<VV> 828 miles this weekend - car running lean - advice appreciated

[Guus de Haan]

Yesterday evening we came back from our trip to Germany with the  
Corsa. Total mileage was 828 and the car ran very well. Most of the  
time we drove 75 mph (indicated on the GPS system) on the autobahn  
with a short burst to 94 mph to see if the turbo still works. Well it  
did and I was again surprised how much more fluent extra power is  
there when the turbo kicks in. This was nowhere it's maximum but I had  
to stop because the warning light and the buzzer came on. The fan belt  
was on so I just slowed down for a few miles and took the next exit to  
park and let it cool down a bit. After that everything was back to  
normal.

What causes the temperature to go up too fast is a to lean mixture.  
The car knocks a bit when accelerating but not when maintaining a  
steady pace. I also noticed that when the turbo kicks in the knocking  
disappears. On our trip to Germany it was almost on lambda 14,7 all  
the time (mine has a Safe Guard system with sensor in the exhaust).  
But on the way back home it started running leaner and leaner (near  
11). Does anyone have an explanation what could cause this? I could  
change the YH to a size bigger jet but would like to know first what  
could cause this change this during the trip.

Fuel consumption was 19,3 mpg over the total trip. Since I drive the  
car without using the performance most of the time I run it on  
regular. I don't mind putting higher octane in, but since the turbo's  
have such a low compression they don't really use it most of the time,  
do they? And I always check the Safe Guard indicator and listen to the  
engine when pushing it.

Great weather, great people, great car, what more do you want!

Guus de Haan
The Netherlands
'65 Corsa Turbo-Charged Cvt