1985 Nissan 720 truck Can't keep carb fuel bowl full

[fatdogsdaddy]

I have hit a block wall for ideas as to why my truck can't keep fuel in the fuel bowl. I'll give my chronology of were I've been with it so far

I replaced the fuel filter and then the fuel pump after it wouldn't start one morning and it ran fine for almost 2 weeks. On my way home from work it starting lurching from what I found to be fuel starvation and died. I came back the next day when it was cool and still didn't start so I'm not thinking it is vapor locking. It fires up and run just fine when fuel was poured down the carb barrels until it burnt it off. I have pulled off the fuel supply to the carb and I am getting fuel flow to the carb but I blew out the fuel lines with compressed air to make sure i didn't dislodge something during the fuel pump replacement that is intermittently blocking the line. The truck ran fine for two 15 minute drives then dies the 3rd trip out with an empty fuel bowl. Next step was pull the carb which had been rebuilt by prior owner 14 months ago and replaced needle and seat and sprayed out passage ways, put in a new filter in the banjo fitting and adjusted the float to the proper settings. Put it back on and got two 15 minute test drives and back to empty fuel bowl and no start on the third drive.

I am running out of ideas. I know I am getting fuel to the carb and needle and seat all seem to be working properly as well. My next ideas are to do a volume and pressure test on the fuel pump and make sure its not weak. I also have a fuel pump relay on order but i doubt that’s it because i jumpered it into the on position for over a minute and saw no rise in the fuel level but could hear the pump ticking away. thought number 3 is I may have a loose fuel line connection and I'm sucking air (any tips on how to check for that).

Does anyone have any ideas what I may be missing? fastboatman29212 if you are out there thanks a lot for the carb rebuild posting, you made it too easy


1985 Nissan 720 with Z20 and hatachi carb

[fatdogsdaddy]

Problem solved. The new fuel pump was bad and pumped intermittently, unfortunately for me it was working the day I checked fuel delivery when I was chasing down the problem. On the pump number 3, hoping it holds out longer than 2 weeks this time.

[picturearts]

Find out if your 720 needs a spacer block between the pump and the engine. I read about it, and its needed on the 521(1972) and ordered one on ebay, supposedly it will mess up the pump without it. Install in this order: Pump/gasket/spacer block/gasket/engine. My pickup is doing the same thing. I suspected an intermittent faulty pump, I'm going to replace mine tomorrow.