I got one of those float level gauges but found it doesn't work that well and isn't very easy to use. It's biggest issue is that you check the float setting by measuring off the gasket surface but most of the time, the gasket remains stuck to the carb body so is in the way. You run the risk of breaking or damaging the gasket if you have to remove it all the time. I've reverted back to my old tried and true method of using a 6" steel rule graduated in MM along one side. These are thin enough to stick down in between the float bowl gasket and the outer lip around the carb body, to get to the gasket surface. With the BS38s, you can (and should) place the rule on the far side, then sight over the tops of both float "bulbs". Adjust your "view" angle so that the tops of both "bulb" align .....
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Sight from too high or too low of an angle and the reading will be off. And you'll want to check from both sides. Often, the float is tweaked or twisted on it's bracket and one "bulb" sits higher or lower than the other. You won't catch this unless you check from both sides.
If you want to buy something, get one of these clear tube fittings .....
https://www.ebay.com/itm/274881260720
It will let you check your float setting externally like so ......
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