AZ260Z

You're AWESOME FastWoman. You're tip about checking the float bowls jogged my memory of the last time I had checked to see if fuel was getting to the front carb by disconnecting the hose and having the fuel pump pump fuel into a container. Right afterwards I checked the front bowl and it was nearly empty with just a residue of fuel. I also noticed that the float seemed to hang up when you moved it up & down so I adjusted it. I thought that was odd but figured since I disconnected the hose that maybe it didn't get a chance to replenish itself. Also, since The problem surfaced while I had my original flat top carbs and wasn't cured by replacing with rebuilt round tops, I guess I didn't want to believe it was the front carbs on both sets. Anyhow, once I checked the front float chamber today, it was bone dry and when I checked the rear one it had fuel in it. I then compared how both floats were adjusted and made the front like the rear and "bingo" that solved the problem. She started right up, cranking on all 6 cylinders, took it out for a test drive and it ran great. I had taken the car to 5 different mechanics but am especially disapointed in the "Carburetor Specialist" who had previously owned 2 different Z cars, but although it has been a long and expensive process, I've learned a lot and wish I had had your tip when it first occured. This forum is great, I owe you big time, if you ever get out to Arizona, I'll buy you a drink , hell I'll buy you dinner. Thanks again and thanks to all that responded.

When the problem first occurred I had the original flat tops but replaced them with rebuilt 72 round tops thinking that may have been the problem. That costly bit of troubleshooting did nothing to resolve the problem and the symptoms remained the same. As far as ensuring the carb getting fuel, I personally have removed the fuel line to the carb and turned the ignition to on and pumped gas into a container on multiple occasions. I also took the car to a carburetor specialist who checked both fuel pressure and volume, adjusted the carbs and said it wasn't a fuel issue. This was after going to 2 other mechanics who thought it was a fuel issue. I'd like to find out what is causing the low (rapid fluctuating) vacuum readings between 8-10".

I have a 1974 260Z. I'm getting low vacuum reading between 8-10" with very rapid fluctuations of the needle. Also, I can pull the # 1,2,& 3 plug wires off individually or all at once with no reduction in rpm's. I've checked and/or replaced the plugs, wires, cap, rotor, etc. I've also tested to see I was getting good spark to all cylinders, ensured the front carburetor was getting fuel. I've done a compression test and a leak down test all with good readings. Also checked for vacuum leaks using propane and a hose (very thoroughly). Also did a soapy water test around the head checking for a leaking head gasket even though I'm not losing any coolant nor are any exhaust gases getting into the radiator. I've also had it checked to ensure it wasn't a back pressure problem or that the timing chain hadn't jumped a tooth. This problem started occuring intermittently sometime (but not right away) after a serious overheating incident where the fan clutch had failed and has gotten progressively worse over time. Needless to say the car is not drivable, running on 3 cylinders and I've spent countless hours and $$$ at mechanics trying to figure out the cause. Is there anything else I can check before removing the intake/exhaust manifolds and head to inspect and/or send to a machine shop? I've run out of ideas.

Yeah, we did that and the groove in the fixed plate was just to the right of the notch, like the manual said. We even checked for stretched chain by hand cranking until the rotor started to turn, marked and then cranked in the opposite direction until the rotor started to move. It was only 1/4" which is less than 5 degrees, and from what I've read, is acceptable. My only concern was if it is "Normal" for the slack side (driver's side) of the chain to slap the guide when you have the valve cover off and stop cranking the engine at short intervals, as in trying to adjust the valves?

No, I think I misspoke about the timing being set at#3, should have prefaced this by stating that we had #1 piston at TDC and I was checking out the cam sprocket and looking for (chain stretch) or slack prior to adjusting the valves. Looking at timing mark#3(at approx 11o'clock), the groove was just to the right of the notch, where its supposed to be, but am concerned about the slapping of the chain on the guide, since the mechanic didn't think that was normal. Based on what I saw, and the before and after adjustment pictures in the Haynes manual, it appears it's been set to #2. There was no shiny link in sight.

I noticed the slack side of the timing chain would slap against the guide while remotely cranking the engine on and off to adjust the valves. The slack is removed while continuing to turn the crankshaft. The cam sprocket is set to timing mark #3 and I did a slack measurement test and there was just under 5 degrees of slack. Is this slapping of the chain against the guide on the slack side "normal" on "Z's'" when cranking the starter on & off in short intervals? I'm asking this because someone else who is a mechanic witnessed this and said that didn't seem right but he was not familiar with older "Z's"

There's nothing showing on the top, I wonder if Haynes' lingo for sending unit is Transmitter unit? I'll look in the FSM and see if there is a better description and picture. I hope it's something like that also, because if it's electrical, I can look for chewed wires but I'll need to read up on how to check for good grounds.

