TinyTach question

[carbineone]

Heres the deal.I have been trying to figure out the correct setting for my Teleflex 7000RPM Tach and my motor is a 1974 50HP Lark two cylinder..I have a Tinytach here that was on a Briggs 5HP 4 stroke on the kids go cart..I have the Teleflex Tach set to the 6p setting and the Tiny tach hooked to the top plug wire.When I run the motor the boat tach always reads exactly half what the Tiny Tach RPMs says.2000RPM on my Teleflex Tach says 4000 on the Tinytach,3000 on the boat tach and the Tiny Tach says 6000RPMs and so on. This is the older style Tinytach and not the newer type that are adjustable for differant engine types so would it be normal for the Tinytach to always read double than my teleflex in the boat because of firing differances possibly between the two differant motors?

I am just trying to temporarily use the Tinytach to get confirmation that my Teleflex one is reading correctly and set to the right setting....Thanks

 

[Vic.S]

Re: TinyTach question

If the Tiny tach was set for a 4 stroke it will read double the correct rpm on a 2 stroke. Your boat tach is correct

You've already figured it out for yourself. A 4 stroke only fires once every two revolutions but a two stroke fires every revolution ... twice as often.

 

[carbineone]

Re: TinyTach question

Vic,thanks for the reply but I called my buddy at the Mower store today and he said a Single Cylinder Briggs 5HP is going to fire once every stroke also.Thats what I thought the Briggs should do.They fire every time the flywheel makes one revolution past the magnets whether its on the compression or exhaust stroke.Then using just one cylinder on the 2 stroke two cylinder Evinrude it should fire one time each revolution also so I should get the same reading on both the Briggs and the Evinrude motors with the Tinytach.I called Tinytach but the tech guy is gone till Wendesday...Thanks

 

[wilde1j]

Re: TinyTach question

I don't think a B&S four stroke motor can be coaxed to fire every time around, unless your mower shop has invented something really special. I don't think it's possible.

 

[Vic.S]

Re: TinyTach question

my buddy at the Mower store today and he said a Single Cylinder Briggs 5HP is going to fire once every stroke also

In which case you should get the same reading on your outboard. Your boat tach must be wrong.

 

[carbineone]

Re: TinyTach question

Well simply the reason the old Briggs fires everytime as he described it is they are ran off a magnet on the flywheel and everytime the magnet passes on each revolution it fires.I sure would think he would know as hes about 65 and has had a little Mower small engine repair shop for about 40 plus years but maybe hes wrong and the little older Briggs do fire off the camshaft but he thinks they fire off the magnets on the flywheel so it would have to fire every revolution if this is so...Just was a easy simple way to do it as he said....Thanks and maybe someone knows Briggs better than Mel to let us know 100% for sure.....