dan williams

Whether four stroke or two stroke the octane required depends mainly on compression ratio. A higher temperature in the combustion chamber is what causes detonation so anything that raises the mixture temperature too high before the proper ignition time will cause detonation. That includes advanced ignition timing/poor cooling (yes mud in the radiator) /lean mixture/ flogging the engine under heavy load. Different fuels will spontaneously ignite at different temperatures. The trick in an engine is to maintain the mixture temperature and pressure just under the point where the fuel ignites without the spark. The common misconception about race gas is that it makes more power. That has a grain of truth to it but the main feature of higher octane fuel is that it has a higher flash point so it self ignites at a higher temperature then lower octane fuel. This allows more aggressive ignition timing and higher compression ratios to be used. It also allows for a leaner mixture since there is less need for the cooling effect of fuel vaporization.

I hate to say it but you need to throw a timing light on it to make sure the spark is in the right spot and also check that the ignition is advancing properly at the higher revs. That way you'll be able to eliminate any doubt you have on the ignition. I learned that from a Can-Am with the Hiro motor. Fought with it for years changing parts and tuning to no avail. I even checked it with a timing light and it looked good until I revved the engine and the spark retarded instead of advancing. Turned out the trigger and charge wires to the CDI were reversed. Flipped the wires and the bike ran perfectly. Also be careful what you remove. Years ago it was chic to remove the regulator from Betas to save weight. It seemed like a good idea since it was only a one wire device and didn't seem to do anything. Problem was it was a shunt regulator that dumped excess current above a certain voltage and without it you fry the cooling fan.

Agreed, higher octane gas. Even though the throttle setting is the same in the higher gears you are putting a heavier load on the engine and that can cause detonation to be much more prevalent. Also realize pump gas is notoriously inconsistent. Even premium fuels like Sunoco Ultra which I used to run until I got a few bad batches. A car is so mildly tuned it'll just suck it up and run lousy but a trials bike tuned to within a gnats *** will let you know immediately when you've got a bad batch. See if you can get your hands on some race gas. It won't make any more power but it will dramatically reduce the occurrence of detonation and it's consistent batch to batch.

If it's pump gas it could be due to moisture absorbed by the ethanol.

Er not to put too fine a point on it but is there a problem with damping while the suspension is working? It may be that the shock is actually working properly. If you haven't found fluid leaking out you may be looking for a problem where one doesn't exist. In the past when I've had new shocks that had pressurized internal volume when I ran them through the stroke I would notice the same effect. There seemed to be a dead zone of no damping at the start of the stroke and then heavy damping. If I went faster though the damping occurred throughout the stroke. My theory was that there was probably some dead zone until the internal volume taken up by air was filled with oil/air emulsion. As for the bottoming you may need a few turns of the spring preload there bubba. Of course if you do have a loss of damping the cranked up spring can make for an exciting ride.

Ah my buddy with an '07 Raga is getting one soon. Can't wait to give it a spin.

http://www.bsr-aerotek.com

Excellent, I'm all about the cheap solution. Glad it's nothing more.

Heh heh like I'm ever over 3/4 throttle.

Website looks legit but I'm always suspicious of such obvious mistakes.

We're just scared of your avatar. What year bikes? Any exhaust or airbox modifications? Mikuni or Keihin. You see it's not a cookbook question. There is no "correct jet" There's only the correct jets for your bike, altitude, air density, temperature, riding style. That's one reason people are a little leery of wading in with a set of numbers. Carb tuning information is readily available on the web. Google for the Mikuni tuning guide I think from SUDCO. That should give a rough estimate of how many jet sizes you'll need to go down for altitude but you really need to spend the time to do the testing with the bike and a set of jets if you want it done properly. I usually carry a couple of sizes plus and minus of both pilot and mains when tuning. Yes it's a pain but it's so worth it. Having said that usually around here people go down one size on the pilot to a 27.5 and one size on the main to a 130 for the 270 with a Mikuni but we're at sea level.

I got to compare a stock '08 270 to mine yesterday. Interesting to see the differences the clutch mods, Akropovic pipe and VForce reeds make when you can hop off one bike onto the other. For one thing my clutch is very progressive and the pull is significantly less. My buddy's clutch is like a light switch and I don't think I could ride a whole event pulling in that clutch. The engine feels very different on the bottom. Mine is very smooth, almost soft from idle to about 1/4 throttle feeling like there's more flywheel then there is. His snaps right off idle and quite frankly almost got away from me a couple of times. Above 1/4 throttle the power curves converge so above 1/2 throttle they feel virtually identical. At least that's how they feel for the very short amount of time I can spend in that part of the power curve without kissing a tree. Also worth noting I had to change my jetting for the VForce reed his seemed right on stock. It'll be interesting to ride his bike after he puts the heavy spring on the rear.

Finished on one peg? Yikes. That takes guts.

I was thinking about a plastic float bowl but then I remembered my friend who broke his cylinder head in a crash and thought better of it. A broken float bowl could be very dangerous. I still give him a hard time about it. How do you break a cylinder head? He literally caved it in on an easy flat rock that everybody just rolled up on the first loop. After he doused the rock with antifreeze it was impossible to ride. Of course nobody knew that until they came around again and found out too late that it had become slippery as ice. Almost put me on my head.

My first answer would be, More trouble then it's worth. That's a pretty sad looking machine.

I'd be inclined to go for the basics first, make sure throttle cable didn't get yanked out of fittings, kill switch jammed and stuck, flooded engine causing wet spark plug. Past that look for the basic things it needs to run. Fuel, air, compression, spark. My money's on the wet plug which has probably dried out by this point and the thing will just run. Always have a spare plug in the tool box. Let me know if I win .

