ATX PLT ABORTED TKOF DUE TO ACFT BUFFET DURING LIFTOFF RESULTING IN RUNNING OFF END OF RWY.

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ON THE MORNING OF APR/WED/94; I HAD A CHARTER FLT FROM JAC TO CYS. I HAD 5 PAX TO TAKE ON THE FLT. THE ACFT WAS IN A HEATED HANGAR ALL NIGHT BUT SINCE IT WAS SNOWING WHEN THE ACFT WAS PULLED OUT; I WAS FORCED TO DEICE THE ACFT. WHILE THE PAX WAITED; I DEICED THE 421 MYSELF. I WAS IN COMPLIANCE WITH GND ICING RULE REQUIRED BY MY MANUAL AND FAR 135. I LOADED THE PAX AND TAXIED FOR TKOF TO RWY 18 AT JAC. I CALLED SLC FOR MY IFR CLRNC AS I TAXIED OUT. I COMPLETED MY RUN-UP AND VISUALLY CHKED THE WINGS FOR CONTAMINATION AND THERE WAS NONE. I TAXIED ON TO THE RWY AND APPLIED TKOF PWR. UPON REACHING ABOUT 100 KIAS; I BEGAN ROTATION; THE ELEVATOR FELT SLUGGISH AND BEGAN A SLIGHT BUFFET. I IMMEDIATELY CUT THE PWR AND ABORTED THE TKOF. IN AN ATTEMPT TO STOP THE ACFT; I WENT OFF THE END OF THE RWY BY ABOUT 25 FT. I WAS ABLE TO TAXI THE ACFT BACK ON THE RWY WITH NO TROUBLE. THE ACFT WAS DAMAGED IN NO WAY AND NONE OF THE ARPT PROPERTY WAS DAMAGED. NONE OF THE 5 PAX ON THE ACFT WERE INJURED EITHER. ONCE I WAS BACK ON THE RAMP; I BRIEFED THE PAX ON WHAT HAD JUST OCCURRED. I THEN CALLED ARPT SECURITY AND NOTIFIED THEM AS TO WHAT HAD HAPPENED. I THEN CALLED THE SLC FSDO AND TALKED TO MY POI. I INFORMED HIM OF THE PROB AND HE COMPLETED AN INCIDENT FORM OVER THE TELEPHONE. HE SAID THAT THIS WAS BASICALLY THE END OF THE WHOLE THING AND THE INCIDENT RPT WOULD BE FILED IN THEIR OFFICE IN SALT LAKE CITY. HE REASSURED ME THAT I HAD DONE THE RIGHT THING. IT IS MY OPINION THAT THERE WAS PERHAPS SOME CONTAMINATION ON THE TOP OF THE ACFT THAT WAS NOT VISIBLE WHEN I DEICED AND THAT CONTRIBUTED TO THE BUFFET I FELT ON TKOF. PERHAPS THE ACFT WOULD HAVE FLOWN IF I HAD ATTEMPTED TO ROTATE AT A HIGHER SPD; BUT THAT SEEMED TO BE A POOR CHOICE ON A 6299 FT RWY AT GROSS WT. I STILL BELIEVE I DID A PROPER JOB OF DEICING AND MADE THE CORRECT CHOICE TO ABORT THE TKOF. I AM STILL NOT CERTAIN; HOWEVER; WHAT CAUSED THE BUFFET IN THE CTL ON TKOF. ONCE I COMPLETED MY PHONE CONVERSATION WITH THE FAA; I DEICED THE ENTIRE ACFT WITH HOT GLYCOL AND DEPARTED JAC WITH NO PROB.