kyle you need to ask some more questions. say on forums. the cap on that plug will spin off revealing the threaded screw. and xr racing? its a heavy bike for dirt. and the way the engine puts power down is slow. its a great trail bike play with the kids putt around all day. but to race one...you will just be following and getting passed. the end of the world in revs on that engine is about 5500 modern four stroke mx bikes are spinning up to or exceeding 10,000rpm.
not hating on the xr/xl line but i wouldn't take one to a race. I own a xl600r. there is a guy who hare scrambles a xr650l and does pretty well. but thats against bikes with 350 less cc's. and that guy would probalby do much better on a 450 or ktm
You are correct, a modern 450 easily makes triple the power at 80% of the weight. However, I am not a good enough rider to use a 450 to its capability. In fact, me on a modern 450 would not end in a podium, but a hospital bed. Also, I am going vintage racing--and six different forms of vintage racing at that. This is not the best tool for any of the jobs I am taking on, but it will certainly do each respectively. The XR250R is a neutral bike that I can tailor to each event fairly easily. If and when I get faster as a rider, there will certainly be a more modern machine in my garage.
100% sure. It was an interesting conversation with the NGK representative on the phone. Switching out the spark plug boot is very simple, just a $2 part. You are correct that a lot of plugs have the threaded cap, but with the thread change I shifted from the powersports and small engine portion of the NGK catalog to the motorsports section. Solid top plugs are much more common in automotive engines than motorcycle/snowmobile/ATV engines.
I'll admit I have a spare, but questionable, engine in the corner. The work to finalize the assembly on this engine is worth it for the fact that I know what is inside. There is a halfway point where I could have attempted to call up that spare engine but likely would have spent as much time getting it into running shape as I did fixing the problems I came across here. Figure I might as well get the fresh engine after the work rather than all the work and having something that may or may not make it.