If it's coming from the overflow tube at the bottom of the float bowl then it is usually one of several things. As already pointed out, a piece of dirt holding the needle valve open. Disassemble and clean compressed air works but I'll throw a Q-tip up there as well being careful to not let any of the fibers escape and stick in the valve. There have been a few reports of floats binding on the float bowl gasket and in very rare cases a leaky float filling with fuel. If it's coming from the vent tubes that come from the brass fittings near the top of the carb that's a different matter and is simply the tubes acting as siphons. Easily cured by nippering a small hole in the tube above the float bowl. I usually just do it at the bend at the top. You may also want to do a sanity check on your float level adjustment. I've done it wrong on occasion. Lets face it, float level adjustment is like the refrigerator light. When it's all closed up you don't really know whether it's on or off do you. Hmmm gives me an idea for a tuning accessory. A plug for the bottom of the float bowl with a tube that runs up the side of the carb. The float level would show up as the level of fuel in the tube.

Iridium plugs are really a waste of money on a dirt bike. They don't have any effect on performance. The reason for iridium plugs in automotive application is the iridium is extremely hard and erodes much slower from the spark then any other material. For car engines like the GM Northstar with supposedly no maintenance for 100,000 miles or a car that requires removal of the engine to change all the plugs it makes sense. For a single cylinder premix two stroke it makes no sense at all. Even platinum is somewhat overkill but at least they're cheaper.

I'd be inclined to fix the pinch bolt. The strength of the front end is really a combination of all the pieces working together. That and you really wouldn't want to snap the other just because it is carrying the full load now. Then you'd have twice the work and you'd have to fix it. When you assembled the bike you must have really laid into the bolts. When assembling a bike it's better to make sure everything is aligned properly and snug the bolts. Check the alignment again and go for the final tighten but don't overtighten. After a few hours of riding you'll find several of the bolts loosen up as the frame and forks settle in. Just give them the once over with the wrenches to snug them down proper after every couple of rides. I like the T-handle allen wrenches for this because they're fast but also give good tactile feedback of just how tight a bolt is. After a few cycles of this the frame and front end will have settled down and won't need more then the occasional snug. 70:1 works OK. A trials bike will smoke after putting around for a while because they tend to pool a bit of oil in the bottom of the crankcase. If you watch the world or national guys they'll rev their motors up before a critical part of the section to make sure they are running clean and purge the residual oil. As for the creaking, aluminum frames tend to creak. I've chased creaks in Beta frames since my '91 Zero and only managed to get about half of them. Usually I find bouncing on the pegs I get creaking from the frame at the skidplate mounts or the footpeg brackets. If you decide to chase the noise down don't try to fix it by just tightening the bolts as you'll end up having to fix them like your fork pinch bolt. try some lube on the frame where parts are bolted together as the creaking is pieces rubbing together under pressure. A squirt of WD40 or lithium grease can quiet down a creak not only locating it but often fixing it. The other thing to keep in mind is eventually the pieces that are creaking against each will wear in and the creak will usually go away on it's own.

Carl Sagan "Imagine if you will... Billions and billions of chickens crossing the road."

Hi Skidmeister, Are you having a cooling problem or just stressing over a something a little odd? Almost any time you have metal and fluid in contact in a hot engine they're gonna cook up something unpleasant. Could be residual gasket goo or assembly lube or myriad other things. If the fluid looks good that's a pretty good sign that there's nothing major going on. It sounds like this tan gunk is floating on the top of the coolant which would indicate it's not water soluble i.e. oil or some kind of polymer. First step is drain and refill with good coolant preferably something that is magnesium friendly (propylene glycol) like Engine Ice, Maxima Coolanol, or Silkolene Pro Cool. Ride for a while and see if there is the same amount of goo. It may be this is something that is just leaching out of the system and is relatively harmless. To be honest unless the thing is spitting steam out I rarely look at my coolant and then I'd have to see something really funky with the coolant to get me worried. A little scum on the surface I expect. Ewwwwwww!

Hi r2wtrials, I don't have to look down the intake throat. Asked Ron Commo Sr. while picking up a US world round minder's bike for my buddy. Ron said that the VForce on my '08 is machined out to 26mm for the Mikuni and he is talking to the Moto-Tassinari guy about making a batch machined out to 28mm for the Keihin carbs. Ron also said, and I have to agree, that unless you can ride a Rev3 wide open there's going to be very little difference between the 26/28mm throats. While I was there I did get to try a used 125 Junior WR bike he had in the shop for sale. Impressive. I tooled around the driveway for about ten minutes. Just to see if it would pull my fat ass I tapped it into third and snapped the throttle at a crawl and the front end snapped right up and stayed till about 3/4 of the rev range at which point I decided to stop goofing around and give it back before I hurt myself. Nice motor though. It obviously doesn't have the grunt of the 270 and I stalled it a few times (yes in third) but I could easily see riding this bike in an event and having a blast.

From the box the same one that fits the Sherco. I'll get the number off the box and let you know but don't be surprised if it is the same one as the '05. I have both the stock reed blocks for the '05 and '08 and they are identical. "giggity"

If the engine still spins and there is compression there it probably isn't that bad. Usually the result of no oil is a stuck piston and or damaged ring grooves causing the rings to stick. The above advice is about all you can do short of a teardown for a look.

Man that hurts. When the kicker went on my buddy's Raga he felt it wasn't right and parked it. I gotta give GasGas USA credit. They took care of him and it didn't cost him anything other then a few weeks of down time. Good object lesson though. If it doesn't seem right, park it until you know what the problem is.