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Flooding on SU HS-4, what am I doing wrong?

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RobSelina

RobSelina

Jedi Warrior
Offline
Okay, my HS4 leaks fuel into the intake. That's what's causing it to run rough. Last time I took the carb off and found fuel in the intake, I assumed it was because the piston wasn't traveling freely. I took the carb apart and cleaned the damper well. There was some grit in the chamber.

Pulled the carb this morning after I could not get it to run consistently last night. Here's a description of the details I've noticed:

* Standing fuel in the intake. Roughly 1/16"

* There was no fuel pressure on the fuel line. Note that during testing last night, after firing up the pump and then cycling the ignition off, there was good fuel pressure when I pulled that line. I'm relatively confident the float/intake valve are operating correctly

* The float bowl was nearly empty. Even if the foat was malfunctioning, this wouldn't explain why the fuel leaked into the intake right?

* This time, everything is sparking clean. The damper comes down with an authoritive thud when lifted. The rate at which it falls and the resistance it presents when lifted, all seem appropriate.

* The needle isn't straight on the piston. It's spring loaded and offset slightly to the engine side. After reading the Haynes SU manual, this apears to be a design feature. There's a slight dimple in the metal piece that holds the needle to the piston.

* The jet is clean and shows no signs of irregular wear. I had previously blown carb cleaner through it to remove any sediment. I don't really know how to inspect a jet or needle, but the needle seems straight and does not have any visible scaring, neither does the jet.

* During reassembly last time, I only applied WD40 on the exterior of the jet to allow it to move up and down. I gather I should have used petroleum jelly according to the manual. I don't think this explains why the fuel was leaking but I mention it for completeness.

I'll also mention I'm using a Facet electrical fuel pump with no external regulator. Although I've always had a positive impression from this pumps operation, I'm reading some nasty stuff about it on google. Could my fuel pump pressure be to high?

The float presntly sits at a 20-degree angle to the carb body, I'm planning on grinding down the grommet so it sits level & rotating the float so it actuates front to rear, not left or right.

Related question - when the manual says to oil something, what am I suppsed to use as oil? motor oil? I'm planning on putting a little wheelbearing grease on the throttle shaft and exterior of the jet (where it slides inside the housing). On the piston/dome, I'm planning on using a little motor oil on the housing, just to provide light lubrication.

This one has me stumped. How/why is this thing leaking? could I just have the jet adjusted too low so it doesn't close against the piston?

Thanks!

Rob
 
Float body is supose to be verticel I beleive, Don't grind anything.

I think your fuel pressure is only supose to be 2 or 3 pounds, more and carb will flood. Hmmm, fuel in intake manifold.

We have some experts on these things, give em a chance to reply. Oh yea, oil for where, what?
 
Rob, I occasionally have this problem on my injected Midget, and I am pretty sure it is due to crappy manifold design.

One thing that may help is to reconnect the manifold heater line. I noticed in a picture you posted earier you bypassed your manifold coolant line. The advantage of a heated manifold is when fuel stikes it, it will evaporate and burn much better. In an ideal world, liquid fuel should never enter your manifold.

On a side note, I have an adjustable fuel pressure regulator I will happily give to you if you would like to experiment.
 
[ QUOTE ]
Float body is supose to be verticel I beleive, Don't grind anything.

I think your fuel pressure is only supose to be 2 or 3 pounds, more and carb will flood. Hmmm, fuel in intake manifold.

We have some experts on these things, give em a chance to reply. Oh yea, oil for where, what?

[/ QUOTE ]

Too late, ground down the grommet already. This will put the fuel bowl vertical instead of at an angle. It's something Jeff recommended to me a while back when i first started talking about this swap.

As for the oil, the haynes SU/webber manual talks about oiling the throttle shaft & piston. I've described what I plan to use above. Thoughts?

BTW, after removing the throttle shaft, it's clear I do have shaft and bushing wear, just only on the throttle spring side. the other looks great....
 
[ QUOTE ]
Rob, I occasionally have this problem on my injected Midget, and I am pretty sure it is due to crappy manifold design.

One thing that may help is to reconnect the manifold heater line. I noticed in a picture you posted earier you bypassed your manifold coolant line. The advantage of a heated manifold is when fuel stikes it, it will evaporate and burn much better. In an ideal world, liquid fuel should never enter your manifold.

On a side note, I have an adjustable fuel pressure regulator I will happily give to you if you would like to experiment.

[/ QUOTE ]

Don't have the option of reinstalling the heater lines on the intake. I ground them off when I was playing around with it last....As you noted though, I shouldn't have to do that. Also, with how much fuel was ponding in there this morning, i'd hate to rely on the intake heater to evaporate it.

As for the fuel pressure regulator, after reading up on my pump, it seems to put out 4psi, which is supposed to be pretty high for an SU. How low does that regulator you have go? Sounds like Nial (who has a pretty similar setup) is running 2.5psi, so if I could test it out at that pressure I'd very much like to take you up on your offer! /ubbthreads/images/graemlins/wink.gif I had purchased a fuel pressure regulator when i bought the pump, but the ZS didn't need it and it was used on another project...
 
