jse

As an addition to that, the best gauges I found were from a company that sells supplies to serious dragracers. Tire pressures are important business in dragracing, where a pound of pressure can make a difference. I bought a Longacre 0-30 large dial gauge years back and at the time the price made me gulp a little, but it's been bulletproof, extremely rugged and I've had it calibrated several times and it's been spot-on every time. So, in the long run it was a bargain. Jon

What year and model is your 280? Jon

I haven't figured it out either. I know I've run into riders who boast how lean they run their premix ratios (I guess thinking they are getting more power by using less oil, unaware of lubricity and ring sealing issues) and how cheap the oil is they are using "yea, well, I pick up dis here Dino-Squeezings Premix Oil for almost nothing and I run it at 130:1 and my bike runs great!. It doesn't matter what kind of oil you use, it's all the same". We run the Pro MX and SX'ers on 32:1 (Roadracing is a different issue) with no problems ( and Honda set their jetting for their two-stroke production MXers at 20:1), but in the relatively understressed engines in Trials use, a high-quality full-synthetic should be able to run fine at up to 100:1. For my personal use, I've weighed all the variables and decided that 70:1 makes me most comfortable, but it amazes me how premix ratio is such a "personal" thing with riders, I guess myself included. Jon

Yea, me too. I weigh about the same (hmmmm, 1 stone equals 14 pounds?) and I usually run 4 rear, 6 front under most circumstances. I may run 5 rear if there are sharp-edged rocks and 3 if it's sloppy wet but no nasty sharp thingies. You'll want to get a good tire gauge, you will use it a LOT in Trials and try to get one that has a low range (like a 1-15 psi range here in the States) because most gauges have a percentage of calibration inaccuracy, generally about 2-3% which, for instance would be 2-3 psi for a 1-100 psi gauge (not good for Trials) but that would only be about .30-.45 psi for a 1-15 psi gauge. Jon

It does get a little confusing, this "weak"/"rich" thing, kinda like talking about raise needle/drop clip or the air/fuel screw adjustment. He had framed the question in fuel/oil ratio, i.e. "is this specific to each bike, i have a montesa 311 and been told to mix 50-1 but this seems very weak, do different mixtures give different performance? what would you advise?" so I answered in kind, but you're correct on both counts, additional premix oil would have probably resulted in a slightly "weaker" air/fuel ratio and it probably would be hard to measure exactly. Jon

My current favorite is also the Castrol TTS, although I've tested a bunch of other oils with favorable results like Silkolene Pro2, Rock Oil etc. Just make sure it's a "full-synthetic" and not a blend. I run 50:1 in my air-cooled TY and 70:1 in my Pro but I agree with Woody, if you have a smoking problem and you're running a full-synthetic, it's probably not the slight amount of extra oil that is causing the problem. I've run 50:1 in my Pro, when I was too lazy to mix another batch and used the TY can (I like to mix in small 1 gal. cans to keep it fresh) and didn't notice any excess smoke with the TTS. As I remember, the 311 is water-cooled so cylinder distortion is not a problem and a 50:1 premix ratio, provided it a full-synthetic, is actually a "rich" mixture for Trials use. 50:1 is a 2% mixture and in checking the GasGas factory website I see they recommend a 2.5% premix (and a 3% for the 2005 models!) for the larger Pros, but I'm assuming that is for the possibility of the rider using a mineral-based oil, but synthetics seem to work well at leaner ratios. Jon

Good advice. Probably if you're starting out, one of the best ways to break-in a new bike is to ride reasonably easy sections and concentrating on the basics (like practicing figure 8s on a slight hill) will help you get a feel for how this bike is different from your other ones. The on-off throttle works to bed in the machined parts without causing localized "hot spots" in the engine and you won't get bored riding around in circles I like to change the oil after a fairly long first ride which is when there will be normal swarf in the transmission oil from the machining operations. Jon

