# Old style auto engine analyzer...need answer fast **URL:** \ **Category:** Factual Questions\ **Created:** [May 17, 2016, 2:09pm UTC](https://boards.straightdope.com/t/old-style-auto-engine-analyzer-need-answer-fast/754993 "2016-05-17T14:09:51Z")\ **Posts on this page:** 16\ **Page:** 1
**Author:** ![HotDogWater](https://avatars.discourse-cdn.com/v4/letter/h/35a633/32.png) [@HotDogWater](https://boards.straightdope.com/u/HotDogWater)\ **Post date:** [May 17, 2016, 2:09pm UTC](https://boards.straightdope.com/t/old-style-auto-engine-analyzer-need-answer-fast/754993/1 "2016-05-17T14:09:51Z")
I have an old style engine analyzer that has a positive and negative cables for power from the battery, and an alligator clip that attaches to the coil for RPM measurement. I would like to use this on a motorcycle, should I select 4, 6 or 8 cylinder for the most accurate measurement? ---
**Author:** ![excavating\_for\_a\_mind](https://avatars.discourse-cdn.com/v4/letter/e/e8c25b/32.png) [@excavating\_for\_a\_mind](https://boards.straightdope.com/u/excavating_for_a_mind)\ **Post date:** [May 17, 2016, 2:19pm UTC](https://boards.straightdope.com/t/old-style-auto-engine-analyzer-need-answer-fast/754993/2 "2016-05-17T14:19:12Z")
How many cylinders does the motorcycle engine have? What measurement are you interested in? ---
**Author:** ![HotDogWater](https://avatars.discourse-cdn.com/v4/letter/h/35a633/32.png) [@HotDogWater](https://boards.straightdope.com/u/HotDogWater)\ **Post date:** [May 17, 2016, 2:21pm UTC](https://boards.straightdope.com/t/old-style-auto-engine-analyzer-need-answer-fast/754993/3 "2016-05-17T14:21:04Z")
V twin harley sportster. Trying to set rpm at idle. ---
**Author:** ![HotDogWater](https://avatars.discourse-cdn.com/v4/letter/h/35a633/32.png) [@HotDogWater](https://boards.straightdope.com/u/HotDogWater)\ **Post date:** [May 17, 2016, 2:41pm UTC](https://boards.straightdope.com/t/old-style-auto-engine-analyzer-need-answer-fast/754993/4 "2016-05-17T14:41:18Z")
V twin harley sportster. Trying to set rpm at idle. ---
**Author:** ![Gary\_T](https://avatars.discourse-cdn.com/v4/letter/g/3ec8ea/32.png) [@Gary\_T](https://boards.straightdope.com/u/Gary_T)\ **Post date:** [May 17, 2016, 3:15pm UTC](https://boards.straightdope.com/t/old-style-auto-engine-analyzer-need-answer-fast/754993/5 "2016-05-17T15:15:25Z")
Select 4 and double the reading. ---
**Author:** ![HotDogWater](https://avatars.discourse-cdn.com/v4/letter/h/35a633/32.png) [@HotDogWater](https://boards.straightdope.com/u/HotDogWater)\ **Post date:** [May 17, 2016, 3:21pm UTC](https://boards.straightdope.com/t/old-style-auto-engine-analyzer-need-answer-fast/754993/6 "2016-05-17T15:21:25Z")
Thanks! ---
**Author:** ![Isilder](https://avatars.discourse-cdn.com/v4/letter/i/cc9497/32.png) [@Isilder](https://boards.straightdope.com/u/Isilder)\ **Post date:** [May 17, 2016, 4:36pm UTC](https://boards.straightdope.com/t/old-style-auto-engine-analyzer-need-answer-fast/754993/7 "2016-05-17T16:36:37Z")
> [@Gary\_T](#): > > Select 4 and double the reading. yeah , based on car engine knowledge, that would make sense… but doesn’t the motorbike fire off the sparks twice as often as needed, because they can’t be bothered having a half speed cog ? Select 4 and see what the reading says. Its either accurate or in need of doubling. ---
**Author:** ![jz78817](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jz78817/32/1028_2.png) [@jz78817](https://boards.straightdope.com/u/jz78817)\ **Post date:** [May 17, 2016, 5:19pm UTC](https://boards.straightdope.com/t/old-style-auto-engine-analyzer-need-answer-fast/754993/8 "2016-05-17T17:19:34Z")
> [@Isilder](#): > > yeah , based on car engine knowledge, that would make sense… but doesn’t the motorbike fire off the sparks twice as often as needed, because they can’t be bothered having a half speed cog ? > > Select 4 and see what the reading says. > > Its either accurate or in need of doubling. it depends how old it is, Harleys used to have “wasted spark” ignition but I don’t think they’ve done that ever since moving to fuel injection. ---
**Author:** ![Hail\_Ants](https://avatars.discourse-cdn.com/v4/letter/h/dc4da7/32.png) [@Hail\_Ants](https://boards.straightdope.com/u/Hail_Ants)\ **Post date:** [May 18, 2016, 11:55am UTC](https://boards.straightdope.com/t/old-style-auto-engine-analyzer-need-answer-fast/754993/9 "2016-05-18T11:55:37Z")
Forgive the question/comment, not really a motorcycle guy but still, every single motorcycle I’ve ever seen in my entire life had a built-in, factory tachometer on its ‘dash’… ---
