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Throttle Control - 2 Stroke Gp Bike


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I have recently bought a Yamaha TZ250 GP bike to start club racing, maybe a little ambitious I know, as I am used to riding a CBR600 on the track. My fear of the throttle when exiting a turn has somewhat increased, now that I have a bike with a fairly vicious power band, meaning that at about 9000 rpm, the power really packs a punch to what I have been used to.

 

This is especially the case when exiting slow turns in 1st gear, as I start to bring the power on (I keep a constant throttle as soon as I've finished braking), I am constanly dogged by the fear of the power violently kicking in and the rear letting go. I seem to be waiting until the bike is nearly upright until really bringing on the throttle, it shakes its head when on full power coming out!

 

Is there a slightly different throttle control technique to riding these bikes in this situation, as opposed to riding a 4 stroke with a much gentler power delivery?

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Hey Alan,

 

 

The throttle technique remains the same.

 

With that in mind, the powerband will be higher in the rev range and a bit narrower. The first trick is to keep the motor in that rev range and "on the pipe" in the first place. As far as falling out of the powerband, slipping the clutch is the standard technique to build revs back into the power band. So, when exiting a slow first gear turn, try "fanning" or slipping the clutch a bit to get the motor back into the powerband if you can't carry more speed.

 

Inside the power band you shouldn't be experiencing any sudden or "light switch" power changes. That being said, two stroke roadracers do require critical tuning of the carburetor and there might be some adjustments needed there. The airscrew adjusts the first 1/8 of throttle opening and overlaps a bit with the needle diameter as the fuel circuit shifts to the main jet tube at the 1/8-1/4 throttle opening.

 

Though I am planning to return to NZ soon, I can't tune your bike over the internet. In the meantime, I can refer you to a friend of mine who is an excellent 250 tuner and a NZ 250 national champion named Dave Cole who lives near Pukekohe outside Auckland. He has a motorcycle business under the same name. Dave Cole Engineering I think. He won't be hard to find. Everyone knows him and I know he raced last year as I saw his results online. You can tell him I sent you if you want.

 

 

Keith Code himself has raced more than a few laps on a TZ250 and should be able to offer more riding advice.

 

 

Cheers

 

 

Oh, tell Dave that Bill from America said "HOWDY".

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Hey Alan,

 

 

The throttle technique remains the same.

 

With that in mind, the powerband will be higher in the rev range and a bit narrower. The first trick is to keep the motor in that rev range and "on the pipe" in the first place. As far as falling out of the powerband, slipping the clutch is the standard technique to build revs back into the power band. So, when exiting a slow first gear turn, try "fanning" or slipping the clutch a bit to get the motor back into the powerband if you can't carry more speed.

 

Inside the power band you shouldn't be experiencing any sudden or "light switch" power changes. That being said, two stroke roadracers do require critical tuning of the carburetor and there might be some adjustments needed there. The airscrew adjusts the first 1/8 of throttle opening and overlaps a bit with the needle diameter as the fuel circuit shifts to the main jet tube at the 1/8-1/4 throttle opening.

 

Though I am planning to return to NZ soon, I can't tune your bike over the internet. In the meantime, I can refer you to a friend of mine who is an excellent 250 tuner and a NZ 250 national champion named Dave Cole who lives near Pukekohe outside Auckland. He has a motorcycle business under the same name. Dave Cole Engineering I think. He won't be hard to find. Everyone knows him and I know he raced last year as I saw his results online. You can tell him I sent you if you want.

 

 

Keith Code himself has raced more than a few laps on a TZ250 and should be able to offer more riding advice.

 

 

Cheers

 

 

Oh, tell Dave that Bill from America said "HOWDY".

 

Thanks Bill, I guess it's just a case of getting used to more useable power with the TZ, I just need to trust myself and the bike a bit more. I find this bike so much harder to ride than my CBR, although the handling is amazing.