Jaan, I'm not very familiar with the OKO so I don't know if the internal circuits are as sophisticated as the PWK Keihin, inspite of the exact external copy. Of the three flatslides (four if you include the Dellorto VHST) carbs, the PWK would be my favorite due to the excellent low-speed metering circuitry. I'm sure riders have had good luck with all the carbs, when properly set up. I put a Mikuni flatslide on my son's Fantic 309 with good results and I ran a PWK on my JTR370, also with excellent results. I've found the VHST a little twitchy to jet properly for all conditions (it was only used one year on the 2003 GasGas Pros, the PHBL thereafter, except for the Raga, of course). I would think that coming off a well-worn 900 Concentric, you have no place to go but up..... Jon

Jaan, The Dellorto on the Fantic is the "large body" Dellorto (oval bore), like was used on the 96' JTR 370 GasGas (the "hot setup" for the 370 was to adapt a Keihin PWK28 off a KX80, which I soon did). I put a "small body" PHBL 26mm (common to most modern Trials bikes) on a friend's 348 and it did wonders over the Amal 900 Concentric (no more listening to the slide rattling around...... The PHBL is easy to get parts for and easy to jet. The advantage of a "flat" or "D" slide carb is that the airflow is directed over the main jet tower, rather than "around" it as a round slide does, so the carb is much more responsive due to the increased velocity of air over the tower at just about all throttle openings. Jon

I just replaced the rear wheel bearings on my 85' TY. I'm not aware of new bearings ever being that loose and they are usually fairly solid feeling. You'll want to get the "2RS" type that have the steel/rubber shields on both sides and then carefully pry them off with a thin pick and pack the bearing with waterproof grease and re-install the shields. Use a little anti-seize in the cleaned up hubs to ease the bearings in (start by tapping around the outer race to get the bearing started in square) and a long socket that fits the outside race (attaching a 6 or 8" extention helps you keep the socket at the correct right angle to the hub) is a good installation tool (don't pound them in by hitting the inner race, you'll damage the internal surface). Another trick is to use the axle (minus the snail cam adjusters) as an alignment tool to keep the bearings at right angles to the hub when installing them (put a bearing and spacer on the axle and install loosely in the hub and add the other bearing on the other side, tapping it in slightly and then tap in the bearings and the axle will also keep the spacer aligned inside till you're finished). The rear axle nut on the TY is torqued to 85-Nm or 61-ft lbs. Michael has a point. I'd guess that a compressed spacer would allow a lot of side pressure on the races and those are fairly small bearings and 85 Nm is a lot of pressure, but I would expect you'd get more than a few miles before they failed. Jon

The "O-ring on a Trials bike" controversy is a real can of worms and when mentioned, evokes the "Ford vs. Chevy vs. Dodge" type of emotions. I've run an o-ring chain on my TY350 for years (same chain and sprockets) but run a regular non o-ring on my Pro (no particular reason other than I had a new one at hand when I changed gearing to 11/44). Cons: Riders will argue that an o-ring is stiff, eats power, is too heavy and too expensive. The thick sideplate o-rings will cause clearance problems, especially at the chain tensioner slipper and are generally not worth the extra money. Pros: The new thin sideplate "X" ring chains are essentially as light as a regular chains, over time will transmit power much more effeciently with less power loss, do not cause clearance problems, don't attract gunge as they don't need heavy chain lube, decrease sprocket wear and over time, will more than pay for themselves. You get to choose. Jon

That's weird, I usually only see that when riders mix DOT-3/4/5.1 with DOT-5 or the fluid is really old. Don't forget that the rear brake reservoir on the GasGas is not vented like the clutch/front brake ones (which should be a little overfilled when attaching the cap/bladder to prevent moisture getting in) and should only be filled about 2/3rd's of the way, so there's room for expansion. Jon

