View Full Version : Low altitude to high

05-30-2014, 07:33 PM
Anyone bringing your carbureted Mastercraft from low to high altitude will have to make some adjustments. These are what worked for me. Boat was from Phoenix, and now in Denver. Stock 351, 240 hp.

4160 carb had 65 jets changed to 63. Before change did not run well and blackened the stern of the boat.

Propeller was changed to a 3 blade OJ 304 13x11 on Erics recommendations, tachs out at 4100 RPM, and gps measured 40 mph with 3 in the boat.

Timing was adjusted to 14 degrees BTDC instead of the stock 10.

Idle mixtures were adjusted by handheld tach, and also by the vacuum gauge method. Tach method worked just fine, nothing better was accomplished with the vacuum gauge.

Used paper clip to check that secondaries were opening.

That is the extent of what I did to get it to run well here. This info may help so someone else may not have to do so much trial and error.