rotary_fan

Hello,

Ive tried to search for the answers and watch some YouTube videos about the Nikki but I need some pointers please.

I’ve removed the air horn on this 12a nikki, removed all air bleeds jets etc. They all flow well and I can see daylight, hit them with carb cleaner etc. The auto choke works well and turns off after it’s warmed up. But the car doesn’t run smooth and seems to idle rough. I noticed if I point a laser thermometer at the header the front rotor seems much cooler than the rear one, like say 200 degrees difference. I then noticed when looking down at the carb, the front rotors primary, I don’t see an obvious flow of fuel from that Venturi. Mean while the rear rotor primary Venturi has good flow. The AP circuit seems ok, if I tap the throttle, fuel squirts out of both sides from the Ap squirter. Float bowls seem normal I have fuel in both and can see the front level is near the top of the window.

So with that said, I’ve tried 2 more times to clean the jets etc but end up with the same result. It’s almost like the front float bowl circuit that feeds the front primary Venturi is perhaps dirty. Even though when I hit that jet with carb cleaner, I see the carb cleaner shoot out the front rotor primary Venturi port. I also see the same carb cleaner shoot out of the bottom of the float bowl making me think it’s clean.

The only other thought I have, is can I take the air horn back off. Remove the jet that goes to the front rotors primary Venturi, and see if that Venturi can be removed for closer inspection cleaning? Hope that made some sense, it’s hard to visualize what I’m explaining. Any other suggestions are welcome!

rotary_fan

For reference, at the blue circle I don’t see fuel coming out when car is idling. How ever on the rear rotor primary I see it drizzling out. Is it possible to remove the red section by removing that jet, so I can clean it and inspect it more closely? I’m not sure what else would limit fuel flow at the blue section.

Benjamin4456

So funny enough, you have the opposite problem that you think you do. There in fact should be no visible fuel dribbling from the booster venturi at idle, and that's what is causing your rough running. The boosters shouldn't come online until around 2k rpm on a stock carb. This all means that the carb is flooding on the front circuit, which is also why it's running so much cooler than the rear.

The process now is to inspect the floats, needles, and seats to make sure they're all in working order. Something on the front float isn't sealing and is causing the bowl to overfill.

Edit: I believe I may have flipped front for rear, but regardless, whichever is leaking fuel at idle shouldn't be and the float assembly for that side needs to be inspected and/or cleaned.

rotary_fan

Interesting, I wasn’t expecting that ha. This is my first carb rodeo so lots to learn.

So follow up question. The floats and needles. I didn’t remove the needle “mount” but I did remove what I assume is the needles and cleaned them. Meaning under the float, it’s tabs press against the brass I think needle and on the end of this piece it has a rubber arrow point that stops fuel when pressed into the seat. I tested that fuel can’t flow into the bowl when the float is “full” or in the up position. And also tested the opposite to ensure fuel comes into the float bowl when the float is down or low. But now I’m trying to understand what let’s the fuel come through the jets at the bottom of the float bowl up into the Venturi. Assuming it’s some how related to vacuum? Like what makes it allow more fuel through at 2k vs idle just Venturi effect related to the engine vacuum? Just wanting to understand this more, as it sounds like that area is where my issue would be.

Slow_sevens

Quick way to test if the floats/needles are the issue.
Remove the fuel pump fuse. (Vertical fuse top right on my panel).
Start the engine and run it until it dies and the carb bowls are thus empty. Turn off the ignition and put the fuel pump fuse back in.
Get a flashlight and a dental mirror (for the rear bowl window, it’s a pain to see). Watch the bowl windows and have someone turn the ignition to the point where the fuel pump comes on (you can hear it hum) but starter is not engaged.
The fuel level should rise to the middle of the window of both bowls then stop rising. If you listen carefully you can hear the noise of fuel passing the needle change and go quiet as the needle closes.
If the fuel continues past the middle of the window, watch the venturis and if you see trickling fuel then floats / needles are the issue.

Let me know if you don’t have an assistant to turn the ignition key… I have a trick for loaners like us who work alone.

