So I just purchased another 79 RX-7. The car was modified back in probably the early 80's with a Mikuni 44 and a full RB exhaust (Yes, the old school one). The car was running fine at idle and light throttle but when I tried high throttle and high RPM acceleration it just fell on it's face. I put on a fuel pressure gauge and it read 3psi. My understanding is that aftermarket carbs need around 4.5psi. I swapped in a new 6psi pump and added a fuel pressure regulator. I was seeing 4.5 to 5psi for a bit and then it just took a nosedive.

I noticed that the fuel still goes through the check valve after the pump. Can the check valve cause this? Should I bypass it or should I try to replace it?

Thanks for the help!

 

First off, some fuel pressure gauges read incorrectly once they get hot. I know mine does and its the typical Summit 0-15 liquid filled gauge. Also Dells/Weber/Nikkis all like about 3 psi, more than that and they will all act goofy.

I would try a quick test bypassing the check valve to see if it's the issue. Most folks do just bypass it.

 

The check valve you are talking g about is a roll over valve and will shut the fuel flow off if the car is upside down. I haven't seen one fail but I suppose it's possible. If you do bypass and it runs better then that's awesome. If not, when is the last time the carb was rebuilt? You may be seeing sediment from the float bowls coming up and partially clogging the jets. How old is the fuel filter?

 

Agree, check the obvious: fuel filter. These should be replaced yearly. Has the car been in extended storage? If so and old gas was left in the tank, untreated, and/or an air gap (tank partially full) would give corrosion (from the air in the tank) a place to start causing the inner surfaces to 'slough-off' into the fuel. This debris then drifts to the output line and plug it. or thru it into the filter. Been there.
A new filter should be checked for rapid debris collection from the tank. If this is the source, then the only remedy is drain, removal, clean out (rad shops will do this), then reseal the insides with a liner-kit like the one POR15.com sell for gas tanks.

Stu A
80GS
AZ

 

Thanks for the replies! The car has been sitting much of the last 25 years I suppose.
I will check the new filter for debris. Odds are that the tank as well as the carb need refurbished.
Definitely going to do a bypass test on that check/rollover valve since it is pretty easy.

 

There's no doubt that the tank and carburetor need refurbished if the car has been sitting for 25 years. I would go through the entire fuel system, to include testing the fuel pump and go from there.