ANY QUES­TION AN­SWERED How do I get the most from an after­mar­ket ex­haust?

If we don’t know the an­swer, we’ll find the per­son who does

Motorcycle News (UK) - - Garage -

I’ve had my 2012 Yamaha R1 for a while and I’ve saved enough pen­nies to fit a £2500 Akrapovic Evo­lu­tion full-sys­tem. What other com­po­nents or work do I need? Guy Al­cock, Crewe

An­swered by Tony Scott, T3 Rac­ing A man­u­fac­turer’s fu­elling map tends to make the bike lean low down to pass the emis­sions regs, and rich at the top to keep the en­gine cool.

If you just fit the pipe and do noth­ing else the bike will sound good, but it will have a snatchy throt­tle re­sponse, and most en­gines tend to run even leaner at the bot­tom-end if they have a freer­flow­ing pipe. You’ll have trou­ble start­ing and pulling away from lights and it will get hot in traf­fic, push­ing past 85 de­grees, which saps power. Be­tween 7000 and 10,000rpm it will feel OK, but then it’ll get re­ally heavy on fuel at the top-end – as low as 18mpg.

The fu­elling maps in the ECUS of Ital­ian bikes, KTMS and pre2012 Tri­umphs are tune­able, but Ja­panese kit is locked down tight, so you’ll need an ex­ter­nal fu­elling mod­ule such as a Power Com­man­der. Fi­nally, bud­get for £200-300 set­ting it up on a dyno.

Tempt­ing as it may be to ex­change maps on­line with other rid­ers, a good dyno op­er­a­tor will check the base fu­elling through the rev range at 5% throt­tle in­ter­vals in ev­ery gear. Not only will that give you up to 15bhp more, but it won’t pop and bang on a closed throt­tle and it will pull cleanly too.

I’m look­ing to re­place the rear tyre on my Honda 125 Forza scooter. I do about 6500 com­mut­ing miles each year, in a mix of dual-carriageway and ur­ban town work. Stu­art Allen, email

An­swered by Bryn Phillips, Cam­brian Tyres There are many good choices for the Honda 125 Forza these days in the 120/70-15 and 140/70-14 sizes which fea­ture on lots of scoot­ers. Bridge­stone’s new Bat­t­lax SC is prov­ing very pop­u­lar with a good bal­ance of per­for­mance, dura­bil­ity and price. Con­ti­nen­tal’s long-serv­ing Con­titwist and Dun­lop’s Scoots­mart have sim­i­lar per­for­mance to the Bridge­stones. The only tyre that I can think of that might give bet­ter dura­bil­ity than those three would be Miche­lin’s City Grip.

If you are go­ing to shell out on a full sys­tem, don’t skrimp on dyno time

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