1974.5 - 260Z (Won't Idle)

I have reviewed many of the discussions that were archived, have tried several but still nothing works.

I have a 1974.5 260z that won't idle properly or at all. When the engine is cold it runs rough, when it is warmed up it does not exist and the car stalls.

The engine has had the pollution stuff off for several years and ran great until I got into a fuel problem last year. I have completely gone over the fuel delivery and I am getting 3 to 4 psi static off the fuel pump, so lots of fuel to the carbs. The bad fuel was removed, the tank relined due to rusting , the system (lines) blown out.

The carbs, unforunatley are the flat top - Tuna cans (HBW46W-4), though they did run great until this fuel problem.

As a result of the fuel problem the rear carb started to overflow fuel, so I assessed the float level and it was to high, I adjusted it and cleaned out the float bowl. It now reads on the bulls eye. I also removed the carb pistons and cleaned them, as well I looked at the needles and they are straight. Some wear but still they look pretty good, the shoulder of the needles are flush with the main bottom of the pistons not the slot of the pistion. Both were the same when assessed.

So the floats are bull eyes level and the needles are straight, I tried the lift and drop, and the piston clunk so the needle seems to seat okay and they is a good pressure to lift the installed pistons with my finger, they go up maybe a 1/4 inch when the engine is not running. The float adjustment stopped the carb from leaking.

As part of other issues I have come across, I had a head gasket problem which resulted in a warped head that was shaved, as well during this maintenance I replaced the intake valve guides which were brass and starting to sink. The valves were cold adjusted and in tolerance but now with the rough idling I can hear some small rattling of the valves.

The distributor was old and it to was replaced with new remanufactored one, I performed a "retarded" timing test and it was within spec at 600 rpm.

I have done all the checks except for engine compression prior to adjusting and trying to balance the carbs. I have the Haynes manual and FSM and have followed the procedure excately except that my adjustment system does not seem to work as it should, the Idle speed adjusting screw does not affect the engine rpm (can not get to 750 rpm) , the Idle Mixtrue adjusting screw (no idle limit switch) as well ,seems to have no effect on the engine rpm, though the balance adjusting screw does affect the front and rear carbs.

The carbs are running very rich so at this time I now have the Idle Mixture Adjustment screw turn about half way out. Though turning it when the engine is running does nothing, just like the slow idle speed adjust screw does nothing.

Any rpm below 1000 the engine runs rough and it spurts, I think the system is too rich and it not getting enough air. But, I do not know how to get more air with the four adjusting screws (Idle mixture, slow idle , fast idle and blance screws), nothing seems to work. If I keep the intake manifold vaccum hole open the engine idles better, but once I put the vaccum hose from the air cleaner back on and put the air cleaner back on even without the filter, the car wont idle.

By the way the engine runs great at high speed no problems with the carbs, except again they still run rich and eat up a lot of gas.

Another thing I have not done is assessed the power valves maybe they are the problem.

I have looked at the choke mechanism and throttle linkage and everything is okay.

I have sprayed the intake/exhasut gasket, and around all the parts of the carbs with carb cleaner to check for vaccum leaks but none found.

I do not have access to the Ztherapy video.

So, what am I missing. Any input will be accepted and I will be gratiful.

Thanks