Britbike forum Forums British Motorcycle specific Brands Bsa bulletin board Float Height Adjustment

Would there be any information on this site on how to check and adjust the float height on AMAL 930 carbs?

Thank you in advance

Drill a hole in a spare drain plug and fit a hose barb. Use a piece of clear fuel line to make a u tube. Zip tie the free end to the float bowl. Turn the fuel on and check the level in the tube and it should be close to .21" below the top of the float bowl, not the gasket.
https://www.ebay.com/itm/203741006826

Does AMAL have a spec for this when fuel is used and when measured from the top of the float bowl when the float is manually pressed?

there is a spec for fuel level ... but not if you manually press down the float, because this is what the Tickler does
and this is what causes the Bowl to Over-fill and prime the carb .

the AMAL fuel level spec is ... 0.21" plus or minus 0.040" ... below the top edge of the float bowl. ( or between 0 .17 and 0.25 )

the dry float level spec is 0.08" below the bowl , at the back-side away from the pivot .

CBS , has a good write-up of both methods with pictures .
https://www.classicbritishspares.com/blogs/news/amal-concentric-float-height

htown70 assumes ALL Concentric carbs had drain plugs.
That feature didn't appear until 1971.

Might be worth adding that those values are only for the white plastic float, not to be used with the stay-up float

The floats were set to .080" below the bowl. When the carb is filled with gas with the clear tube attached the gas level is about 1/4" below the .210" mark on float bowl. So now I have some figuring out to do, should the float bowls be raised and then check the float level again to see if it is closer to the .210" mark?

Assuming all the parts are original, the float height is changed by using a flat tipped punch and moving the brass needle seat up or down, tapping lightly with a hammer. You do not bend the float tab.

Do not press down on the needle or tangs to measure this. Correct procedure is to hold the pivot pin in place while inverting the float bowl.
Allan is correct, the right level for the stay-up floats and Premier carbs is closer to level with the top of the float bowl.

according to AMAL .,
. 08" is correct for all floats . ... allan may believe differently ... and 0.08" is close to the top ,
( more than 1/16" , but less than 3/32 )... or 2 mm

Float level is the same
Method of adjustment is different ( for all plastic float )

.
https://www.triumphrat.net/attachments/AMAL-stay-up-float-level-sheet-pg-2-jpg.656764/

I have always measured by pushing the tangs down while simultaneously holding the pivot pin from rising. Works for me!

Ed from NJ

And make sure it’s actually holding the needle down in the seat. Something I got wrong for years.

G

There's more than one way to skin a cat .
i like this method .

with lower bowl assembled . ( float , pivot pin and needle )
hold only the pivot pin down with one thumb , on one side ,
The rest of your hand underneath the bowl .( fat thumb to one side , so float will freely swing )
Flip the whole thing upside down ( fingers now on top , thumb on bottom )
and gravity will show you where the float will stop .
( gravity is doing what the fuel will normally do )

+1 to that!
Pressing on the needle or the tangs puts more pressure on the needle than fuel under the float ever will.

Have you tried adjusting the stayup float to .080” below the top of the float bowl as you could do with the plastic floats, you’d be lucky if it runs. Then check the fuel level and it will be well off.

If you get a brand new carb (and I’ve checked a few as I check each carb I sell) you’ll notice that the float will sit ever so slightly proud of the top of the bowl. With the gasket in place it wouldn’t see the top of the gasket.

Leave them how they come set from Burlen and they will run spot on. Whether it be a pre 72 bike or not. If it runs rich then investigate.

the plastic float isn't adjustable . ( didnt stop many from trying )

plastic flexes and returns to original shape ... in its plasttic zone .
It must be fractured beyond plastic to take a new set .. ..
Which introduces weakening, micro fractures into the plastic .

one of the touted design points of the metal tabbed stay-up floats is that the metal tabs are adjustable
.

That answers my question to you in no way at all, it’s also taken out of context by only answering part of it. But I assume a miss understanding. I did not mean by the same method of bending the tang(s) but by setting the top of the float as a datum. Anyway it was a rhetorical question. Hopefully I explain a little better below….

I think we have already established that the seat needs to be adjusted with the plastic float, you could do the same with the stayup float too and this would be my preferred method, however it seems that the new float bowls have much tighter tolerance's around the seat or are bonded - I don’t know.

The old (say 15/20 years ago) you could drop in boiling water and reposition with a suitable drift. The new ones don’t seem to move at all with the boiling water method like this, given the float height works just fine from the factory I have yet to want to change it again.

I did change the stay up float on the tangs with the first one I had (for my own bike) did it to the .08” and had an incredibly lean mixture. Leaving as preset gave me much the same running condition as I had with the top of the plastic float set to .08” from below the top edge of the bowl.

I've installed stayup floats on 7 bikes, either on new Premier's or retrofits. Not sure about the plastic floats but with the stayups you want the float to be just proud of the top of the bowl when you lightly press down the tangs. I've checked all of them with the u-tube method and the just proud setting gives the correct fuel level very close to .21" below the top of the bowl.

Is the fuel level measurement made with the carb held vertically or when the carb is bolted to the bike?

What sort of bike do you have? Is the carb tilted? Shouldn't make much difference whether on the bench or on the bike. Set it close on the bench check it on the bike. On Commandos with titled carbs I always measure at the center of the bowl where the intake needle is.