Matt_79SA

Hey y'all, I got a strange one for ya.

So I've had my 1979 SA RX-7 for a couple of years now and aside from a few issues it has ran great until about a week ago. It was sitting idling for about 15-20 minutes on a warmer day after it was hot and when I started driving again it acted like it ran out of gas (could not accelerate, full throttle barely kept the current RPMS, just fell on its face). I pulled over let the fuel pump run for a few minutes and it started and kept dying after a few minutes. I changed the filter and it got better. and was acting normal. That was until I was in the middle of a 4 hour drive a few days ago and it started doing the same thing. I was able to accelerate for a few seconds, maybe 10-20 before it fell on its face and sputtered, I would then put it in neutral, coast for about 30 seconds and was able to accelerate for a few seconds more and kept repeating this until I made it home.

Since I got home I have changed the fuel filter, blown the lines, dropped and cleaned the tank. After that didn't fix the issue I changed the fuel pump, (EDELBROCK pump, 3-7 PSI 38 GPH), adjusted the float levels, tuned the carb, and the problem persists. I also checked the plugs and the lead plug was a little white but mostly black/brown and the trail was pretty white so I assumed they were functioning well.

When I checked the fuel pressure I simply blocked the line with a gauge and it read about 6 psi (With the new pump). I then ran a T-fitting to check it while running as well and it read at 2-3 PSI with only the key on, and when running it was very slowly creeping down. The volume test also seemed to be correct, but with where the fuel inlet line is I was unable to run the pump the full minute but after about 30 seconds it seemed to have roughly 0.7 Qts. in the container which was more than it would need if doubled for the full minute. I have been debating on changing back to the old pump that was on the car for about a year since the problem is the same and I know that pump worked well prior to this issue. I am simply stumped on what to try next.

The car has a few modifications, a full racing beat exhaust, and a rats nest delete. These are really the only things I have done to the car (aside from rebuilding the carb about a year ago) and as I said it was running fine for about a year with these mods. I have been thinking about getting a 4 PSI fuel regulator as I am not sure how these NIKKI carbs act when over pressured, if it is over pressured. Any and all advice to get this running right again would be incredible. I am nearly positive it is a fuel issue as I ASSUME it runs off the fuel in the bowls when I accelerate, and when I idle it is able to refill the bowls and the process repeats. Any ideas?

j9fd3s

iTrader: (3)

well if it passes the pressure and volume tests, you might look at the voltage at the pump, particularly when its acting up

Matt_79SA

I checked voltage at the pump like you suggested and it was getting 12 with just key on. I can’t really check it when it acts up as when I let it slow down and idle the problem goes away until I accelerate hard again for a few seconds. Getting some plugs to curb that possibility so I’ll update if that helps at all.

Never got the plugs, will have to order some. I only have until tomorrow to do work for the time being. So likely not going to find the issue soon.

midnight mechanic

The is a physical connection the the right side of the carb that increases fuel when accelerating.

Shelford141

I have twin SU carbs on my ‘85 FB, and I’ve got some trouble myself with them but i think mine go the other way, and i believe the problem is to do with the way the carbs work, might be worth doing a bit of research into how the carbs work - I know with SU’s there are 3 kind of levels with the fuel flow, where you have an ‘idle’ flow, then a ‘driving’ flow, and a ‘foot to the floor’ flow. Mine over fuels slightly when i have my foot to the floor, perhaps if NIKKI carbs work in a similar way you are under fuelling when accelerating.
I would also check your air intake situation to make sure theres nothing wrong, causing too much air in your air/fuel mix.

hope this helps or sparks an idea somewhere!

Shelford141

if you can get access to a rolling road, you might be able to simulate the problem and then test?