Tach question

[vucelick]

I was checking to see of my tach was set to the proper engine size the other day. When I removed the tach there was a rubber plug in the back that covered the hole for the "number of cylinders" switch, when I looked inside the hole there is no pointer or dial to turn, it looks like there should be one, but there is not. The tach is a quicksilver brand, and seems to work fine, however when the key is off the tach reads 2100 RPM, it returns to zero when you start the motor. I am trying to determine the correct prop size and every prop I use over revs the motor. The boat is an 18' aluminum center consol flat bottom with a 100 hp mariner.

 

[Bob_VT]

Re: Tach question

Read this link http://www.tflx.com/PDF/99320.pdf it is the trouble shooting link for telflex tachs and it is about the same infor as other brands. The tach will not zero until the key is on.<br /><br />Your motor over revs at WOT? Well, by how much? If you increase your prop to a higher pitch it should drop the rpms. You can also set the motor about an inch lower and this might do it too. What size prop are you running now?<br /><br />Bob

 

[Scottj25]

Re: Tach question

I had the same type of tach. The tach. reading 2500 until the key is turned is normal, as for the plug in the back with no adjustment this is normal for this tach. it gets it reading from the alt/stator my counting the pols that are being put out. My guess is that its hooked up to a force o/b.

 

[vucelick]

Re: Tach question

Actually it is a mariner outboard, although the motor is newer than the hull/console which has the tach in it. The motor will easily over rev the 5250 redline for this motor even with a 13 3/4 x 23 pitch prop, the boat came with a 17 and a 19 but both of them were much to low, I can see 5400-5600 until the rev limiter kicks in, so my question about the tach is really to determine if the RPM I am reaching is actual or is artificially high because of a mismatched tach.