72 240z - Problem with mechanical fuel pump?

[SBK86]

Hey everyone,

I bought my 240z a few months ago and ran into some fuel problems. I was getting a lot of junk clogging my fuel filter and I had a small leak from my fuel filler hose so I decided to drop the gas tank and redo the entire fuel system. I replaced all the hoses, lines, fuel filter, restored the fuel tank and I got a new mechanical fuel pump. I just put everything together and I'm having trouble getting the car to start.

Basically after reconnecting everything I needed to get the lines to refill with gas so I figured if I poured some gas in the carb float chambers the car would run for about 30 seconds and refill everything and I'd be good to go. To do this I disconnected the fuel hose from the fuel rail and poured some gas into the hoses that lead to the float chamber. I started the car and it worked... was a little rough but the car ran for about 15 seconds and I saw gas in my fuel filter.

I tried to start the car again but it wouldn't go so I tried pouring more gas in the carbs thinking maybe it didn't get all the way through yet. Again it ran for about 15 seconds and the fuel filter filled all the way up but then the car cut off. Tried to start the car again and it won't start even though filter is full.

My guess is I screwed something up with the mechanical fuel pump and gas isn't running past that or maybe there's a clog somewhere else in the line? I checked the lines though and they all seemed fine.

Anyone have some tips? Maybe I installed the fuel pump wrong.. it only seemed to fit in one way and I replaced the gaskets and that spacer when I put the new one back on. Thanks!

[SteveJ]

You can easily test the mechanical pump off of the car. Remove it. Put fuel lines on it, and actuate the lever arm repeatedly to see if it can transfer fuel from one container to another.

[SBK86]

So simple how did I not think of that.. I'll try it out tonight when I get home from work.

[SBK86]

Hm.. fuel pump is working. There was even gas in the hose between the pump and fuel rail. I also found gas in the hose from rail to the carbs but maybe its not enough getting through? Not sure I'm kind of stumped. If I pour gas into the hose going to the carbs the car runs for about 30 seconds and dies. If I just try to start it.. I get nothing.

[Patcon]

So you pour gas into the rubber line that goes to the float bowls and it runs. After getting it to run 3 times you had fuel in the same line from the fuel pump? Correct?

C

[SBK86]

Correct. I've run it several times and there's gas in the line going to and coming from the fuel pump. The fuel filter is also about 3/4 full.

[SteveJ]

Look upstream of the pump for something that may cause air to get into the line.

[SBK86]

Maybe one of my hose clamps isn't tight enough and it's sucking in air? I'm not sure how else air could get in the line.. I haven't seen any gas anywhere from a leaking line.

I think this weekend I'll take the hoses off again and double check everything and take the cover off the float chamber and take a look. My best guess is that there's something blocking the line somewhere so not enough gas is getting through to the carbs.

[SteveJ]

The four most likely things I can think of (off the top of my head)

1. Air leaking into the line.

2. The pump is weak.

3. The diaphragm on the pump is damaged. (You would have seen fuel coming out if it's leaking.)

4. You have a blockage upstream.

You may want to ensure the lines are clear with some compressed air. Once you verify the lines are clear, you may want to install a fuel pressure gauge near the carburetors to see if you have fuel pressure.

[beermanpete]

There is a filter screen in the fuel inlet to each carburettor. Perhaps those are blocked with dirt.

[SteveJ]

True, I forgot about those.

[SBK86]

I'll try to check that out as well. I have a haynes manual to help me with the carbs which will hopefully be good enough to figure out getting to those filters. This is my first car with carburetors so I'm learning as I go along. I really need to order one of those ztherapy carb videos.

I'm just in kind of a rush because I have to move at the end of the month. Luckily my new house is only 4 miles away so just gotta get it to limp that far for the time being.