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About HeadTrauma

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    The eternal quest.

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  1. HeadTrauma

    What oilfor vntage premix

    Use something similar to what would have been used in the bike originally. Modern chainsaw and outboard oil is probably fine. Castor is usually a safe bet, but it's also associated with increased varnish (dat smell tho). I doubt that using any quality oil would have a detrimental effect on engine life. Likewise I doubt that using expensive zooper racing oils would noticeably extend it. You didn't distinguish opinions from facts and anecdotes from objective scientific evidence. The source of your information prefaced everything multiple times with this disclaimer: Thus making your conclusion opinion that "Super-M sucks" a poorly informed one. Super-M has been my go-to two cycle oil for over 20 years now. Does that mean it's great? No. I could provide anecdotes that Super-M is great. Does that mean it's great? No. It just means that I like it (opinion) and experience no problems with it (anecdote and fact).
  2. HeadTrauma

    Organic Dirtbike Film coming soon

    Does anyone else think that ripping across pristine wilderness on a bike and then dramatizing it is irresponsible? Even disrespectful? I ask not to be mean or negative for the sake of being, but out of genuine concern for the "unintended" consequences.
  3. HeadTrauma

    Easy beginner question about chains

    If you're a beginner, how would you know it's an easy question? There are lots of threads on this. I generally set chain slack at full rider sag. It looks too loose on the side stand, but the slack varies with swingarm movement.
  4. Depends on how much power you're making.
  5. I have a '72 DT2 (250cc) engine that is on the ragged edge of needing a bore and piston. I can find slugs and rings all day long, but finding the right combination is proving difficult. What I know now is that my engine is standard bore and likely has the "short" 125mm connecting rod, not the 130mm used in others like the YZ250. More power is great, but I don't care if the piston has one ring or two. The problem is that ring sets almost universally have a Dykes top ring while many pistons do not. Can a regular second ring be used as a top ring with pistons that have only one regular, non-Dykes ring groove without any problems? That's usually a no-no with four strokes and I'm not that experienced with smokers.
  6. HeadTrauma

    Practically free xr600 roller

    ANY XR600 is worth the price of a 12-pack, even as scrap. If it wasn't a 10-hour drive, I would have jumped on it myself. What year was it?
  7. HeadTrauma

    xl600r dual carb swap questions.

    1.) I've seen this happen on the Keihin PD/PE when the slide bore starts to wear, but I don't know if the dual-carbs are affected in the same way. I'd suggest making sure that the twist throttle and cables aren't dragging, then see if the carb slides or linkages are sticking. You probably need to work on the hard starting first though, so see #3 below. 2.) What does that mean exactly? The clutch is dragging too? 3.) Will the bike fire up quickly on ether? If not, then fuel isn't the problem. A common cause of hard starting with the early RFVCs is a failing pulse generator and/or failing stator. Tight valve clearances can also cause it as can a compression release that's not working properly. 4.) Then you've never experienced a twin-carb RFVC that's working well. Nearly the response of a pumper, nearly the fuel economy of EFI, and more power than a single. You might have the wrong kind of bike then...
  8. HeadTrauma

    xr650l MEGAJOLT cdi conversion

    Under throttle, 40° is a truckload of advance for just about any engine, period. My turbo Pinto has 40° in a few cells, but only up to about 65kPa of manifold pressure. By the time manifold pressure reaches atmospheric (~100kPa), timing is down to 31° and it drops rapidly from there. It's an old 2v '70s design, so it wants more timing than newer "fast-burn" and pent-roof architecture. RFVCs have a big, hot, open chamber with little quench and unknown swirl, so less timing is probably safer than more.
  9. HeadTrauma

    Exterior cylinder crack

    Are you sure the crack wasn't there before? You would have to get pretty aggressive to push the backside out like that. It could be that the thread or hole wasn't deep enough from the factory and installing the head bolt may have been what started it.
  10. HeadTrauma

    EFI Conversion Sensor Locations

    Aside from facilitating "sequential" fuel and spark, the cam sensor would also allow you to sample MAP in any specific window of the engine cycle. It can be quite useful as single-cylinder engines with tiny plenum volumes like ours have very wide MAP fluctuations at lower RPM. Does the TRX brain generate any sort of data stream that can be tapped? It would be interesting to see the inside of one.
  11. HeadTrauma

    XL600R Ignition or Carburation issue?

    What jets do you have? The hesitation on throttle snap is common. You can jet around it somewhat and change your technique, but the only cure is a pumper carb or EFI. The pulse generator resistance spec varied over the years and models. My '88-90 factory manual says 360-440Ω at room temp. The earlier engines' resistance range was 510-560Ω, so I don't think there is anything with yours. Besides, bad pulse generators usually cause either problems at low RPM like hard starting or work fine when cold and start failing when hot, not tip-in stumbles.
  12. Why do you need calipers for a valve adjustment? Aren't feeler gauges suitable? Are the shims not marked? IMO, if you really want a glorified ruler, fine, get some vernier calipers. If you want something comparable or even better than digital calipers, get some good dial calipers with 0.000-0.100" dial. I tend toward Mitutoyo, but Starrett, Tesa, Brown & Sharp, Fowler, etc are good. Keep in mind that all of them are really only trustworthy to about ±0.001". With technique, dials can be repeatable to much less than that. Digitals round off the fourth digit for you. If ±0.001 is not accurate enough, then you need micrometers and that's what I would be using to measure valve shims. Harbor Freight and other no-name Chinese calipers are "use at your own risk" IMO. There's no cert of accuracy and unless you maintain some gauge blocks for checking them yourself, you're left with blind trust. I have 6" Pittsburg (HF) and some 4" no-names for beaters that were given to me. They flex more, drag more, drift more, feel like crap, eat batteries, and aren't as repeatable as the 50 year-old Tesas I still use. Properly cared for, calipers are tools and something you'll not have to replace for 30+ years, so why not get something worth having?
  13. HeadTrauma

    1995 XR600R Project

    It looks like the divots are in carbon deposits on the valve like someone tried to chip them off. It's probably fine, but are you going to feel fine saving $50 on new valves if one of those cuts loose and takes the engine out? I hate replacing good parts, but some times it just isn't worth the risk of keeping unknowns. It looks like the retainers, intake valves, and springs are all aftermarket. The cam alignment is pretty typical for an RFVC that has ever been run longer than two seconds. On the "boost bottle" mod again, they are of little to no value on most two-strokes and of zero to negative value on a thumper. Better off without it.
  14. HeadTrauma

    1995 XR600R Project

    Now I know, but that makes it even more horrifying. Butcher the carburetor for a mod that works on 0% of four strokes and 1% of two-strokes.... Anyway, I think a 38-40mm pumper will work fine as a replacement, although something larger would still work well and provide some room for growth. I had planned on using a 46mm Mikuni before cars and work got in the way of my 600.
  15. HeadTrauma

    1995 XR600R Project

    Being a crackhead is my first guess. And my second....and third.....and fourth...I'm also wondering what that epoxy-covered plate next to it is all about.