 

I read in Kenny Robert's book that slipping the clutch was a big no no! and to be avoided (I have read twist 2 several times by the way) :)

 

I'm going to the track (Ruapuna near Christchurch on the south Island) and am eager to try a few new techniques. I'll try to keep it buzzing.

 

I don't think there is too much wrong with the carburation, but my good friend Lester Ferdinhand, who is husband of current NZ 250GP champion, Karel Pavich and who I got the bike from, should be able to check that all is well.

I have heard of Dave Cole and if I bump into him, which I may at this years national championships, I'll say hi for you.

 

Thanks again Bill for your advice.

 

PS how do you know Dave?

 

Anything to add Keith?

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Hey Alan,

 

 

The best throttle technique is to begin dialing on the throttle smoothly as soon as possible after getting the bike turned in.

 

 

"...as I start to bring the power on (I keep a constant throttle as soon as I've finished braking)..."

 

I'm not exactly clear on what your comments here mean. Are you trailbraking into the corner or finishing your braking before you start to turn? Properly, one finishes braking prior to turning in with the throttle closed and once a lean angle has been established, cracks open the throttle and continues to apply throttle in a smooth and progressive fashion. So, I'm not quite clear about where or why you are holding a constant throttle.

 

 

"...at about 9000 rpm, the power really packs a punch to what I have been used to."

 

The power distribution of a two stroke roadracer is different than a four stroke. On a four stroke, there is usable power pretty much throughout the rev range with progressively more power as the revs rise. On a two stroke roadracer, there is practically nothing below the "powerband" at the top end of the rev range. The goal is to always keep the revs in the powerband which seems to start at about 9000 rpm on your bike. That way there shouldn't be a "violent kicking in" of power when you cross above 9000 rpm into the powerband.

 

Yes, slipping the cluch is not a desirable thing to do. Neither is falling below 9000 rpm a desirable thing to do. In that situation, without being able to carry a bit more speed or the luxury of a lower first gear set for the tranny, slipping the clutch is the only answer to get the bike moving back into the managable power band and avoid "power violently kicking in" in a first gear hairpin.

 

 

"I am constanly dogged by the fear of the power violently kicking in and the rear letting go."

 

Keith Code has many excellent chapters or articles on this website regarding one's mental or psychological frame of mind and approach to riding and how to overcome barriers like fear of the violent power monster kicking in... :(

 

 

You are right. I have to agree that starting your club racing career on a 250 might be a tad ambitious. However, racing is all about ambition, so, you seem to have the right attitude. And since you already have some track experience with a 600, I see every reason to believe that you can slay all dragons with more good information and riding experience. What else can you do? Eh? :P

 

 

As for how I know Dave Cole...

 

I helped out with Dave and Trisail tuning for Midge Smart during his 03-04 NZ 125GP champs campaign. Needless to say it was an awesome summer traveling around NZ in a caravan with the likes of Dave Cole and the rest of the utterly mad Kiwi racers on the circuit. Not to mention winning all the races...except Ruapuna, of course. I'm sure that had nothing to do with the all night out in Kaikoura on our way south to Christchurch, but, that's another story. One of so many. :rolleyes:

 

Anyhow, it sounds like you have good support with Karel and Lester there. And I'm certain Keith will be about to add his nickel. It is his website after all.

 

Please let us all know how you get on.

 

 

Cheers mate.

 

Bill

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post-1286-1160214865_thumb.jpgpost-1286-1160214770_thumb.jpgpost-1286-1160214683_thumb.jpgpost-1286-1160214476_thumb.jpg

 

Hi Bill,

 

I am off the brakes as I turn in, what I mean is what you said, I keep a constant throttle as soon as I've turned and then gradually increase the throttle as the exit appears (as much as I dare anyhow)

 

I very rarely brake whilst turning, unless I've overcooked the entry speed. I just need to be a bit braver coming out.

I'll try and keep it in the power when I go to the track at the end of the month.

 

I would really love to do a Superbike School, but the nearest is Phillip Island and that makes it a very expensive trip, maybe they could do an Aus Superbike School "roadshow" in NZ.

