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Discussion Starter · #1 ·
For those of you who want to learn more about 2 Stroke engines, carbs & spark plugs, surf:

Engine:
http://science.howstuffworks.com/two-stroke2.htm
* Animation and lots of other 2 stroke informative info...

Carb:
http://www.motocross.com/motoprof/moto/mcycle/carb101/carb101.html

Spark Plugs:
http://www.motocross.com/motoprof/moto/mcycle/plug2/plug2.htm
http://www.ngk.com/sparkplug411.asp
& As seen on its left side index, this site is full of lots of details. For NGK coding details, see its "Manufacturer's Numbering System - NGK" at the bottom left of the page. Very interesting stuff...

Hope this helps someone who wanted to know more of "how does it really work?" inquires.....
 

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what do you think about 14/39 gearing on a jetted and filtered l.e 2005 for desert
 

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Discussion Starter · #3 ·
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We have a 39T sprocket on the rear of our Pred-90 (using stock tires) It works great with the factory chain guard and HPD Spring Loaded Chain tensioner. Wouldn't want to go too much bigger. On the front sprocket, we're using an 18T. With 18T, the chain has enough "gap" at zero compression and at full compression. Since 14T is a much smaller sprocket, it "might" make the chain rub the Swing Arm bar. Especially if you are doing "full suspension compressions" like our Pred-90. If you know the physical size of the 14T, use a long stick and compression test to determine if its chain will rube.


With 14T on the front and 39T on the back, it will give your mini more "bottom end" spin from the 5 mph to upper ground speed. It will make your engine rev higher compared to stock sprockets (going the same MHP). However, these sprocket sizes will reduce top end speed. For example, 30mph down to 22ish (or even less). Not too sure what your max ground speed is "your average". For us, we rarely go above 20 mph. Your young rider might. For sprocket ratio to ground speed chart, surf: http://community.webshots.com/photo/284402100/284403055gNZGAV Note: Select "View Full Size" at the bottom of this page to read its fine print.



If you are looking for "more zip" from 0 to 8 mph range, changing the sprocket sizes won't help (very much). For this area, it's beter to install clutch upgrade. Or in simple terms, change the weight of the clutch rollers. By doing this, it makes the engine rev higher before its belt engages. Much the same as reving a little higher on a manaual tranny car before letting its clutch out. It revs higher on take-off and thus, more power at the bottom end (compared to sprocket size changes).


We changed the sprocket sizes on our Trail riding Pred-90 (left its clutch as stock). It gave us higher "momentium" RPMs when going from dips to little hills. Worked great for us. For for sand, I would imagine you'd want more "immediate" power gain in the 0 to 10 mph range. Thus, changing the rollers might work better for you.


Note: Some people perform roller changes and sprocket changes. Thus, giving them more "immediate" bottom end zip increase and also improved RPM momentium increase. If you are more comfortable with external changes (like me), change the sprocket sizes and see how you like it. If you need more immediate zip (for soft sand at take-off), you can always change the clutch rollers later.


Hope this helps....

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