David Downs

I rebuilt an original pump and it seems to have fixed my issue. The check valves in the aftermarket pumps are junk. I would take apart one of your failed pumps and look closely at the check valves. It was obvious my check valve failed.

View Advert Kyosan Denki Fuel Pumps Wanted Message me if you have some old Kyosan Denki fuel pumps you want to sell. They don't have to work. Advertiser David Downs Date 08/23/2020 Price $25.00 Category Parts Wanted Year 1971 Model 240Z

I have taken a few apart to rebuild some Kyson Denki pumps. Enlighten us on what you expect us to see. I can tell you when I removed one of the caps on a GMB or Delphi the top of the rubber gasket was wet (one side only). I believe this pump failed because the gasket didn't seal properly around the cap screw. One of the other pumps had a bad check valve and you could see the seal damage.

Today I rebuilt 3 Kyson Denki pumps using the Delphi/GMB internals. I used the original housing and swapped out all the rubber diaphragms. The check valves were removed, cleaned, and reinstalled. My o'rings were is great shape but I did install some Permatex fuel resistant gasket dressing to make sure there was a good seal. Next, I tested each pump manually by pumping fuel. Installed one and she runs great. I did notice while disassembling the Delphi/GMB pumps that the screws were a little loose which could be the reason some of them fail. I had another Delphi/GMB pump with a bad check valve. As mentioned, the Ampco and Atsugi have different internals and the top diaphragm holes do not line up.

I'm going to add the electric fuel pump soon.

I installed the check valve between the fuel filter and metal fuel rail to the SU carbs.

Clearly I'm not the only one having these issues. The only difference we are having is my car will start right away if fuel is in the float bowls. The problem for me is when the fuel drains back to the tank and my car burns all the fuel in the float bowls before fuel returns to the filter. I'm assuming by installing the check valve my fuel will always be in the filter and eliminate the air gap between tank and float bowls. Looking forward to a fun day of driving and not being towed.

Fuel check valve is installed. Going to drive Lori (my 240z) this weekend and report back. This is the valve I installed. https://www.amazon.com/gp/product/B07HNQVF5B/ref=ppx_yo_dt_b_asin_title_o02_s00?ie=UTF8&psc=1

Only if the car was parked for a little while. After restart she will run on the fuel that is in the carbs and filter until its dry.

I have not performed the specific test. However, I think it's clear the Delphi fuel pump is the issue. Maybe the non original pump design is actually a better design.

The car should run as long as there is fuel in the fuel bowls. Every time the filter runs out of fuel the car will keep running until the carbs are dry.

I removed the valve cover and manually operated the fuel pump arm and was able to pump fuel (full pump motion). Using pump action similar to the eccentric resulted in very little fuel movement. Sometimes after sitting the fuel in the filter would drain back toward the tank. The delay in filling up the fuel filter would cause the engine to starve for fuel (too much air in the system). We could have two issues here. The aftermarket pumps won't hold vacuum keeping the fuel in the filter and the eccentric needs more lift to pull fuel faster to the filter. A new eccentric with more lift may be a solution to compensate for pumps not meeting original manufacture specifications. The fuel check valve will fix the issue with the aftermarket pumps not holding vacuum. Looking forward to an update this weekend after the fuel check valve is installed.

When I purchased the car I replaced the fuel pump without the spacer. I didn't realize the spacer was still attached to the original pump that was covered in grease. The car ran fine for about a month. I thought the pump was damaged from leaving off the spacer. Ordered another Delphi pump with spacer and installed it. Drove it around the neighborhood for an hour until she left me stranded. Towed her home, ordered the GMB pump, and got her running again. I will give her a long test drive after the fuel check valve is installed between the filter and carb. In my opinion, the pump lever needs more lift. It's like pumping up a bike tire and not giving it a full up and down motion. Wish I had a Nikki pump as well so I can compare them.

Yes I tried installing the pump without the spacer. The pressure between the pump arm and eccentric was really tight.

Yes, I have tested the pump function. I really think installing an eccentric that has more lift would increase the pumping function. Does anyone make an eccentric with more lift?

I noticed online a factory electric pump upgrade kit to install the pump. It included the small wire harness you mention, pump and bracket, 2 relays, and harness A&B. I would prefer to use as much factory wiring and install the inertia switch near the console. Can you recommend a parts list?

I will update the group next weekend. Amazon Prime is not on the 2 day schedule.

I started my car with full choke as well. My float bowls should be fine but I'm going to get some clear fuel line to confirm. I just read your post and sent it to a friend that is having the same issue. We both have the same fuel pump (on our 3rd each). Went with the GMB to confirm if the Delphi pump is bad. Wish I had an original pump. I tried the vacuum on the previous pump don't remember the results. I'm hoping the fuel check valve will solve the issue.

Update on my mechanical fuel pump issues. I received a replacement pump (GMB brand from RockAuto) that is the same style as the Delphi. Installed the pump, cranked the engine for 10 mins plus until fuel filled the carb bowls. Once I had fuel in the carbs she ran really well. I let the car sit overnight and noticed the fuel in the filter had drained back to the tank. She fired up with ease but the fuel filter was slow to fill and the engine experienced hesitation. Today, I started the car on the first crank but there was no fuel in the filter. While running you could see the fuel begin to fill the filter but the pump could not keep up with the demand and she ran out of fuel. Is there a fuel pump eccentric with a larger lift (more than 7mm) that could increase the pump lever action (Manually you can pump plenty of fuel.)? My factory cam eccentric has been inspected and looks to be functioning as designed. I ordered a fuel check valve to install between the fuel pump and filter. I'm hoping this will keep the fuel filter full so the fuel is closer to the carbs and less work for the mechanical fuel pump.

Funny you mention adjusting the arm. I tried on one of the other two pumps and damaged the arm. The arm cracked. Probably needs heat but fuel residue and heat don't mix to well. I ordered the least expensive GMB pump just in case it's not the Delphi pump. Thank you Z friends for all the support. I will let you all know the results next weekend once I install the new pump.

Which pump would you purchase? I purchased my Delphi from RockAuto and they stopped selling it. Makes me wonder after installing 2 of them. The same pump was installed on a friends car and he is having similar issues.

It's possible my tank has debris. However, I can use a vacuum pump and suck fuel to the filter. I can remove the Delphi pump and hand pump fuel to the carbs as well.

I will try this as well. Though I don't think this is my issue. At least I will have my floats at the correct level. Thank you!

Today I drove the car around and stopped at 2 locations. Once I left the second stop the pump stopped pumping. I confirmed this by opening up the float bowls and cranking the engine with the fuel line to carb off. I could not get any fuel to squirt from the carb hose. The carbs were rebuilt and floats adjusted per the instructions. I adjusted the floats again just in case they were set too low. Also, I removed the pump and manually pumped fuel back to the carbs to see if she would start. She fired up and ran out of fuel 200' from my last stop. I don't think I'm having an ignition problem because she always has great spark. My impression is the fuel pump is not getting enough motion. I believe the pump should pump on a 7mm lift. I think it needs more lift to get a full pumping stroke. Time to add an electric fuel pump.

Pertronix and everything looks stock.