**Author:** ![Joey\_P](https://avatars.discourse-cdn.com/v4/letter/j/919ad9/32.png) [@Joey\_P](https://boards.straightdope.com/u/Joey_P)\ **Post date:** [May 18, 2016, 12:06pm UTC](https://boards.straightdope.com/t/old-style-auto-engine-analyzer-need-answer-fast/754993/10 "2016-05-18T12:06:56Z")
> [@Hail\_Ants](#): > > Forgive the question/comment, not really a motorcycle guy but still, every single motorcycle I’ve ever seen in my entire life had a built-in, factory tachometer on its ‘dash’… [Mine doesn’t](http://www.motorcycle-usa.com/photogallerys/AERO4.jpg?378220), so there’s your counterexample. (note, not a picture of my actual bike, just a picture of the same model I found on the internet.) ---
**Author:** ![HotDogWater](https://avatars.discourse-cdn.com/v4/letter/h/35a633/32.png) [@HotDogWater](https://boards.straightdope.com/u/HotDogWater)\ **Post date:** [May 18, 2016, 1:08pm UTC](https://boards.straightdope.com/t/old-style-auto-engine-analyzer-need-answer-fast/754993/11 "2016-05-18T13:08:56Z")
This sporty I’m working on has no tach, and neither does my honda shadow. Back to the OP, my buddy did not bring the bike over yesterday as planned. When I get to check the RPM at idle, I will update you guys. ---
**Author:** ![Hail\_Ants](https://avatars.discourse-cdn.com/v4/letter/h/dc4da7/32.png) [@Hail\_Ants](https://boards.straightdope.com/u/Hail_Ants)\ **Post date:** [May 18, 2016, 1:10pm UTC](https://boards.straightdope.com/t/old-style-auto-engine-analyzer-need-answer-fast/754993/12 "2016-05-18T13:10:59Z")
> [@Joey\_P](#): > > [Mine doesn’t](http://www.motorcycle-usa.com/photogallerys/AERO4.jpg?378220), so there’s your counterexample. (note, not a picture of my actual bike, just a picture of the same model I found on the internet.) Oh that’s right\*!\* The big chrome retro gauge on the gas tank is a _speedometer_ not a tach. I assume this must have something to do with Harleys not being nearly as ‘revy’ as Japanese bikes? ---
**Author:** ![Common\_Tater](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/common_tater/32/13846_2.png) [@Common\_Tater](https://boards.straightdope.com/u/Common_Tater)\ **Post date:** [May 19, 2016, 8:24am UTC](https://boards.straightdope.com/t/old-style-auto-engine-analyzer-need-answer-fast/754993/13 "2016-05-19T08:24:00Z")
Harley’s are a bit different. The two pistons are not opposed at 90 degrees or whatever with a heavy counterweight, each piston instead is connected to one pin on the crank, fires fairly close in sequence right after each other with a long pause in between. This gives them a lot of low end torque and their unique exhaust note. ---
**Author:** ![Just\_Asking\_Questions](https://avatars.discourse-cdn.com/v4/letter/j/ba9def/32.png) [@Just\_Asking\_Questions](https://boards.straightdope.com/u/Just_Asking_Questions)\ **Post date:** [May 19, 2016, 2:42pm UTC](https://boards.straightdope.com/t/old-style-auto-engine-analyzer-need-answer-fast/754993/14 "2016-05-19T14:42:22Z")
> [@Common\_Tater](#): > > Harley’s are a bit different. The two pistons are not opposed at 90 degrees or whatever with a heavy counterweight, each piston instead is connected to one pin on the crank, fires fairly close in sequence right after each other with a long pause in between. This gives them a lot of low end torque and their unique exhaust note. Potatopotatopotato… Whenever I see a Harley idling, I’m temped to tell the rider “I can tune that thing up for you so it runs good.” ---
**Author:** ![jz78817](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jz78817/32/1028_2.png) [@jz78817](https://boards.straightdope.com/u/jz78817)\ **Post date:** [May 19, 2016, 2:53pm UTC](https://boards.straightdope.com/t/old-style-auto-engine-analyzer-need-answer-fast/754993/15 "2016-05-19T14:53:12Z")
> [@Just\_Asking\_Questions](#): > > Potatopotatopotato… > > Whenever I see a Harley idling, I’m temped to tell the rider “I can tune that thing up for you so it runs good.” trust me, they’ve heard it a million times. you’re not being witty or original. ---
**Author:** ![Just\_Asking\_Questions](https://avatars.discourse-cdn.com/v4/letter/j/ba9def/32.png) [@Just\_Asking\_Questions](https://boards.straightdope.com/u/Just_Asking_Questions)\ **Post date:** [May 19, 2016, 5:09pm UTC](https://boards.straightdope.com/t/old-style-auto-engine-analyzer-need-answer-fast/754993/16 "2016-05-19T17:09:06Z")
> [@jz78817](#): > > trust me, they’ve heard it a million times. you’re not being witty or original. Neither are bikers that run straight pipes. I’ve heard that a million times, too. You run a bike that sounds like that, you can stand to hear my “witty” remark again. It’s less annoying than hearing straight pipes night and day.