First Tests

KTM 250/300 EXC TPI and Honda SH125

Motorcycle News (UK) - - This Week - MICHAEL GUY SPORTS ED­I­TOR michael.guy@mo­tor­cy­cle­news.com

Who says two-strokes are dead? Sure the in­tro­duc­tion of Euro4 and its strin­gent emis­sions con­trols looked to have struck the fi­nal nail in the stro­ker cof­fin but where there’s a will – along with huge mar­ket share and fi­nan­cial gain to be had – there’s a way.

It’s taken 13 years of devel­op­ment but fi­nally, here at the no­to­ri­ous Erzberg off-road venue in Aus­tria, KTM are let­ting us ride their new Euro4 com­pli­ant fuel in­jected two-stroke en­duro bikes – the KTM 250EXC TPI and the 300EXC TPI.

Gone is the need to pre-mix fuel, in­stead there is an oil tank which holds 700ml of black gold, which runs to the com­bus­tion cham­ber at an av­er­age of 80:1 fuel to oil ra­tio, mean­ing up to eight full fuel tanks per top-up – de­pend­ing on your type of rid­ing. It’ll trans­form longer rides, with no need to carry oil – so long as eight tanks will get you home. The in­jec­tion tech­nol­ogy also makes the bike in­cred­i­bly fru­gal, us­ing up to 30% less fuel than its car­bu­ret­ted pre­de­ces­sor. It also negates the need to jet for dif­fer­ent con­di­tions or al­ti­tude as the in­jec­tion sys­tem and ECU au­to­mat­i­cally com­pen­sate, mean­ing it will run per­fectly in sea-level dense woods up to the high­est moun­tain climb.

I have to ad­mit that I was slightly ap­pre­hen­sive about how it would ride, af­ter all this is a bike de­signed to com­ply with bu­reau­cratic edicts. So, has it lost the qual­i­ties that make KTM’S two-strokes so spe­cial? The cur­rent model range was the pin­na­cle of this with beau­ti­ful bot­tom-end power and torque com­bined with a blis­ter­ing top end and ex­plo­sive power when needed. And the new in­jected model de­liv­ers this same char­ac­ter and more. Blast­ing up the im­pos­si­bly big and long hills of the Erzberg (the home of the Erzberg Rodeo and also the largest iron ore mine in Europe) the drive is in­cred­i­ble. A mix­ture of torque and out­right bhp – a claimed 51bhp for the 250 and 54bhp for the 300 – make it an even bet­ter propo­si­tion for club rid­ers through to ex­treme en­duro com­peti­tors. There’s less smoke, crisper power with the only slight glitch be­ing when you’re on a con­stantly in­creas­ing throt­tle where there is a small step in the power. I also felt the 300 ran a lit­tle rich at times when on small throt­tle open­ings.

How have they done it?

“There are two ma­jor ar­eas which has made this pos­si­ble,” says Michael Viertl­mayr, Head of en­gine off-road and mo­tocross R&D at KTM. “The first is hav­ing the best pos­si­ble ther­mo­dy­nam­ics in the en­gine. A lot of ef­fort has been put in to the shape of the com­bus­tion cham­ber, trans­fer ports and spray tar­get­ing and pat­tern of the in­jec­tors. An­other cru­cial area is the de­sign and shape of the ex­haust.

‘Blast­ing up the im­pos­si­bly big hills, the drive is in­cred­i­ble’

“The sec­ond as­pect and even more im­por­tant part is the en­gine man­age­ment sys­tem. The con­trol strat­egy has been de­vel­oped over al­most ten years and this is where the ma­jor know-how is lo­cated. We are able to de­tect flame out and cylin­der charge cy­cle, and this is what you re­ally need to un­der­stand to make a fuel-in­jected two-stroke bike work. The in­crease of the new ECUS and faster cal­cu­la­tion time was a big ben­e­fit to us. This would not have been pos­si­ble ten years ago be­cause the cal­cu­la­tion of the en­gine man­age­ment sys­tem was not fast enough.”

Crisp power and con­trol from the 300

HIGH­LIGHTS O Fuel-in­jected two-stroke O 700ml oil tank O 80:1 fuel-to-oil ra­tio O 54bhp for the 300 O In­cred­i­ble drive

Your eyes aren’t de­ceiv­ing you, it’s an all new 250 two-stroke

The en­gine is in­cred­i­bly clean burn­ing

Eas­ily-ac­ces­si­ble air fil­ter

Elec­tron­ics squeeze un­der the seat

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