Yamaha TRX850 Enthusiasts Forum

I've got a question. I really want to move my engines powerband lower. Currently it pulls great from 3500rpm and up, and pulls nicely when accelerating hard. However, its feels woolly and off the powerband below 3500rpm. As the bike is used a lot on dirt roads and narrow country roads, and rarely if ever gets revved above 5000rpm, I'd love to get it pulling better from say 2000 to 5000rpm. I'm quite happy to lose top end power to achieve this.
I've done a bit of research and it seems the Mikuni vacuum carbs may be the key. Designed to produce good power at higher engine speeds, not so good down low(on my bike anyway).
I'm wondering if a pair of 34mm, or smaller, non vacuum carbs would give more grunt down low at the expense of top end power? Also maybe different camshafts (TDM?) may help.

I know Keihin FCR41s give a substantial improvement over the BDST38s, but is that just at higher revs or do they improve the power at lower revs too?

Nope! Just fit a larger rear sprocket if you're using it on dirt roads & want more 'squirt' You can alternatively drop a tooth size off the front sprocket (or +/- both) but make sure you check clearance over swingarm pivot.

Don't over do it or you'll end up on yer arse!!

Already running 17/45 sprockets. I still need to be able to punt along at 70mph on the freeway, which current sprockets allow me to do. Gearing any lower will stuff this up. I just want the engine to pull better at low revs.

smaller header pipes, get your cams ground different, change the timing curve, fit FCRs too.
Simple really

There's only so much you can do withoout spending big - it's a TRX engine designed for street use not an off roader.

Personally I'd recommend 'living with it' or buying a new bike that actually does what you want. There is a reason we have the phrase "you can't polish a turd!".

My FCR41's will pull from 2000rpm on std gearing albeit a bit lumpy in top gear. It will pull from 1800rpm in 3rd without hesitation ok its not going to pull your arms off but it will do it. Much better than the std carbs though as they hated being below 3000rom in any gear.

dumb post deleted

you can try to adjust cam timing.
In Yamaha YZF250/450 motocross vs enduro models have mechanically same engines and only difference is exhaust cam timing. I have herad that even camshaft itself is totally same, only timing mark is punched one teeth earlier or later (?). Here someone must help.
Anyway my friend had YZF450 in hobby-cross and it was too much to handle such a sunday rider, but he managed to have enduro cam and was pleased to smoother powerband.

TDM camshafts are the same profile