Madkaw, Just to be clear, when you referred to the fuel sending unit from the tank, is it what the Haynes manual calls the Transmitter unit which is located to the left of the return nozzle?

Good question, since the "carb specialist" is relatively nearby I will drive the car back to him and if it wasn't done, I'll have him do it. Thanks

When the problem first occured, I still had my flat top carbs, which were rebuilt as part of the restart in 2003. Problem first occured in 2006/2007 timeframe.I replaced them with '72 rebuilt SU's in 2008, thinking that would cure the problem, which was a costly assumption. I don't know if the float bowl screen was checked by the "Carb Specialist", but I will definitely do that myself when I get the car back. Any other input on the timing set up/slack in chain or possible damage to head or intake/exhaust manifold gasket from overheating? You can't imagine how disappointed I am and have searched for a "Z" mechanic in the area but haven't been able to find one. Thanks for the tip/input.

Back in 2003, first thing we did was to drop the fuel tank and send it out for cleaning, it's so long ago, can't remember inspecting the the sending unit.I'll definitely look into getting a compression gauge, so I can feel confident about the readings. Thanks for the tip on borrowing the pressure tester from Autozone. I was able to get (2) brain boxes(TIU's) and swapped them out, so I think I can eliminate that possibility. As far as the coolant, back in 2003 I drained the system, backflushed until it was clear, pulled the radiator and took it to a shop for repair. I didn't add any rust removal product, but on a tip from my old mechanic, made a screen filter and put it in the top radiator outlet to capture any rust particles and periodically would check and replace it. The amount of rust particles diminished to almost nothing. Guess it wouldn't hurt to add some rust removal product now? Do you have any input on the questions regarding the timing set up and slack in the chain as well as possible damage to the head caused by overheating? Thanks for your input and tips.

