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Advice on rear sproket for 07 model

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Hello!

Currently the bike has Primary Drive front sprocket w/ 14 tooth, and rear sprocket w/ 53 tooth. I ride mostly tight single track and some moderate hill climbs, and I find that on single tracks the first gear is way too jerky and while second gear is what i use mostly, when it comes to sharp bends I will have to shift to first gear to prevent the transmission from plodding and stalled engine -- i am an intermediate rider at best :)

It would be awesome if I can use first gear all the way for the tight single tracks. Currently I use third gear for hill climbs, and i wouldn't complain if I have to use second gear.

What do you guys recommend I use for rear? 48 tooth? 45 tooth?

The whole chain/sprocket set is around 6 months old, and looks good, so I was wondering if I can change just the rear sprocket or do I have to change the whole set?

Thanks much in advance for your help!

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Not the preferred practice but I don't hesitate to install a new sprocket on a pre-used chain

to run a different final drive ratio, as long as everything is in good condition (chain not stretched).

 

As for choice of ratio, I went the opposite from you adding extra more leverage to the stock gears.

 

It depends on everyone's specific usage, stock 14/53 was way to fast for my tight rocky trails so I can't imagine running a 48 or 45!

I've tried 13/53 (tons of grunt but 1st is almost useless), then went 13/51 and now settled on 13/52 with a heavier flywheel.

 

Here's a handy gear ratio calculator: http://www.sprocketcalculator.com/

 

I think even a 48 would be too drastic, maybe try a 50 at most. 

Too bad you're located far away, I'd sell you my barely used 51 for cheap.

Edited by mlatour

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I believe stock is 53/14, mine is plated and I've run 48/14, currently for trail  51/13.

I've found several things really help:

Fix the snatchy throttle response so you can use first gear, and second will also be more useful.
My first suggestion is get the heaviest flywheel you can buy, I have a Stealhy and it transformed the bike for tight trail riding.
The carb has a slight lean spot just off idle that makes for a snatchy throttle, get it jetted correctly, JD is your friend. You can find the spot by slowing opening the throttle in neutral and the engine will blubber a bit at about 2500rpm.  There are instructions in the Jetting and YZ450 forums on setting up the AP squirt.
Adjust as much slack as possible out of the throttle cables with out causing too much drag. Cable routing is important on this bike to avoid cable binding, read the Owner's Manual.
Turn up the idle speed a bit, I have mine at 1850rpm but you could try 2000rpm. That will help stop flame outs, reduce engine braking, help reduce braking stalls, and help reduce snatchy throttle at slow bike speeds.
Get a RD remote mixture screw so you can adjust idle mixture while riding, I've noticed that my engine's idle mixture is sensitive to coolant temp.  
I have a Vapor that displays rpm and coolant temp. 

I've done all of the above and with 51/13 (with a larger Trials tire that is like adding about 1/2 tooth to the counter sprocket) and I ride gnarly tight ST; usually in 2nd gear, and I can ride fast climbing switchbacks in 3rd because any surprises on the exits don't bother the engine because it pulls from 2000rpm.  I do use 1st for difficult sections to avoid a possible flame out, and I always cover the clutch for a difficult section. A slipping clutch really smooths out power delivery to the rear wheel.

IMO my X as set up has bottom end throttle response that is a lot like a XR250R.

Some sprocket combos and their ratio:
53/13 = 4.077
51/13 = 3.923 (my current)
53/14 = 3.786  (Stock)
49/13 = 3.769
51/14 = 3.643
48/14 = 3.429 (my street)
 

Edited by Chuck.
added final drive ratios:

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@mlatour, @chuck: Thanks much for your detailed responses. The bike has most of the mods needed to run better -- FMF Q4 exhaust, JD jetting, Boyesen AP. I am inclined towards trying 51 tooth and flywheel. Maybe I will try flywheel first, and later on when I am used to flywheel setup, I can try 51 tooth, instead of doing both at the same time. Cheers.

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