It's been a long time, but I seem to remember 0.004" Intake & 0.006" Exhaust.

There is some minor variation by model.

>> The big takeaway is that Airhead valves tend to tighten up over time, not loosen. You'll want to adjust your valves at least every 3,000 miles until you get a "feel" for how fast the process occurs on your machine.

R75's were a product of the "leaded fuel" age. The lead commonly found in fuels of the 1970's cushioned the valve seat. Now that we have only "lead free" fuels, the valves tend to slowly "recess" into the valve seats, which closes the valve clearance. Running the engine without any valve clearance will tend to allow the lifters to burn up the camshaft lobes. So not checking valve clearances regularly can get expensive. 

.006 intake and .008 exhaust has become the most universal recommendation. BMW did spec some tighter clearances for some models, but then fell back to .006 and .008. Personally, I tend to give a little room to shrink and go .006 / .009. 

I was told by a mechanic who went to BMW school back in the 70's, he was told they should be "tight on the .004 and loose on the .006".  I've read they could be 4/6; 6/8, or 4/8.  They also say it doesn't matter much as long as both sides are the same.  If you start losing top end, my experience is the exhaust is down to almost 0.  

Posted by: @4949

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.006 intake and .008 exhaust has become the most universal recommendation. 

Valve clearance is not one of those tuning tips that's going to give measurable results in "quarter mile drag strip times". Yes, valve clearance IS necessary, but only to allow motor oil to lubricate the camshaft. For this reason I can believe and see the practicality of  the somewhat larger 0.006" and 0.008" suggested by David. 

And yes, you should feel about 1oz of drag on the feeler gauge as it's being pulled out. Not too tight, but not loose either.