Ghettopoptart Posted October 30, 2011 Share Posted October 30, 2011 First of all, I recently purchased a 74 260z from a gentleman, the car is everything i've wanted in a Z car, with the exception of a running engine. I've read up TONS of "Search button" topics, and looked all through diagrams of these darn carbs but cannot seem to figure the damn things out. The carbs that are on the car are a set of 3 screw bottle top SU's, im assuming late model 72's that the gentleman put on there, when i bought the car, he said i could fill the bowls of the carbs up with gas and it'd run like a champ and that it had only sat up for long enough for the gas to go slightly bad, but the fuel pump wasn't kicking on, so what i did was after purchasing said beautiful car, i went to my local autozone and bought a Mr.Gasket 5-7lb fuel pump, i am now getting fuel TO the carb, but couldn't get the car to run. The engine would just spin over, can spray fuel in it, and it runs off of that like a champ. But soon as the fuel dies out, so does the motor. So in screwing with these things ( not knowing what i was doing) i found out how the choke works on them, (the lever isn't working seemingly) i could pull down on the bottom of them , and the choke applys, i got in the car, and BAM fired right up, until the vibration of the engine closes the choke, and it dies, i let it sit for about 10 min running on its own on a nice warm day (65) and then let the slide back up, and it just died , even under constant rev. I just don't know what would cause that, for them to run perfect up until that point. It had SOME bad gas in it, but the bowls looked clean and so did inside of the carb and needle , no clog between the bowl and carb, due to being able to spray fuel between the both of them and it come out both sides. I just cannot figure it out, is this so simple that im overlooking whats going on? HELP! (Ps, im taking the wing off ) Quote Link to comment Share on other sites More sharing options...
morbias Posted October 30, 2011 Share Posted October 30, 2011 Have you adjusted the fuel/air mix? Sounds like it could just be running too lean. Quote Link to comment Share on other sites More sharing options...
Ghettopoptart Posted October 30, 2011 Author Share Posted October 30, 2011 To be starving 100% out of fuel when choke is off? Quote Link to comment Share on other sites More sharing options...
Robzzzz Posted October 30, 2011 Share Posted October 30, 2011 5 to 7 psi is pretty high for SU's , you sure its not flooding ? make sure the piston damper assembly moves freely so you know the needle can lift up out of the seat for fuel to flow , the choke drops the seat to allow fuel to flow , but when the carb is working the piston and needle lift up out of the seat and allow fuel to flow ,so from what you have said ....the piston may not be lifting the needle out of its seat so it could be the needles are not centered or things are just gummed up .....more info ! Quote Link to comment Share on other sites More sharing options...
beermanpete Posted October 30, 2011 Share Posted October 30, 2011 It sounds way too lean. Check the fuel filter (if you have not already replaced it), float level, the condition of the fuel hoses connecting the float bowls to the carbs, and the filter screens built into the top plate of the float bowls. Quote Link to comment Share on other sites More sharing options...
Miles Posted October 30, 2011 Share Posted October 30, 2011 Go here and buy the video tape "Just SUs" http://www.ztherapy.com/ Quote Link to comment Share on other sites More sharing options...
Ghettopoptart Posted October 30, 2011 Author Share Posted October 30, 2011 Well guys, i was going to say, the float bowls are full at the time when it does all of this. you can drop the screw and gas pours out , so the bowls are definitely full , its a starvation problem, not a drowning problem. Quote Link to comment Share on other sites More sharing options...
Miles Posted October 30, 2011 Share Posted October 30, 2011 I agree with Morbias. It sounds like a lean problem. On the bottom of each SU there is a knurled mixture adjusting nut. Here is the basic starting point for setting the mixture: 1 - Looking top down at the SU turn the mixture nut counter clockwise (leaner) until it stops. This is the absolute lean condition and the starting point for the mixture adjustment. 2 - Looking down on the SU turn each mixture nut clockwise (richer) 2 1/2 turns out. Normally the engine will run with this setting which can be further refined to get the best mixture setting. If you are going to keep the SUs you can rebuild them with Z Therapy kits or or buy their rebuilt SU carbs. Quote Link to comment Share on other sites More sharing options...
