jse

What condition is the plug in after a top end run and did this condition exist before the carb swap? Jon

And a little trick to scrape off burned on clothing material is to use a piece of sharpened copper (I use a piece of flattened copper pipe). The copper will scrape off the gunk and as it's softer, will not take off the plating with it. Jon

Ah yes. The 2T inline twin sounds like a takeoff of their old 250 roadrace engine. I found it to be a good, strong unit that made good horsepower. Is the microlight a fixed wing? The ultralights here are like motorized parasails.

Good info for me. I live a mile from a small airport and guys here (they call them "ultralights" here, propably the same thing as the micros) run a 2 cylinder, boxer air-cooled 2T for the most part. I imagine the Rotax is probably a more sophisticated 2T. Do they run the rotary-valve types? Jon

You've touched on a problem area that we are dealing with. Two-stroke engines are used in a wide variety of ways and I don't think you can extrapolate "correct" ratios without knowing the operating conditions and engine design parameters, to do so is comparing apples and oranges. The 2T aircraft engine mentioned sounds like an ultralight type two cylinder. This is a relatively constant lower RPM use, reasonably long operating time, constant soft load with a trend towards overcooling. It is difficult to compare it to McGrath's CR engine which is relatively short duration operating time, liquid-cooled, wide open/trailing throttle, heavy load, frequent over run RPM etc. AND, you would need to know if that was his outdoor or Supercross engine, trust me, they are very different animals, having built both types. Another interesting twist is that Honda usually sets their production MX 2T bikes to a 20:1 premix ratio (first thing a rider would do with a Honda is change to 32:1 and drop the main jet 3 points) so the factory engineers were, in actuality, leaning out the ratio for a full-on race bike as compared to a standard production bike. Based on general use over a number of years (time-based experiential data), I think we can safely assume that a ratio in the area of 80:1 seems to work well for the average Trials rider running a liquid-cooled engine and that a rider should also take into consideration any unusual conditions that would dictate adjusting that ratio. Because of the wide variables involved, the "perfect ratio" is ever elusive and may, in fact, be non-existent, or only exist for a snapshot in time for a specific engine running under specific conditions. When building a racing engine (or choosing a premix ratio), the race tuner is constantly compromising and making a balanced decision between performance and reliability and I think it behooves any rider dealing with this issue to do the same. Although this horse has been dead for a very long time, we do enjoy giving it a couple more whacks now and then, just for fun..... Jon

What ratio and mixing conditions do you recommend? Jon

I had a rider in New Zealand ask me about damping adjustments on the new Tech forks. I haven't had a chance to work with them yet but I'm sure some of you out there have. How do you find the adjustment proceedures and what final settings seem to work well? I'll pass on any info to him. Thanks in advance. Jon

Cool idea, the long hose would probably help maintain a constant, low level, vacuum in the line and aid removal of trapped air. As we all know, it only takes a very small air bubble to make the rear brake feel spongy. Jon

I don't know if we ever really answered buck's question. From my experience, most riders use a full-synthetic premix oil in ratios ranging from 60 to 100:1, so an 80:1 ratio is about in the middle and also seems to be the most popular. A good rule is to try to mix a fresh batch (fresh oil and fresh gas) before each ride. Jon

I'm not sure if you have an older bike or a new model (the new bikes have enough room around the M/C) but sometimes turning the installed M/C upside down and slowly pushing in/out on the piston with a Phillips screwdriver will bleed the air from the pocket at the top of the bore area. The difficulty is that the feed line from the reservoir is below the pressure outlet when the M/C is normally installed so the usually large air bubble has to be forced down to the reservoir feed outlet. It's difficult to move enough volume/pressure of fluid in these narrow lines. Jon

"Hey Jon ; Isn't your brother supposed to be wearing safety Glasses ???"........No problem, he's a Lumberjack and he's o.k....... Not sure how long but it was good enough for a first place. As you can see, even with a temporary bog from the engine, it cuts quite quick. I had run a load of Nitro in it and it was a tad too much. A "full load" of Nitromethane is usually between 87 and 92%, more than that and you can't always light it off with any degree of certainty (learned that from the fuel dragsters). Percentage of Nitromethane is determined by using a hydrometer and reading the specific gravity of the mixture. Jon

It's not the fuel screw, Lee. What main jet are you running? Are these top gear runs and how long at wide open throttle? Jon

Sometimes an emulsion type shock (oil and gas mixed) will not work as well when switched, but the ones that have a floating piston between the oil and Nitrogen usually work both ways. With the body at the "top", unsprung weight is reduced slightly, but possible damage/shaft pitting from flying dirt is increased. Jon

Just tried it, works fine here. Jon

Yep. The "tighter is better" crowd has snapped a bunch of those tripleclamps. I use 18 lb ft with a light application of anti-seize on the capscrew threads. I make sure all the fasteners are loose in the front end and start with the top of the tripleclamps, working my way down to the axle capscrews and "centering" the front end by pushing up and down on the forks each time a new set is tightened. The fender brace is last. This will preclude the possibility of "stiction" caused by mis-aligned components. Jon

Oh, and sometimes you just have to guess what ratio to run: one of the competition chainsaws I built for my Brother. Twin pumper carbs, welded cylinder for large ports, tuned expansion chamber and a very healthy dose of Nitromethane......(20:1 worked well). Jon ps. I thought we were getting a little too serious.....

