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My brother just got a 1996 Montauk with a Yamaha 70HP 4 stroke on it. It looks like it has the stock aluminum 17" pitch prop. What prop do some of the other members like with this combination?
It has a top end close to my 1988 Montauk with the ETEC 90 and Viper 15" but does not come up on plane near as fast

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These recommendations came from members with the F70.

Note the F70 has a WOT RPM max of 6300.

Engine should be mounted two or more holes up.

13 x 16 PowerTech SCD
13.25 x 14 SCP (6100 rpm's, 3 holes up)
13 x 17 Yamaha Painted SS
13.25 x 14 Yamaha Performance Series (polished)

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A different prop may help, but a 70 HP 4-stroke engine probably won't compare too favorably with a 90 HP 2-stroke for hole shot.

If the new prop makes a big improvement, be sure to let us know. It would be very impressive if the Yamaha 70 can close the gap with that ETEC 90. The Yamaha 70 4-stroke is a nice lightweight engine, which may make all the difference.

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I have a 1970 Katama 17 with powertech 13.25 x 14 on a brand new 70 hp Yamaha 4 stroke . I also have a 1988 Custom 17 with a Yamaha 90 hp 2 stroke . The 70 hp 4s performs almost identically as the 90 hp 2 s. Hole shot very close , but from 5000 to 6100 rpms , the 70 hits a passing gear and really takes off . The only real difference I see between the 2 engines is the 4 stroke gets incredible fuel economy .