  We analyzed a Kepler light curve of KIC 8751494, a recently recognized
novalike cataclysmic variable in the Kepler field. We detected a stable
periodicity of 0.114379(1) d, which we identified as being the binary's orbital
period. The stronger photometric period around 0.12245 d, which had been
detected from the ground-based observation, was found to be variable, and we
identified this period as being the positive superhump period. This superhump
period showed short-term (10-20 d) and strong variations in period most
unexpectedly when the object entered a slightly faint state. The fractional
superhump excess varied as large as ~30%. The variation of the period very well
traced the variation of the brightness of the system. The time-scales of this
variation of the superhump period was too slow to be interpreted as the
variation caused by the change in the disk radius due to the thermal disk
instability. We interpreted that the period variation was caused by the varying
pressure effect on the period of positive superhumps. This finding suggests
that the pressure effect, in at least novalike systems, plays a very important
(up to ~30% in the precession rate) role in producing the period of the
positive superhumps. We also described a possible detection of the negative
superhumps with a varying period of 0.1071-0.1081 d in the Q14 run of the
Kepler data. We also found that the phase of the velocity variation of the
emission lines reported in the earlier study is compatible with the SW Sex-type
classification. Further, we introduced a new two-dimentional period analysis
using least absolute shrinkage and selection operator (Lasso) and showed
superior advantage of this method.
