240z runs very rough hot, intermittently

[FilipeA]

Hi Chris

Why are you asking that? is there any case related to that... so here goes what`s happen with me.

I did a big restoration on my car , and engine was one of the parts that i restore as weel.

I changed the piston rings, timing chain kit, gas, water and oil pumps, new hoses, etc...

At beninig I run it and felt like the carbs were stop working and the engine stop working too and i was forced to pull side of the road.

I changed the correct termostat degrees for 76.5 C, not 81C, because i saw a little high tempetarure on gauge them normal. I change it and keep it running and he did it again for a couple of times (only)...

Now i put new carbs and everything works fine... but still don`t know what it was...

Now i have a friend that has this problem as well, and i want to help him, the engine was redone, and car works fine at idle readlly good engine sound, but at road he can not put the throttle down as car might stop working. The carbs or engine start to fail and he has to pull over and wait a little of time, them it starts again and run a little better...

Any solutions?

Filipe Azevedo

[Nigel1943]

The pump came off a carburated car.

Back to basics then.

Cracked distributor cap

One or more ignition leads breaking down

Carb needle valve sticking

Carb float levels incorrect

Mixture incorrect

et al

Have you checked the color of the spark plugs after a run?

[whamo]

Back to basics then.

Cracked distributor cap

One or more ignition leads breaking down

Carb needle valve sticking

Carb float levels incorrect

Mixture incorrect

et al

Have you checked the color of the spark plugs after a run?

I havent and Im out of town currently, but when I return Im installing my wideband o2 sensor on this car to monitor mixture when the problem occurs. That should tell me if its ignition or fuel.

[MikeW]

Now i have a friend that has this problem as well, and i want to help him, the engine was redone, and car works fine at idle readlly good engine sound, but at road he can not put the throttle down as car might stop working. The carbs or engine start to fail and he has to pull over and wait a little of time, them it starts again and run a little better...

A partially clogged fuel filter can exhibit those symptoms. Enough fuel gets through to idle fine but not enough for more throttle. It's even possible that the clog of debris shifts as you drive such as when going up a hill.

[ChrisZ]

Did you or did you not get new pistons/rings recently ?

Chris

[FilipeA]

Hi Chris

My friend did a engine rebuild recently

Filipe A

[whamo]

I did some searching and couldn't find a solution to this problem. I have a 1971 240Z that I have recently restored. We have had an intermittent problem that has popped up occasionaly since we purchased the car 3 years ago and it continues to this day. It will intermitently run extreamely rough and virtually stall when hot. Its is like its dropping one carb. I dissassembled and cleaned the SU carbs per the Z therapy video (several years ago). The fuel tank has been cleaned and treated with POR. The fuel lines have been cleaned, flushed and all of the hoses replaced. I added an electric fuel pump from an RX7 in the back and replaced the mechanical fuel pump up front with a new MSA replacement pump. I recently replaced the fuel inlet valves and reset the float levels. The car has a 280zx distributor with new plug wires, cap and rotor and we have replaced the module once trying to resolve this issue when it completely quit one time. I am begining to think that one of the carb slides/pistons may be sticking when the engine gets hot. I don't remember this problem occuring right after I cleaned and adjusted the carbs. I'm looking for any suggestions.

It seems that the problem is occurring upon hot restart after the car has sat and heat soaked, therefore I believe it is a classic case of vapor lock. Any suggestions for alieving this problem? My thought is to insulate the fuel rail brackets from the cylinder head with a rubber or phenolic spacer/insulator. Any other ideas?

[whamo]

Update on our problem. We drove the car up to Seattle and back this weekend and the car ran fine the whole way with one exception. cruising back on the freeway we lost some engine power. I was cruising about 75 and suddenly it dropped power and I was only able to maintain about 60 for about 45 seconds or so, then the power cam back and it ran fine the rest of the way home. I just determined that the vacum advance was bad and not operating and was leaking vacum. I replaced the distributor with another I had in the shop. We will see if this cures the problem we were experiencing.