Steve Adleman

so, my 79 SA 12a is running, but I was trying to adjust the air adjust and mixture screws and they had virtually no effect unless i screwed them all the way in, then it would die, shut it off and looked in the carb and fuel was pouring in,looked like the bowls were empty, so tried tapping on the inlet bolts to free up the sticking floats, to no effect. I have another carb that I just rebuilt (the original that was on the engine) and it did the SAME THING! tapped on it again with hammer, no effect. so far I've cleaned and sealed the tank, new filter, new pump, blew all the lines out with air, new hoses, everything seems to be connected correctly, getting fuel to the carb, return, vent lines working. but these carbs are driving me NUTS! I'm surprised it runs at all, but it does start and run, but not well

Joekaistoe

You mentioned a new fuel pump. Is it an OEM replacement, or aftermarket? If it's aftermarket, do you have a fuel pressure regulator installed?

On the driver's side of the carberator is the float bowl vent solenoid. Is this clicking when you turn on the key? If it doesn't open it can cause flooding.

Steve Adleman

vent solenoid working/clicking I believe, there was a little thing that looks like a mini fuel filter that screws into the aftermarket pump, is that the regulator?, if not, are regulators available anywhere?

tommyeflight89

iTrader: (4)

Oh no!! Why an aftermarket fuel pump?

The OEM pump is available from any local Mazda dealer and will cost you about $90. Install that with a proper OEM fuel filter. There is no point to run anything other than OEM.
Part Number: 8871-13-400B They can probably get it in a few days.

Unless you convert the fuel system to a properly plumbed regulated return setup, aftermarket pumps will cause flooding, the Nikki will only work with a very low fuel pressure.

Steve Adleman

because 1. any mazda dealer is a 2 hour drive away, and 2. others here have said the pump I used should be okay. 3. because the dealer part is 2X+ the price

tommyeflight89

iTrader: (4)

Well you might save a few bucks finding an aftermarket pump, but now you most likely need a fuel pressure gauge and a regulator. Also depending on flow rate of the aftermarket pump, your OEM return line will prove to be too small, it is only 0.25" DIA, which will backpressure the return side too much and mean you will never be able to adjust your fuel pressure low enough. If this is the case, you will need to run all new larger dia return line. To me $90 - $120 bucks for a 100% drop in and run solution.. seems pretty reasonable.

A new OEM pump can be shipped from any vendor... Atkins Rotary... Mazdatrix... etc, and you can have confidence it will run for another 30 years.

I think step 1 is to get a fuel pressure measurement. The Nikki will need only about 2psi I believe?! Someone else will chime in with the real value. If you indeed have reasonable fuel pressure, then the problem could lie elsewhere. The fact that you are flooding on two different carbs means its probably fuel pressure.

Carl

iTrader: (2)

Yes. The fuel pressure for the NIkki should be 2-2.5psi. I use a Carter P4070 which can put out 4-8psi. I use a low pressure Holley pressure regulator and have no problem with the stock return line. The pressure regulator obviously needs to go upstream of the carb. I have never had issues with this setup after 10-15 years of racing. Not to say that it is the best, just that it works fine. I am sure there are other options, as long as you get the pressure correct at the carb.

I am not sure that any aftermarket carbs are going to be low enough pressure to provide only 2.5psi, so there is a very good chance, that is why you are flooding both carbs.

If both carbs have new float valves, that could be the problem too. I just went through that problem with two different carbs and only resolved it by putting in old float valves (that matched the floats, since there seem to be different options).

Carl

Toruki

These guys will ship it and the proce is as good as anywhere else at $93.

https://www.mazdabestpartsonline.com...uel-887113400b

I just got all of the coolant hoses for my 83 GSL and they arrived nicely packed and quick.

lwrobins

I don't know about Nikki's, but the stock fuel pump puts out about 6psi and there is a return line. So if your aftermarket pump is a low pressure pump it should work. On my Dellorto which likes low psi, I run a low pressure High volume pump with regulator/gauge and no return line. The fuel pressure and ignition timing are key to a proper tune.

t_g_farrell

iTrader: (1)

Nikki doesn't tolerate anything over 3 psi and does better with a return line. I use a Carter 4070 as well with a Holley low pressure regulator and the stock return line. Works for both my nikki and dellorto at the same settings, about 2.5 psi. Stock pump is around 3 psi and flows about 25 GPH, Carter is 4-8 psi and flows about 70 GPH which is needed for a modded nikki or large weber/dell. If you used new needle and seats swap back in the old ones. Verify your pressure and flow and you should be good.

Joekaistoe

Not to sound like a broken record, but it sounds like you need to install a fuel pressure regulator before your carberator. I use the Holley 1-4 psi returnless regulator with the stock return line still hooked up. You'll likely also need a low pressure fuel gauge in order to set the pressure. I set mine to around 2.5-3 psi.

The factory setup is designed to reduce the pressure to the carb using the return line. Unfortunately, this only works if the fuel pump flow is within factory specs. With an aftermarket fuel pump, the flow is significantly higher which overwhelms the return line and keeps the pressure from being reduced, causing the carberator to flood. This is why a regulator is needed with an aftermarket pump.

Steve Adleman

Thanks everyone, the fuel pressure regulator worked. I still needed to swap carbs again, but it now runs pretty good. years ago a shop installed an aftermarket pump on my '84 gsl and it worked fine, I guess that's why I thought it would be okay. I found a regulator locally so I went with that, next time I'll probably get an OEM pump. it now idles at about 1000 rpm, smells like it's running a bit rich, but it runs good. I just wish I would've known about this 6 months ago, it would've saved me a lot of time, money and frustration. maybe there should a sticky about aftermarket parts that don't work?

KansasCityREPU

iTrader: (9)

I don't think there is a sticky, but I do know that the fuel pressure information is in the Mazda documentation here.

3.70 ~ 4.70 lbs/in2

http://www.foxed.ca/rx7manual/manual...CAL%20DATA.pdf

Steve Adleman

yeah I knew about the fuel pressure specs six months ago, but I assumed that parts houses would be marketing parts that matched factory specs and tolerances, and not selling stuff that didn't work out of the box, I Thought that the little filter that attaches to the pump was the regulator that made the generic pump give the correct pressure.

tommyeflight89

iTrader: (4)

Glad its running better!!

Yes it seems like such a common problem when someone is overhauling the fuel system on these cars. Usually a few things get reported that are easily avoided:

-Not biting the bullet to drop the tank and pay several hundred dollars to have it professionally dipped and sealed... then dealing with endless filter/pump/debris problems.

-Ending up installing an aftermarket pump. I think the old carb'd American car market is why there are so many universal pumps available out there for cheap and seem so tempting. They will work great to replace the mechanical pump in an old Chevelle, but not so much for our cars. I think the American carbs can all tolerate alot more fuel pressure than the Nikki.


A lot of people don't realize that Mazda still makes plenty of OEM parts for these cars that are readily available and well priced for what you are getting.