Bigger downpipes worse running?

[sinclair182]

Hey new to the here so be nice!

My 600 bandit 01 had shot downpipes so got a set of 1200 downpipes which are slightly bigger bore (i think) and put on a straight through can. This seems to make the bike a bit more sluggish at times does that make sense or should it be better????

I did get the carbs balanced which made a difference but still not 100%.

Cheers Mike

[MarJay]

You're surprised?

You'll probably need to re-jet the carbs in order to get the fuelling spot on, and I suspect the best way to measure how far out it is, is probably to get the bike on a Dyno.

I suspect you'll have to become very friendly with your local dyno operator in the coming weeks.
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British beauty: Triumph Street Triple R; Loony stroker: KR1S; Track fun: GSXR750 L1; Commuter Missile: GSX-S1000F; Cheap project: CBR900RR FireBlade
Remember kids, bikes aren't like lego. You can't easily take a part from one bike and then fit it to another.

[Kickstart]

Hi

Exhausts are a lot more complicated than "bigger bore = more power" (often the opposite is the case with a well designed exhausts). Exhausts work by pressure waves bouncing around and sucking out the next lot of burnt gas from the engine, and the lengths and the order that down pipes join is very important to this. Bigger bore pipes will tend to lose the effect of these pressure waves.

That said I doubt the Bandit stock exhaust is particular designed to take any great advantage of these effects, but losing power from big exhaust changes without playing with the jetting to compensate doesn't surprise me.

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[sinclair182]

Cheers guys! Its not my bike if im honest but my brothers and as im only pottering about on it till he passes his test i might just let him deal with it. I apreciate the help though! Any ideas how much it would cost to rejet it for the current exhaust set up?

[Kickstart]

Hi

Probably ~£100 for a dynojet kit to provide some adjustment and then a couple of hours of dyno time. At a guess (with no real idea what your local dyno place will charge for setting up) getting on for £300.

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing