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Twins Technical Talk Technical Talk for Hinckley Triumph Twins: Bonneville, T100, Speedmaster, America, Thruxton, and Scrambler.

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Old 09-16-2009, 02:55 PM   #1 (permalink)
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here's a dumb question, how does the rev limiter work?

i have a carbed bonneville. i think i works by identifying the electrical impulses coming from the engine, but that's the extent of my knowledge.
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Old 09-16-2009, 03:02 PM   #2 (permalink)
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On carburetted models it interrupts the signal to the coil, probably alternating on/off, slowing the firing sequence.

On EFI models I think it cuts the signal to the injectors.

Pieman will know for sure. He mods igniter units before breakfast.

Last edited by Forchetto; 09-16-2009 at 03:06 PM.
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Old 09-17-2009, 12:14 AM   #3 (permalink)
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Someone else posted elsewhere that the ignition control unit drives the tachometer. If so, it knows how fast the engine is spinning and can cut the signal to the coil when it hits the limit. I doubt it's any more complicated than that.

Which makes me wonder how the ignition control unit knows the engine speed, as opposed to just knowing to send a spark at certain points in the engine cycle, as points used to do.
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Old 09-17-2009, 09:03 PM   #4 (permalink)
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Because it's a computer, and it is fed enough data to calculate rpm easily.......Crank Position Sensor inputs to the Igniter on the older ones and I suppose the EFI bikes call this the ECU or whatever. The rev limiter is probably just a value in a read only register that the computer uses for input.
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Old 09-17-2009, 09:42 PM   #5 (permalink)
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Older Beemers like my first (K100RS - 1985 model) used Bosch LE Jetronic .... as it approached red line, it first retarded the spark, which slowed things down a bit. If the rider insisted on keeping the revs rising, next the Bosch system cut off the fuel injection system. No fuel = no go!

Like Larry said, it's digital. All the ECU is looking for is whether the rpm is less than, same as, or greater than a redline value loaded into it. Like other computer decisions. Think it's based on Boolean logic.

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Old 09-17-2009, 11:58 PM   #6 (permalink)
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I found out first hand last week while playing with my buddy on his Yami custom Warrior (that thing eats my lunch). Took first gear a little too far, when it hit the limiter it was like you turned off the key. I backed off hit 2nd at it was firing like a dream. It's the first time I've hit it in 16,000 mi., whish I had of been whatching the Tach but I was busy trying to dust him in vain.
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Old 09-18-2009, 01:58 AM   #7 (permalink)
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It's the first time I've hit it in 16,000 mi.
wow, I hit my rev limiter several times on every ride
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Old 09-18-2009, 08:17 AM   #8 (permalink)
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Quote:
Originally Posted by RedBird View Post
Because it's a computer, and it is fed enough data to calculate rpm easily.......Crank Position Sensor inputs to the Igniter on the older ones and I suppose the EFI bikes call this the ECU or whatever. The rev limiter is probably just a value in a read only register that the computer uses for input.
There must a clock or timing register to get the rpms.
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Old 09-18-2009, 08:52 AM   #9 (permalink)
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wow, I hit my rev limiter several times on every ride

perhaps you should consider shifting up ! those highway speeds in first are he#l.
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Old 09-18-2009, 12:21 PM   #10 (permalink)
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