ericrfx

Graham Jarvis downhill technique

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Have been watching some Graham Jarvis helmet cam videos - wow is that humbling! Noticed on some very steep downhills he hits the kill switch and rides down with engine off then restarts at bottom of hill - obviously intentional but what is the purpose or theory in play here? Using dead engine for rear wheel braking? I recently returned to my 2-stroke roots (Beta 300rr ) after 20 years on various 4-strokes mostly Honda (XR 400 then a series of Crfx 250 and 450 ) is this a known 2-stroke technique? Just trying to learn and improve - i’m only 57 haha 

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I did it on my two stroke sometimes and it really did help when you needed to maintain control and go very slow. My new four stroke has a gaykluse so I haven’t tried it on a thumper. 

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At least I have something in common with him, and that's the only thing. I do this on steep downhills to basically use my clutch as a rear brake. Can be modulated with clutch and rear brake pedal, and seems to prevent the rear locking up as much so you can keep your line better. But I'm on a four stroke which I would assume would have a lot more of a braking effect.

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Is it possible that he gears up to about 4th or 5th and engine brakes with the motor off. I can't see why he would purposely cut the engine, just let it idle. But it would stall anyway if he were in 5th, so cutting it off keeps it from lugging until it stalls. ??????

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Easier to modulate and prevent complete lock-up. Also I'd guess because he can take his foot off the peg for balance and not lose rear-braking ability.

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I don't understand. So he must keep thumb on the kill switch to keep bike from restarting? I have never tried or heard of this. Will two stroke not start if in tall enough or short enough gear?

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If he has a carb, then you may be seeing him restart after a stall. My bike while holding in the clutch will often stall on steep down hills. The fuel in the bowl goes higher when pointed downward, covering the emulsion holes on the side of the idle jet, thus changing the AFR ratio. I often have to restart at the bottom of a hill. Question is, have you seen him kill it before diving off?????

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1 hour ago, crankee said:

I don't understand. So he must keep thumb on the kill switch to keep bike from restarting? I have never tried or heard of this. Will two stroke not start if in tall enough or short enough gear?

Not if the electronics are turned off.  Can't run without spark.

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1 minute ago, CDNSXV said:

Not if the electronics are turned off.  Can't run without spark.

Still don't understand? Do they have ignition switches on their bikes? What do you mean if the electronics are turned off? So, he turns them off when starting down the hill and then turns them back on at bottom? That sounds really strange to me???

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ALL motorcycles have a kill switch.  Switch that to Off and the motor won't run.

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2 minutes ago, CDNSXV said:

ALL motorcycles have a kill switch.  Switch that to Off and the motor won't run.

Ok, got it. Not connecting the dots as both of my bikes have kill buttons that you need to hold in but mine are old.

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I've watched him do it on several videos. It's very obvious what he is doing. I assume he does it for better, more control of engine brake. As for why it doesn't restart going down the hill, not sure. Maybe he is keeping the kill button pressed? When at the bottom, bump start and on he goes.

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I always assumed it was to let the motor cool down a bit.  Never would have thought it was for engine braking, when there's a perfectly good rear brake that I'm sure he knows how to use.  Plus, you don't have to kill the motor to get the engine braking.

I took a trip out to Moab a couple years back with a few friends, which included several days on a guided tour.  Our guide was a top level A-class Baja racer (a VERY good rider, like take-a-CRF150F-and-wear-out-most-people-on-450s-in-the-desert, kind of good rider), and he provided a lot of training / schooling with us during the trip.  The single biggest thing I remember from him was his phrase on how to brake:  "clutch, front, rear".  As in, that's the order you pull/press levers when needing to brake.  Clutch first (as in disengage it), then the front brake, then the rear.  He was very adamant about NOT using the clutch / engine braking to brake, for several reasons, but primarily because it's significantly less precise and dependent on a lot of other factors (what gear you're in, what rpm you're at, etc.), versus just using what's designed to stop the rear tire anyway.

To this day, I still instinctively grab "clutch, front, rear" when I need to brake.  It works well, and if you're dragging the rear tire, then you need to simply ease up on the brake.  The only time I'll cut the engine and use engine braking is on something ridiculously nasty where I'm near 100% certain that my right foot is going to come off the peg/lever at some point, and such an action would likely end up with me upside down somewhere down the hill....

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I like engine off to get a better feel/sound on what the suspension and tires are doing.

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For ultra-steep downhills, I hold the throttle at a high idle and ride the rear brake, all while just modulating the clutch to keep it from stalling. The high-idle keeps the tire from skidding.

 

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16 hours ago, crankee said:

I don't understand. So he must keep thumb on the kill switch to keep bike from restarting? I have never tried or heard of this. Will two stroke not start if in tall enough or short enough gear?

He uses his clutch. Bikes usually needs some throttle to bump start depending on clutch input.

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11 hours ago, sneaky98gt said:

He was very adamant about NOT using the clutch / engine braking to brake, for several reasons, but primarily because it's significantly less precise

This is 100% the opposite of what most are taught... Engine braking when used correctly is a very efficient tool, as well as dragging the rear brakes to stabilize the chassis/suspension... 

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