts, while the car is running. If the idle bogs or changes, you got leaky shafts, and will need to get new carb bodies, either from Motorsport or Ztherapy. A rebuild kit may be in order too. Also to tune them at ALL you really need the flow balance gauge thingy... it's just a restrictor type thing that you put over the carb mouths and a little float will move up and down telling you how much air is passing thru it... gotta get the airflow on both carbs matched. If you're just trying to get the car driveable in the meantime you can attempt to tune them just the way the car is now, follow the link datsunlover posted and you should be okay... just dont expect to be able to tune them perfectly. Quote Link to comment Share on other sites More sharing options...
Guest Zachb55 Posted January 11, 2004 Share Posted January 11, 2004 Well i think ive got my timing down, after driving around a bit it seems like the ignition is working well, but theres some issues in the carbs still for sure. What the symptom seems to be is that when i throttle it up or go to floor it, it just dies out, and when it gets really warmed up that goes away a bit but i start getting lots of popping. not sure exactly what this is but i guess thats lack of experience for you... what do you guys think it is? i will check for the vacuum thing because i could see how that could mess things up at the higher intake speeds. is that Z Therapy thing about aligning the gas nozzle tube have anything to do with my problem? i think my pistons in the carbs are sitting and lifting just fine... well what can you parse from what ive given you so far? maybe i just need to do a complete rebuild? but i did one when i had the car apart without replacing anything because they were in pretty good shape. well thanks for the help so far. i will look in to getting ahold of a syncrotester so i can get the flow adjusted right. how do i change the flow though? -Zach Quote Link to comment Share on other sites More sharing options...
Guest Nic-Rebel450CA Posted January 11, 2004 Share Posted January 11, 2004 Did you find the adjustment procedure on Ztherapy.com? If so, add this information to what they provide: If you are looking down from the top of the carb you turn it clockwise to richen mixture. Turn them totally full lean by turning counterclockwise to the stop and then turn them out 2 1/2 to 3 turns and then lift the front piston up an inch. If the car dies your back carb is too lean if it idles rough it is too rich. Next lift the back piston up an inch if car dies front carb is too lean, if it runs rough front carb is too rich. You probably dont need to do a rebuild, these carbs arent very intricate. As long as your floats are working right and shutting off then there isnt really much else to worry about. My guess from what you are saying is that either the mixture is off, or the choke is getting stuck. Due to my accident, I may be parting out my Z pretty soon. I'll let you know if I do and when the SU's will be available if you want them for a good price. Quote Link to comment Share on other sites More sharing options...
Guest Zachb55 Posted January 12, 2004 Share Posted January 12, 2004 well i know that my Choke is going on or off when i use the lever, i can hear the difference, and it seems to run much better with the choke on for a good portion of the time. this leads me to think im really lean right now, i looked at that page the link sent me to at Z Therapy and it didnt seem to be a tuning thingy, i guess i didnt look hard enough, ill read through it anyways and follow what it says. when i look at my carbs the "mixture adjustment nuts" as detailed in my haynes manual, look way different, the closest one i can find is the model with a plastice round knob, mine are skinny metal gear-like deals (anodized i think) that have notches in them (for different general setting i would presume) are these the things i should be adjusting my mixture with? like turn them in all the way then come out about half-one turn or so? -Zach Quote Link to comment Share on other sites More sharing options...
Okimoto Posted January 24, 2004 Share Posted January 24, 2004 well i know that my Choke is going on or off when i use the lever' date=' i can hear the difference, and it seems to run much better with the choke on for a good portion of the time. this leads me to think im really lean right now, i looked at that page the link sent me to at Z Therapy and it didnt seem to be a tuning thingy, i guess i didnt look hard enough, ill read through it anyways and follow what it says. when i look at my carbs the "mixture adjustment nuts" as detailed in my haynes manual, look way different, the closest one i can find is the model with a plastice round knob, mine are skinny metal gear-like deals (anodized i think) that have notches in them (for different general setting i would presume) are these the things i should be adjusting my mixture with? like turn them in all the way then come out about half-one turn or so? -Zach[/quote'] I seem to be having the same problem as you are. Were you ever able to correct it? Quote Link to comment Share on other sites More sharing options...
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