I wouldn't trust that Stoodley guy if I were you.... I agree, I'm not always right (just ask my wife) and other tuners will disagree with me at times, just like I disagree with their findings now and then. But generally we will not be that far apart and can usually understand the other guy's opinion based on their background experience and level of expertise. I think part of the problem we deal with when choosing an oil ratio is that we are dealing with multiple variables, such as rider level, quality of premix oil, machine condition, state of tune, duration of running time, operating conditions such as a lot of high-speed road work etc. If you want to feel safe, you should go by the manufacturer's reccomendation which is usually on the "rich" side in order to try to cover worst-case riding conditions. Even manufactuers are unsure what the "right" ratio should be: the 04' GasGas owner's manual states to run a 1.5% ratio and the 08' manual calls for a 2% ratio for essentially the exact same engine. Personally, I probably run a 65/70:1 mix as I always fudge a little more in the measuring container because it makes me feel better (there is also a psychological component to ratio choice as it is not all a mechanical absolute). So, I guess my advice would be to stay within "normal" rider usage range, but also take into consideration any unusual conditions you will encounter that may call for an adjustment. Jon

Stu, It's been quite some time and the notes and photos have probably been lost. All the modifications on the bike were specific to my riding style so there is a good possibility they would not work as well for you. It would be best to evaluate what type of performance you want out of the bike as that will dictate the modifications needed. The shock internal/external changes were based on frame modifications, engine changes and alterations to the front forks so the bike is designed to work as a unit rather than a collection of parts. I noticed you have "ty hybrid", what has been done so far and how do you like the bike's performance? Maybe I can give some suggestions that you might consider. Jon

I used a Works Performance body with my own internal modifications, added a steel braided line and a reservoir (the 85's don't come with one so I added a mount to the frame) that has external damping adjustment (with my internal mods). Jon

A "rev plate" is the small thin, sheet metal plate (often gold in color) to equalize clamping pressure on the reed base, a "reed stop" is the, usually longer, thicker, curved plate used to dampen reed flutter as well as equalize clamping pressure. Jon

Sounds like a little file work with a rat tail file on the inside of the spacer would do the trick? Jon

I think you're right. For some reason I kept thinking about all the later hubs. Haven't worked on the early ones for some time ( and I'm old and feeble....). I think the inner hub should just push out from the basket and I'd take that stepped washer from the center hub out just to keep track of it. I looked up the part numbers for the basket and the primary shaft (essentially the inner and outer "races" for the needles) for the 2003 (bushing) and 2005 (needles) and they are both the same, so I'm assuming that the needle bearings are a direct replacement for the bushing. Jon

No, it can't. It looks like the needle support collar may still be in the hub, but can't see clearly. If you would, remove the clutch pack from the hub/basket and take a photo of the inside of the hub bore. Trust me, those bearings are made to fit inside the basket hub and you will ruin that engine if you do not install them. Jon

Jimmie, the nice thing about the rebound/compression separation is that you can adjust the viscosity/damping independently. You can stiffen the compression and still keep the springy rebound if you want by upping the viscosity on the comp side. The shim stack seems to work well with 7.5 wt. oil. If you are having bottoming problems, up the oil level, which affects tha last third of travel. I like the synthetics as the anti-foaming agents and lubricity is more advanced than the mineral-based oils If static sag is an issue due to over-design rider weight, go to heavier springs before trying to compensate with damping changes (over correcting with damping to make up for incorrect spring rate never really works out well). If you have the experience, you could go two-stage shim stack and piston port changes but I think that would be over-thinking the issues and more in the area of Adam Raga riding level. Such as, going to a 16mm backing shim on a two washer stack might be a little much and you might be better off with a .2 13mm. If you are coming over to Trials from speed-based competition like I did, one of the adjustments I had to make was that you will need to make little, if any, modifications to have a competitive bike (a lot of the changes we do on our bikes is just to make us feel good and I do a lot of stuff on my bikes because I have a lot of fun with that). Good, routine maintenance and adjustment will work wonders. Trials is a skill sport, which can be tough on egos, as I found out the first event I rode.... This was brought home to me when I was hanging around the GasGas tent at the World Round at Duluth in 2005, talking with the riders and seeing what they did to their bikes. Other than Raga and Fajardo's bikes being shipped in, all the other riders were on dealer-supplied stock bikes with a few special parts (to suit their riding styles) that the riders had brought with them. Jon. ps. I'm guessing that you, like me, enjoy working on bikes as much as you like to ride them....

I use a combination of the o-rings and carefully applied hi-temp Silicone, but I like a tight exhaust system. I'd do the hi-temp and see how long it lasts. The o-rings are hi-temp Silicone..... Jon