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I have a 260. Bought it new and had it since then. Car set up for 2 years. After that it has not run right. Before then, it ran perfect. The problem began by pouring gas out of both carb vent tubes. Bought 2 kits, floats and power valves and had a guy who says he used to work for nissan rebuild the carbs. Since then it is no better. In fact it is worse at times. It still runs good when the operating temp is cold but when it reaches a certain temp. it goes crazy. It stars to cut out and goes dead when it is sitting still. I will welcome any suggestions to remedy this problem, however I do want to keep the car original.
 

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Obieport ! Do You Copy ?

Search on 'Flattop Owners Unit' for mucho prior posted info.

Think you got other problems besides carbs. You will need to carefully rule out all other problems before getting deep into carb diddling. I'd pull and cap all vacuum ports including anti-backfire valve (but not PCV valve - leave that in place - maybe renew PCV valve w/ OEM part, $10.) Test all vaccuum servos w/ MightyVac prior to reconnection. Get an accurate low pressure gauge (10 psi full scale) and verify fuel pressure to carbs - it should be 3-5 psi - or check fuel level in float chamber windows. Check engine compression and set valves carefully. Verify ignition timing and spark plug condition. Then try to get car to run smooth w/ no vac auxiliaries in place. I suspect your throttle butterfly iidle stops may have been messed with in the work you described.

Be aware that early Z's had soft brass or bronze intake valve seats. These get loose and cause erratic bad running conditions. If you get intermitant loud valve lash noise, then suspect intake seats. I fought this problem for over a year before I was sure what the problem was.

Good luck!
Al
 

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Re: Obieport ! Do You Copy ?

AL 260Z. Out of all the things that you have mentioned, what is the most likely to cause the carbs on my 260 to load up with gas and then have gas coming out of the vent tubes on the sides of the carbs. And do you know anyone that you'd recommend rebuilding these carbs to factory specifications. Or where I can buy a set of factory rebuilt ones. As I said before the carbs ran just fine for 20 years, then because of a health problem I had the car set up for 2 years and it has been doing this ever since. I had 0 problems with the running of this car before and it has always been maintained. Frustated!!
 

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Obieport ! Do You Copy ?

Obie-one-kenobi!
How ya doin? Can you read the Hitachi No. on the top of the carbs? It should be HMB46W -*4 or *5 with * = F or R for front or rear carb. These should be excellent carbs. (The early carbs on the 73 240 had -1 and -2 versions which had problems.)

The excess fuel thing is due to one of two things:

either your carb fuel bowl inlet needle valves are sticking open, or the floats are badly adjusted. Did you find the little round window on the side of each carb. Best observed with a flashlight and small mirror. Needles sticking open could be due to crusty fuel (sitting up for two years). Maybe the mech didn't change the needles?? Or crud from the lines is causing them to hang up. Before you start stripping off the carbs to tear down, it would be a good idea to change your fuel filter. Cut it open and check for fouling. If bad, then tank flush may be recommended. Also, were the fuel supply lines hook onto the carbs, I believe there is a banjo fitting relatively easily removed with a fine screen which could be checked (I'll check that out when I get home). I'm a big believer in Marvel Mystery oil. Very good at disolving gas deposits and unsticking sticky carb parts (also hydraulic lifters when added to engine oil). Try chemical warfare before resorting to serious wrenching! If you do get to point of pulling carbs, let me know and I'll get you detailed info on setting floats - although the proof of pudding is in the level in the window.

or you've got excess fuel pressure which is forcing the needle valve open. Check that your fuel supply and return flex lines are not reversed, both at the tank and at the engine bay. (Note the cap with orifice on the return end of the engine fuel rail.) This could cause both pumps to pump into the fuel rail and could well overpressure the needles. Should be only about 3-5 psi. Beware FI fuel pumps. These look the same but pump way too much fuel for n/a carbs.


Good luck!
I'm pullin for ya!
-Al
 
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