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 Post subject: Re: Strobe light
PostPosted: Fri Apr 13, 2018 7:00 pm 
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Moto GP
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Joined: Mon Dec 13, 2010 4:32 pm
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Location: southwestern Pennsylvania
Country: USA
Bikes owned: 69 T350 thru 75 GT750
A 4-cylinder 4-stroke has two coils.
Each coil has 2 HT leads that feed 2 cylinders. The 2 cylinders are 360 degrees apart.

For example here is a GS1000 crank:
Image
One coil feeds cylinders #1 & #4 (outboard cylinders). The other coil feeds cylinders #2 & #3 (inboard cylinders).

For example look at the coil feeding the inboard cylinders. The two pistons are 360 degrees apart.
The coil fires both plugs as piston #2 is reaching the end of the compression stroke while piston #3 is reaching the end of the exhaust stroke.
360 degrees later the coil fires again with piston #2 reaching the end of the exhaust stroke & piston #3 reaching the end of the compression stroke.
So on the GS1000, the coils every revolution.


A simple timing light like the one I have has no info about the rpm. It just fires the strobe light every time the HT lead is fired. How that relates to rpm depends on the engine.
I also have a dwell & rpm meter from back when cars had points. The readings on that meter depend on the number of cylinders.

And from a bigger picture…
When using a timing light to set the points, it doesn’t make a difference if the strobe fires every time the points open or every other time. In either case the strobe tells you how accurately the points are set.

_________________
BAS (Bike Acquisition Syndrome) - too many bikes but have room for more

Suzuki:
GT750 2x75
GT550 72 project & 75
GT380 72
T500 73 project
T350 69, 71 & 72 project
T250 72
Honda 85 CB650SC & 86 CB700SC
09 Triumph Bonneville SE


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 Post subject: Re: Strobe light
PostPosted: Sat Apr 14, 2018 9:58 am 
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Novice racer
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Joined: Wed Jan 18, 2012 8:01 pm
Posts: 922
Location: North of Albany, NY
Country: USA
Bikes owned: T500R (now), T500M (30 yrs ago)
Talking about the 2-strokes we typically discuss here - T500, GT380/550/750, all have no timing advance, so there is no need for checking timing at higher RPM. It is the same regardless of engine speed.

If you have a motor with variable timing, then you may wish to see what it is doing at a higher RPM. As 2-stroke engines, as well as 4-stroke 4-cylinder engines with only 2 coils, fire every revolution, vs every other in a typical 4-stroke automotive engine, the strobe light will need to fire twice as often.

So how does a strobe light work? Power charges a capacitor. It senses the spark plug firing, and quickly allows the capacitor to discharge through the lamp, creating a flash that illuminates the crankshaft mark and a reference mark. In all, a pretty simple setup.

So what is the difference between a quality timing light and a cheap one? besides build quality and brightness, they have a couple of upgrades:

-- Fast response time - There is a delay between the time that the spark fires and the strobe flashes. A good timing light senses the spark, and fires the strobe, faster than a cheap light does. This is important, for the delay illuminates the timing marks late, looking as the timing is more advanced than it actually is. If you adjust the timing to the marks, you will actually be a slight bit retarded in your timing.

-- Strobe lockout - If the spark signals come too quickly, there isn't enough time for the capacitor to recharge before needing to discharge again. This could happen if the engine is running at a high RPM. The circuitry will prevent the strobe from firing until there is sufficient voltage across the capacitor for a solid flash. A timing light really only needs to flash 15-20 times a second, to see what you need to see. At 4000RPM, there are 65+ sparks a second. The timing light doesn't need to flash that fast, you aren't playing Call of Duty.

So you get what you pay for. If you pick up the cheapest timing light off eBay, shipped from some guy in Hong Kong, don't expect much. But a reasonably priced, middle of the market timing light should be more than sufficient for us guys who may pull one off the tools shelf a few times a riding season.


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 Post subject: Re: Strobe light
PostPosted: Sat Apr 14, 2018 12:34 pm 
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Moto GP
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Joined: Mon Dec 13, 2010 4:32 pm
Posts: 3194
Location: southwestern Pennsylvania
Country: USA
Bikes owned: 69 T350 thru 75 GT750
For an old-school V8 with points. Run the motor at 2k to make sure the mechanical advance is working. That gets to 133 sparks per second.

You might be able to borrow a good timing light from an auto parts store for free.

_________________
BAS (Bike Acquisition Syndrome) - too many bikes but have room for more

Suzuki:
GT750 2x75
GT550 72 project & 75
GT380 72
T500 73 project
T350 69, 71 & 72 project
T250 72
Honda 85 CB650SC & 86 CB700SC
09 Triumph Bonneville SE


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 Post subject: Re: Strobe light
PostPosted: Sat Apr 14, 2018 1:50 pm 
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Novice racer
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Joined: Wed Jan 18, 2012 8:01 pm
Posts: 922
Location: North of Albany, NY
Country: USA
Bikes owned: T500R (now), T500M (30 yrs ago)
Well, total sparks. But at 2000 RPM, cylinder #1 (where you attach the timing light) will fire 16.6 times a second.


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 Post subject: Re: Strobe light
PostPosted: Sat Apr 14, 2018 4:27 pm 
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Moto GP
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Joined: Mon Dec 13, 2010 4:32 pm
Posts: 3194
Location: southwestern Pennsylvania
Country: USA
Bikes owned: 69 T350 thru 75 GT750
Oops. Trying to be too smart. The V8 coil is firing at 133 sparks per second but plug #1 fires at 16.6 times per second.

_________________
BAS (Bike Acquisition Syndrome) - too many bikes but have room for more

Suzuki:
GT750 2x75
GT550 72 project & 75
GT380 72
T500 73 project
T350 69, 71 & 72 project
T250 72
Honda 85 CB650SC & 86 CB700SC
09 Triumph Bonneville SE


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 Post subject: Re: Strobe light
PostPosted: Sun Apr 15, 2018 9:51 am 
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Yeah Man, the Interstate

Joined: Wed Apr 01, 2009 11:47 pm
Posts: 554
Location: NM USA
And a good timing light "for 2 strokes" can also tell you about ignition break up at higher rpm if you are tracing a problem. :up:

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