tight."

"Aye, aye, sir!" answered Ned with a laugh.

Then he set at his task, tightening the small nuts, and screwing up the
turn-buckles, while Tom busied himself over the motor. There was some
small trouble with the carburetor that needed eliminating before it
would feed properly.

"How about the tires?" asked Ned, when he had finished the wires.

"You might pump them up. There, the motor is all right. I'm going to try
it now, while you attend to the tires."

Ned had pumped up one of the rubber circlets of the small bicycle wheels
on which the aeroplane rested, and was beginning on the second, when a
noise like a battery of machine guns going off next to his ear startled
him so that he jumped, tripped over a stone and went down, the air pump
thumping him in the back.

"What in the world happened, Tom?" he yelled, for he had to use all his
lung power to be heard above that racket. "Did it explode?"

"Explode nothing!" shouted Tom. "That's the re-built motor in action."

"In action! I should say it was in action. Is it always going to roar
like that?"

Indeed the motor was roaring away, spitting fire and burnt gases from
the exhaust pipe, and enveloping the aeroplane in a whitish haze of