1972 Float Adjustment ...

[240Z240Z240Z]

I have a 72 with 3 screw SU's and they have the long and short arms in the float bowl lids. Long in front carb, short in rear.

I intend to set the floats on my bench top by setting the lid with its float and gasket on top of a small clear drinking glass with a 23mm scribe mark at the correct spot.

Can anyone tell me whether the distance between the inside of the float bowl lid and the top of the gas is 23mm for both the front and the rear carbs on a 1972, or is the front 23mm and the rear something less ?

I'm looking for a definitive answer for myself and all my 72 brethren

[Jeff G 78]

The 23mm mark is the same for both when you measure the bowls. If you use the upside down lid method, you use 16mm and 12mm. There was a huge thread on this in July.

[240Z240Z240Z]

The 23mm mark is the same for both when you measure the bowls. If you use the upside down lid method, you use 16mm and 12mm. There was a huge thread on this in July.

Thanks for the quick on point response!

What's the title of the thread from July ?

[Jeff G 78]

I found it.

http://www.classiczcars.com/forums/carburetors-s30/49599-su-sightglasses-available-see-fuel-bowl-levels.html

[240Z240Z240Z]

I found it.

http://www.classiczcars.com/forums/carburetors-s30/49599-su-sightglasses-available-see-fuel-bowl-levels.html

Yeah I had read that one, that's where I got the idea for the clear bottle, which I think is a genius idea BTW!

Thanks for ferreting out those numbers, until I hear otherwise I'm using them for my 72 carbs

[Stanley]

Because of the tilt of the engine, and the front float bowl being in front of the nozzle while the rear bowl is rear of the nozzle, the level in the front bowl needs to be lower than in the rear bowl by 2 mm. This puts the fuel at the same level in at the top of the nozzles. That's why the ears on the front are longer by 2 mm. The FSM for 72 SU's just says 23 mm down from the underside of the lid. So 23 mm rear carb, 25 mm front carb for equal level at the nozzles. I guess you could go 21 mm rear, 23 front - I had trouble with the rear carb overflowing out the vent when I tried that, but can't say for sure it's wrong.

[240260280z]

The engine does know know where the floats are... it only sucks in air. The fuel level in the jet should be the same for both carbs so that the suction at the top of the jet draws the fuel up the same height.

It is like drinking from a long straw vs. a short straw when you simply the process. The length of the straw is more important when the suction is weak due to gravity... as the suction force increases, gravity forces matters less.

[240Z240Z240Z]

So I created this apparatus to help set the floats accurately and now I have even more questions.

To achieve a gas (water) height 23mm from the inside of the lid the float is nearly contacting the inside of the lid, that's doesn't seem correct. Its that way on both lids and floats.

Some assumptions :

1. The gasket and the inside depth of the lid adds up to about 4mm. So I marked the outside of the glass at 19mm.

2. Water behaves similar the gas for this test.

3. My valves are correct and in good shape.

Since I have them apart I thought I would use my calipers and calculate where the top of the gas is relative to the carb bridge assuming a fuel height of 23mm.

Here's what I got :

The bridge to the dome surface is 44mm

The top of the float bowl to the top of the dome surface is 33mm

So from the top of the float bowl to the bridge its 11mm

Add 4mm for the gasket and lid and you get 15mm from the inside of the lid to the bridge

Subtract 15mm from 23mm and you get 8mm, not 10mm as I've seen elsewhere ?

I'm thinking I should replace the values anyhow, where's the best place to get a proper set ?

[Patcon]

A gallon of water weighs about 8.33 #'s a gallon of gasoline weighs 6.07 #'s so the float is going to ride higher in the water versus the gasoline because it has to displace more gasoline to equal its weight than water to equal its weight...

Charles

[Patcon]

Theorectically you could multiply the desired dimension by 1.3723 and that would give you the correct value for float setting in water. But I am not sure I did the conversion right... somebody want to check that?

C

[240260280z]

I am in love with that lab calibration!

[240Z240Z240Z]

Well, I'm back at setting the floats and have fitted them with some new valves I ordered. I'm still using the glass jar setup, but I've eliminated the water pump arrangement and have a small funnel attached to the inlet port by means of some tubing. The glass is marked at 21mm as a reference and I can poor gas into the funnel and watch where the level stops. I was able to get the short legged cap set to stop at 21mm with the black plastic float about 1/8" from touching the inside of the cap when inverted, however, the long legged cap with the taller valve could not be adjusted enough to allow the level to come up to the 21mm mark. I stopped when I noticed that the tang was bent so far in that it was contacting the body of the valve when inverted and the plastic float was hitting the inside of the cap. I ended up using another short valve body and bending the tang up so that inverted the float was about 1/8" from touching the inside of the cap and that put the level at the 21mm mark. I think this is where I'm going to try them.