SU's suddenly running rich

[Captain Obvious]

It sounds to me that you're thinking the needles cause the fuel level to rise when they are inserted into the nozzle? If that's the case, you have to remember that unless you pulled the needles out first with the fuel pump still running, the fuel level was established with the needles submerged. That means the fuel level will go down a tiny bit when the needles are pulled out and then return to "normal" when they are reinserted.

And the amount of that change (either up or down) is only by the volume of fuel displaced by the portion of the needle that is submerged and that volume is very small. The needles are not splashing fuel up into the venturis when the pistons drop. If you've got fuel puddling in the carb throat, it's not because the needles splashed it there or caused the bowls to overflow because the volume of a submerged needle raised the bowl level.

That said, how are you regulating fuel pressure and what does that fuel pressure do when the engine is shut off? I'm wondering if the pressure goes up higher than intended when the engine is shut off and the fuel in the rail expands from heat soak. Are you sure that you're never exceeding 3 psi at any time? Ever?

Also, when you found fuel puddled in the venturis, how long had the car been shut off? I know you said you ran the pump with the pistons out and the level didn't change, but if you're looking for a slow leak and the car sat overnight? You could have a small seep around or through the needle valves that you don't see with the naked eye, but over a 12 hour sit maybe it adds up?

And about the poor fuel mileage and only getting 115 miles to a tank... Are you sure your needle and nozzles are in good shape? If they had been rubbing in the past or if material has left through corrosion, that will throw everything off. It doesn't take a lot of material removal to have a big impact. If you ovaled your nozzles and/or grooved your needles, then you could be sucking down way more fuel than intended even if the bowl level is correct.

Bottom line? My suggestions:

1) Check and set your bowl levels with a clear tube on the bowl outlet.

2) Put a fuel pressure gauge on the rail and make sure the pressures are what you expect at ALL times.

3) Inspect your needles and nozzles very closely for wear or corrosion.

[metalmonkey47]

Well to a degree I'm sure it displaces a little fuel in the nozzle, maybe not as much as I think. Probably not my issue now that I think about it.

My pump is installed at the fuel rail level with the pick up tube in the tank, and I have a regulator installed post filter set to 3 PSI. I have no gauge installed to verify at the moment, but I guess I'll have to put one in tomorrow. I happen to have one laying around if I can find it. I have no idea what the fuel pressure does when the engine is off, but I'm sure it's not dropping off. Now that I think about it, I've had a few times where I've pulled the float bowl cover and has fuel spurt from the needle and seat.

The only time I've looked was the other day, when I pulled the pistons/needles before starting the car to try and diagnose the hard start condition. That's when i notice raw fuel settled in the venturi. I'm curious if it's spilling over into the intake manifold as well.

The car is running terribly rich on both carbs, I've never had an issue with it rubbing or binding in the nozzle, but I can't speak well for the PO.... he was a bit of a tard and never touched the carbs so there's a chance that he never touched them in the 15 years he owned the car. When I disassembled and cleaned the carbs off of the car, the nozzles and needles were in awesome shape with no visible corrosion. They both drop fine with no binding.

I've gotta change the exhaust flange gasket tomorrow morning before doing any carb work (gotta get some of that rich exhaust away from the cab) and I'll reset the needles and get a fuel pressure gauge in place. This is annoying.

[Captain Obvious]

Yeah if you've got fuel pressure on the needle and seat even with the engine off it's possible that you're bleeding that pressure off into the bowls slowly overnight and starting flooded every morning. The original system with it's orifice based regulator allowed the fuel pressure in the rail to drop to zero as soon as the pump stopped moving. Sounds like your new setup doesn't allow that and you're asking your needle valves to hold that pressure back 100% forever and I'm not sure they're that good. Especially if you're getting a heat soak induced pressure spike after shut down. It might be part of the problem.

But that won't cause the long term high fuel consumption while driving though. That's got to be an adjustment or needle or nozzle issue. Keep in mind that the needles and nozzles can look fine to the naked eye and still be out of whack. My experience is that five thousandths (.005 inches) was enough to make the difference between purring like a kitten and stinky eye burning exhaust.

If you've got any doubt as to the condition and you've exhausted all other possibilities you might want to think about replacing them. 115 miles to a tank is certainly low.... BTW - How do the plugs look? Are they also indicating a rich condition?

[metalmonkey47]

Problem #1... I hooked up a fuel pressure gauge and found that with my regulator set to 2.5 PSI, I was getting double that at 5psi. Had to bottom it out to .5PSI on the regulator to get 2.5.

I reset the height on the floats, and the needle/seat are NOT leaking at all. In fact a detail I think I left out is that they are brand new.

