85 Nikki Carb Flooding - RX7Club.com - Mazda RX7 Forum

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85 Nikki Carb Flooding

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Old 09-12-17, 04:49 PM
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85 Nikki Carb Flooding

Rebuilt and stripped (still has vacuum secondaries) 85 Nikki carb.

Floods when fuel pump is running (most of the time it floods). I have the air vent solenoid POWERED and it still seems to flood.

I took the air horn/top of carb off (with floats in tact) and flipped it upside down. I plugged the outlet/return and blew into the fuel supply side. I hear NO air escaping either needle/seat, and both seats/needles flow air when the float is lifted off the needle.

I am hoping there could be another cause of this issue, like a poorly routed line, either vacuum or fuel. Currently running about 3.1 psi fuel supply.

Thanks guys
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Old 09-12-17, 05:06 PM
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Is the fuel level high on the sight glasses? Did you change out the seats with those in the rebuild kit, or leave the stock ones in?

I've heard there is a problem with the seats in rebuild kits that make them prone to poor sealing. If you still have the factory seats, you might want to swap them back in. You might not be able to tell by blowing into the supply by mouth, as you won't be able to blow at a high enough pressure.

If the needles aren't seating, you can try whacking the top of the fuel banjo bolts with the handle of a screwdriver to get them to seat.

Things to check:

Is your return line check valve oriented properly?
Does the vent solenoid move when you power it?
Can you see fuel coming out of any place other than the boosters? (if the weights and check ***** in the accelerator pump aren't put in right, gas can syphon out of there)

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Old 09-12-17, 06:58 PM
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Originally Posted by Joekaistoe View Post
Is the fuel level high on the sight glasses? Did you change out the seats with those in the rebuild kit, or leave the stock ones in?

I've heard there is a problem with the seats in rebuild kits that make them prone to poor sealing. If you still have the factory seats, you might want to swap them back in. You might not be able to tell by blowing into the supply by mouth, as you won't be able to blow at a high enough pressure.

If the needles aren't seating, you can try whacking the top of the fuel banjo bolts with the handle of a screwdriver to get them to seat.

Things to check:

Is your return line check valve oriented properly?
Does the vent solenoid move when you power it?
Can you see fuel coming out of any place other than the boosters? (if the weights and check ***** in the accelerator pump aren't put in right, gas can syphon out of there)

​​​​
So i have opened up a nikki before, but this one was "as is." I am pretty sure that the seats are aftermarket rebuild kit quality. Also, I have not touched the return line check valave and am not too familiar, is it easily pointed out?

The vent solenoid DOES work when powered.

Also, I could investigate the accel pump for missing weights and check *****. Is the best bet to refer to an assembly drawing to see if they are where they need to be, or are installed at all?

Thank you guys.
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Old 09-12-17, 07:17 PM
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If this is same car RB Holley was on,fuel pressure that was ok for Holley more than twice what Nikki is comfortable with and likely pushing fuel right past needles and seats. IMO most likely reason carb is flooding without engine even running. This COULD happen even with good oe needle/seats with proper float level adjustment, aftermarket needle/seats more prone to this,but can be burnished to minimize this condition. As mentioned previously you'll want to make sure your fuel return line is unobstructed.
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Old 09-12-17, 07:24 PM
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Originally Posted by GSLSEforme View Post
If this is same car RB Holley was on,fuel pressure that was ok for Holley more than twice what Nikki is comfortable with and likely pushing fuel right past needles and seats. IMO most likely reason carb is flooding without engine even running. This COULD happen even with good oe needle/seats with proper float level adjustment, aftermarket needle/seats more prone to this,but can be burnished to minimize this condition. As mentioned previously you'll want to make sure your fuel return line is unobstructed.
Running 3.1psi or so, my understanding is that is not too much pressure. Also, the stock needles and seats on this nikki are long gone so I know that aftermarket are installed. How does one burnish the needles?
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Old 09-12-17, 09:21 PM
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2-2.5psi max is what you'll want to be feeding a Nikki. Try to adjust your fuel pressure to that.Where is the float level in the windows-while its flooding? Burnishing the needle-if that is determined to be the problem(needle sticking in the seat or being held slightly off(center) the seat is done by rubbing the side(corners of needle that slide in seat assembly) on backside of a spoon taking off the sharp edges from poor/unfinished machining of needle until needle slides in easily without binding or hanging up.
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Old 09-12-17, 09:24 PM
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Needle/seat issue and nikki likes less than 3.0 psi.
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Old 09-12-17, 10:01 PM
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I will set the pressure to 2psi, and try to smooth out the needles. Thank you guys for your continued help!
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Old 09-12-17, 11:30 PM
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Do you have a spoon? You can burnish the sharp edges of new needles on a spoon. But only if you still have OEM seats for them to go in. The aftermarket seats are garbage.
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Old 09-14-17, 11:31 AM
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Does anyone know where I can get OEM seats or needles for these nikki's? Other than a used Nikki of course....

