240z runs very rough hot, intermittently

[carguyinok]

If you are running the stock SU carbs. Have you checked or cleaned where the coolant runs through the carbs? I pulled apart where the line enters the rear carb on mine and found that it was plugged up bad.

Follow the hardline that runs around the back of the block/head and you will see a soft line that hooks that line into the carbs. Remove that soft line and unscrew the nipple where the soft line hooks into the carbs. You will see there are 4 small holes inside that fitting that restrict the flow of coolant. I have found these small holes will get plugged up over time. If thats the case it could cause you headaches much like what your talking about.

It's a very easy fix that gets overlooked.

Hope it helps.

Edited March 8, 2009 by carguyinok

[carguyinok]

[a7dz]

Jeff;

Thanks for that picture of the restricter on the carbs. I have never seen one installed and know my 70 never has had one. I have had this car in every southern state in the us in the summer and have not had the vapor lock problems. The flat tops were known for vapor locking.

[carguyinok]

Owell, cant say I didnt try. I will ask around and see if I get any new thoughts. I hope you get it taken care of soon.

[a7dz]

Jeff;

Steve is fighting this problem. I am glad to see the pictures. This is new info to me. I am looking into a similar problem. Steve could have this valve. Again thanks for the info.

[Arne]

Interesting. My '71 does not have that restrictor either. I wonder what years it normally came on?

Edit: Looks like it was available as a dealer installed option or fix of some kind. Perhaps part of the '73 "fixes" for hot running. The parts list shows it as 14100-E8850, and calls it a "ASSY - THERMO MANIF WATER CONTROL".

[carguyinok]

I know this car came from Texas. So I would rule out that its being used for a cold weather fix of any kind. Maybe if you slow down the coolant flow in the intake that would let the coolant pull more of the heat from the intake and carbs?

Atleast thats my guess. Then again I have been wrong before......

[Nigel1943]

Just a thought. Do you know what pressure the RX7 pump is running at? Needs to be 3-4lbs.

[whamo]

The coolant flow through the intake has been bypassed on my car. I didn't think that restoring that flow would reduce intake heat issues but I suppose it might. Also, I was reminded by Gary (beandip) that we installed a 280zx coil on the car in place of the MSD blaster coil I had been using previously.

I dont know the fuel pressure delivered by the RX7 pump but I'm sure its not more than 5. Of course mine is a used one so it might be weak.

Edited March 9, 2009 by whamo

[Nigel1943]

The coolant flow through the intake has been bypassed on my car. I didn't think that restoring that flow would reduce intake heat issues but I suppose it might. Also, I was reminded by Gary (beandip) that we installed a 280zx coil on the car in place of the MSD blaster coil I had been using previously.

I dont know the fuel pressure delivered by the RX7 pump but I'm sure its not more than 5. Of course mine is a used one so it might be weak.

I take it the electric pump isn't off an injected RX7. If it is it will have way too much pressure. What year was it off? I agree the intake coolant flow is not your problem.

Edited March 9, 2009 by Nigel1943

[whamo]

I take it the electric pump isn't off an injected RX7. If it is it will have way too much pressure. What year was it off? I agree the intake coolant flow is not your problem.

The pump came off a carburated car.

[ChrisZ]

I have a thought here, when you say it feels like it is dropping one carb, is it then dropping one or does it just feel like it do ?.

have your engine been getting new pistons/rings recently ?.

It might sound stupid to ask this.

Chris