DivinDriver

iTrader: (15)

OK, so I get to the moment of joy, and twist the key to "ON" on my fresh rebuild today.

Pump starts mumbling as expected.

I hop out to check the bowl levels, just in time to see the last bubble of air at the top of the bowl window vanish.

Uh-oh. Key off!

Looking down the carb throats, both secondaries have 1/4" of gas sitting on top of the butterflies. The gas on the primaries is leaching down the idle open set, and also out the butterfly shafts onto the carb insulator.

Crap.

I realize that the most likely cause for this is stuck needles: they were installed fresh for the rebuild back around August/September, and the carb has been wrapped and shelved since then. I've read the archive threads and know that it's probable that tapping, or popping the bowl cover & fiddling with them, might get things moving.

But I have a question:

How much resistance should there be when blowing through the fuel return line?

I pulled the return line off the carb, and tried blowing through it. Air seems to go, but with quite a lot of resistance. I tee'ed a pressure guage to it, and I'm getting a back pressure reading of about 1.2PSI, regardless of whether the fuel cap is on or off. It takes quite a bit of lung to blow that hard - - even for a diver. Nice head-rush.

At the risk of jinxing my project, "How hard should it be?" Anyone else check their return line recently, and if so, how hard was it to blow through?

Tank's only got 2 gallons of fresh fuel in it. The check valve in the return line checked out fine, and is installed correctly.

I'd rather not have to pull the bowl cover if I can avoid it.

Experience/advice/suggestions?

DivinDriver

iTrader: (15)

Update:

I managed to get a service mirror in place to where I can check the rear float bowl level (difficult due to all the junk on the backside of a stock Nikki). The level back there looks damn near perfect. It doesn't appear to have drained down, so it appears that I indeed have a stuck front float or needle.

Still interested in the answer to the return-line back pressure question, though.

bad 83

iTrader: (3)

If you pulled the line right off the carb, there is an inline check valve on the return line going to the firewall. This will give resistance. I have never rebiult a Nikki, and not had to readjust the floats a little.

trochoid

iTrader: (6)

If the fuel level at the rear bowl is in the middle of the window, you're good for that needle and float. Bowls should never drain, but you can draw the rear one down by continually pressing the pedal with the engine off. That's where the accelerator pump draws from.

Tap on the front banjo bolt to loosen the front needle.

Megabridge

iTrader: (2)

Your needle and seat problem is just that. You need to pull it apart, make sure everything is alright. No magic there.
The return line is part of the same problem all of us 1st. gen guys face. Our fuel systems are getting older, and the supply and return lines are getting clogged. The thread on the first gens here has some great info: "GSL SE fuel system problem resolved". Basically the lines get clogged. The screen at the bottom of the tank gets rust and gunk on it and needs to be cleaned.
If I were you, having a brand new engine, I would take out the tank, clean the screen, supply and return lines. It doesn't make sense to put in a fresh motor, new oil, fuel filter,antifreeze and have a clogged fuel system. I want ALL of the power my engine makes! I know it's just one more pain, but the tanks really come out easily. and we all know that smile we get when our rotaries pull hard thru the gears.

DivinDriver

iTrader: (15)

I bit the bullet and pulled the air horn, & will pick up tomorrow AM. Didn't see anything obviously out of whack, but had the company Xmas party tonight, so haven't had time to actually measure anything.

Still, I wanna know, please: How hard should it be to blow through the line, if all is good?

I took the inline check valve out and re-tested; the required force to blow thru the line dropped by about a third. Blowing through the check valve by itself takes about o.3 or 0.4 PSI. It's still working right.

j9fd3s

iTrader: (3)

since the line is really long, and goes into the gas, its not easy. man i havent done that in a decade....

DivinDriver

iTrader: (15)

Got the air horn back on, after checking the float measurements and free travel (were fine). I even tested the needles by blowing into the fuel feed; they seal fine, and open fine.

Powered the car back up, switched to IGN... front bowl flooded again, dammit! Back bowl is just fine, fuel level right on the line.

This is making me nuts, and I sure don't want to pump even MORE unburned fuel into the engine.

A can't think of any other possibilites, though, beyond:

Sticking needle
Float getting hung up somehow
leaking past needle seat (checked that already)

I know the float is good; I tested them all (I have a couple sets) for flotation during my rebuild, by putting them in a glass jar of gas and observing them. All floating fine overnight.

What am I missing that could be forcing the front bowl to flood? There's really not that much to the inlet system.

Argh.

Hyper4mance2k

iTrader: (40)

the stock return line is only 1/4" so it has terrible flow and has alot of resistance.

DivinDriver

iTrader: (15)

I have the sneaking suspicion that I have a bum needle seat... trying to think of a good way to test it out of the carb. Tricky, as the buoyant force on the float is pretty tiny.

j9fd3s

iTrader: (3)

you tap the carb? sometimes it just sticks.

also a possibility is a sunk float

DivinDriver

iTrader: (15)

Floats were both tested before reassembly in September, and both floated well (used best 2 out of 6 I have; all were within 'spec' after 24 hours in fuel).

The flood takes place within 10 seconds of turning the key on with empty bowls - - if the float was so bad it sinks in that period of time, I've seen it when I tested. I will check again, though, in case something "happened " to it since the build.

I did do the tapping thing, before the second attempt. Didn't help.

I'm now deciding between just replacing the needle set with another new one, or swapping the front and rear needle sets and seeing if the problem follows or not. hell of it is that I have to tear down and re-assemble between each attempt.

I'm going to try filling the bowl in my spare carb body with gas (water wouldn't work; too dense) and lowering the air horn onto it on the bench, where I can actually see the floats operate (or not) through the windows. Then, I'll try feeding low-pres air (less than 4PSI) into the fuel feed, and see if it flows or not.

Worse comes to worst, I'll get a few extra feet of fuel line and bench-test the floats fed from the fuel pump.

When in doubt, test EVERYthing. There's really not that many things that can be wrong.