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Old 05-05-2014, 09:52 PM   #11
CAMPERCART2013
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Default Re: Analogue Tachometer

equus 8068
I need to update my opinion on this tach. since we found and fixed the problem with the ignition this tach functions GREAT I truly feel all the erraticness of the tach was due to the cdi/ignitor I also just wanted it to prevent over revving seems to work great
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Old 05-10-2014, 01:10 PM   #12
OgreTX
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Default Re: Analogue Tachometer

Ok some more questions, and to throw another idea into the mix.

I understand the 8068 will work with our G1 2 cycle carts to give an accurate RPM reading. My only issue is I really don't want a GIGANTIC TACH (3 3/8") sticking up on my cart. A smaller one would be good, since I only expect to look at it when I am WOT to see if I am over-revving.

From my old car work, I have a modified (and duct tape is wonderful) small SunPro Super Tach II (very similar to the Equus 6086 (2 1/2") tach on Summit) attached to my dial back timing light (#1). The tach is attached to my ignition source (pic 3) and is adjustable for 4, 6, or 8 cylinder. In reasoning through, the tach must internally take the number of ignition impulses depending on the cylinder setting, and divide (4, 6, or 8 ) to get a RPM based on how many impulses it received.

So if I connect it to my G1 ignition, and set it for four cyl, I should get a number on the RPM of four times less than what my actual RPM is ... right? IOW, if I read 1500 RPM, the tach thinks that 1 revolution is 4 ignition impulses, but I only have 1 impulse/revolution, and therefore I have an actual RPM of 6000 ! Stated another way, if the tach “sees” four impulses from my cart, it is actually four RPM, and not one RPM like a 4 cyl.

Something is wrong with my logic, and I need some input. Have I got the logic backwards? The reason I ask, I attached it (cart up on jack stands and revved the engine up to 3,000 ... that should be 12,000 RPM No way! Also, on 8 cyl, the high rev is around 1,000 RPM, and on 6 cyl, the high rev is around 2,000. (equal revs according to my highly tuned ears … not) The sound of the revs with those rough readings is about the same … pretty high, and I wouldn’t want to go much higher based on the sound of the engine when I drive it on the road.

So two questions, really: Is my reasoning logical on how the tach works (?), and why am I getting possibly a “correct” reading on the 4 cyl setting? The tach reads around 1,000 at an idle RPM, and the service manual says the governor (which I have mechanically disconnected, drilled out, on the governor shaft) is set at 2,700 RPM. Those two numbers 1,000 and 3,000 seem to be in the ballpark about what I am reading on the tach. And if my logic is backwards, I am only revving at 750 RPM with a 3,000 reading … not possible!

The small tach is so close to what I expect, I am tempted to use it as my analog tach, but I wouldn't be here asking for advice if I didn't feel a little uncomfortable doing that.

INPUT???

Thanks in advance,
Ogre
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Old 05-10-2014, 09:01 PM   #13
SandbaggerYDRA
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Default Re: Analogue Tachometer

Quote:
Originally Posted by OgreTX View Post
Ok some more questions, and to throw another idea into the mix.

I understand the 8068 will work with our G1 2 cycle carts to give an accurate RPM reading. My only issue is I really don't want a GIGANTIC TACH (3 3/8") sticking up on my cart. A smaller one would be good, since I only expect to look at it when I am WOT to see if I am over-revving.

From my old car work, I have a modified (and duct tape is wonderful) small SunPro Super Tach II (very similar to the Equus 6086 (2 1/2") tach on Summit) attached to my dial back timing light (#1). The tach is attached to my ignition source (pic 3) and is adjustable for 4, 6, or 8 cylinder. In reasoning through, the tach must internally take the number of ignition impulses depending on the cylinder setting, and divide (4, 6, or 8 ) to get a RPM based on how many impulses it received.

So if I connect it to my G1 ignition, and set it for four cyl, I should get a number on the RPM of four times less than what my actual RPM is ... right? IOW, if I read 1500 RPM, the tach thinks that 1 revolution is 4 ignition impulses, but I only have 1 impulse/revolution, and therefore I have an actual RPM of 6000 ! Stated another way, if the tach “sees” four impulses from my cart, it is actually four RPM, and not one RPM like a 4 cyl.

Something is wrong with my logic, and I need some input. Have I got the logic backwards? The reason I ask, I attached it (cart up on jack stands and revved the engine up to 3,000 ... that should be 12,000 RPM No way! Also, on 8 cyl, the high rev is around 1,000 RPM, and on 6 cyl, the high rev is around 2,000. (equal revs according to my highly tuned ears … not) The sound of the revs with those rough readings is about the same … pretty high, and I wouldn’t want to go much higher based on the sound of the engine when I drive it on the road.