Anyways, everything I did is hard to put into detail in one post so I made you guys a video, hoping maybe you'll catch something I don't. To be hones though, I'm about 90% sure at this point that the nozzles are going to be my issue. Bruce, I'll probably be giving you a call in the AM.

http://youtu.be/jXMM4uWU5dY

[240260280z]

From the video:

- you are running on your rear carb only.

Q. What needles do you have?

Experiment: Try dropping the front jet down enough so that the car will run when you disable the rear carb... if it is at ~2.5 turns down and there is enough air to chug along then your front carb is fine. If this is the case then focus on the rear carb.

Edited October 30, 2014 by Blue

[240260280z]

also disconnect the choke cables when trouble shooting.

[Captain Obvious]

What Blue said.

When you lift the piston with the little test rod, you disable that carb. So when you lift the front and nothing changes, it's because the front carb isn't doing anything to run the engine and those front three cylinders are just along for the ride. When you lift the rear carb and it dies, it's because the rear is the only carb that's adding fuel and you're running on just the rear three cylinders.

If the needles are installed properly (with the shoulder flush with the bottom of the piston),

and the nozzle adjustments are turned all the way up (zero turns down),

and the nozzles are fully seated all the way up (not stuck down or held down by the choke system),

and everything is in good shape (not worn or corroded away),

Then I would expect it to be so lean at idle that wouldn't run at all.

So again, what Blue said.

The fact that the front carb isn't running the front three cylinders with the nozzle all the way up is probably a GOOD thing. If the rear carb is still supplying enough fuel to run the rear three cylinders even with the nozzles all the way up (and even smoke at that!), then that rear carb is most likely a problem.

As for checking the needles and nozzles for wear or oval shape? If it's so bad that you can see it with the naked eye, then it's really bad. I can tell under magnification with measurement tools, but I don't have a quick and easy way for you to verify. How much do new nozzles cost? Can you borrow a pair from a known good set of carbs just to see what happens?

You're positive you've got the needles installed properly, right?

Edited October 31, 2014 by Captain Obvious

[Stanley]

2.5 psi is a little low and 5.0 is a little high, book says about 3.2 to 4.2, both carbs get about the same fuel pressure/flow unless the rail is blocked. If it's a Mallory low-pressure pump I think there's an adjusting screw on the pump, 3.5 to 4.5 psi or something. Maybe those regulators are crap.

Both carbs same fuel level at the nozzles. Hold sight glass next to nozzle to check.

The old emissions needle, the new needles, and the modified needles all look the same to me, even with my glasses.

[bartsscooterservice]

I looked up the FSM, the stock fuel pump should deliver a static fuel pressure between 0.24 and 0.30 kg/cm2

[bartsscooterservice]

Did you fix the problem >?

[metalmonkey47]

Sorry guys I've been trying to find time to tinker with it. 50 hours a week at work is not Z car friendly. 

Anyways, in the video it was running on JUST the rear carb. I took some time to pull the nozzles and inspect them, and they look just fine so I swapped the nozzles from carb to carb to see if the problem followed. Didn't seem to. 

 

My fuel pressure gauge that i WAS using was far from accurate. It read a lot higher then reality. I have a new gauge (designed for EFI levels but still accurate at low psi) and it seems that the regulator is working just fine. 

When I was tinkering around with fuel PSI I was looking for regulator output pressure with the engine running to see if it varied at a higher voltage , which it did not. I pulled the pump fuse for one reason or another and noticed after about 30-40 seconds the idle stabilized and the car seemed to run better and didn't smell even a lick rich. I let it run until one carb finally shut off, killed the motor, and found that the rear carb (the one that was still running the car with the nozzles turned up) had emptied a slight bit quicker then the front. The fuel level in the bowls is identical when they're full. 

I'm assuming that my issues seem to be float level related. I'm gonna grab a clear hose and see if I can re-check that to make sure nothing changed. 

[metalmonkey47]

Alright, so here's what I've found: 

I used a clear hose and the nice little measuring tool that came with both rebuild kits for the carbies. (I ordered it for a '73 from oriellys because they didn't list a '70. I'm assuming both year 4 bolt SU's use the same float) 

 

The level in BOTH carbs was about 10mm too high. I adjusted both floats starting with the rear carb and found that BOTH seemed to still hold the same amount of fuel as before. in fact, regardless how low I set the floats, they seem to both sit about the same height as before the adjustments. 

I pulled both floats and layed them in a bowl of water, they're both buoyant. Holding them below water neither seems to leak and I see no bubbles. 

I blew some gunk out of the return line, which seems to be operating perfectly. I verified I'm still getting 2.5PSI to both carbs

Now I'm just about as annoyed as ever. I cannot seem to decide what's malfunctioning or what I might be doing wrong. 



Needle & Seat - Sealing fine

 

Float - Floating/Not leaking/Not hanging up

 

Fuel Pressure - 2.5PSI

 

Fuel Return - Free & Clear. 



So what's the next step?