Outdoor Power Equipment (Lawn Mowers, Snow Blowers, Chain Saws and more) Discussions

Hi all,

I need to adjust the RPM of my Tecumseh L-Head (9 HP / 318 cc) engine that I bought in 2007.

For that purpose, I plan to purchase "digital photo (laser) tachometer".

From my understanding this tool works by sticking a piece of reflective tape on a rotating part of the engine (such at the shaft near the pulley where the belts are located). The tool then counts the number of time this piece of tape passes in front of the laser beam in one second and multiplies by 60 to display the RPM.

Did anyone ever used such a tachometer? If yes how are you satisfied with this tool?

Also, I need to know the RPM values that this engine should be adjusted to at: full throttle and also when idling. Do anyone know these RPM values.

"Borat, what is your's like?  Does it get instantanous readings and always on the money or does it goof up and sometimes hunt for a few seconds for the right rpm especially with speed changes? "

Normally, refresh rate is probably between .5 to 1 second and is generally accurate.   Mine are getting old already and the batteries might be starting to lose some power.  On really cold days ( colder than below 0F, the lcd is a bit slow.  The tach is refreshing the readout but the lcd cannot seem to respond quickly enough thus causing partial number drop outs.  Overall, I can still get enough of the readout number to know  see the engine speed.   

   Some guys claim they can get much longer than 5 years but possibly they were tractor guys posting from Arizona.  The general spec is 5 years and probably true for a mild temp place or heated garage. 

   Mine were advertised as able to change the bats but their all potted and no instructions on how to change the bat.  Some guys on the net have changed the bat on one that looks like mine with the S1 S2 buttons.  They say it's fairly easy but the soldering of the bat delicate. 

   I'll keep fiddling with the wire hookup placement and number of turns.  Maybe this is the time to switch to an R plug to reduce noise.  Some of them come with shielded hookup wire.  It might help to cut the sensor wire close to the reader and put on thin shielded wire which I have.  Yours and relics have a ground wire and probably a better setup.  The choise was replaceable bat and no ground clip.   

UPDATE: 3/29/2011.  The three cheap tachs (not the lazer tachs) for $18 came without a ground wire and worked but were fuzzy.  After installing a ground wire inside the gage they worked fine.  The response is good and they are on the money compared to the vibratach which is very accurate.  I've quick disconnect wires on all three so can plant them on any machine I put a wire on perminantly.  An aligator clip is used on the wire from the gage to ground.  They all read the same when put on a machine. 

There are many variations of these tachs which are like the one posted by relics.  They all have the same basic board inside but there are 4 board revisions that are around.  Also, some come with a ground wire some don't.  Some are listed as replaceable battery and some not.  Some say they are potted and some not but all the same design.  Mine were listed as potted but not potted.  Mine were also listed as battery replaceable which they somewhat are.  There is no battery compartment and the case is sealed.  You have to open the case with a knive to get at the bat.  The bat is soldered along with having some silicon type glue.  Not a big deal to replace the bat but not exactly what I expected.  Still for $18 they are a good deal and accurate.

I see what you mean Dave i will have to play with those pictures and see if i can get them smaller.I noticed the battery in my tach is glued in.It looks like i could get it out though.For cheap tachs even with slower refresh rate i found measureing sag was ok.I tryed to pick areas were i went at least 10ft and mostly longer.I did have to use a small flash light as most was done after dark.Than i noted my average was between 3050 and 3300 sag rpm from 3600