1998 gl 1500...134000 miles...Regular oil changes since day one. Crusing at 55mph engine stumbles for about 2 or 3 seconds when I hit the gas. Same thing happens at any speed when accelerating and when taking off from a dead stop. Other than that it runs like a top. The bike sat for 4 years and Ive ran 1/2 tank of gas mixed with SEAFOAM through it. Any sugestions would be appreciated. I do all my own maintenance. Thanks