Bugga bugga chugga bugga cruise

The 1406 has a reputation for doing that if it;s on anything other than a stock or mostly stock engine. It is the economy version. The 1405 is the performance version. The 1406 is jetted VERY lean. Just because it;s a 600, doesn't necessarily mean it's "big enough" for even a 273. It's all in the jetting. Also, you cannot turn a 1406 into a 1405.