The Problem: What started out as an intermittent power loss during acceleration has progressed to nearly a constant problem including at start up. I am now relegated to starting the car in the driveway and an occasional trip around the neighborhood. It does however has it’s moments. Just 2 months ago after not starting it for a couple of weeks, it started up, idled smooth and revved up smoothly so I took it out and it didn’t act up so I took it on the closest highway and had it up to 80mph and had a lot more but was afraid of getting a ticket. The total trip was only about 30 minutes, I was elated. Decided to try it the next day and it acted up on start up. This has been going on for the past 5 years and am on the 5th mechanic not counting the countless hours myself and friend have spent trying to diagnose the problem. Background: I am the original owner of the 1974 260Z w/manual trans. I drove the car for 14 years, parked it for the next 14 years(Bad Idea!!), then decided to get it running again in 2003. After a lot of time, $$$, a friend, my old “Z” mechanic(who has since retired & moved out of state) we got it running. It ran great but after a few hundred miles I noticed condensation coming out the tailpipe. I took it into the shop and discovered the water jackets in the head had rusted out and couldn’t be repaired so had to put a rebuilt head on. Drove it occasionally around town for the next few years for another 1300 miles. The only problem it had before and after head replacement was it would get hot if sitting at idle for any length of time. Decided in spring of 2005 to give the car more of a driving test by taking a day trip from Phoenix to Flagstaff. About 30 miles into the trip it started overheating so I pulled off the highway (steam was coming out the overflow tube) let it cool down, then added water and took it easy, monitoring the temp gage all the way home. Shortly thereafter I had the radiator rodded out and replaced the fan clutch which seemed to cure the overheating problems. The car seemed to be fine, so I put that incident behind me. It could have been months or even up to 2 years before this current problem arose. It’s hard to pinpoint the timeframe(sometime in 2006/2007) because of the infrequent use of the car but I know it was long enough not to associate the overheating with this current problem. In 2008, thinking it was a fuel issue I replaced my original flatop carbs with older roundtop rebuilt SU’s with the hope it would solve the problem. It had zero effect. In 2009 I took the car to Mechanic#1, he too thought it was a fuel issue. He drained some fuel from tank, poked around inside the tank looking for obstructions, replaced electric fuel pump & filter, all with no improvement. He swapped out the coil and ballast resistor with no improvement so reinstalled mine. He then replaced distributor cap, rotor, plug wires & plugs, no improvement. He had the car for 4 months and finally gave up (under duress from his boss to either fix it or move it). During this time I was reading literally hundreds of posts on this site looking for similar symptoms and solutions. Unfortunately these symptoms can run the gamut from fuel, electrical, spark, timing, etc. After getting the car back, I replaced the alternator, voltage regulator, and swapped out a pick up coil, spare distributor, spare transistor ignition unit, all with no impact on fixing the problem. I also pulled all the electrical connectors apart and used deoxit on them, nothing. In 2011 I took it to mechanic #2 which in addition to general work, they specialized in electrical problems. They called me and said they suspected it was a fuel issue but couldn’t be specific. They even took the car to their other shop who had an older mechanic. He checked it out and said it could only be 1 of 2 things, either back pressure or the timing chain had jumped a tooth. They called back a few days later and said it was nether of those things and they still think it might be a fuel issue and recommended a carburetor specialist. So to put this to bed I took the car to him (Mechanic#3). Turns out, he’s an older guy, runs a 1 man shop and does nothing but work on carburetors. He even owned 2 different “Z’s” in the past, so he was very familiar with SU’s. He went completely through the fuel delivery system, checked pressure, volume, plugged lines, etc. He fine tuned the carbs and said it was running great. He then went to back the car out of the bay and it went into the no power mode. He called me and said I don’t have a fuel issue. I still had a gut feeling it was an electrical issue so after researching and talking to mechanics. I was referred to a guy that did nothing but electrical and had a mobile service and did consulting work for several repair shops in the area. I contacted him(Mechanic#4) and he gave me his rates and said it would be cheaper if I could bring the car to him. So I raced over to his place(max speed of 25-30mph) He called me that afternoon and said I didn’t have an electrical problem and was getting spark to all cylinders. He did notice that there was no discernable difference when pulling the plugs out individually on the front 3 cylinders. He then suggested I take it to Mechanic#5 who he said was honest, reasonable and knowledgeable. He called ahead and told him I was on my way. After having to climb some inclines and venture into a rotary at rush hour, I finally made it. He’s had the car for more than 6 weeks now but has only recently spent time on it. When he first looked at it, guess what? He thought it was a fuel issue not getting to the front 3 cylinders. I asked him to do a compression test which had not been done by any of the previous mechanics. He called me and said he got around 100 on all 6 cylinders and did it twice (cold & warm). He didn’t seem concerned that they were all this low until I told him that everything I’ve read says the compression should be around 150. In fairness to him, he had a Haynes manual for the car but it doesn’t state what the numbers should be. If the numbers are all pretty much the same, that’s supposed to be a good thing, right? As a caveat, he said he wasn’t 100% sure his gauge was accurate. He threw out some possible causes: head gasket failure, or cam/valve timing issue. I read up on the cam/valve timing and came across timing chain stretch and asked him to check the slack while I was there. [He did and it was approximately ¼” or less than 5 degrees. I also noticed that when the #1 piston was at TDC on the compression stroke, the cam sprocket was set to timing mark#3 which was at 11 o’clock and the groove was just to the right of the notch. I did not see any shiny link the manuals talk about but that may only pertain to when you’re installing the chain. Does this all sound OK to everyone?] [While he was adjusting/checking the valves, he noticed the slack side of the timing chain would slap against the guide when he would crank the engine with a remote starter button, other times the slack was gone. He seemed concerned by this and wasn’t used to seeing this on other vehicles. Is this normal on “Z‘s”?] He also noticed some water/coolant residue on a nut & bolt located just behind and to the right of the thermostat housing. It’s the same area that I’ve heard a slight hissing sound after the car is at normal operating temperature and I shut off the engine. He then raised the car on the lift and we could see residue/stains on the side of the block below. He said I might have a leaking intake/exhaust manifold gasket. [He’s seemed to have dismissed the head gasket as a cause. I am not getting any coolant in the oil. Also, I checked for exhaust gas bubbles in the radiator and didn’t see any. I don’t remember having to add any coolant since the overheating issues were resolved. Is there any way my overheating episode could have damaged the head gasket or warped the head, causing the low compression #‘s yet I‘m not loosing coolant?] If this hasn’t put everyone to sleep by now, I would greatly appreciate responses to the questions in brackets along with any other suggestions or questions. I would love to be able to drive my Z again and resolve this problem before I either run out of $$$ or time left on this planet.