Yamaha TRX850 Enthusiasts Forum

Hi folks. I would like to fit a K&N filter to my TRX. The bike has Staintunes on it but other than that no mods. If i add the new Filter, will i need to re-jet?. I have also heard that drilling the Airbox is a common mod?. Would removing the foam seal under the Tank and around the Airbox have the same effect?.
Thank you for any advice, Anthony.

I reckon it depends on the type of K&N u wanna fit. The type u fit into the airbox or the ones u attach directly onto the carbs.

Im kinda curious myself too.

I would like to replace the stock Filter so i guess thats the one in the Box.

therigger wrote:I would like to replace the stock Filter so i guess thats the one in the Box.

I cut a large hole in the airbox and used K&N filter with racecans, the trix was still fat due to worn emulsiontubes.

Rejet the carbs and get a better bike with more milage to the liter!

The TRX runs rich as standard so having open cans and a K&N in the airbox should level things out. That said, it may run a touch lean so best bet is prob a quick run on a dyno to make sure.

I replaced my standard filter with a K&N. The rest of the bike was standard apart from a Foran 2 into 1. I got tyhe bike Dyno'd before and after the K&N. Standard, the bike was running slightly rich on idle and at full throttle, with the K&N, It was running pretty well spot on and increased the hp by 1 bhp.
Air box mods on CV carbs are not really worth it IMHO.

The increase in Induction 'suck' with the K&N filter makes it worth doing it on it's own.


I say 'suck' cos it's not really a Roar.

Is there a concensis on what air box mods are best for a Trixy?
On most bikes removing the top access panel does the trick but on the TRX it also secures the air filter so cannot simply be ommited.

I've got no idea on jetting, but mine has staintunes and I just fitted the K&N airbox filter, its also got two 20mm(ish) holes drilled into the front of the airbox 'scoop' (which faces backwards anyway).
The thing I noticed on fitting the K&N (exhaust and airbox holes were there when I bought it) was the hole in the middle of the rev range has pretty much gone, and the whole rev range seems smoother and its easier to rev the engine out. Doesn't quite feel like theres more power but definitely runs nicer.

Thanks heaps for the advice and various personal preferences in regard to the Air Filter modification.
I am located in Sydney Australia. I have never used a Dyno or a Mechanic that has one. Can anyone recommend a Sydney Based Shop that can Dyno and Rejet accordingly at a reasonable price and have some knowledge of the TRX. Cheers and thanks again.

DynoBike in Sydney gets a lot of exposure in Rapid Bikes mag, and the boss Dave sounds very knowledgable. No idea if they know trx's but I think the prices are reasonable.

Good call. I read Rapid as a rule, top little mag. I will get in touch with them and maybe use them. I kind of like the idea that they advertise in Rapid. Gives a bit of cred i think. I will certainly post the outcome in this Forum with the outcome. Cheers.

Yeah, and given the fact Jeff Ware seems to know his stuff, and he's now got 'Dyno Dave' on the panel for the mechanical/modification 'help' page, there's certainly some cred there.

On the subject of air filters, has anyone removed the airbox completely and just fitted appropriate filters on the standard carbs. Would it work, would it make any difference? I was thinking that more air would make a noticeable difference.

to a degree, if there is no wind/turbulance then yes but as soon as you get a gusty cross wind your going to be sputtering and farting flatout. CV carbs are very sensitive to sudden air pressure fluctuations.