Hello all - This is a great forum, long time reader; first time poster. <br /><br />Boat in question is a 1985 BAJA Force 220, mercruiser 350cid/260hp, carb, Alpha drive. <br /><br />I have recently installed a new replacement marine long block into my project boat (same CID and HP), along with rotten stringers, and an outdrive rebuild... <br /><br />Upon breaking it in I am experiencing back firing/sputtering out the carb under load at RPM's between 1800 and 2600. At 3000 and above (only slightly as I am on hour 3 of the 20 hour break in) no backfiring at all - very smooth. The back firing just kinda comes and goes every 30-45 seconds. When it fires once there are usually a couiple of backfires that follow immediatly after. <br /><br />It occurs whether it is a fast or slow ascent or descent to the 1800-2400 RPM range. Engine starts ok, needs a little gas to fire, and idles a little rough - but I am not sure if that is just because it needs breaking in.<br /><br />The RPM range seems to be the repeatable aspect. I do not think it is valve/cam related nor fuel pump/fuel flow specfic as it smooths out so much at the higher RPM. any ideas would be apperciated.
