last guess

[boaterntexas]

Is it typical for a 1990 mercruiser alpha 1 out drive to have the ablity to turn at almost 6k rpm, on a 17' fiberglass runabout the wiegh 1900 lbs typically loaded with another 700lbs the prop is 19 pitch ss 3 blade vengance , LH rotation brand new, no dings on nicks, hull is in level straight and immaculate shape I don't think ventalation is a problem. everythign checks out, tach, prop hub, not metal filling in gearcase.. any Ideas or more trouble shooting tips?<br /><br /> Is there any way a shop could test this with out putting it in water?<br /><br /> Thakns,<br /> Thomas

 

[denniz]

Re: last guess

Dont know what engine you have, but if your tachs right you need ALOT more prop.23P minimum.

 

[denniz]

Re: last guess

WHOA!!!! read your other post.. Youve got a 3.0 I doubt your really turning 6grand unless your trimming too high,better recheck your tach.

 

[boaterntexas]

Re: last guess

yeah 3.0,, I put it on another tach out of the water with muff on, and only idled, they both read the same, is there another way to test tachs?

 

[boaterntexas]

Re: last guess

I was told the prop I have ss mecr marine vengance, 19' LH rotation, is actually made for an inboard, and would cuase my high rpms, since I have a stern drive, and that I should just get another prop same pitch ( 19 is what the factory stocked this thing with) and aluminum would be fine.. True or false?

 

[flashback]

Re: last guess

your crazy, there is NO WAY an inboard prop will fit on an I/O...........

 

[boaterntexas]

Re: last guess

Well i guess they guy who told me that was a crazy nut, and hey is a local mech. ummm<br /><br /> I did go home and check my tach last night, on the back of it it has 6 setting 1, 2, 3, 4, 5, 6<br /><br /> it's a faria 6k guage, what would be the setting for my 4 cyl? I put it on setting 4 and it and that was obvoisly wrong when the rpm jumped to 6k<br /><br /> THanks, <br /> Thomas

 

[akriverrat]

Re: last guess

sounds like an o/b tach to go with your o/b prop. if it is you need to set it at 8. i know.

 

[boaterntexas]

Re: last guess

O/B ? as in Outboard?. Set on 8.. I will do.. wait a min it only goes to 6. I guess I'm begging to pickup on the blatent sarcasim here.. I have called faria and he told me that that 1 was the right setting.

 

[gaugeguy]

Re: last guess

There should be a label on the back of the tach that tells you the position to put it in. I believe it is going to be position #1 (4cyl or 2p). Here's the kicker though, if you had it in the wrong position, the tach is going to read slower than it should, not faster.

 

[boaterntexas]

Re: last guess

Thanks guageguy, is it possible for the tach to be on a lower revs 0 - 3000 then be off at 3500- +

 

[gaugeguy]

Re: last guess

I guess anything is possible, but unlikely. If the tach is reading OK at idle it should read correctly at higher RPM's. The best way to test the tach is to know somebody with a frequency counter or an oscilliscope. That engine will put out 33.3 Hertz for every 1000RPM it is turning (66.6 Hz @ 2krpm, 99.9 Hz @ 3krpm etc.)