Oh, grinding good, fuel float chamber should be vertical, yep yep.

If it was not I guess it might stick a bit.

Hows it work now?
 
[ QUOTE ]
Oh, grinding good, fuel float chamber should be vertical, yep yep.

If it was not I guess it might stick a bit.

Hows it work now?

[/ QUOTE ]

Don't know yet. Carb is still in pieces on the work bench. Figured I'd wait a few hours, see if anyone chimes in with anything related to reassembly.

After reading through the manual again, it speaks of centering the jet on the needle before clamping down the jet bearing. I didn't do this last time, I'll see if I can get that a little better....
 
What they mean is let the needle drop lots of times while you are tighting up the seat so the needle falls square on it and does not bind.
 
plot thickens. I purchased a pressure regulator at autozone to test it out, couldn't get any flow out of it. Even at 1.5psi, nothing came out. Went back, exchanged it, new one does the same thing.

I was getting some flow/pressure on the inlet, but as a sanity check, I ran a 3/8" line out of the engine bay into a bucket. The flow from the fuel pump w/o any restrictions was probably on the order of 20 gph, so that seems fine.

What the heck are wrong with these regulators? Guess I can't run a cheapy one from vatozone. Oh well, wanted to get her running today...
 
[ QUOTE ]
What they mean is let the needle drop lots of times while you are tighting up the seat so the needle falls square on it and does not bind.

[/ QUOTE ]

Oh, okay. Definitely no problem there then, it moved up and down freely and definitely came down all the way.

So at this point, it sounds like it can only be one three things:
1- excess fuel pressure
2- worn needle/jet
3- malfunctioning float

Any other options I need to look into?
 
Think that's it. You are moveing in on it now. All these easy by the way.

Worn needle or jet, look at the end of the needle with a glass, my eyes not so good. Should not show wear marks.

Bad float seat, needle, remove and inspect the same way.

Fuel pressure, we don't know if it was ever running correctly do we?
However from what you say it is way way too high. Change to a low pressure pump or get a regulator that works.
 
The ZS carb ran fine on that pressure, but the SU has never worked with this pump. I'll get a regulator, sounds like I need one either way. I'm really starting to think this is the problem.

Going back out to inspect the needle, yet and float assembly.
 
?? would the fact you only have one carb on there make some difference? fuel pressure wise?

mark
 
In my opinion (uh-oh)...

You should ditch the single HS-4 altogether and go with the dual HS-4, since your class will allow it. quantumechanics.com has the set up pretty cheap.

But, if you want to continue to pursue the single carb thing, PM me your address and I will try to get that pressure reg out to you Monday. I also have a Spitfire manifold I can throw in if you want to try to reconnect your heater lines. It needs to be cleaned up, but, hey, it's free.
 
Now theres a deal. God I love you guys.
 
Okay, inspected the float assembly - it's a-ok.

Needle & jet mostly look fine. The needle has a slight amount of wear on one side towards the piston. This is very, very hard to see, it's minor, but it is there. I'll mention that the needle and jet have a lot of clearance between them, even with the needle all the way in.

I started thinking about the fuel pressure and did a little test on the facet pump. It took 4.5 minutes to fill a 1 gallon jug. That's only 13.3 GPH. Should I consider swapping it out for a carter pump?

Morris - as for dual carbs, just don't have the money for it, and if I do any track racing, my class there will require the stock intake manifold it seems. Thanks for the generous offer, I'm about to send you a PM.
 
[ QUOTE ]
?? would the fact you only have one carb on there make some difference? fuel pressure wise?

mark

[/ QUOTE ]

Correct me if I'm wrong, but dual or single carbs should accept the same pressure, though dual carbs may require more flow, right? Though flow should be close to the same with a single or dual carb too I'd imagine...
 
i was just a thought.

mark
 
Mark - didn't mean to sound like I was jumping on you. I appreciate the thought!


Status:

I've put everything back together. I'm tempted to try it now with the float chamber rotated to a level position, but I'll wait until I have a regulator in the fuel line. I don't really want to have to pull the carb AGAIN to mop up the excess fuel.

The good news is I'm getting better at these SU rebuilds /ubbthreads/images/graemlins/wink.gif I had a small amount of fuel leaking down the jet bearing before, but a new o-ring seal and some grease between the jet and bearing should cure that. Also lubricated the throttle spindle and threw some o-rings on each side. It feels a lot better now.

I'll update this next week when I have a new regulator. (Thanks again Morris!)

Thanks! /ubbthreads/images/graemlins/cheers.gif

Rob
 
I haven't seen the obvious mentioned here, so I will make the mention. Do you have a good fuel filter near the carb? 30+ year old cars are known for contributing unwanted stuff to the fuel flow. Was there any debris in the bottom of the float bowl? Even the smallest spec of stuff is enough for the needle valve and float to fail at their jobs.

Now that I have mentioned the obvious, here's another take on your problem.. You mentioned that the float bowl was empty. Could the fuel that was supposed to be there "boiled" or percolated into the manifold because the carb is too hot? Are you missing some heat shielding around the carb that would make this more likley?

Good luck, keep at it, you'll get this tracked down.
 
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