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Yamaha TRX 850 tuning with TuV
Yamaha TRX 850 tuning with TuV
Full pipe
Two slim mufflers with a crisp sound and fine Mikuni flat slide carburettors should give the Twin from Yamaha specialist Theo Laaks legs – and the TuV shouldn’t worry.
Werner Koch
01/14/1998
May it be a little bit more? No problem, tuners and fine screwdrivers offer pretty much everything that promises power and thrust. Hocus-pocus, the horsepower is promised by the dozen. But the lofty promises are often refuted on the test bench by ruthless reality, or the engines roar their extra power through “silencers” that are so open that with a little skill you can check the candle image. Theo Laaks, Yamaha dealer and engine specialist in Gudensberg, Hesse (phone 05603 / 9317-0), is therefore looking for the legal way to give the five-valve engine a boost for his TRX 850 conversion.
The stimulant for the street version is mixed according to a traditional recipe. Instead of the standard constant pressure carburettor with a 38 millimeter cross-section, two Mikuni TDMR flat slide carburettors with a generous 40 millimeter passage prepare an ignitable mixture (price with wages for attachment, air filter and test bench tuning: 2190 marks). So that nothing stands in the way of full throttle, aerodynamic air funnels smooth the way between the filter box and the carburetor battery. A more permeable K&The N filter element makes it easier for the twin to breathe. The intake manifolds also had to bow to fine machining. Complex work on the cylinder head itself was excluded from tuning level one. “The time and money required to dismantle the engine is a bit too big for many TRX drivers,” comments Theo Laaks the reluctance to optimize the flow.
This is only returned to the fuel / air mixture after the work is done, when the exhaust gas flow through the huge, 40 millimeter manifold with an elegant two-in-one-in-two merging in the direction of the MAB aluminum silencer (price for complete system: 1799 marks) is steered. They delight the ear with a pithy blow from the exhaust, which is accepted with a nod of their head even by strict “loud is out” representatives. Only the sharp-edged tailpipes of the flawlessly manufactured dampers are literally defused with a flanged, rounded end.
Measured 90 hp are not a sensation in relation to the financial outlay, but the ease of revving paired with a consistently high final output make the difference to the constricted series engine more than clear. Fears that the tricky racing carburetors could make it difficult for the TRX to slip away in city traffic dissolve after just a few meters. With a flawless cold start, spontaneous acceleration and buttery smooth load change processes, the TRX also convinces critical minds. The Mikunis only get away for a moment when the comfortably smooth-running flat slide, which is mounted on roller bearings, is opened uncontrollably below 4000 rpm. And this in spite of the mechanical accelerator pump, which injects additional fuel into the intake duct when the throttle valve is opened. But that’s it, the real racing carburetor. Without the necessary sensitivity and intuition, it just doesn’t work.
The slight losses in the middle speed range (see performance diagram) stem less from the amply dimensioned carburetor diameter and more from the excessively large manifold cross-sections. Slightly slimmer manifold pipes could not damage the draft without questioning the targeted end performance. Theo Laaks has already initiated attempts in this direction, which, if successful, will immediately flow into the production of the MAB exhaust system.
With the free gallop with the Tuning-TRX, the aha-experience sets in. If the production version jams tough and rubbery at 8000 rpm, the pepped up engine brings together all the spirits and, according to the rev counter, clicks cheerfully up to over 9500 rpm. Exactly the kick that the production TRX engine misses.
There are other ways of getting around quickly and easily. With a special release on Dunlop D 364 sports tires, the TRX swings lightly into an inclined position, where, due to the slick-like grip, notches, side stands and levers burn up in the rain of sparks. Between MAB exhaust pipes and asphalt there is still a thumb’s breadth of space during such actions, and the small front fairing (price unpainted with bracket: 379 Marks) survives the oblique hustle and bustle without damage to the paint, which is not a matter of course with many accessories.
And if that little more is not enough, you can get it right from Theo Laaks: The 960 motor with a longer stroke is already in the works and with the remaining tuning accessories from Gudensberg you can easily win a whole lottery.
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