Float Height

Hi,

As a frequent visitor to this board I have been getting little tidibts and pieces of info quite often. Have been trying to trace some rough running problems on one side of my early '72 roadster and looked at float height. After looking at different sources and looking at some of the posts on this board, I am a little confused.

I have seen two different methods of checking float height:

One method is with the float bowl in its normal upright position and pressing down on the float tabs to seat the float, with the proper float height .080 from top of the bowl edge to top of the float.

Another method is to invert the bowl, holding the float pins firmly in place. With this method, I have seen different measurements. One is that the top of the float should be even with the edge of the inverted bowl.

Another if I understood correctly, was the edge of the float should hang down below the edge of the inverted bowl .080.
I believe I have also seen 3/32" in this measurement.

Or, am I misunderstanding this inverted bowl measurement, and perhaps the top of the float should be .080 above, or inside the top of the inverted float bowl.

What is the definitive, final opinion on how to set this float height?

Boy, sometimes this old bike humbles me, makes me feel like a dummy. Thanks for any help.

Art :roll:

Amal float height

Art,

I use the inverted float bowl method. Upside down the float should be 3/32" inside the bowl referencing the joining surface (not above the joining surface). If you don't get a smooth idle after adjusting this, clean out the idle circuit from the mixture screw port to the float chamber. Also make sure the air bleed circuit from the back mouth of the carb is clear. The other circuit is the very small two holes at the front of the carb throat. Use carb cleaner to blow these out as well.

Art, I have saved some postings from other boards about this. I hope they help to get this right in your mind. You can set floats to known distances all day but you don't really know the effect till you make a service tool. You will need to drill and tap the bottom of a float bowl drain plug or and old spare plugless bowl for ten thirty two barb fitting. Then you need a 10/32 brass barb fitting. You can use other sizes as well depends on what's around. A small hose gets attached. This hose is run up with nothing on the end to well above the float bowl joint hieght. You can zip tie it to keep it from flopping around. Now when you reassemble and turn on the petcoks you can see the real effect of your float valve seat adjustments. This is a good thing for getting two carb machines right. Sorry this is so long everyone you can stop reading now if you don't belive this boat load. norbsa
FINDING HOW MUCH THE
FLOAT LEVEL AFFECTS ACROSS THE WHOLE BAND. A BASELINE CAN
BE ESTABLISHED [ONCE ONE KNOWS THE PILOT FUEL AND AIR PASSAGES
ARE CLEAR], IS TO ADJUST FLOAT SO BEST IDLE SPEED IS WITH PILOT
NEEDLE 1.5 TURNS OUT. IF MOTOR FALTERS MOST ON CLOSING NEEDLE
THEN LEAN SYSTEM BY LOWERING FLOAT, IF IT FALTERS MORE ON OPENING
PILOT SCREW THEN RICHEN SYS BY RAISING FLOAT. IF THIS IS DONE ALL
ELSE IS PLAINER IN EFFECT AND IF IT CAN NOT BE DONE, THE FAULTY
COMPONET BECOMES APPARENT. KEEP IN MIND OIL WILL SOOT PLUGS TOO.
BY: HOBOT




August 16, 2004 By: Dyno Dave

One added note about float levels.
The concentric may be able to run through a range of down draft angles but in all the articles I have seen published and experts quoted, none mention the effect of angle on "fuel" level which after all is what you are after.


I'm still in the debugging process with the Dunstall engine so...
I was having idling inconsistency. So, yesterday after I flattened my warped float bowls, I did the test I have long been threatening to do.
I have a "sectioned" away concentric. I can therefore see the FUEL level in my now doctored up bowl while installed on the sectioned body. I set my floats about 1/16" above the bowl edge.
I turned on the petcock with the carb body level and observed the "fuel" level, it showed about 3/4 of the way up the needle jet metering aperture.
Repeating the test with the tilt angle of the commando the "fuel" is only about 1/4 of the way up the needle jet metering aperture. I repeated the test several times to be sure I was doing it right and getting consistent results.

This is the primary reason that the tech digest refers to putting the float 3/32 above the bowl.
If the gasket is added...... the remainder of the added height should never cause the float to hit the carb body.
An atlas has an even steeper down draft angle and could theoretically require more float adjustment up to get the required "fuel level" correct in the needle jet metering aperture.

After all this exercise is to have the fuel always at the same level where it counts...where the needle and the needle jet meet. I always try to keep the "fuel level" in the top 1/3 of the needle jet aperture, but never above it, i.e. into the spray tube area.

So I am not necessarily fully endorsing the quoted 3/32" value as my float level, but I also don't bother to listen to triumph or BSA guys with flatter mounted carbs. Carb mount angle matters. On a Norton, I would never put the float below the edge of the bowl.

My Dunstall idle circuit air leak is now gone and it idles smooth and consistently. Both carb fuel levels are set to my desire and the idle screws respond correctly.
I DO REFERENCE THE FUEL LEVEL TO THE BODY. THAT IS WHAT THE JET, JET HOLDER AND NEEDLE JET ATTACH TO. IIRC FUEL LEVEL 3/32-7/32 BELOW THE EDGE OF THE BODY. TO MKE SURE, I'LL FIND THE SHEET WITH THE DATA TONIGHT WHEN I GET HOME.

I HAD ALL THIS STUFF IN THE TRAILER AT THE RALLY BUT NOT THAT MANY ACTUALLY SEEMED INTERESTED FOR TECH TALK.

ADDED: THE NEEDLE JET METERING ORIFACE IS AT 4/32 (MAYBE A TOUCH MORE) BELOW THE BOTTOM SURFACE OF THE CONCENTRIC AND THIS IS THE LEVEL THAT I TRY TO GET THE FUEL LEVEL UP TO NO MATTER WHAT THE ANGLE OF THE CARB IS. THE COMMANDO IS ABOUT 13º AND THE ATLAS, 5 MORE, AT 18º. THE STEEPER THE CARB THE HIGHER THE FLOAT NEEDS TO BE TO GET THE FUEL TO THE RIGHT LEVEL, BECAUSE THE FLOAT BEING NONSYMETRICAL IS GETTING PUSHED DOWN INTO THE FUEL AND SHUTTING THE FUEL OFF SOONER.


Dave
BSA-Dunstall-Norton-Ducati
http://www.gis.net/~dynodave

Thanks for the info, guys. Checking the float height as it is was, seems to be 2/32" past the top of the inverted fuel bowl. Am going to see about tapping the bottom of the bowls. Did the tube trick on the bottom of the bowls when working on my son's Yammmerhammer, but it had some nice conveniently placed short drain tubes on the bottom of each bowl. Am also considering new needles and jets.