Draggie, k&n filter, power and mpg

[Toutsuite]

Some time ago, I posted how I was getting very high mpg's (60+) even riding through London traffic on the drag 650 (which is supposed to do 45-50 mpg). I couldn't figure out what was causing this blessing, but was worried she might be running way to lean. However having checked my sparks it turns out she was running a smidge on the rich side.

So still couln't figure why I was getting such good mpg figures. Could it be the V&H pipes alone doing this? Even after a re-jet done shortly after fitting them?

Then recently I was playing about with the airbox, thinking of ways to increase airflow a bit, since she was running slightly rich. Looking on a website reading up on something called a RAK, or a home-made air intake mod, I noticed this duct in the chamber behind where the filter sits. Now my airbox didn't have that. It had obviously been removed by a previous owner. Without that duct, the airflow is way too high, even with the stock paper filter, so you get a lot of sputtering and hesitation. I found this out when I removed a bit of plastic that had been screwed in place over about a third of the duct aperture to compensate for the absence of the duct itself. So this, combined with the V&H cruzers was what was giving me high mpg's.

When I finally received the duct from Japan (via Fowlers) and installed it, my mpg went down to 47. Crap! What to do?

Well I decided to give the K&N filter a try. I'll get the numbers out of the way first: I did a 50 mile test run today, through central London, Spitalfields, City, then out to Richmond, then back through the other side of the park, up the A3, south circular and back to Brockley. Some bits of heavy traffic, some clear bits and a good run up the A3, with a mix of economical and aggressive use of the throttle. Result? 61.8 mpg! That's up from 47, with just a change of filter in my setup.

But that's not all. There was a very noticeable improvement in throttle response across the power band (though I didn't take it up to the limiter, I never do that, so can't say if there's an improvement right at the top). The bike launches more readily, pulls harder and climbs faster through the revs. It were great! I might get her dyno'd again to see if it's real or whether I got a bad case of the placebos - though I really don't think so.

Conclusions: It think a quick, easy (and free!) way to improve airflow to the filter in order to increase mpg would be to shave some length off the duct, or even to remove it completely and then place a bit of plastic over a 3rd of the hole. I imagine this would have some benefit even with the stock pipes on. You won't get any power gains though. For that you'll need a K&N filter. (and no, I don't work for them!) Now I'm off to order one for the CB500 and the car!

[blackhat250]

Great resuts touts" when it fell to 47mpg , did the plugs get black, [ ritch] ? and have you checked the plugs now at 61mpg, to see if lean,

byetheway" I "v just fitted a K&N filter to my tiger , and deristricted the air box. [ speed triple mod] sounds throatier

[Toutsuite]

I only did about 45 miles with the airbox restored (with the duct) before switching to the k&n filter, so don't think the plugs would have had time to change colour. So no, didn't check.

Does the tiger feel any vrrrroooomier?

[blackhat250]

Hard to tell, as its got more Vrooom than I can handle,

[KevtheRev]

Where do we get these "placebos" , are they expensive ?

[Toutsuite]

They can be!