Tack OK at low RPM, reads 1/2 of what is should at WOT

deerhuntre

Petty Officer 2nd Class
Joined
Apr 26, 2007
Messages
186
1978 Inline 6 115.

"Air Guide" tach spliced directly to the wires coming from the connector on the front of the control box. This is how it was when I got the boat.

I think the motor is healthy and working well. Here's why:
The boat weighs about 2100 lbs loaded. At idle, the tack reads 800 rpm out of gear. I'm using a 17" pitch prop (17 x 13) and at WOT the boat goes 38 mpg using the GPS. That seems about right, I think.

The tach at WOT reads 2500 RPM!!! So, either something is making the tach skip a beat and read 1/2 the correct RPM, or something is awry. And I'm not sure how the tack could seem to register correct RPM at idle or just over but 1/2 the apparent correct value at WOT.

I'm thinking the solution may be a new tach, but I just wanted to find out if there's anything I should check and verify before pursuing that route.
 
Top