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  1. Well that is pretty cool. I Googled "chapman bsa trials" and the first hit is here: Looks like the original builder was a member here (mick_99) and replied, "...20 production bikes and there were 3 prototype made:..."
  2. konrad

    Need help with VIN

    Although this information is for North America https://en.wikipedia.org/wiki/Vehicle_identification_number many European manufacturers use the 10th character in the same way. So M would be 1991 or 2021. Does that seem reasonable for the bike?
  3. That monoshock configuration is reminiscent of mid-1970s Yamaha MX bikes. Some interesting backstory here: https://motocrossactionmag.com/classic-motocross-iron-1974-yamaha-yz360b-monoshock/
  4. The first time I used the steam cleaning trick was with the bike running on a stand while strapped to the trailer. It was the rear, and I just applied brake pressure while the wheel was turning. I could easily monitor the rotor temperature with an IR thermometer (which is totally unnecessary). Get the rotor so hot you can smell the pads cooking. More than one application may be helpful.
  5. Thought of another thing I will add for completeness. Pure water has the best heat transfer properties, but we typically use antifreeze for a variety of reasons. A 50/50 mix of ethylene glycol / water has very good heat transfer properties. Pure ethylene glycol has quite bad heat transfer properties and why it's not used above 70% concentration. Straight ethylene glycol as coolant would definitely cause the fan to run much sooner than normal.
  6. The exhaust system of all 4-strokes runs much hotter than 2-strokes. I did very few mods to my 4RT, but one was applying “header wrap” to the exhaust system between the heat shield and muffler to prevent melting nylon riding pants. As suggested, checking the oil and coolant levels is a good idea. Also check for a blockage in the radiator: mud, collapsed fins, etc. How soon the fan turns on depends on engine load and airflow through the rad. For a given ambient temperature, high load and slow ground speed turns the fan on quicker than light load and a lot of airflow. The bike is new to you, but how new is the bike? Due to friction, the entire engine will dissipate more heat during the break-in period than afterwards. Scariest of all, it's possible you may have a mis-drilled oiling system. See: https://www.trialscentral.com/forums/topic/78761-montesa-4-ride-oil-filtration-issues/
  7. konrad


    Igor, I don't think the selling price of my bike is relevant and that's why I did not mention it. A long list of modifications, spare parts (and the promise of technical support) was part of the sale. Local market conditions play a huge role in price -- look for comparables where you live. Condition has an even greater effect on price. The bike looks clean, but as a wise man one said, the cheapest restoration you can do is with a camera. Is the shock leaking, does it need crank bearings, etc.? When was the last fork service performed? Does the clutch operate properly? How old are the tires? In the end, it's worth what you and the seller agree it's worth.
  8. konrad


    I had that exact bike in my stable until just a month ago. Although called a 200, it actually displaces 163cc. It exhibits all the desirable characteristics of a 125, with just a bit more torque. It is the most beginner-friendly reliable trials bike I could imagine, and super-easy to start. It's the one trials bike I said I would "never sell" because it was perfect to introduce anyone to the sport of trials. But alas, I ran out of newbie friends and space. The only possible downside is the ignition system. My 2003 had the bulletproof Ducati Energia system. Slightly later models used a vastly less reliable Leonelli system. Follow this link to see a picture of the two flywheels side by side: https://www.electricmotiontech.com/home/what-makes-a-good-trials-motor/flywheel-inertia The Ducati is marked 200, the Leonelli is marked 125.
  9. So true! To the OP, it's often difficult to tell the difference between an electrical misfire and a fueling misfire. I'd richen the jet needle clip to see if you can move the misfire to a differed throttle position.
  10. Below are the gearbox ratios of all GG Pro models. 1st, 2.996 2nd, 2.571 3rd, 2.187 4th, 2.112 5th, 1.125 6th, 0.821 Below is the % change between those gears. 1-2, 16.5% 2-3, 17.6% 3-4, 3.6% 4-5, 88% 5-6, 37% As you can see, a 15% change in overall gearing is significant -- almost like the difference between 2nd and 3rd. You can also see that the difference between 3rd and 4th is not much by trials standards. GG's patented "4 gear pairs provide 6 ratios" is pretty much a gimmick in my opinion. Contrast this with the old GG TXT321 which had a conventional 6-speed gearbox (and was was ideal in my opinion). Below is the % change between those gears. 1-2, 16% 2-3, 27% 3-4, 28% 4-5, 57% 5-6, 50%
  11. 46/9 = 5.11 49/11 = 4.45 46/9 yields a higher gear reduction ratio than 49/11. 46/9 will yield more driving force at the rear wheel than 49/11 (for the same engine speed). 49/11 will yield higher ground speed than 46/9 (for the same engine speed). Those sprocket combinations are nearly 15% different -- that will produce a very noticeable change.
  12. Kudos on your persistence! But it should not have been nearly that much effort for you. Wishing you a positive end result.
  13. The Dellorto is unlike a Japanese 2T carb (where 1.5 turn out is the normal starting point). Despite being on the engine side of the slide, the Dellorto's mixture screw controls fuel (out is richer). For the Dellorto, 3 to 4 turns out is typical. If it runs best at 2 turns out, that's fine. But don't be afraid to experiment with the mixture screw (just remember that the spring needs to be somewhat compressed to ensure the screw does not vibrate loose and fall out.) Most manufactures have a procedure for setting the mixture screw that optimizes idle smoothness or minimizes idle emissions. I set the mixture screw for best performance just off idle. Attached a pic for reference. Mixture screws on the right left are for fuel, mixture screws on the left right are for air.
  14. Your colored arrows are correct. Dellorto PHBL 26 mixture screw is typically about 4 turns out from fully seated. The pilot jet (and possibly starter jet too) is plugged from sitting for years with old premix. Usually, spray carb cleaner is insufficient. You need to clean the jet by passing a fine wire through the orifice. But the diameter is critical, so I use pin gauges for that job. Some people are uncomfortable using that method and should replace the jet(s) instead.
  15. That's not true. Power is proportional to torque times RPM. Increase the voltage available to a DC motor and you can increase its maximum RPM capability. Whether or not that will improve an Oset, I have no idea. Whether or not the reliability of the Oset system degrades to an unacceptable level, I have no idea. I've outlined some basics here (and in subsections): https://www.electricmotiontech.com/home/ev-tech-101
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