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Yamaha Tech Originally the Yamaha XT600 Tech Forum, due to demand it now includes all Yamaha's technical / mechanical / repair / preparation questions.
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  #1  
Old 20 Dec 2013
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Tall gearing coupled with elevation

Got a 1993 XT600e 3tb 3uw and am finding with the elevation here (6,500) and normally ride 9 - 10K (power loss) 5th gear is really tall. In light of no tach and heard not to ride in 5th under 80kph want to add a couple of teeth to the rear sprocket. I have a real dead spot between 80 - 95 kpm.
Anyone done this and if so will two extra teeth do the job?
Do you know how many teeth in the stock rear sprocket?
Thanks -
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  #2  
Old 20 Dec 2013
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Honestly i dont understand what you write here, but the sprocket is 45 rear.
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  #3  
Old 20 Dec 2013
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Proper jetting for higher elevation helps a little to minimize hp loss, but only to keep the mixture right. You would probably want to go with a 1 size smaller front, it will drop about 5 kpm at 90kpm for the equal rpms. 4-5 teeth in the rear equal approx. 1 tooth front.
Just count the number of teeth on the sprocket to know how many you have. Some sprockets do have the number stamped on them.

Last edited by jjrider; 20 Dec 2013 at 23:26.
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  #4  
Old 20 Dec 2013
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Ok, riding at 9-10K you loose about 25-30% power. This coupled with the tall 5th gear makes the bike a dog. If I go 2 extra teeth on rr would this help eliminate the 4th gear (to high rpm) 5th gear (to low rpm - lugging).
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Old 20 Dec 2013
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Try a 14 sprocket up front, they're cheap and you can use the stock chain with it.
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  #6  
Old 20 Dec 2013
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Lower gearing WILL help ... but nothing will bring back your Sea Level HP riding up over 6500 ft. ALL bikes lose power at altitude. Physics.

A couple ways to help:
1. Jetting
Leaner jetting could be helpful if you are now running TOO RICH. (a quick look at your spark plug will tell you: black plug = too rich) So get your jetting right first.

Also ... adjusting the Low Speed Fuel mixture screw will help a lot with low speed running, including allowing smoother running, better throttle response, and better starting and idle.

I believe you can install an "extended fuel screw" on your Carb. These are easy to reach and adjust. Idle speed should be adjusted too. Changing low speed fuel mixture takes just a minute with the extended fuel screw. XT Vendors must sell something like this?

If you go back to Sea Level, be sure to change Main jet back to a larger size
(richer), then re-adjust low speed fuel screw (takes 20 seconds) and idle for Sea Level operation.

2. Gearing
Two ways to affect gearing.
1.Rear sprocket change
2. Front sprocket change.

I don't know stock sprocket sizes on your XT but most likely a SMALLER front sprocket is available. As mentioned above, ONE tooth smaller on front sprocket equals 2 or 3 tooth difference on rear sprocket. It may be possible to go 2 teeth smaller on your XT ... this I don't know ... but for sure One tooth smaller should be possible and WILL make a nice difference.

In you case, riding up SO HIGH, I would DO BOTH. Go up two or three teeth LARGER on your rear sprocket and go ONE tooth smaller on your front sprocket.

This should help make the bike more ridable and help keep you out of that low RPM lugging zone. (never good on a single cylinder bike!)

Your top speeds on highway running will be limited just a bit but overall performance should be better and ... MORE FUN!

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Old 20 Dec 2013
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Done, looking forward to being able to have more powerband in lower 5th gear.
Thanks
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  #8  
Old 20 Dec 2013
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Have tried 14 in front and cant say that it did any major difference to the bike, actually its better stock.
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  #9  
Old 20 Dec 2013
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It should make a difference:
http://www.jtsprockets.com/catalogue/model/6583
Still going to give it a go. At worst I'll add a couple teeth to the rear.
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Old 20 Dec 2013
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Not a direct answer to your question, but when I put a one tooth smaller sprocket on the gearbox of MY Enfield (23 bhp) I actually made more miles per day than before. with no adverse effect on Mpg. ( normal cruising speed pretty much the same at 50-60 Mph). With a LOT less gearchanging.
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  #11  
Old 10 Feb 2014
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Wow, what a difference! Probably gained 300 rpm in 5th.
Getting 55 mpg now also, worked out very well. :-)
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