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240z runs very rough hot, intermittently


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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.

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I see you are running a 280zx distributor. Do you have the matching 280zx or similar electronic coil? The coil could break down when hot. Have you bypassed the ballast resistor?

Actually I am running the stock 240z coil. I previously had a Mallory or MSD coil (can't remeber which) but that was removed. I had the same type problem with that coil.

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It will run with the stock coil but not properly. Have you bypassed the ballast resistor? You will need to do this even with the stock coil.

I did bypass/remove the ballast resistor. Are you telling me that I should use a 280zx coil instead of the original 240 coil? I haven't tried that.

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Vapor Lock ? The car is famous for this....


Not just a Z - zdisease

Yeah, I know. I installed an electric pump in line with the mechanical, I believe that was nissans solution for the problem. Are there any other "solutions" to the vaporlock problem?

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