Prop for 1975 50hp Merc

[joblo33]

Hi,<br />I have a 1975 Merc 500 on a very light (I can easily pick up the front or back) aluminum boat and am trying to decide on a prop. I'm currently using a 13 pitch which I have two of and they're great for getting out of the hole and wakeboarding behind, but the engine is screaming at full throttle and isn't as fast as I had hoped. How much prop is too much? I have a 16P sitting in my shop that I'll probably try this week. Is that too much of a jump? Anyone else been through this with a 50 on a tinny?

 

[Dunaruna]

Re: Prop for 1975 50hp Merc

What's your WOT RPM? That's the key.<br /><br />Aldo

 

[joblo33]

Re: Prop for 1975 50hp Merc

Sorry, don't have a tach or anywhere to mount one. If I were to borrow one how many pulses do I set it to?

 

[Dunaruna]

Re: Prop for 1975 50hp Merc

Originally posted by Eric B:<br /> Sorry, don't have a tach or anywhere to mount one. If I were to borrow one how many pulses do I set it to?

6P.<br /><br />Your recommended WOT is 4800 - 5500. Being an older motor, maybe 5000 - 5200 is the target you should aim for.<br /><br />From what you have described, going from 13 to 16 is a step in the right direction.

 

[Greg New Zealand]

Re: Prop for 1975 50hp Merc

I have a 1976 50 on a 13'2" glass boat (heavy for it's length). Prop is 10 3/4 x 14P. Top speed on salt with 1 POB is 40mph. If your boat is that light I would go to 16P. You have a great motor!

 

[joblo33]

Re: Prop for 1975 50hp Merc

So do you <br />And I bet you've got that fancy Electronic ignition too I'm stuck with the discontinued cap and rotor.

 

[Greg New Zealand]

Re: Prop for 1975 50hp Merc

Nope - mine has a rebuilt '73 powerhead with the old dizzie and coil setup. Just bought a tach on a local online auction site and can't wait to fit it and check my revs

 

[joblo33]

Re: Prop for 1975 50hp Merc

Ya, they're nice engines. A little picky, but hey, fixing 'em is half the fun.