Tachometer for testing

[Mezadami]

Hi, Any suggestions for a tachometer to link and sync the carb and timing? I bought a Dwell/Tach tester at Canadian Tire, which I was later told that this may not work since a vehicle is 4 stroke and I'm workign with a 2-stroke. Can I just buy a tach gauge (which I want to buy to install on the boat anyways) and test it that way or will this not work properly?

Any suggestions would be greatly appreciated.

Thanks,
Mike

 

[Chris1956]

Re: Tachometer for testing

Mike, Most OB Tachs count the number of pulses in the alternator coils. You can try the dwell-tach and see if it works. If you have a multiple ignition-coil motor, you will need to hook it to the alternator to get any kind of decent reading. You may need to use the six cylinder scale and divide or multiple the reading, since most mercs would appear(to your dwell tach) to be a 12 cylinder 4 cycle motor.

 

[Mezadami]

Re: Tachometer for testing

My OB is a 4 cyl. This tach tester does have 4, 6, 8 cyl reading. Would I still need to divide or multiply?

 

[Silvertip]

Re: Tachometer for testing

Each cylinder on older 4-stroke car engines fires once every two-revolutions of the engine. A two-stroke fires every revolution. If you hook the tach to just one coil and use the 4-cylinder scale, you would multiply by two to get the proper reading. To clarify, on the 4 cylinder reading, the tach is is looking for two pulses every rev (two cylinders fire each revolution on a 4 cylinder 4 stroke). On the two stroke, each cylinder has its own coil so you are sending only one pulse per rev to the tach. Therefore, you need to multiply by two. All of this of course depends on whether the tach will work off the coil. You do realize of course, the meter does not hook to the high tension lead. It hooks to the small terminal on the coil.

 

[Smig]

Re: Tachometer for testing

Can I just buy a tach gauge (which I want to buy to install on the boat anyways) and test it that way...

By all means - just buy the correct gauge, put it in and you are set!

 

[Mezadami]

Re: Tachometer for testing

Thanks everyone for your response. As per my manual, I does say to connect to the negative on the coil and also to a good ground onthe engine. I think I'm just going to buy a tach which I was going to install next spring. I might as just as well do it now and get it over with. Thanks again...

Mike