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Sorry in advance for making yet another one of these threads - but, I've searched, and I'm convinced I'm missing something.
Been batting flooding issues with my Nikki carb since I got the car. I did a full rebuild (even used the new needles and seats) and got the floats adjusted properly. Started to encounter a recurring issue where after I'd drive the car, restarting it would result in the motor sputtering and running rough for the first 20-30 seconds before it cleared up. Checked the floats and discovered it was flooding again. Thought it might be a fuel pressure issue due to an unknown fuel pump, so I installed a fuel pressure regulator set to ~2.5 psi (verified w/ gauge). Still flooding. Starting searching old threads at this point and put the old needles and seats back in after reading about how the new ones can be problematic. With the new needles and seats in, when I turn the airhorn upside down and blow into the supply while plugging the return with my finger, no air escapes through the needles. Still flooding. I can feel and hear the float bowl vent solenoid clicking with the ignition on. Just to be extra sure, with the airhorn removed I put +12v directlyto the solenoid and verified operation (see attached photo).
So... fuel pressure isn't excessive. I'm pretty sure floats are adjusted correctly to the 16mm +/- 0.5mm specified in the manual (see attached photo). Vent solenoid is functioning properly. What am I missing? At this point I'm wondering if it's a fuel tank issue. I'd fixed the incorrectly routed lines from the previous owner (see my last thread) but now I'm wondering if I did something wrong there. I removed and cleaned the return line check valve and verified proper orientation (allows flow back to tank). When I blow into the return line with a handheld compressor, I get 0 psi backpressure with the gas cap open. With the cap shut, backpressure rises to about 3.5-4 psi until fuel starts pouring out of the supply line. Does this sound right? My understanding of the fuel vapor valve is that it's checked such that it'll let air in to compensate for the loss in volume as fuel is pumped, but won't let fumes back out? Is the tank supposed to be venting excess pressure and can't? Once the float bowls are full, it makes sense to me that the fuel would just circulate in a loop, but heat expansion has me wondering if this is my issue... it also takes me back to the hot restart flooding issue mentioned above.
Have I missed something obvious or should I drop the gas tank again? For context, I have the '79 with the four tank connections.
Is your fuel pressure regulator adjustable? If so, try setting it even lower. After months of truly frustrating Nikki flooding issues, that was the fix for my flooding. And has now run many months with no carb issues. I get my car back from painter later this week and will confirm psi but memory says 1.5 psi. Only other difference was I wedged the vent solenoid open with a washer, but have not removed the washer as I dare not touch the carb now it’s working so well!
Adjusting the FPR down made some progress, now it's just flooding one of the bowls. I've tried swapping needles between seats and swapping between the old and new needles/seats but it appears to be random which of the two decides to flood each time I put the air horn back on to test it again.
I'm starting to think I've messed something up during the carb rebuild, unless the float adjustments are really this finicky... any obvious things I should check?
Someone with more carb experience please let us know if I am in the wrong track here.
From what I experienced and researched when I had flooding issues, float bowl level is not effected by anything else but the needles/seats and the floats that activate them. I don’t believe fuel overfilling the bowls can be caused by anything else you did inside the carb. It’s like the tank on your toilet, it doesn’t care what toilet cleaner you used or even what you try to flush down the toilet….when set correctly the toilet tank just fills until the float mechanically closes the valve.
To prove/test this… empty the bowls by turning off the fuel pump (pull the fuse) and running the engine until it dies. Then turn the fuel pump on and watch the fuel levels through the windows. If one of the windows shows fuel is filling past the window, give the top of the banjo bolt where the fuel enters that particular bowl a sharp thwack with the handle of a screwdriver and see if it causes the fuel to stop flowing. This would prove the needle was stuck, and was freed up by the vibration of the screwdriver thwack.
Let me know what happens. Really want to help if I can. I suffered through the same thing and I darn near ended up selling the car!
And a couple of ideas that helped me run repeated tests on the carb needles and floats:
- Pull the fuel pump fuse and replace it with two wires with male spade connectors. Run the two wires to somewhere near the carb and wire a simple on/off switch. That way you can turn the pump on and off easily whilst actually looking at the carb. Eg if a needle sticks and a bowl starts flooding you can turn off the fuel before it overflows.
- Remove the top half of the carb, but leave fuel lines etc connected. Then slide a plastic storage box or dishwashing bowl under the removed carb. That way if you test a needle and end up flooding the gasoline is not ending up in your engine and removing all the oil from around the seals making for a difficult restart. Also makes it sooooo much easier to see in the bowl windows. That rear bowl window is pretty much impossible to see when the carb is in place. Stole that idea from another member here, and really helped
And in the window thing…. If simply trying to see if the needle has done its work and stopped fuel flow into the bowl, just listen! I could hear when fuel was flowing, and hear it slow down (or not) as the float rose and closed the valve. Back to the toilet analogy…. Like listening to the toilet tank refill so you know it’s full before you try that second flush!
Appeciate all the advice so far! Confirming that it's almost certainly a needle/seat issue does help, because it confirms my prevous statement that apparently the floats really are that finicky. I saw a tip on here to burnish the corners of the needle with the back of a spoon, I'll give that another shot and see if maybe the floats themselves are sitting slightly crooked and hanging up somehow. I'll give that tapping the banjo bolt trick a shot too.
Love the idea to adapt a remote fuel pump kill switch, I might use this idea so I don't have to run back and forth when the wife isn't available to assist lol. At this point I think the engine is already flooded, so I'll sort that once this float issue is sorted. Will try again tomorrow and report back!
For burnishing I used qtips cut in half then inserted in a drill. Dip the qtip in brass polish, turn on the drill and use it to burnish needles and seat. I then assembled the floats and needles and jiggled them up and down for ten minutes each hoping that would help bed them in! Don’t know if this actually fixed my problem, as did it at the same time as fuel pressure regulator, but I was getting pretty desperate.
For anyone else reading who's having a similar issue post carb rebuild, here's another vote for "don't use the new needles and seats." Slow_sevens, I admire you went through the work to get your replacement needles working properly. I kept polishing/burnishing/working the needles and wasn't making much progress, then had the lightbulb moment that I hadn't checked the performance of the original needles/seats since turning down the fuel pressure. Swapped in the original stuff and the float bowls filled perfectly the first time and stayed there. So in the end it was a multi-part issue of a) too high fuel pressure and b) crappy replacement needles.
Still having the sputtering issue on hot restart I mentioned in the original post, although not quite as severe. Looks like flooding wasn't the issue there, now I'm thinking ignition or maybe a vacuum leak that's only appearing when hot? I'm planning on upgrading from the points ignition to an '81-'85 anyway so I'll probably get started on that.
Excellent! Glad it’s fixed. I didn’t have the option of reusing the originals. I carefully saved them in a plastic box, which I then dropped and scattered the original needles to somewhere I could never find them. Ironically months later I was working under the car in the driveway and noticed something shiny on the ground. Sure enough…. Original needle.
I had the same issue. What fixed it was used floats from unmolested carb. Adjusting for the new **** needle and seat jacks up the float. Couldn't get it adjusted right. Atkins sells a good float valve from what I hear.
06-17-23, 01:40 PM
