Not whating to beat a dead dog,but lately their has been plenty on the how critical and necessary it is to check and properly set float level.
Write ups and everyone is saying to push down on tab of float,no doubt this is true,but I`ve been taught by a Guru an easier way.Hold the tips of each thumb on each end on the pin.(to keep it in place) and turn the bowl upside down and look to see that the float doesn`t drop below top rim of bowl. very simple and easy,no tools.
I like to detach the bowl from the upper carb with hoses still attached. I hold the bowl level, with a couple fingers over the ends of the pins, and open the petcock. When the bowl is full you can see the exact level. It will also show you if your float isn't. Floating, that is!
The above methods vary in certain aspects but don't address what must be done if they are out of spec.. Mr Healy addresses this in another post in detail if you search. Below is an article touching on float levels.
Several articles have been published about setting the float level on Concentric Carburetors and this is a summary of the important points from people in the know:
The actual specification, from the engineer who designed the Concentric Barry Johnston, gives a gas level of between .170" to .240" below the top edge of the float bow, 170” being rich and .240" being lean. This level has a dramatic effect on the running of a properly tuned motorcycle. It pays testaments to the design of this carburetor that the range of miss-adjustment it can tolerate and still have the motorcycle run, if only poorly. It is suggested that you set the float level first before doing any carb adjustment.
The level can be estimated by placing the round edge of the plastic float between .060" and .090" below the edge of the bowl when the needle is depressed by a slight force on one of the float's needle tangs. You can turn the bowl upside down to establish this. With the float above the top of the bowl, as described in the Norton Tech manual, the float can contact the bottom of the body and not allow the float needle to seat firmly. It also makes the carb rich through the jetting range. With the float, level with the top of the bowl, although not as rich as when it is above the top, it is still out of the specified range.
The brass needle seats are installed and adjusted cold by the factory. Using a proper sized drift, you can adjust the brass seat on a solid surface.
All - Don't feel bad, after working in a large Triumph dealership for several years, it wasn't until 1973 when the Triumph rep stopped by and showed me the trick that I learned!!
The rep taught me to turn the bowl up-side-down; my boss (who is BSA and Norton factory trained) does the push method. I think there is a difference, and the difference is the wear and fit of the brass pin.
To see why I consider up-side-down a better method you have to consider the forces at work. The fuel is trying to raise the entire float. This will tend to raise the float position on the pin also.
The "push method" lets gravity hold the float down against the pin; the up-side-down method lets the float rise against the pin. Yes, it's a very small amount at the pin. But due to the pin being offset to one side of the bowl, that amount of free-play is amplified by the offset ratio of approx 5:1. Therefore .008" at the pin becomes .040" at the opposite tip of the float. IMHO 1mm (.040") can be significant.
The "push method" has weaknesses in that it really matters where you push and how hard you push. These are very hard to explain. On the other hand, in the "up-side-down method" gravity (a rather universal constant) supplies all the forces.
However, I will admit that the most important thing for you to remember is that whatever method you like, then do it the same way on all your carbs. Especially if you are tuning dual-carb twins or triples. The need for identical setup on multi-carb bikes cannot be overstated.
John posted above "The actual specification, from the engineer who designed the Concentric Barry Johnston, gives a gas level of between .170" to .240" below the top edge of the float bow, 170” being rich and .240" being lean."
When I look at Bushman's Carb tuning secrets, he indicated .080" below the rim of the bowl.
Any suggestions on which level to use.
I'm running rich now on AMAL 930's using 180 Mains. If I adjust the floats to what John suggested, will that lean it out?