Setting dry float levels on the bench

[maleko89]

Set for 1.125 inches to get a 17 mm wet level.

Picture courtesy of Icepick.

Mark
#1098

 

[vmaxman99]

That setting will make it rich. 1.125 inches will set them on the lean side.
Mike Costa
VMOA #3531

 

[vmaxman99]

One other thing that I've noticed when doing these carbs and has been confirmed. See the shape of the float and that casting mark circle on the jet block? When the float height is set correctly, the edge of the float will be exactly the same as the casting mark, like the edge of a circle on the edge of another circle. The carb on the right is set rich, and the one on the left is set lean, but close to where it should be (see the circular casting mark?)

 

[gleno]

Hi Mark.

I've read your excellent sticky threads on carb tuning and you appear to be in your element with carbs.

(I’m carbophobic and feel at home with EFI.)

So I ‘d like to ask for some education about float levels and their effect on fuel mixture.

I've stripped down the carbs and get the replacement parts tomorrow.

In this thread there is discussion about the correct level being either 'too rich' or 'too lean'.

I don't understand this reference.

I can appreciate that you could flood or starve the fuel bowl if the level changes were large but isn’t fuel metering regulated by the size of the main jet in the jet block?

I’ve looked at the main bleed pipe and can’t see how miniscule (mm) changes in float levels would create gross changes in mixture strength.

Can you explain?

 

[maleko89]

Hi Mark.

I've read your excellent sticky threads on carb tuning and you appear to be in your element with carbs.

(I?m carbophobic and feel at home with EFI.)

So I ?d like to ask for some education about float levels and their effect on fuel mixture.

I've stripped down the carbs and get the replacement parts tomorrow.

In thread thread there is discussion about the correct level being either 'too rich' or 'too lean'.

I don't understand this reference.

I can appreciate that you could flood or starve the fuel bowl if the level changes were large but isn?t fuel metering regulated by the size of the main jet in the jet block?

I?ve looked at the main bleed pipe and can?t see how miniscule (mm) changes in float levels would create gross changes in mixture strength.

Can you explain?

Gleno, sure can.

The way it was explained to me was that if the fuel level is higher, say 15 mm below the mark, then the fuel is closer to the venturi and it's "easier" for the change in pressure to pull the fuel out. Now, if the fuel level was too low then the opposite is true. It's harder for the fuel to push out into the carb bore.

The Venturi speeds up air flow and drops air pressure at all rpms so that's why it's important to set float level first. You can change needles and jets to kingdom come but if you floats are all different or out of spec then your carburation will never be right.

I hope this helps....

 

[gleno]

Praise to the Oracle :eusa_pray:

Thanks Mark. That makes sense to me now.

 

[gleno]

One other thing that I've noticed when doing these carbs and has been confirmed. See the shape of the float and that casting mark circle on the jet block? When the float height is set correctly, the edge of the float will be exactly the same as the casting mark, like the edge of a circle on the edge of another circle. The carb on the right is set rich, and the one on the left is set lean, but close to where it should be (see the circular casting mark?)

Just finished carb rebuild. Big thanks to Mark & vmaxman99 for their advice. Used the casting mark (moon shape) on the jet block to set the float levels.

I reckon that is pretty much the sweet spot.

Big improvement and so simple to do.

Thanks again guys.

 

[44 magnum]

I was looking over the "Carb Bible" and was wondering if someone could tell me the reference point when they talk about the float level being 17mm?

Thanks guys.

 

[maleko89]

If you look at the float sticky you'll see a 1/2 moon circle on the jet block.

 

[godsend1]

Mark,

Is it possible to set the level without splitting the rack?

 

[maleko89]

Probably,but would take much longer. Bowl cover screws are usually on pretty tight and using a ratchet would be difficult. Also, harder to fit a caliper to measure distance. It's very simple to split the rack. Just a fuel rail, choke linkage e-clip on #3 carb and e-clip on sync rod between #3 and #4 carb.

 

[godsend1]

Mark,

Mine were all low, which would indicate a lean setting right? I have an extremely rich condition when running, I went ahead and raised them all to the correct level, aligning with the casting mark.

Is there anything short of an entire rebuild to look at while I have them off?

I need to pick up some replacement float bowl screws, mangled 8 of them taking them off. You were right, they were extremely tight.

Tom

 

[naughtyG]

I need to pick up some replacement float bowl screws, mangled 8 of them taking them off. You were right, they were extremely tight.

Tom

How can you mangle 8 screws when there are only 4? Got a V8 max? :ummm:

 

[m-cman]

Aren't there 16 float bowl screws?

 

[naughtyG]

oops I zoned out I thought they were float bowl purge screws lol

 

[maleko89]

Tom, did you measure wet level or dry? What was your initial measurement?

Nothing short of a rebuild. Just carefully inspect the rubber parts for wear, bowl needle valve, etc.

For new screws, get the button head allen screws. It's much easier getting those off with a T Handle. I get mine at Ace Hardware.

 

[godsend1]

How can you mangle 8 screws when there are only 4? Got a V8 max? :ummm:

4 per float bowl.. it took vice grips to get them off.

 

[godsend1]

Tom, did you measure wet level or dry? What was your initial measurement?

Nothing short of a rebuild. Just carefully inspect the rubber parts for wear, bowl needle valve, etc.

For new screws, get the button head allen screws. It's much easier getting those off with a T Handle. I get mine at Ace Hardware.

The carbs had been sitting drained on the bench for a month, so I would say dry. Initial measurement was visually they were below the casting mark. I'll measure them as they sit and verify they are at 1.115.

 

[maleko89]

1.125 is about 17 mm wet level. The smaller the dry measurement, the richer you get.

 

[godsend1]

That would make sense, so I need to set them to 1.115?