First rule of carb club. Do NOT discard or lose the original needles.

rotary_fan

I like it! So mine is an 85, I’ve noticed the fuel pump doesn’t seem to turn on unless the key is in the start position basically with the engine rotating. I’ll double check that today but if that is the case maybe I can power it up manually some how. Thanks all for the assist! Luckily I have a helper to lend me a hand so I can see into the carb while attempting this.

More to come

rotary_fan

Got a late start today with my testing and tshooting.

But I was able to empty the bowls, then fuel pump filled bith sides at the very top of the glass in both windows. I’m not sure I was able to hear the needle noise. Once it reached the top of the viewing windows I did not see any fuel come from the booster on either primary. I’m assuming it should be lower since you mentioned they should be half way in the view windows.

Im going to hit up the fsm and that carb manual on foxed to see if I can spot something.

Ive found a great thread here with some info I’ll run through: https://www.rx7club.com/1st-generati...-alone-206255/

Slow_sevens

Yes the FSM manual has heights to set the floats in their up and down positions. Measure with the horn gasket in place. With the floats set to the correct heights fuel should fill to the middle of the window. Let us know what you find.

rotary_fan

Today I was able to mess with this thing some. I adjusted the float drop and confirmed the float level was good. I now have fuel in the middle of both sight glasses. However now I’m unsure if the boost Venturi is drizzling or not after that because it won’t idle on its own long enough for me to check. If I run the choke it’s fine for maybe 30 seconds and then does a surge in rpms and will then just die. If I keep my foot on the throttle with the choke off I can keep it running at about 2k.

Some back story,I bought this off a member and was told it’s been sitting since 2015. I was told he put in a new fuel pump(looked new to me) at that time. Ive taken care of a few trouble spots. Tank was rusted, dropped it cleaned it, new fuel filter, all new return and feed lines.

It doesn’t help I’m a carb noob but I’m trying things. I’ve checked compression(rotary compression tool) 2 different times now and getting 115-120ish all around.
It does have an FC coil for the leading and an aftermarket trailing coil in the factory location.

I probably won’t get much time to work on it until later in the week. Any ideas? Thanks in advance!

Slow_sevens

Do you know what psi that previous owner installed fuel pump is putting out? Needs to be surprisingly low… check the number in the FSM but if memory serves its somewhere in the 2.5 - 3 psi range.
Logically is should not be the fuel pump as if pump was flooding the carb you would not be able to start the car at all without deflooding…. (And previously your car ran well with same pump?). However the cure that worked for my carb issues was installing a fuel pressure regulator. It was a final mad nonsensical desperate move but it worked, so would be good for your diagnostics to rule out high fuel pressure. Maybe see if you can see any stickers or numbers on the pump and Google the specs?

And another quick check… after the car runs for 30 seconds and dies, is the fuel
level in the bowls still at middle of window? If so…. Then fuel pump is not issue.

rotary_fan

I ordered an inline fuel pressure gauge but it’s not going to be here until Sunday. But I might not need it as I noticed the bowls will run dry when the car is started after about 20 seconds. I then noticed the fuel pump strangely does not run once the car starts. It runs at the on position and I thought used to only run when it was starting (it’s an 85).
Anyway, I jumpered the pump relay or whatever it is under the dash and it now runs while the car is running. So that’s something I need to tshoot next, replace the relay or could just be a bad ground etc.

On maybe a related note….although I’m not sure. On the passenger side that ecu box in the floor board. The cover was rusted about half way up and the cover mounts that attach to the floor board were barely hanging on. Not sure yet what all that box controls but that could cause me some issues perhaps.

Back to the carb primary boosters, now that the car runs I could lay eyes on the boosters at idle. Strangely I still have some splatter or dribbling of the rear booster at idle but even so the car doesn’t seem to run that bad.

So I’ll track down that relay situation and atleast now I know the dribble of the fuel at idle out of any booster isn’t normal.

More to come.

Slow_sevens

I used to run a high end mountain bike shop. My chief mechanic would say that the path to diagnosing a problem involves working out what the problem isn’t as much as what the problem is.

mwpayne

One thing I ran into, car would start, flood, die.
Finally found the return tube to fuel tank clogged. Weird one but it had me stumped and pulling carb apart several times.

rotary_fan

Oh wow, that one would be tricky. It gets to be a pain after while but the joy of figuring it out or fixing it is certainly rewarding and keeps one motivated to keep working on it.