motoDNA: The Jerkiness of Jerky Motorcycle Throttles

02/14/2014 @ 3:45 pm, by Mark McVeigh34 COMMENTS

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Asphalt & Rubber is please to bring you the motoDNA column, which will be written by our good friend Mark McVeigh, of the motoDNA Motorcycle Academy.

Mark is a former international 250cc racer, as well as a former MotoGP engineer. His unique experience and perspectives on motorcycle dynamics and racing will be a regular feature on A&R. Enjoy!

In these high tech days of electronic fuel injection, you would expect motorcycle throttle response to be smooth as. However many of the latest bikes have a snatchy and jerky throttle response; especially around town at low speeds — feeling more like a switch than a throttle.

This is not just plain annoying, but makes holding a steady throttle in corners and riding in town tricky, often becoming a bigger problem in wet and slippery conditions. On the track, life can be even more difficult when the bike is closer to the edge of the tire, due to higher lean angles.

The throttle controls not only acceleration and traction but has a large influence on our bikes handling including weight transfer, steering and stability. The throttle is also our connection to the rear tire. If it’s linear and smooth, this is reflected in our riding performance.

We expect modern bikes to have smooth and accurate throttle response; but in fact throttle response is worse these days compared to carburettors of old. Why? In one word – Emissions.

Engines are more efficient and powerful than ever, however ever-tightening emissions laws mean that engine engineers have to lean out the engine map at certain speed and load points, where emissions are measured in the power curve.

You may notice flat spots in your throttle curve; this is often the point on the engine map that these emissions are measured, and therefore the engineers have reduced the amount of fuel available to the engine.

You may also feel some hesitation getting back on the throttle. For best ride-ability ideal fuelling ‘wets’ the cylinder head intake ports, which smooths out initial throttle application. However, the latest emissions laws also remove this ‘wetting’ strategy, adding to the harshness of modern motorcycle throttles.

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Emissions are the nasty byproducts of engine combustion that come out our exhausts such as carbon dioxide, carbon monoxide and hydrocarbons.

There are lots of strategies to clean up emissions, such as air injection and catalytic converters; however the easiest method is to reduce the amount of fuel injected into the engine or to run a lean air-to-fuel ratio.

Ideal combustion is to burn all the fuel in the engine, and reduced emissions occur at a ratio around 15 parts of air mixed with 1 part of fuel; however maximum power and smooth throttling needs around 10% more fuel.

This fuelling is generally controlled using a lambda sensor in your exhaust, which measures the air-to-fuel ratio, while a control loop strategy in the ECU adjusts the engines fuelling to match the target mixture.

All the trouble started when Euro carbon monoxide emission laws effectively halved ten years ago — and then halved again two years later. Motorcycles are different to cars, that’s why we love them; however motorcycles by nature make engine mapping even more difficult compared to four wheels.

Extra challenges for the motorcycle engine engineer include starting, higher revs, lower weight, lower engine inertia, and transient fuelling.

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This intricacy is also reflected in the racing world where MotoGP ECU engineers, who work on fuelling, traction control, engine braking, etc, are amongst the highest paid. This complex role is pivotal to a team’s success and is reflected in their pay packet.

What does the future hold? Apart from electric bikes, which have a superb torque curve, we are looking at larger catalytic converters, faster ECU processing performance, throttle cam development, and advanced ride-by-wire.

Common aftermarket mods include changing the exhaust to match an ECU change, either via re-flashing or a Power Commander. This basically involves removing the catalytic converter and adding fuel. It is most likely this setup has been tested on a dyno and a plug in is available for your bike.

Or we could just buy an old bike with carbs?

Mark McVeigh is a former international motorcycle road racer and MotoGP engineer who now works as a moto-journalist and development rider. He currently is also the Director of Coaching at the motoDNA Motorcycle Academy. Read more of Mark’s work on the motoDNA blog, and follow motoDNA on Twitter and Facebook.

  • Glad to have you onboard Mark. Great piece, can’t wait for the others!

  • crshnbrn

    Mr. McVeigh, I am looking forward to more technical articles from you on A&R. If I may ask a question of you, do you see direct injection being applied to motorcycles as a solution to reducing jerky throttle response with leaner air/fuel ratios?

  • Ken C.

    Great explanation. Makes me want to go change out the stock exhaust, and reflash my ECU or get a power commander for my R6 right now.

  • Gonzo

    Spot on article! I must say, however, that my 2011 S1000RR is quite smooth…as long as you leave the mode selector in Rain or Sport. Flip it to Race or Slick, and you have an abrupt on-off switch. True to your article, I turn faster laps at track days in Sport than Race or Slick.

