>>Are you sure? When I drive more than five upfilled tanks with
>>unleaded gas I start hearing the work of my vents. When I filled
>>up with leaded gas it stops. So I'm driving with relations of
>>1 leaded to 3 unleaded.

Lead lubricates and quiets the valves where the valve contacts the seat. =
 The issue is when using leaded gas, the lubrication will somewhat =
buffer the noise.  However, from your symptoms of running unleaded only, =
I wonder about clearances or if you're experiencing valve float.  Some =
of the 2000cc motors I've rebuilt had hydraulic and some solid lifters, =
but in the case of hydraulics and the age of the engine, there may be =
more noise than one would normally consider.  If your engine has solid =
lifters, then check the clearances every 3000mi (4800km). =20

Every Type IV head I've every taken apart has had steel seats with =
either the tri-metal or sodium exhaust valves which work fine with =
unleaded fuel.  Also, Gene Berg writes this in his Tech Specifications.  =
*(for those of you unaware of this person, he had done probably more =
testing on aircooled VWs than anyone outside of VW)

"The VW factory head offers the best of everything from cooling to life. =
 I must say that VW has done some fine engineering when it comes to a =
product that does the job.  In about 1967 they made a transition to =
chrome stem valves with the tri-metal exhaust valve.  This, along with =
the steel seats and brass guides that have always been used, allows =
these heads to run unleaded fuel from that time forward with no adverse =
wear problems." - GB 801-Heads

Our leaded fuel had about 3 grams of lead per gallon (when it was =
available) since I don't know what your leaded content is, I can't =
speculate on your amout when mixing, but it's obviously only 1/3 that of =
the fully leaded mixture.

I hope this helps, like I said, even in 72 Type IV's I've always had to =
run unleaded.  The heads that I've torn down and rebuilt have come from =
Germany and Brazil and all exhibit the same characteristics that allow =
them to run unleaded fuel.  Since I'm in the U.S. there may be some off =
derivitive that VW built, but I doubt it.  The steel seats and chromed =
valves offer the best life but it is always critical to check the =
clearances when using solid lifters in an aircooled motor.  The 1700, =
1800 and 2000cc aircooleds all had problems with seats dropping out.  =
This became worse in the 2000cc heads.  So, I hope you're not dropping a =
seat!

Regards

Will
61 Single Cab
63 23 Window
64 Crew Cab
93 Euro (my wife's)
80 Rabbit
81 Rabbit