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372
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1/24/2011
Location
Clinton, IN
US
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1195th
Hi guys, I'm old and slow but racing a 78 YZ 250 in vintage motocross. Just wondering what gearing people are using ? Right now I have 13-50 on the bike. Any better choice ?
you also need to be careful about detonation on that bike.
also, if eric did not put boysen ports into the crankcase, you could ask him about doing that.
you can also try lowering the front if you want it to turn better but make sure you don't lower it so much the tire hits the fender.
The Shop
raise the forks in the clamps until the front tire is almost touching the bottom of the fender then tighten the clamps.
then sit where the seat meets the gas tank in the turns and lean over the bars. if you don't sit here it will be harder to turn, plus the front tire will try to push towards the outside of the turns (basically loose traction).
in your case, you can add around 25 - 30mm to the head pipe where the pipe comes across the front of the engine, but i have never used a pfr pipe on my bike so i don't know how the pfr pipe changes the performance from a stock pipe but this mod should work on any pipe. i use a stock pipe with an answer silencer with the head pipe mod.
you can also have the boysen ports added that i previously mentioned if they are not added already. this will give it more mid range, but again, ask eric about it first.
also, if it hits too abruptly for you and looses traction, you can make a weight for the flywheel or use an ignition that has an external flywheel but this is a little complicated.
your cranking compression should be around 180. if it is much less than that you will get more power by increasing it which might mean just new rings or a cylinder head mod etc.
my bike is capable of hole shotting and winning the vintage expert class so i know the mods i have work for me at least, but a box stock 1980 yz250 could hole shot the local pro class back in 80 anyway.
I will look at my countershaft sprocket in a couple hours and let you know what it is.
my countershaft sprocket is 13 so i would leave your gearing exactly where it is unless you are tapping out in 6th gear half way down a straight. in fact, i may try a 50 on the rear also.
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As far as sitting forward more, you can only do what you can do but it really is the only way that bike will turn half decent and not push the front much. Also, if sat back on the seat over bumps I would need an operation as well because the bumps just kill my back now that I am old and weak and brittle, lol.
Here's a story on woods newest back surgeon that did that operation.
https://sportsday.dallasnews.com/other-sports/golf/2018/03/10/exactly-r…
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