View Full Version : Front Carb Fuel Level Too High, Rear Too Low

10-24-2003, 09:39 PM
I've been playing with the floats, but I'm afraid of breaking them and don't know exactly where to bend them.

My last try, I bent the back one to look exactly like the front, and the back is still way lower. Do I bend the metal right in the curve in the middle? I've got a feeling someone messed with the flat surfaces and therefore even though I've adjusted the float correctly (1/8" from lip of cover at the non-hing side of the float), the surface of the arm may be shutting off the valve too soon.

so if this is the float arm:


I bend the backslash part, right?

Dave Russell
10-24-2003, 11:29 PM
Can't tell from your illustration what is what.

Not sure which float you have. If it is the brass float, with separate arm -- 5/16 measured between the high part of the arc & the lid.

For the early type Nylon float with steel needle --1/8 to 3/16 measured from lever to face.

For the newer spring loaded Delrin needle style -- 1/8 to 3/16 measured at the point most distant from the needle in the horizontal plane. Eg. if the lid is inverted & you are looking down, the needle is at 12 o'clock & measure at 6 o'clock. This should also be the closest point between the float & the lid. Measure with the needle spring NOT compressed. Bend the tab which contacts the needle to adjust.

There is one other style with Delrin needle & all nylon float which should measure -- 1/16 to 3/16 at the same location but is not adjustable.

[ 10-24-2003: Message edited by: Dave Russell ]</p>

10-25-2003, 12:06 AM
Woops, looks like my illustration didn't transate quite right to the actual message board. Oh well, you still answered my question.

I've been messing with it for a couple hours, and the fuel level has barely moved, if at all, after what I feel to be some pretty major changes. But on this last try, the fuel spilled out over the top, so I should be able to find a level somwhere in between and call it good. The weird part is the car still ran the same, even with all that gas going into the rear carb.

Even if it doesn't entirely solve the problem, it will be one less thing wrong. Ah, back to the garage. My neighbors love me.

Thanks again, Dave. graemlins/cheers.gif

10-25-2003, 12:54 AM
Now I'm really stumped. I switched the floats, expecting the front to then be lower and the rear to be normal. No change!! Apparently British engineers have the ability to defy the laws of physics. What else could possibly cause the rear carb to be consistently low?

Dave Russell
10-25-2003, 03:00 AM
Oh boy,

What next? The only other thing that I can think of is that the two needles or their springs are different lengths. You DID verify that the two floats are the same, didn't you.


the needle seats are different types or damaged or sitting at different heights from the lid.

A remote possibility is that the two float bowls or carbs themselves are different. It IS possible for parts to get mixed up between carbs once in a while. Especially at volume carb rebuilders where a bunch of different parts are all out at once.

10-25-2003, 04:22 AM
Have you checked that a needle and seat is not clogged? This would provide constant high readings at one carb as it would be pushing fuel in regardless of float height.

Can you add small fibre washers to the base of the needle seat (where it screws into the lid) so that the float closes off earlier? That's what I do to lower a float height.

Are you checking fuel level at the jet to see that it is correct?

If one fuel bowl seems low all the time it may have a blocked inlet. This would give greater inlet pressure to the other one and may explain the high/low reading spread.

[ 10-25-2003: Message edited by: britishcarfreak ]</p>

10-26-2003, 03:53 PM
Hello CC,
how are you checking the fuel level?

Alec graemlins/cheers.gif

10-27-2003, 02:14 AM
Checking fuel level at the jet. I've taken both needles out and they are squeaky clean. They look brand new!

I'll give you a quick recap of everything I've done, just to clear things up:

Raised the rear float level as high as it would go, fuel still an inch low at the jet.

Bent the float arm to match the front float, no change.

Bent the face down that strikes the needle, then bent the non-hinge end of the arm (where the float is) up, so the float would theoretically rise higher and close the needle valve later. No change until I did it even more drastically, which caused the fuel to spill over the top.

Reversed this a little and fuel was all the way back to an inch low!!

This should tell me that it's a float related problem, but when I switched the two, the front remained high, despite the different profile of the float arm and it was quite a curveball. But since the fuel level did change once when it spilled over, the valves are clean, and the fuel pump is brand new, I suppose I'll just continue messing with that stupid float.

How long do you recommend I let the car run while waiting to see if the changes I make with the float have had any effect? I've been running it for a minute or so, which seems like more than enough...

I've been toying with the idea of tossing a nut or something in there to displace the fuel, just to see how the car would run...I've considered that the bowls are different, but they look identical to me. The fuel inside the jet rises and falls with the fuel in the bowl ruling out any obstructions between the bowl and the carb.

I think the ghost of that ZS carb is haunting me!!

11-03-2003, 09:58 PM
Okay. Temporarily found a way to get the fuel level up to where it's supposed to be by taping a quarter to the float. Worked like a charm. Problem is...the car STILL runs the same!!

This is incredible. The only thing I can think of is that this is an ignition problem. There are no vacuum leaks, the needles are correct, fuel level is where it's supposed to be, mixture is right, and I even put the muffler and air filters back on. The car still runs a lot stronger with the choke out.

I don't know where to go from here, guys. graemlins/nonod.gif