My guess it that the warped disc is the secondary problem leading up to the overheating, which is the primary one. A warped disc would tend to push the pucks back so that when the lever is pressed, it would feel like there are no or weak brakes and the lever would have to be pressed a couple of times to take up the "slack". A rider may then think that by tightening up the pushrod (lengthening the pushrod) that goes into the M/C, that will fix it, which it does in a way, but it creates a much more serious problem by closing off the system (the M/C piston must retract back to the circlip stop in order to open the system) and causing drag, which heats and expands the fluid, causing more drag, more heat etc. and the condition you describe. Take off the rubber boot and double check that the piston comes down to the circlip and it takes a little pressure to push in (the return spring may be sacked) and you can feel slack before the pushrod starts to press into the M/C boot where it contacts the piston. 99% of the time, thats the cause of back brakes overheating. Jon

I agree. When you're in the spiraling vortex of an important race, you take mechanical chances you would not normally take during testing and the possible cost of an electrical component is far outweighed by the cost of a DNF. On a Trials bike, and paying mind to a cost/benefit ratio, I would always take off all the electrics before welding. Jon

Biff, As mentioned, the 06' and 07 up has the thinner spring. The DOT-5 will give a lighter pull and I'd use Ford Type-F ATF (rather than the GM AutoTrak or Dexron II) in the tranny (for the 06' on up Pro's also), as it has a slightly better heat tolerance and a little more "bite" that will compensate for the lighter spring. If you really want to get a little crazy, I polish the M/C and servo cylinder bores with Cratex (a rubberized abrasive) and it makes the clutch pull like through soft butter with no slippage. Jon

Having to adjust the carb after doing what you describe sounds "normal" and it's a fairly easy process. When weather conditions change a fair amount, you'll probably want to do it again now and then, just to keep the throttle response sharp. I think you have the PHBL Dellorto on your bike, which has a fuel screw for adjustment, but just to be sure (I've seen carbs substituted so it's always good just to check to be sure) look at the side of the carb and you'll see two adjustments. The one in the center of the carb body (it usually has a knurled knob) is the idle speed screw and turning that in or out mechanically raises or lowers the slide slightly to control the tickover speed. I usually set my idle with the engine warm, bike in gear and clutch pulled in to the normal point I would use for disengagement when in a section, for instance. This way my idle speed in normal operation would be high enough that stalling is avoided. The other screw on your carb is probably to the Left of the knurled center idle-speed screw (closest to the manifold/cylinder) and that's a fuel adjustment. I adjust mine with the engine warmed up and in Neutral, by blipping the throttle quickly from idle and turning that fuel screw in or out slightly (maybe 1/8th of a turn each time) until I get the best throttle response. Carbs with an air adjustment screw (like the PWK28 Keihin on the Raga) have the adjustment screw to the Right on the idle speed screw (nearer the air box) but the proceedure is essentially the same. The difference between them is which way they are turned to, for instance, lean out the mixture. A fuel screw is turned "in" (clockwise) to lean out the mixture as it would be decreasing the amount of fuel in the air/fuel ratio and an air screw is turned "out" (counterclockwise) as it would be increasing the amount of air in the ratio, both of which would result in leaning out the mixture. Jeez. I made that sound complicated, didn't I, but the actual process is simple. I added the explanation because I always like to know what's really going on when I do an adjustment, rather than just how to do the adjustment. Jon

Ya know, Alan, I was thinking about your post and had noticed the same thing about seeing the pit welding. My guess is that it's like some of the full-on race cars I was involved with in the past. We really didn't use the frame as ground (no lights or stuff to worry about) but ran dedicated ground wire to the components we needed to, so frame/suspension welding would be isolated from the electrical stuff. My guess is that's how they get away with it. Jon

\Before doing anything else, make sure there is a little slack where the adjustment screw on the lever meets the plunger pin that goes through the rubber boot at the master cylinder and that the piston is fully returning back to the stop at the circlip (under the boot). It's the number one problem I see with dragging clutches. Jon

Darn, Mark. I thought I had you fooled. One of the cool things about my age is, when people ask me questions and I don't have the answer, I can just make up a bunch of obtuse stuff and people think I know what I'm talking about and those who know I'm fulla bs put up with me because I remind them of their old, beloved, senile Grandfather....... I think it's time for me to go into politics. Jon ps.The bit about the sparkplug centers is actually true.

