[Elecraft] K1 help please

[K2TL]

Hello
I just picked up a used K1, meaning I did not build it.  It seems to be 
in FB shape and I am having a super time with it.  However, I found that 
the power output on 40 meters is not consistent across the VFO tuning 
range. I get at least 5.5 watts from about 7080 down to about 7020.  
Above and below this the power drops off, to maybe as low as 2 or 3 
watts.  I can not bring it up any higher using the methods described in 
the manual.  This K1 has the 4 band filter and the internal ATU.  SWR is 
always 1:1 on 40...even tried it into a dummy load.  The VFO range is 
set to 180 Khz..  Now, before I start diddling with an alignment , is 
this normal transmitter bandwidth?  How can I bring the power output up 
more towards the low end of the band?
Thanks a bunch guys!
Jim, K2TL