fuel pump question

[madsoul]

I just bought my first 73 240z and I am having trouble with my high end fuel delivery. I just replaced both fuel filters, and I think its time to buy a new fuel pumps too. So basicaly I wondering if I should buy both pumps, or if any one has found that one pump fails more then the other? How can I tell which one has failed. I would like to be able to drive on the freeway again, so any advice is helpful.

-Jesse

[2ManyZs]

First item before anyone can answer your question is which carbs are you running? If you are running the flat top carbs you may need the extra pump. If you are running the round top early carbs I would say you could do without one of the pumps.

73's came with only the mechanical pump from the factory, but because of cold start issues and vapor lock problems with the flat tops they recalled the cars and installed the electric pumps.

If you are running the round tops I would say you could do without the electric pump and just run the mechanical pump. The electric is no more prone to failure in my experience than the mechanical pump.

I know this doesn't really answer your question. If you are still running the flat tops, my first bit of advice would be to block off the water to the carbs and try it with just the mechanical pump. Blocking off the water should help cure any vapor lock problems and you should be able to go with just the mechanical pump, the electric pumps (especially stock replacements) are a bit expensive.

To check your electric pump, just unhook the fuel line before the mechanical pump and run it into a gas can and turn on the key, if you have no gas it is the electric pump that is not pumping. While you have it unhooked you can then take the fuel line off the fuel rail and run it into the gas can and turn over the engine to see if the mechanical is pumping any fuel.

[madsoul]

I still have the flat top hitachi's. You are right it could very well be a vapor lock issue. I was thinking that vaporlock was the kinda thing that would only happen once in a while one really hot days if the engine runs hot and stuff like that. Now I will definatly try to block the water to the carbs. I will see if I can get results like that then I guess I will try replacing the Mech pump. I really don't want to have to replace the electrical pump.

I just rebuilt the carbs and have been blocking off stuff llike the throttle positioning valve and the gulp valves. I would also like to unistall the smog pump. I have read that you are a big fan of the Ztherapy carbs. If I can't get these carbs to run well, then what kind of replacement carbs would you reccomend for a guy can't spend the money on ztherapy stuff.

[2ManyZs]

If the water control valve is not working as it should, it will vapor lock on a cool day. The water control valve is intended to shut off the water at about 70 degrees if I remember right. So if it is not working, it won't matter what the temp is outside. So I would suggest blocking off the water first, see what happens, and then take another step. If you do more than one item at a time, you really won't know what was causing the problem.

It is possible to get the flat tops to run decent. They just aren't as easy to work with as the round tops. You should be able to pick up a decent set of round tops for 100 bucks or so. That will save you a lot of money over the ZTherapy carbs, although you never know what condition the carbs you are buying are in. If you look around enough you should be able to find a decent set of round tops. But, if money is a problem, try to work with what you have first. It may not be as hard as you think to get yours to run with a little tinkering.

You may also have a vaccum leak somewhere that is affecting things to. You say you have begun to de-smog the car, so I'm wondering if there may be a vaccum leak somewhere. Make sure you have everything blocked off completely.

There are enough people here to help with questions, sooner or later we will hit on the right combination.

[madsoul]

thank you, youv'e been very helpful