  • Bazerko

    Those morons at Ducati with that underslung exhaust. burning up the rubber on their tires. When will they X that dumb panigale bike and build a V4 with exhaust once again under the tail

  • coreyvwc

    in reply to @bazerko

    Have you noticed lately that not one single manufacturer in the industry is still using an under- tail exhaust…? and yes Ducati once built a V-4, it cost $60,000. It won’t happen again.

  • Norm G.

    re: “Those morons at Ducati with that underslung exhaust. burning up the rubber on their tires.”

    don’t look now, but you just save hundreds of dollars by switching to Gei… errr… you just saved $300 bucks on tyre warmers.

  • Norm G.

    re: “Have you noticed lately that not one single manufacturer in the industry is still using an under- tail exhaust…?”

    see entry for Yamaha R1, see entry for CBR6.

  • Norm G.

    re: “do you see direct injection being applied to motorcycles as a solution to reducing jerky throttle response with leaner air/fuel ratios?”

    before he answers, you may first want to answer, are you willing to come off the dime…?

  • Halfie30

    Ummm… The Desmosesici RR had an undertaking pipe and an under tail pipe….

  • Halfie30

    *under slung

  • Manny varela

    Thanks for this excellent article.
    I hope to see more like this on here.
    Welcome to a&r

  • TexusTim

    I got a 2008 cbr 1000rr when they first came out, it had injection snap after a lot of mods it was pretty good. now I have a 2012 cbr 1000rr and honda really cleaned it up but it still had throttle jerk.
    so changed out the exhust with a full yoshimira system, did the pair valve mod,did the ram air flapper mod and the bazzaz z bomb and now its smooth as silk..so it doesnt take much some hours in the garage and about1500 bucks
    I think the biggest difference is the 2012 has a o2 sensor(wide band) so it can tell whats going on the older versions did not so no matter the mods it was allways there. I kept the o2 sensor as the full system has a bung for it and it is located right at the header collector the stock one was located after the muffeler..many aftermarket exhaust company’s recomend an 02 delete mainly for a universal fit I dont recomend ditching the 02 sensor.

  • Keith

    “or buy old bikes with carbs” hmm, really irritate the power that be…but an only 2stroke street bike, install modern carbs. Ride the heck out of it. Yep…that could solve the problem.

  • Nerve

    mister McVeigh, please tune it up a notch, your article was not exactly Keith Code ‘throttle control’ level stuff. Looking forward to some real insights, as you clearly have the mileage.

  • Sportbikes will follow the lead of super cars with direct injection, higher compression, and lower number of cylinders to reduce blow-by. I’d also expect to see internal exhaust coatings and leaner fuel mixtures to keep the temps higher. And the upper limits I’d expect them to simply cheat with a dual cam system, like Honda does with their cars.

  • crshnbrn

    @ Norm G.

    “are you willing to come off the dime…?”

    To me the sweet spot of fuel injection is the period after the first crude replacement for carburetors and before modern, strict emissions standards. For the most part rideability, idle smoothness, and fuel economy were acceptable during that time. When emissions standards got tighter, rideability and idle smoothness suffered while there was little if any improvement in fuel economy. If direct injection can restore rideability and idle smoothness, then I “might” come off the dime as you like to put it. If not, then the answer to your question is a resounding “NO”.

  • Nick R

    Its a fine article indeed, but I love those photos! Im sure Im not the only one who loves seeing the insides of bikes as much if not more than the outsides, please feed us more!

  • TexusTim

    @crshnburn..the first generation of fuel injected bikes had the worst throttle snap or jerk, it was very hard and jerky not smooth at all. like the 2001 cbr 6000 f4i with the added injectors and ecu adjustments the later generation bikes are a lot easier to deal with and doing the mods to the emissions makes it a lot better it makes it run leaner as well.

  • Westward

    I would be interested in knowing which manufacturers and teams the author of this article worked with, also if he was associated with a factory effort or a satellite outfit. My reason for asking this, would be to say, is it possible that it different depending on where was is at. Could it be not an issue at HRC in MotoGP but an issue in WSBK. Or Yamaha Factory MotoGP is better at resolving the issue than Tech3.

    After all are there not trade secrets, hence why pay packets are higher than others….?

  • Norm G.

    re: “If direct injection can restore rideability and idle smoothness, then I “might” come off the dime as you like to put it.”

    right then, talk to your compatriots. help them see your valuing mentality. unfortunately, their never-ending quest for free lunch (consequences be damned) makes bike world’s wilful adoption of DI… DOA.

    re: “If not, then the answer to your question is a resounding “NO”.

    and there it is.

  • TexusTim

    @ westward..dont you think he is talking about street bikes ? emissons and catalitic convertors are not used on race bikes right? although there is pictures of motogp bikes I belive he means factory stock bikes as the motogp and wsbk bikes dont suffer from these issues.

  • Mike

    Good article & one that follow conventional thinking about emissions etc.