 

Sounds like you had fun in NZ, there are some great riders here who I think deserve a crack on the International scene. It'd been a long time since Aaron Slight and Simon Crafar.

 

 

Attached is pic of me on the TZ at Ruapuna, Christchurch a few weeks ago, I rode like a granny! Will be in the right headspace next time.

 

Thanks Bill.

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Hey Alan,

 

 

Good looking photos!

 

 

Let's not forget the rest of the international racing Kiwi's, eh?

 

Shaun Harris, Andrew Stroud and Jason Easton to name a few!

 

All of whom have shone their light on the world stage kicking arse on the big dogs!

 

Or some credit to John Britten and Burt Munro!

 

And the many up and coming riders and those who support them at home in New Zealand!

 

 

 

Good luck! Let us know how you do!

 

 

Bill

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Of course, Andrew Stroud is still kicking arse, and had a wildcard at Australia last year with a 12th place finishing above Garry McCoy for the year, Shaun Harris, not sure what he's up to this year, he was getting some young riders to the USA. Dominic Jones is in AMA and doing ok.

 

Thanks for your replies Bill and hope to see you in NZ soon. Sam Smith is doing good so there is some potential coming through.

 

BTW, I am English (been living here 3 years) and watching the young British guns coming through, including Bradley Smith on the World 125 championships, Chas Davies and Leon Haslam, to name a few.

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Hi Alan,

 

I remember Dominic and Sam. Maybe Dominic can lead the way and open the door. Sam's a good guy, too. I hope he does well.

 

I must say it was pretty cool to get to participate in that legendary racing community I had read about in books and magazines. I met Andy several times up here with the Britten. And I only knew of Shaun from his Isle of Mann races, but, never imagined then that I would get to hangout with these characters in their hometown element so to speak. Not to mention everyone else.

 

Anway, it's my pleasure to make your acquaintance. I hope I can visit again soon.

 

Bill

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Hey Alan,

 

A couple thoughts going back to your first post I forgot to mention...

 

When the front gets light exiting corners under power, your weight on the handlebars or even a tight grip can really amplify or even cause that "headshake" you describe. I like sitting back in the seat with my weight more in my feet and I try not to lean on the bars or hang on too tight.

 

Also, I used some potentially confusing phrasing in the second paragraph of my long second post to you. I try to keep the ideas of throttle and acceleration separate in my mind for just this reason. One can hold a constant throttle and still be accelerating. So, what I meant to say was that I crack the throttle on and try to be slightly accelerating as soon as possible to keep the weight distribution toward the rear.

 

I really need to dig my books out of storage and order new ones to go over this stuff again as Keith has really worked it all out quite well.

 

And, yes, I entirely agree with you. I think Keith should train me and send me to New Zealand to open a school there. B)

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I will keep this short because these replies tend to overlap one another in the advice that they give. I ride my dirtbike for a two reasons. One, because it is fun and two, because it helps develop a better sense of throttle control. Today, I rode in my backyard. My course only has a few turns and is on a grassy slope. It was wet today so throttle control was key. I was riding a 125cc two stroke so same power/on concern. The fastest corner out there is a slightly off camber left hander. I can hit it in 3rd gear and just blip into the power bnad before I have to let off but that was whiping the back end out each time. So what I did was keep it in the power band in second and while leanded over I was already in the powerband and could stear the back with slight variations in throttle input rather than these huge slides. This way ended up being faster in the end. Basically, be gentle with the throttle and be in the pb if you can during the begining of the turn.

 

 

~Wip

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Thanks for all your replies, I have some things to think about now and I'll let you know how I get on at the end of the month. I'll definately monitor how much pressure I'm putting on the bars and try to put more weight further back and on the footpegs.

 

I read recently in BIKE (UK) magazine that John Hopkins puts a great deal of force on his footpegs, so there must be something in it!

 

Keep the rubber side down!

 

Thanks again.

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