Boosting performance.

[kar_the_terrible]

hi,
i took my yam on its fis extended road trip. Pittsburgh to Phlly and back... 350 mi, and it happened to take me 8 hrs along the back roads. My only problem is that I was fighting to keep the bike above 65, especially on t he divided sections of the road. while the speed limits are always 55, you still need to keep up with traffic which is normally doing 70+.

Q.1) Im wondering what are the ways to get that extry performance from the bike.

Q.2) my carbs were synced and tuned. But I figured that t he air-filters could be replaced. I know k&N filters are the best, but other than the high price, i dont think they make them for my bike, so i might have to re-jet and stuff. is it possible to replace only the filter element, with something more performance enhancing, and recycle the metal cage??

Q.3) How advisable is it to play with the sprocket ratios and trade low-end torque for high-end speed or vice-versa?

[ronboskz650sr]

If the bike is struggling, putting a smaller rear sprocket will probably make it struggle more, especially on an inline four with the power up in the rpm band. Is this an inline four, or an inline twin? My son's vulcan 500 is an inline twin, and it makes power lower in the rpm range, due to the bigger jugs, and some other cam and valve related features. His bike even has a 6 speed tranny. Is it hilly where you ride? I know this is a personal question, but how heavy are you? The combo of hills, wind and a heavy rider will eventually win the battle if you are on a low-powered machine. If the bike is naked, sometimes a front faring can help a little with wind resistance, but a 400 will have problems with wind, hills and a heavy rider if the combo is just beyond its capabilities.

[TechTMW]

If you want to go this route, you probably need to get the pod filters, rejet, and may need a new exhaust ...

K&N pods are the best, but Uni (foam) filters work OK too, as long as you keep them clean and oiled. Oh and they are cheaper.

If you want to go the rejet route, you need to use a Dyno, or at least an exhaust gas analyzer for proper tuning. I run Uni foam pod filters on my xj650 w/ stock jetting and exhaust - the only reason I did this is because I could confirm with a Dyno AND EGA that everything was ok. Simply replacing the filters like this could cause an overly lean condition which is death for an older air-cooled bike.

[kar_the_terrible]

So do I need to rejet even if Im putting in Uni filters?? Or is that going to vary from model to model.

I guess the first thing to do then is to see how/where I can get access to a Dyno or how much it might cost...

[TechTMW]

Depends on the bike. Find a dyno

W/R to your first post - everything you do at this point is probably going to trade off low end torque for horsepower. Not only that. ut if it's not done right, you'll wind up with a loss in all areas. If you replace the stock air filters w/ foam pods, you may very well lose some bottom end torque. However, without proper tuning, your bike may never see the expected gains on the top end.

Dynos are not cheap to buy - so shops w/ dynos tend to charge above shop rate for dyno time ... in Half-hour increments. Many shops that have dynos today are speed shops - guys who are used to the most modern bikes ... guys who wouldn't know a needle jet from a needle valve. You'd probably get the most help from a Harley or chopper speed shop - one used to working with carburettors ... but the trick there is finding one that will work on a japanese bike. (they are few and far between if they even exist)

Anyway - what I'm getting at is - Save your money for another bike, don't start messing with the stock setup.

[kar_the_terrible]

Yup i did find a harley dealer with a dyno in house. Said he would charge 60 bucks an hour.

Yeah I think after much pondering.... I think I'll just spring for new stock filters, and yeah save my money.

K

[Aggroton]

Yup i did find a harley dealer with a dyno in house. Said he would charge 60 bucks an hour.

Yeah I think after much pondering.... I think I'll just spring for new stock filters, and yeah save my money.

K

the fairing will make all the difference...my buddy has the same bike as me but with a fairing...once your over 55 its sooo much smoother.

82 xj550 seca btw.

[ronboskz650sr]

Yup i did find a harley dealer with a dyno in house. Said he would charge 60 bucks an hour.

Yeah I think after much pondering.... I think I'll just spring for new stock filters, and yeah save my money.

K

the fairing will make all the difference...my buddy has the same bike as me but with a fairing...once your over 55 its sooo much smoother.

82 xj550 seca btw.

You will notice less fatigue, at least. It may take some adjustments to get the max benefit. When I put mine on, after a couple of test runs and adjustments, I experience 50 mpg and more on the highway, also. I used to hover between 45-48. I would think there's more power in reserve, but my bike never lacked, even at higher cruising speeds, so I can't be sure.

[Aggroton]

yeah i have to stop every 45minutes because my arms feel like jello. im looking for a fairing...

[kar_the_terrible]

Hmm... I never really heard or pictured a fairing on a xs400/xj550 type (cruiser?) bike. How would one even go about fitting it on... and do they make stock ones or are they custom made....

I suppose ou could mount one where the crash bars are supposed to go... but where would the back/bottom be attached.. motor mounts?