Ghettopoptart Posted October 31, 2011 Author Share Posted October 31, 2011 I have that adjusted, it still goes dead Quote Link to comment Share on other sites More sharing options...
Miles Posted November 1, 2011 Share Posted November 1, 2011 (edited) There is a filter screen at the fuel inlet on the SU. Did you check to see if it clogged? The SU fuel feed is simple. Gravity feeds fuel from the bowl to the carb which is metered by a tapered rod in hole. The tapered rod moves up via the piston according to engine demand allowing more fuel to flow from the bowel. Sometimes refered to as a controlled drip. What can go wrong? The rod can be bent, the rod has some how slipped or moved, the rod has become mis-aligned and is binding, the rod is worn, the pistons are binding and not allowing the rod to lift (happened on my stock Z). In my case disassembly of the dome and piston revealed scoring which was preventing the piston from moving up and therefore restricting fuel flow. You can pull the dome and piston without removing the carb. I ended up buying Z Threrapy carbs as my carbs were leaking badly around the throttle shafts causing a lean sag. Throttle shaft leakage is a common problem on SUs and can make it impossable to adjust the mixture properly. Z Therapy uses sealed ball bearings on the throttle shafts to prevent air leaks from developing at this high wear point. I have also had the needle valves in the fuel inlet stick closed. Inspection showed scoring on the needle valve. Google SU carbs and you will find SU tuning and repair tech write-ups. There are a number of SU repair/trouble shooting tech write ups on various Z websites e.g., Z Home, Classic Z Car etc.. Edited November 1, 2011 by Miles Quote Link to comment Share on other sites More sharing options...
Ghettopoptart Posted November 1, 2011 Author Share Posted November 1, 2011 (edited) Well I bit the bullet and took them off and cleaned them, i figured if they'd been sitting for any amount of time, they'd be gummed up, everything seemed pretty clean , except for on the needle itself, where it seats into the choke, there are indention, seemingly indicative of (for lack of a better term) slamming down too hard. And its not letting any airflow through ( i blew through it) but if you pull the choke, its as if you're manually pulling away from the needle and allowing fuel to come through. Maybe i need new needles because they are sticking due to being worn out? Also , I do not have 600 dollars to drop on a brand new set of Z car therapy Carbs. Edited November 1, 2011 by Ghettopoptart Quote Link to comment Share on other sites More sharing options...
Miles Posted November 1, 2011 Share Posted November 1, 2011 (edited) Motor Sports Auto (MSA) sells SU rebuild kits and parts: http://www.thezstore...TZS/CTGY/SFC01B I found some SU related videos on Youtube that may be of interest to you. Go to Youtube and search on SU carbs. More info here: http://atlanticz.ca/...bs/su/index.htm Click on pictures to enlarge. Edited November 2, 2011 by Miles Quote Link to comment Share on other sites More sharing options...
zbloke Posted November 1, 2011 Share Posted November 1, 2011 (edited) You could have an air leak on the induction system, it would cause the engine to run excessivly lean and may be the cause of your problems if you've adjusted the jet heights to spec and the rest of the carb is in working order Edited November 1, 2011 by zbloke Quote Link to comment Share on other sites More sharing options...
jasper Posted November 1, 2011 Share Posted November 1, 2011 (edited) It is obvious you lack the knowledge needed to resolve your issues. You need to get a book, or video,or both, and use it. Then, try and understand how these carbs work (they are simple), and the terminology involved (much of your's is incorrect), so you can ask intelligent/educated questions. NO AMOUNT of guessing by anyone involved in this thread will fix your car. There is no one adjustment to fix your car. Start at the beginning, read, and good luck. There are MANY here who will respond to INFORMED questions. Myself included. Edited November 1, 2011 by jasper Quote Link to comment Share on other sites More sharing options...
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