i have a 76 18ft baja (1500lbs) with a 72 115hp merc. compression was 110-115 cold, fresh out of storage. Running 93 gas and qiucksilver prem. oil. at 4600 rpms my gps states im doing 30-31mph this doesnt seem right. does anyone have any rough idea of what i should be going? Is it spent? prop...