So two questions, really: Is my reasoning logical on how the tach works (?), and why am I getting possibly a “correct” reading on the 4 cyl setting? The tach reads around 1,000 at an idle RPM, and the service manual says the governor (which I have mechanically disconnected, drilled out, on the governor shaft) is set at 2,700 RPM. Those two numbers 1,000 and 3,000 seem to be in the ballpark about what I am reading on the tach. And if my logic is backwards, I am only revving at 750 RPM with a 3,000 reading … not possible!

The small tach is so close to what I expect, I am tempted to use it as my analog tach, but I wouldn't be here asking for advice if I didn't feel a little uncomfortable doing that.

INPUT???

Thanks in advance,
Ogre
One thing you have to consider is that that tach was designed for 4,6, and 8 cylinder 4 stroke engines. Your G1 is 2 stroke, which fires once per crank revolution, rather than every other revolution in a 4 stroke. Which means in simple terms, that your 4-6-8 switch in two stroke terms would be 2-3-4 cylinders. So if you set it to the "4"(2) position, you'll be reading roughly half of your actual RPM, since you only have a single cylinder.

Make any sense?
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Old 05-11-2014, 09:24 AM   #14
OgreTX
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Default Re: Analogue Tachometer

Quote:
Originally Posted by SandbaggerYDRA View Post
One thing you have to consider is that that tach was designed for 4,6, and 8 cylinder 4 stroke engines. Your G1 is 2 stroke, which fires once per crank revolution, rather than every other revolution in a 4 stroke. Which means in simple terms, that your 4-6-8 switch in two stroke terms would be 2-3-4 cylinders. So if you set it to the "4"(2) position, you'll be reading roughly half of your actual RPM, since you only have a single cylinder.

Make any sense?
Well, doh!

Thanks Sandbagger ... forgot to factor in the every other compression/exhaust stroke of the 4 cycle. So yes, that makes perfect sense.

But it still leads me to question the validity of the tach readings, just by a smaller factor. If I am reading half, then the 3,000 is actually 6,000?

More testing ....
Ogre
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Old 05-12-2014, 08:44 AM   #15
SandbaggerYDRA
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Default Re: Analogue Tachometer

Quote:
Originally Posted by OgreTX View Post
Well, doh!

Thanks Sandbagger ... forgot to factor in the every other compression/exhaust stroke of the 4 cycle. So yes, that makes perfect sense.

But it still leads me to question the validity of the tach readings, just by a smaller factor. If I am reading half, then the 3,000 is actually 6,000?

More testing ....
Ogre
I think the reason why the numbers don't seem to be working as you would think has to do with how the ignition system work on multi cylinder engines. A 4 cylinder 4 stroke engine, for example, makes a spark in one cylinder for every 90 degrees of rotation of the CAMSHAFT (which runs at half the crankshaft speed). Since an electronic tach usually connects to the distributor, it's going to count (or average) each pulse per camshaft revolution (8, 6 or 4). It's not the same as timing by an individual spark plug firing (which shouldn't change based on total cylinders), which is why the numbers don't seem to divide evenly.

The good news is that if you can find an accurate mechanical tachometer, you can probably calibrate the electronic one to agree with the reading on the mechanical unit. Depending on how your tach works, you may be able to adjust a potentiometer or change a couple of resistor values inside the tach until the RPM numbers match what the mechanical tach shows.
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Old 07-02-2014, 03:11 PM   #16
OgreTX
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Default Re: Analogue Tachometer

Ok, pulling up this two month old thread. I finished the oil seals on both sides of the engine, and cleaned up the differential (gear box), with new oil seals and new gasket to stop the leaks. My old G1 runs a lot better now, and I had a chance to do some testing.

Bought a digital tach that works on two/four cycles from Northern Tool: Digital Tach. It lets you select how many spark plug firings you get per rotation.

I set it to one firing per rotation, and compared it to the Sun Pro Tach while driving up and down the street, and amazingly it's the same! Obviously due to the slow reaction time of the digital (sampling rate), it needs to have a steady engine rpm, but even though the calibration between the two may be slightly off, for rounded gross figures the Sun Pro is basically the same readings.

Please don't ask me to do any analysis, since sandbagger already proved that I don't know how many rotations a four cycle makes for each piston firing ... LOL!

Anyway, I am ready to recommend the SunPro II as a smaller analog tach for our two-cycle engines.

As usual with all experimentation, more questions arise ... with the governor engaged, I can still cruise the street and get close to 4,000 RPM on level roadways. My manual says that the governor is set at 3,050 rpm at the factory. So how can I possibly be getting 4,000 rpm (on both tachs), and do I stand a chance of blowing it up? With the governor disengaged, I can get a lot more rpm, but now I'm not sure I want go there anymore. Have any of you G1 owners determined what the "red line" should be for our old tired carts?

Any input is appreciated.

Ogre
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