1988 Dt115 tach problem

[biggy boy]

Hi
I picked up a used DT 115 last month on a 16 foot skiboat. The built in tach only goes up to 4000 rpm
at WOT while hooked up to the proper tach control unit coming from the motor. it is set at 6 pulse.
I added a wire from the top spark coil and ran it to the tach and disconected the other pulse input. I set the tach to two pulse and it reads 2750 rpm at WOT
this tells me that the actual rpm is 5500 at WOT.
What is the likley hood that it is the tach control unit?
or could it be the tach itself that is faulty.
I have also found that my fuse was blown for the charging system. I'm thinking that was do to a loose cable at the plus of the battery, have not run the boat since replacing the fuse.
Any help would be great.
Thanks
Glen

 

[biggy boy]

Re: 1988 Dt115 tach problem

I could go out and buy a new tach but they are well over $100.00. I was told I could not return the tach once I bought it. or i could buy the tach control and find out it is not the problem.
This is why i'm asking which is more likely to fail.
The tach or the tach control unit?

Thanks
Glen

 

[biggy boy]

Re: 1988 Dt115 tach problem

Another observation I have found is that when using the trim button the rpm will eather drop or increase mementarily while pushing the trim button. the motor is not surging just the rmp guage.
I'll just keep talking to myself maybe i'll figure it out!?!?!d

Glen

 

[biggy boy]

Re: 1988 Dt115 tach problem

I went out and picked up a new tach and that fixed the problem.
Thanks to everyone and their great advice and help with my problem.
Without your help I would have never figured it out.

Glen