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Hello everyone, I have a 1985 Mazda rx7 12a engine. This car has been sitting for 2 years and I got the carburetor from a different car. I was missing the fuel pump and replaced it with an aftermarket one. When I turn on the car to the on position the fuel pump kicks in and when you look into the carburetor fuel is leaking out. I was wondering if the fuel pump is too powerful and pushing past the floats or the float is bad and it needs rebuild, or etc… When I start the car it runs for about 5 seconds and then dies. Video is attached of the fuel leaking. Any help or advice would be much appreciated.
bowls are overfilling. needles probably sticking. try lightly tapping on the top of the bowls on each side. may end up having to pull the top of the carb off.
I battled the same thing for months, so hopefully can be of some help. First question….Do you know what PSI the after market fuel pump is putting out? Hopefully you can work out what the pump is and research it’s PSI. If more than 3 or 4 PSI then you will need to replace the pump or install a fuel pressure regulator. Let me know what you find out about the pump.
Running an aftermarket fuel pump, you may find that it may require an adjustable fuel pressure regulator. Too much fuel pressure is not good. On top of that, you may have to rebuild the carburetor that you installed. The floats may be sticking down and gas may just be filling the float bowls.
The fuel pump rates for 4-8psi. Would you guys recommend I buy a correct fuel pump instead of this cheap one or a pump regulator. The floats are also not sticking.
I would recommend buying the correct pump. If you bring the car back to its original state, it will be far easier to diagnose running issues and correct them. Right now you could just be chasing your tail. Once the running issues are sorted out, you can modify or add what you wish.
I do however recommend rebuilding the carburetor if it's been sitting for some time and figuring out why the fuel pump relay has been bypassed. The fuel pump should only turn on when the engine is cranking.
Agree with Mazdaverx713. Replace the pump and see what happens. Quick search shows available on Atkins for $125. That's about the same as what I spent on a fuel pressure regulator and a couple of bits to attach it with... but replacing the pump itself removes a variable and will make the future diagnostic work required on the carb much easier to work through.
Once the pump is replaced, let us know what happens. If you still have flooding DO post an update. I learned a whole bunch of stuff the hard way when I had flooding issues just like yours, and can hopefully help you avoid some of the mistakes I made and get you driving sooner. Working on a driveable car is sooooo much more rewarding.
One preemptive piece of advice ('cause it cant be reversed).... if you start digging into the carb be SURE to keep the needles and seats that are in there. Dont drop one like I did, never to be found again. Hopefully the needles and seats are original, and if so should be re-used. From what I experienced and learned on this website all the replacements available to purchase now are likely to stick and flood.
Forgot a detail for testing the new pump. Each time the engine floods, you will need to pull the plugs and deflood / dry the plugs before you test if the car starts. Not hard, but gets old once you are on to the 12th or 13th time, especially if you leave one of the spark plugs too close to the open spark plug hole and set fire to your car like I did.
A workaround is to run a couple of cables to the fuel pump fuse socket under the dash (On my 81 12a, its the top right vertical one) and wire a simple on/off switch to the other end that you can operate whilst watching the carb. (You can even just touch bare wire ends together if feeling really lazy). Turn the key to ON, exit the car and stand over the carb so you can see whats happening, then turn on the pump using your home made switch. Then, as soon as you see evidence of fuel flooding the carb, turn the switch off. I found that doing it that way limited the amount of fuel getting into the engine and I did not have to deflood to start. If I tried it without the switch, and instead turned the pump on the regular way when sitting in the drivers seat, by the time I had run around the car to the carb, then run back again to turn it off I had enough fuel flooding the engine to require a deflood.
On my car the fuel pump turns on when the key is in the ON position, one notch before the key position where the engine cranks. Sounds like Mazdaverx713 has a different set up where his pump only turns on when engine is cranked. Maybe a generational change in the ignition switch setup? Just wanted to eliminate one other variable!
I believe it was 1984 and up that used the fuel pump relay to activate the pump when cranking the engine. My 1980 RX-7's fuel pump runs as soon as the key is switched to the on position. Again, I think it was this way up until 84...maybe late 83..but certainly in 1984.
I actually found a regulator laying around so I just put that in to see if it would solve the problem. It did solve the problem and it’s filling the bowls but not forcing it out. I took out the plugs and let them dry and tried to start it but it would start and die. I also check the plugs and it sparks so it’s not a electrical issue and it starts on starting fluid but does not stay running. Any ideas what it could be? Also I am not a huge fan of where my battery ground is located, where is everyone else putting there’s?
When you say bowls are filling, I assume filling to the notch half way up the window on both bowls, and not filling to the top of the bowls?
Did you blow the excess fuel out of the housing before trying to start? You prob already know this, but to do this remove all the spark plugs, and remove the fuse that feeds the fuel pump (on mine, the vertical fuse top right in the fuse box). Then crank the engine for a few seconds which will blow any fuel pooled in the housing out the spark plug holes. Be SURE to drape the spark plug wires well away from the spark plug holes... I managed to set fire to my car when I left one of the wires too near the spark plug hole. Before you put the spark plugs back in (or better, new plugs) dribble a couple of teaspoons of engine oil in both housings through the spark plug holes. I used a length of plastic hose that I could crimp, filled hose with oil, then guided it into the spark plug hole and released the crimp. Once done, turn the engine a few times using the bolt on the front of the main pulley to spread the oil around the seals.
If both the above are good, next steps check compression and timing. I would do compression first as easier. Do you have a regular compression tester or access to one? They are pretty cheap. Get hold of one, remove the none-return valve. Attach it to front housing and crank the engine whilst recording the dial of the pressure tester with your phone. Repeat on rear housing. The dial should pulse over 100psi, at even intervals, and each pulse should be the same PSI.
Let me know how the compression looks, and then we can move on to timing. Others may chime in, I am a rank amateur but went through your exact issues very frustrating issues.... and my car now runs lovely!
Here’s an update. The bowls are filling halfway through the lookout glass. It can start with starting fluid and the choke all the way pulled but then dies. I can pump some glass in with the accelerator but then also starts and dies. When it starts it will go up to 5k rpm’s right away. I took apart the carburetor cleaned out all the Jets and passageways and still won’t start. Any help is much appreciated.
This totally depends on the carburetor type. You need to bring a mechanic who knows how to fix it properly so that it wont be a problem for next time. You can even call for company service and book a appointment to repair you car is also helpful. But dont leave it like that only it might be very dangerous.
09-19-22, 11:34 AM
