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General Category >> Rubber Side Down! >> Easy tach installation for dialing-in idle speed
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Message started by rijopiatt on 12/06/15 at 14:46:00

Title: Easy tach installation for dialing-in idle speed
Post by rijopiatt on 12/06/15 at 14:46:00

http://https://www.bikepics.com/pics/2015/12/06/bikepics-2767518-200.jpg
I've use this style of tachometer on an ultralight aircraft. It's accurate, small and reasonably priced at about $65.

http://https://www.bikepics.com/pics/2015/12/06/bikepics-2767517-200.jpg
It has a ground wire (white) and a sensor wire (red).

http://https://www.bikepics.com/pics/2015/12/06/bikepics-2767520-200.jpg
I've grounded to an engine mount bolt and the sensor is wrapped four times around the spark plug wire.

http://https://www.bikepics.com/pics/2015/12/06/bikepics-2767519-200.jpg
My mounting hardware is stainless steel: a cap screw for aesthetics, small washer to distribute the pressure to avoid cracking the plastic housing, fender washer to keep the rubber washer from mushrooming when tightened down, the rubber washer acts as a shock mount (tach doesn't contact the frame) and all secured with a nyloc nut.

http://https://www.bikepics.com/pics/2015/12/06/bikepics-2767521-200.jpg
The unit is mounted thru existing manufacturing holes in the frame. It's hardly noticeable when installed, but easy to read when adjusting idle speed.

This installation was a result of my inability to adjust my idle by sound, which many of you seem able to do. My hearing just isn't that great. My son-in-law said it wasn't a big deal to do so, as he has done it many times in his young life ::) on atvs, dirt bikes, etc. So, reluctantly, I let him do the adjusting about 3,000 miles ago. Now I know why my recent spark plug inspection revealed hotter conditions. When I fired-up the S40, new tach's initial read-out was about 6,500 rpms!
I've reset it so it's running 1,150-1,220 rpms now. I'm interested to see what the plug looks like at the next maintenance interval.

Title: Re: Easy tach installation for dialing-in idle spe
Post by Dave on 12/06/15 at 15:21:03

I find it hard to believe the engine was running at 6,500 rpms....that is the reported maximum HP rpm - or basically at full speed.

Check to make sure you have the tach set correctly for the number of sparks per revolution......you should have it set for 1 spark for each revolution.

If you have it set wrong (1 spark for each 2 revolution or 0.5 sparks per revoluton)........you might be idling at 675 rpm - which would be a death sentence for the cam and head.

Title: Re: Easy tach installation for dialing-in idle spe
Post by justin_o_guy2 on 12/06/15 at 15:34:58

That's all any Good Revolution NEEDS,
is ONE spark.

Title: Re: Easy tach installation for dialing-in idle spe
Post by chzeckmate on 12/07/15 at 00:57:59

1F24293E2F23383E252D203F4C0 wrote:

I think he said he's reset it so that it displays the correct RPM now. I suspect he'd had it set to 4/1 which would mean that his idle had been around 1650 at originally (way to fast) and now he's adjusted to 1/1 and set his idle to around 1200. I have mine set to 1050 and I think it's perfect there. 1200 is on the high side.

By the way, @rijopiatt, cool post!

Title: Re: Easy tach installation for dialing-in idle spe
Post by rijopiatt on 12/07/15 at 08:17:05

Sorry everyone. Mistyped the rpms. Yes, Chzeckmate is correct in all accounts in his reply. The reading was 1650 rpms initially.

Rick

Title: Re: Easy tach installation for dialing-in idle spe
Post by Dave on 12/08/15 at 09:27:30

If you decide to buy a Tiny Tach....order it directly from them and not from a retailer. The battery is not replaceable, and they only last 5 years. When you buy from a retailer you have no idea how long it has been on their shelf.

I bought one of these to use on my lawn mower so I could keep track of oil changes. I bought it from an eBay seller, and the tach/hour meter only lasted two summers. I lost all record of how many hours was on it when the battery died.

I would me more apt to buy the Tiny Tach, or the models from Trail Tech if the batteries could be replaced (or if they were powered by the battery on the bike).

Because I work on so many different engines, I spent twice as much and bought a Fast Tach from the same folks that make the Tiny Tach. It is a digital inductive tach and you just point it toward the spark plug wire and it will give you an rpm reading. (And you can put in batteries when you need to).

http://tinytach.com/handheld.php