rode the old spanish trials and TY bikes since 1960 on single track trails in high mtns of ID and around and want to do some more in old age-66. have heavy dual sports. saw some in southern CO near Pueblo/salida where riders had cured three major comfort hurdles--low unpadded seat height for leg extension and more gas storage. They added an aluminum gas tank above the stock sway-back modern trials bike and padded for seat. probably can be bolt on/off to retain trials integrity. So desire to start with newish 4 stroke trials with headlight about 150 pounds, add the gastank/seat, and maybe gear up slightly. may have to add some stator capability to run few more lights for minimal street legal lighting. hope to end up with something lightweight and torkey (sp), quiet and street legal enough for forest service roads, marginally comfortable and reach ground. want to ride difficult trails without tall, heavy bike. been the pedal route. Doubt there any out there stock? comments or suggestions?
How important is it that it be a 4 stroke? The new Ossa Explorer sounds like exactly what you want, but its a FI 2 stroke. Worth a look, I think.
Gas Gas Randonne, 4 stroke and removable seat! Avaialble at you local dealer or www.LewisSportusa.com
I would suggest looking for something like an SY250 longride, or 4RT with trail seat/tank fitted. Euro made bikes are ok for trials, but mechanical problems are pretty common, so its worth looking at bikes with Jap power.
The GasGas Randonne uses a Yamaha TTR125 engine. Just about as reliable as it gets, and Japanese too.
Is it a genuine Yamaha engine or a Chinese copy? The carb is Chinese, and I haven't seen anything (maybe missed) that explicitly says it's a Yamaha engine. Also, the starter motor looks pretty cobby to me, not really Yamaha-esque, but that could be a GasGas add-on.
A Honda Reflex makes way more power than a ttr125 motor. (Just sold my wifes.) The reflex is already street legal too.
A stock Beta Alp fits all of your requirements. Motor is a bulletproof genuine Suzuki 200cc air-cooled unit. A tad heavier than 150 but it's an easy-to-ride mountain goat.
If you can find a uesd one I know a gal that rides a gas gas pampera and loves it. Dry of 210lbs or so they say... (http://www.gasgas.com/Pages/2003's/Pampera/pro-280-main-specs.html)