Strange performance

[surrender]

1996 88 Special, 17 ' McKee craft
Ok, so after about 40 hours of good use since aquiring dead motor and doing all the things required to get it running some strange things are going on. First the things done:
New fuel in tank, new fuel lines and fuel pump rebuild
New filter
New rectifier(tach was not working,battery was not charging)
New tach
New battery
New plugs, wires, power pack and coils
Changed impeller and lower unit oil

All done a couple of months ago.

Boat was charging battery to 16-17 volts(unregulated system) unless I turned on lights or something else.
WOT 5700 rpm
All good

Last week battery only charging to 13.2 max, most of the time it shows 12.5-12.8 while running. I checked water level in battery and found I needed to add some, maybe I boiled it out from the overcharging. Sat it showed 13.4 max running 5000 rpm

Then Sat, boat WOT was 6050 rpm.

Any thoughts? Did something internal free up(carbon deposits?) to increase the RPM? All seems ok, just dont know if I should go back to the old 17 in prop, running 15 now

 

[surrender]

Re: Strange performance

No one has any thoughts?

 

[jonesg]

Re: Strange performance

This is the 3rd time I've read the post, still can't understand the question, if you installed a smaller prop and its over speeding, go back to the 17.

 

[mikesea]

Re: Strange performance

another possibility is ,the tach is taking a crap because of the electrical glitches,it does work of the charge unit,if something is amiss there ,it could be screwing the tach

 

[surrender]

Re: Strange performance

Ok, first the prop was changed to a 15 some time ago to get the RPM's up. The change in RPM is NOT from the prop. 15 inch prop and 5700 was max for a couple of months. All of a sudden I have 6000+ with the same prop. Could be tach going bad. I'll figure it out.

 

[WadmalawJoe]

Re: Strange performance

I don't know if this helps but, I had a 115hp go up like that on the rpms when I changed over to Amsoil (that synthetic 2-stroke oil). This occured over a period of a month maybe two and I was using the boat a couple times a week.

 

[surrender]

Re: Strange performance

Interesting on the oil changing the rpm's. I did change to penzoil but the change was a day after I noticed the rpm increase. Going to get a hold of another tach and check that before anything else.