    The thing I cannot understand is this.
    I have been using various maps on a EFI controller.
    Maps from many different tuners & without fail all except one
    has the majority of values set leaner than the stock ECU values.

    This goes against the accepted theory of needing to richen the fuel map.
    Even the maps that are designed for after market exhaust & air filter change
    ( less restrictive both ) are showing leaner than stock map values.

    If anything one would think if bike is lean from factory opening exhaust & intake
    to be less restrictive would demand even more fuel no? Am I thinking backwards here?
    Anyone know?

    Thanks

  • crshnbrn

    @Norm G.

    re: “their never-ending quest for free lunch (consequences be damned) makes bike world’s wilful adoption of DI… DOA.”

    Key word being willful. Sadly, it probably won’t be adopted without being required to meet even tighter
    emissions standards. Even then, if DI doesn’t improve throttle response, then I won’t be coming off the dime for it. If technology doesn’t improve the riding experience or make a motorcycle safer, then it is of no value to me.

  • Norm G.

    re: “Key word being wilful”

    exactly, you saw what I did there.

    re: “Even then, if DI doesn’t improve throttle response, then I won’t be coming off the dime for it.”

    no worries, we’ll end up paying for the tech regardless. as they say, the “savings” will be passed along to you. if bikeworld beggars whine that bikes are too expensive now…? good grief Charlie brown, wait’ll the manufacturers are forced to build with DI.

    if there’s a scenario more worthy of being slapped with a “beware what you wish for” warning label…? I haven’t seen it. antagonizing Honda till such time they pull out of grandprix, doesn’t hold a candle to this.

  • Norm G.

    re: “Anyone know?”

    yup.

    re: “This goes against the accepted theory of needing to richen the fuel map.”

    well like you said, that’s a theory. or what I like to refer to as a rule (of thumb). this would be different than LAW, meaning that sure, depending on the vehicle your talking about and it’s set-up, there’s a chance that you might be the exception to that “rule”.

    if your finding 4 outta 5 tables seem to corroborate this…? right then, if it walks like a duck…? and quacks like a duck…? maybe it’s a duck…?!

    get a wideband, zero out the map, and take your own a/f measurements. you may find that 1 oddball tuner is on to something…? or you may find you spent a whole lotta time and money doing duplicate work, only to realize that what the tuner majority had to told you was correct to begin with…?

    ultimately, you have to decide what’s it worth to ya to find this out.

  • Mike

    Norm G. says: “ultimately, you have to decide what’s it worth to ya to find this out.”

    What you say is true Norm & of course the reality is 4 to 1 tuners are going lean.
    They have the time, reason & $$$ to dyno.

    For me my racing days are behind me & I ride for sport & pleasure now.
    So what it is worth to me is just satisfying a curiosity
    I just like tinkering with the maps
    loading 3 or so & trying them/ noting the results
    Just a pleasure/hobby

  • Prich

    +1 on this. Great tech info and a great addition to A&R.

  • Daryl

    Great article, thanks for the explanation. I took a Ducati Multistrada for a test ride and found that at legal speeds the binary “on or off” action of the throttle made the ride most unpleasant. It was such a turnoff I would not buy that bike.

    In this day and age of throttle-by-wire why couldn’t the manufacturers smooth out the throttle speeds to make the engine more tractable? Seems to me if they modulated the throttle inputs such that it smoothed out the harshness it would be better all-round for any non-racetrack riding.

    Having the power come on like a hammer to the back of the head isn’t much fun (or safe) when riding in town…

  • YOLOSKATES

    MELIKES NEW COLUMN GUY

  • Gonzo

    Motion pro makes a throttle called “The Revolver”, and it has different cams you can install, for a different pull. They make one that is slow up to 70% throttle, then fast for the remaining 30% to WOT. I have been considering this on my S1000RR.

  • buellracerx

    good write-up, great perspective!

    Another contributor is higher power levels requiring larger diameter throttle bodies, which have lower flow resolution in the lower opening range. This has an effect regardless of actuation style, ride-by-wire or directly coupled.

    Similarly, higher required peak power levels require ports designed for bulk flow. Intrinsically these generate less charge motion, leading to combustion instability at part throttle conditions.

    As emissions regulations get tighter, MC mfg’s will be forced to adopt (and find ways to make lighter) technologies developed by automotive. Cam phasing and variable lift is one.

    DI will help power (volumetric efficiency) and part-throttle combustion (stratified charge combustion), this is fact. The trick will be getting the fuel spray to vaporize instead of impinging on the walls/piston of an oversquare engine.

  • pab

    nice posting buellracerx
    fiat multi-air is simple and light
    http://www.caranddriver.com/features/fiats-multiair-valve-lift-system-explained

    one thing i’ve never understood is why mfgs still use the primitive butterfly type thottle body, while other designs must exists.

  • Great feedback, thanks very much. Lets see if we can “Get off the dime”