I/o issues.

[slim6969]

hey every one. I have an 80s 19ft tempest with a 4.3 Mercruiser and Alpha 1 out drive. I’m having 3 issues

1. When I first start the boat up the exhaust smells like burnt oil for a min or two

2. I don’t think my tach works but it seems the more gas I give it the slower it gos now you can hear the rpms of the Engine pic up but the boat does not seem to pic up speed

the reason I don’t think the tach works is Because it never seems to go past 2500 rpm even though you can clearly hear the rpms pic up.

My tought is the prop may be slipping ???

3. If I trim up when running it makes a sound like the prop is coming out of the water and my speed falls way Down to the point I’m off plane. Now just so I’m clear the prop is not coming out of the water and the trim switch will only trim up so far and stop.


Any any help would be greatly appreciated. This is the first I/o I’ve ever owned so it all seems new to me.

 

[Jcris]

Random thoughts here,
Check the crankcase oil
Pull the drive and inspect

 

[harringtondav]

My guesses: 1 Oil is leaking down the valve seals overnight, and burning off during start up. Oil is cheap, so live with this one as long as you can stay ahead of the consumption. 2. Get a photo tach and check WOT w/muffs, or on the trailer at the ramp without a prop. Only apply short throttle bursts 'cause the engine should rev. over the 4800 rpm operating max. Also if on muffs, you could suck the garden hose dry, and that's not good. The engine should jump to over 5000 rpm. 3. Any boat will cavitate the prop if trimmed up too high. Trim up just enough to get the max rpm for your engine speed, but stop before the boat starts to porpoise bounce. The faster the boat speed, the higher you can trim up before cavitation. Without a working tach, it's hard to tell of your prop is the right pitch. If you really are only getting 2500 rpm at WOT, your prop is pitched WAY to high. This could be causing a low operating speed, and premature up trim cavitation. I'd guess that vintage 4.3 is 160 hp. On a boat that size I'd guess an 19" prop is about right. Borrow a 17" prop and see if the WOT rpm picks up, but don't run over 4800 rpm.

 

[nola mike]

If you really are only getting 2500 rpm at WOT, your prop is pitched WAY to high.

Or your engine isn't working correctly.

 

[porscheguy]

Or your engine isn't working correctly.

Yeah. Props don’t magically gain pitch overnight.

 

[slim6969]

So the drive has a 19 pitch prop on it

If if I take the drive off what am I looking for ??
Also as I said I can hear the rpms pick up but the tach does not so that.




Is it possible the prop is sliping at higher rpm ?

 

[slim6969]

Also the oil burn seems to happen every time I start it even after say half an hour siting on the water. I did also notice that when I got the boat the round air filter on the carb was plugged with dirty oil. So seems there’s quite a bit of blow by ? I assume if I pull the plungs out I’ll be able to see some oil on them if it is blowing by the rings ??

 

[slim6969]

This is the prop number am I right in saying it’s a 19 pitch 14 inch??? Does that seem like the right prop.



48-78120-19

 

[slim6969]

This is the prop number am I right in saying it’s a 19 pitch 14 inch??? Does that seem like the right prop.



48-78120-19

 

[TurtleTamer]

Very little history on this one. I'd clean up the flame arrestor, perform a compression check and tuneup, change fluids, and mark the prop and hub. Take it out and come home. If the marks moved in relation to each other, you have a hub that spins.

The tach itself could be bad or something else could be going on with the ignition. I'd go the tuneup route and see what happens (plugs, wires, cap, rotor).

 

[slim6969]

Thanks for the reply I’m going to pick up a new tach and see if it reads the same as I don’t have anyway to test it. And will also mark the prop before I take her out again

fluids have been changed. And plugs wires and what not have also been changed.


The flame arrester is the silver thing that sits on top of the carb ??? If so that’s been cleaned as well



what would be good numbers for a compression test. ???

 

[Rick Stephens]

http://www.boatfix.com/merc/Bullet/97/97_25.pdf

 

[slim6969]

Thanks Rick. Very helpful