Right now I just have new (aftermarket) needles and seats.

Also, where do you guys run the float bowl vent port to? (with rat's nest removed).
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Old 09-14-17, 01:01 PM
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Maxfatrix. They are not cheap.
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Old 09-14-17, 06:10 PM
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It looks like the sell the "float needle", which appears to be the seat as well. Throttle, Carb and Choke Parts
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Old 09-14-17, 07:10 PM
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I know this will sound crazy, but when I purchased my 1979 I had a flooding issue. It turned out that the floats were on the wrong/opposite sides of the carb. Nuts, I know.

There is a C shaped indent on each float. The indent is shaped so the two jets at the bottom of the bowls don't hit the float.

Make sure that C shape indent is facing the inside of the carb on each float.
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Old 09-18-17, 09:55 PM
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Update: ~2.3 psi fuel pressure, piston from air vent for float bowls removed.

Secondary butterflies are SLOWLY being covered in fuel while primaries are not. This was with power on but not running. Floats are set perfectly, and the aftermarket needles and seats are as matched as possible at this point. Thoughts?
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Old 09-18-17, 10:01 PM
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I see you said floats are set perfectly,so fuel level is exactly 1/2 way in (both)bowl window(s)? Was it flooding from secondaries previously,what did you do with needles/seats?
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Old 09-19-17, 08:37 PM
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Did you check to make sure your fuel return line and check valve are not clogged? If the fuel has no path to return to the tank when the floats are up, it will flood the carb.
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Old 09-19-17, 08:56 PM
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Originally Posted by dankekong View Post
It looks like the sell the "float needle", which appears to be the seat as well. Throttle, Carb and Choke Parts
My carb had aftermarket needle & seats in it and they were junk. The car was, as you said, flooding horribly when the fuel pump is running. The Mazdatrix ones sorted it right out. Very expensive.
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Old 09-20-17, 10:01 AM
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Return line functional, not clogged. Also, the front float/needle and seat assembly seems to be causing issues. The window is pretty full of fuel where the rear window is at half. I am going to buy a set of needles and seats from mazdatrix for the carb and install. They seem expensive, but I look at it as about 42 dollars for a fuel injector which isn't bad!

I will post updates when applicable, thanks for all the input/feedback guys.
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Old 09-20-17, 10:24 AM
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Hopefully the needles and seats fix your problems, through I've used the aftermarket seats and needles during Nikki carb rebuilds with no ill problems. Luck of the draw I guess.

I'm not sure if you verified this already, but make sure the float doesn't have a hole or crack in it. An easy way to tell is to take it out after it's been submeged in fuel and shake it. You can also submerge it in a bowl of water and see if it fills up.

And double and triple check the float adjustment with the FSM. I know people say don't touch it, but a pervious owner might have messed it up.

Good luck and keep us updated!
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Old 09-20-17, 08:45 PM
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Originally Posted by dankekong View Post
I am going to buy a set of needles and seats from mazdatrix for the carb and install. They seem expensive, but I look at it as about 42 dollars for a fuel injector which isn't bad!.
Just know that they don't come as a set for $42. You need to buy 2 of those. I can't tell if that's what you meant or not. Just a head-up, though.
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