1974 260z, 72' 4screws loss of power, gremlin Help!

[Mytralalas260]

seeing as winter is almost over, i could use some help diagnosing a problem that my car developed last season.

I have a restored 1974 260z with a used set of 72' 240z 4screw carbs that i have installed the Ztherapy rebuild kit into. they have been tuned and tried and drove great for quite a while before this problem arose.

this random little gremlin strikes at the worst possible times and is very unpredictable.

Essentially what is happening is I lose all power, it feels like i am running on only one carb. It has happened while idling, and while at highway speeds. cruising on the highway it does feel like one carb, i lose power, decelerate to the point where i can maintain 30-40mph but i cannot accelerate past that, the sound of my exhaust changes, and sometimes it has just gone and stalled out.

the tricky thing is it can go away as soon as it has showed up, i start to feel it chugging and i'd drop a gear and its gone. other times it lasts until ive limped home.

after the car has started shuddering ive pulled over, fiddled with the fuel lines, checked carb balance, all in check, pull back onto the road and its happens again. (it seems i can simulate the problem by pinching the fuel line from the nozzle to the bowl on the rear carb, one closes to firewall?? )

sometimes it is affected even at idle where it will not run correctly and a couple taps of the throttle and it seems fixed... when really it just shows up again.

to recap, Symptoms are:

initial lag/shuddering

sound of exhaust changes, loss of power

cannot maintain speed, sometimes completely dies.

limp home.

So, I have changed the inline fuel filter after the electric fuel pump, to see if it was clogged i opened it up and sure enough it was clean and not my problem.

I also replaced my cap, rotor, and added a new stock coil. (all stock ignition no modifications)

to satisfy my curiosity i had an inkling that my carb filters might be clogged so i removed them, no better. I then removed the valves in the bowls and cleaned them out, however i have not run the car after that.

besides changing plugs, wires, or fuel pumps im not quite sure what to do. I have a feeling this is fuel related, and related to one carb, as it doesnt just strictly die, it keeps running but with no power. besides throwing more money at my car im not quite sure what else to check.

has anyone had any similar problems, or ideas i may try?:stupid:

- the car runs great until this problem shows up, and its completely random irregardless of speed, rpm, heat, ect. its showed up under almost all conditions. however, after changing the coil cap and rotor the problem minutely surfaced one day, but didnt show up for atleast a week after

kevin

[Gary in NJ]

- Float height adjustment? If the gap is too wide you will starve the carb.

- Pinched or restricted fuel tube (the one between the float chamber and nozzle)?

- A suction piston that gets hung-up?

[SteveJ]

Since you didn't mention any of these:

1. Did all 6 plugs look the same when you changed them?

2. Did you check the oil in the carbs?

3. What oil are you using in the carbs?

[Mytralalas260]

i haven't actually changed the plugs or looked at them since the rebuild. They were Bosch platinum's and they were a light brown i believe.

i had the car tuned at my local zed shop and like i said it ran perfectly for months until the very end of the warm season, then it started showing up, and to be more specific it first showed up on a really hot day.

lifting the piston they both fall with a nice tap. from what i have seen by cleaning and just routine inspection they both move freely. in the carbs i believe i am using SU carb oil, but there is a chance i didn't have any and put dextron transmission fluid in them instead.(acceptable replacement i was told?)

as for the fuel line from bowl to nozzle, while the problem is acting up, wiggling, squeezing, adjusting never helped the problem dissipate so i ruled that out.

kevin

[Bruce Palmer]

So this is a hot weather phenom right? Is your 260 heat shield in place? return springs are hooked to what?. Fuel rail lines wrapped as if they were supplying flat tops?

Happens at idle too? leave your floats alone. Check those plugs after you run it some this spring (if it ever gets here) for color uniformity. Tap the offending float bowl with a screwdriver handle when it happens as you may have a needle and seat hanging shut.....

[Mytralalas260]

yes it happened the first time in the heat, near the end of the fall, but i drove it all summer without any problems as well.

My fuel lines are not wrapped, i swapped out my 260 rail for a 240 rail.

i do have my heat shield on, and my return springs are hooked to that nice and tight.

I had actually thought about it being the needle and seat, last week i took it out and checked it for a good seal, which it had, but i also had trouble blowing air through it while it was open. so i removed it fiddled with it and it eventually started opening up easier and allowing air to flow through uniformly each time. I haven't run it since i tried that (still snow on the ground)

it does sometimes happen at idle, even after just starting it. when i have limped home sometimes i would just raise my high enough i could accelerate and shift without touching the gas and it would get me home.

i figure it shouldnt be the fuel pump/pumps as it doesnt just die, it just keep running, but very poorly.

kevin

[Darrel]

Is it a stock electric fuel pump? If so have you checked the filter inside of the electric fuel pump?

[Mytralalas260]

<a href="http://s110.photobucket.com/albums/n103/garnoff/?action=view&current=35429_413288566763_517616763_4438260_4939494_n.jpg" target="_blank"><img src="http://i110.photobucket.com/albums/n103/garnoff/35429_413288566763_517616763_4438260_4939494_n.jpg" border="0" alt="Photobucket"></a>

i keep it clean, and most everything is new. this gemlin is winning, and id rather not just keep throwing money at it

[Mytralalas260]

Is it a stock electric fuel pump? If so have you checked the filter inside of the electric fuel pump?

it has both the stock electric fuel pump and the one on the block

I haven't crawled under there to check that filter yet but it it has been on my list to check.

could that be the answer?

I did however change the inline one right after the electric fuel pump and it was clean.

[Darrel]

That could very well be it.

ps, can I have your engine bay?

[olzed]

Could be a bit of crud in the fuel tank, getting sucked onto the fuel pipe at odd times. Have you got water into the tank.? Not very likely. I have had this in the past though not on my Zed, given the location of the filler.

Brian

[Mytralalas260]

I wouldn't rule out crud in the tank strictly because I haven't checked the fuel pump filter. I only drive the car on sunny days and I always wash carefully.

However I cannot fill up the tank too full or it leaks out of the filler tube, dirt could maybe get in the same way gas gets out?