The longer one would probably not make any difference in accuracy as the measurement is based on static position, not differential rotational degrees. Don't carry the porcelain centers around in your pocket, in California they are classified as burglary tools under the Penal Code. Car burglers use them to quietly shatter car sidewindows (non-laminated and tempered, unlike the front windshield). Burglers already know this technique, so I'm not revealing any secrets. Jon

I would think that someone on that side of the pond could help you with an 89' "Aire", but as a last resort, you might try the U.S. parts importer, TrialsPartsUSA.com who just might have some of the stuff you need. The overseas freight might be tough to swallow, and as in any old NOS parts, you'll be paying for inflation and "storage" from the year of manufacture. GasGas is good about retrofitting updates so you might be able to use parts from a newer model that is more commonly available. Sometimes, contacting Trials clubs can be a good source as someone may have a parts bike for sale. Trials riders don't throw away anything.... Jon

It's unusual for a shock to crap out on a bike that new. I'd remove the shock, take off the spring (first measure where the preload is so you can put the spring back the same way) and try pushing on the shaft to see if the problem really is the shock. From what you describe, it should be evident. I'm not sure what type of shock it is (Olle'?) but in rare cases, the retainer that holds the "shim stack" (the set of special washers that actually control damping) can come loose which will make the shock "soft". Some shocks have a "top out" spring just below where the seal resides (the seal and aluminum collar combined, held in with the circlip, is called a "seal head") but most rely on hydraulic resistance, like front forks use a "bottoming cone" to soften the stroke on full compression (and cartridges in the forks have top out springs in them to soften full rebound). If the shock has lost pressure, it usually will leak out oil as the seal is designed to use pressure to seal against the shaft, but you should see oil on the shock body. Jon

Those will work perfect. I've used sparkplug shells for various things like a fitting to use low pressure air to pressure test a two-stroke and stuff like that. I've got a lathe so it's easy to machine off the swaged area at the top of the shell that holds the ceramic center in (the whole ceramic center can just be tapped out). I wonder if one could use a grinder to cut the swage off enough to tap the center ceramic portion out? One of my stops is threaded through the center of the shell so I can use a threaded rod and locknut in it to adjust it's length depending on the engine size I use it in. A very useful tool to keep handy for both 2 and 4 strokes. Jon

What Michael refers to is the "positive-stop method" of determining TDC, developed by ole Ed Iskenderian of "Isky Cams" fame in the 1950's, and still probably the most accurate method using "low-tech" tools. It involves using a device (solid, but with a rounded tip to not damage the piston crown) that threads into the sparkplug hole far enough to stop the piston a little before it hits TDC. An accurate degree wheel is attached and the crank is rotated till the piston softly is stopped by the device and the degree wheel is then marked, then rotated back the other way till stopped and the wheel is marked again. TDC (and BTC) is exactly halfway between those marks. I often use that method to check the accuracy of factory timing marks. As Michael also mentioned, depending on rod center length, piston dwell at TDC can make using a dial indicator a little "iffy" if you're not very careful. We use "long rods" in engines (say, using a 105mm connecting rod in place of a stock 100mm one in a YZ250 and installing a 5mm spacer under the cylinder) to get two things: a more advantageous mechanical leverage in the crankpin center to piston pin center angle and also to establish longer "dwell" at TDC (it helps the combustion process) and it's that "dwell" at TDC that you have to watch out for when using a dial indicator. Then again, in Trials engines, we probably don't need to be as accurate in most cases in timing adjustments as, say, setting up a top class roadracing engine, but a lot of us like messing with the machinery and that's part of the fun. Jon