This just in!

We Just got a bulletin from KTM regarding the 2 stroke electric starters. As stated in the Owners Manual; the starter cover should be removed and the starter area cleaned and re-lubricated every 20 hours of use. The bulletin also specifically mentioned that you should do it much more often if you pressure wash the bike or operate it in unusually wet or dusty conditions.

Suspension sag; getting the most from your KTM

The single most important suspension set up that can be done to your KTM is adjusting the correct amount of sag. This will achieve maximum handling performance and will prevent damage to the fork, shock, swing arm or frame. The suspension components must be suitable for rider weight and sag should be set before making any adjustments on the damping control of the fork or shock. KTMs off-road motorcycles are set to accommodate a rider weighing 154-176lbs (70-80kg) wearing full gear. Minor deviations in weight can be compensated by adjusting the spring preload. Alternate springs must be installed for larger deviations.

Determining the Correct Static Sag of the Shock Absorber; You can establish whether or not the stock shock spring is correct for rider weight by checking the static sag. Static sag, which means how far or how much the bike sags under its own weight. (Without rider) The static sag should be as close as you can get to 35mm; deviations of as little as 2mm can strongly influence the motorcycles performance.

Procedure for Checking the Static Sag; Jack up the motorcycle until the rear wheel no longer touches the ground and measure the vertical distance between the rear axle and a fixed point (e.g. a mark on the side cover) and write it down as dimension A. Place the motorcycle on the ground and ask a helper to hold the motorcycle in a vertical position and measure the distance between the rear axle and the fixed point to establish dimension B. The static sag is the difference between dimensions A and B and should be adjusted to a measurement of 35mm by turning the spring preload adjuster.

Determining the Riding Sag of the Shock Absorber; Now that our static sag is set, let’s determine the riding sag by having a helper hold the motorcycle while you sit in a normal seating position (feet on footrests) wearing full gear.  Bounce up and down a few times to settle the rear suspension. Stay on the bike and have a helper measure between the same 2 points as helper measure between the same 2 points as referenced above and write it down as dimension C. The riding sag is the difference between dimensions A and C.  The riding sag should be between 90mm and 105mm. If the riding sag is less than 90mm, the spring is too hard (the spring rate is too high) and if the riding sag is more than 105mm, the spring is too soft (the spring rate is too low) The spring rate is written on the outside of the spring e.g. 80/250 the spring rate is 80N/mm and the length of the spring is 250mm, this is a straight rate spring. Springs that are listed e.g. 76-95/260 has a spring rate of 76N/mm at 20mm of spring compression and 95N/mm at 100mm of spring compression with a spring length of 260mm; these are Progressive Springs or Dual Rate.

KTM 50, 3-Shoe, Automatic Clutch Set-Up and Maintenance

»One of the most important, if not THE most important, performance items on any 50 is the automatic clutch maintenance and set-up. Having the auto clutch in proper working order and the clutch shoe engagement adjusted or “tuned” to the best RPM is the key to maximum performance.

»A worn or not properly maintained clutch will cause problems that sometimes are misdiagnosed as carburetion or even ignition problems and really may be due to a clutch that is engaging far too early or low in the working RPM range.

»A clutch that engages too low in the RPM will cause the engine to “bog”. This bogging is similar to trying to start in too high of a gear, for example, on a multi-gear, manual transmission like in a motorcycle or car.

»The optimum RPM range, for clutch engagement, for a competition KTM 50 automatic is 8,500 RPM, (+/- 100 RPM) and this is how the KTM 50SX-Pro was set-up at the KTM factory.

»There are a few maintenance items that influence or affect the original performance setting and these have to do with the wearing clutch shoes, or clutch material and the heat that is generated by the working clutch. Remember the clutch is a “friction” device and it works by changing heat into kinetic movement. The clutch actually slips for a period of several thousand RPM, from around 8,500 RPM, before making full engagement at or between 10,000 to 11,000 RPM.

»We see the results “graphically” on our dynamometer of several horsepower when the clutch is properly set-up and this is a significant difference on a 50cc mini. The fact that most of us don’t have a “Dyno” or access to one, there are still ways to achieve proper set-up and to achieve maximum performance, even in the home shop.

»Let’s start with the most basic maintenance and that is CHANGE THE TRANSMISSION OIL / FLUID before any competitive use or after every one to two hours of use. Contaminated oil does more to hinder the performance than any other single point.

»The contaminants will get between the “Belleville” disc springs (washers) and minimize how far they compress. The clutch will eventually never fully engage. This constant slippage will further wear the clutch shoes and result in higher engine temperatures and a more rapid breakdown of the fluid. It’s a vicious cycle that can be costly when compared to a few hundred milliliters or ounces of new transmission oil or fluid.

»The next important maintenance is to remove the clutch shoes and measure the diameter of the three assembled clutch shoes. The three assembled clutch shoes are around 82.00 mm when new. Measure the inside diameter of the clutch drum. The drum is approximately 84.00 mm when new. The difference between the clutch drum and clutch shoes should be no less than 1.5mm and no greater than 2.0mm.You can add a maximum of 1.0 mm of shims (see parts information in the engine section of your parts book) to the underside of the shoes, (between the center hub and the shoes), to space the shoes out, to maintain the recommended 1.5mm to 2.0mm clearance. If more than 1.0 mm of spacing is required the clutch shoes should be replaced.

» Next disassemble the disc spring stack by removing the 10mm hex head bolt in the center of the friction material of the clutch shoes. NOTE THE ASSEMBLY ORDER! Clean, and check the Belleville disc springs for wear. Clean the spring discs with a safe cleaning solvent. Check them for wear, by noting the condition of the black coating. Replace them if black coating is worn. We would recommend that highly competitive racers to replace them with new, as they will eventually heat fatigue and not perform to their best potential.

»Reassemble the disc springs and apply Loctite “Thread Locker 243” and torque to 96 lbs/inch - 11 Nm.

»Install the drum and the clutch shoes onto the crankshaft and tighten the clutch assembly nut to 22 lbs/ft – 30 Nm. WARNING: Do not exceed maximum tighten torque spec or the center hub will fracture.

»Now for the under $100 home dyno; There are some nice small battery operated digital inductive tachometers available from some of the lawn and garden power tool manufactures for less than $100.00. You can use these tachs to determine the clutch engagement point.

»To do this, hook up the inductive and with the rider in the seated position and engine running note the RPM when the mini starts to move. This should happen at 8,500 RPM +/- 100 RPM. The rider should be in full riding weight (with helmet, boots, etc., but you knew that) and should not help the mini to move. Sometimes even a little resistance is a good thing, as the clutch engagement will change for the better when it gets to race conditions.

»An adult can straddle the mini and simulate the rider’s weight and resistance to check the initial engagement RPM point too. The key here is consistency. You can also do this in reverse order, if you feel the clutch is working as desired, by checking the RPM and noting it, before you disassemble it or reach a maintenance interval.

»Now that you know the engagement point, how do you adjust it?

»To increase the disc spring tension and raise the engagement RPM, remove the disc spring stack from the center of the clutch shoe (6mm bolt with 10 mm hex head) and place a 0.5 mm shim under the stack. This will result in an approximate 500 RPM increase of the initial engagement point. A total of 2.0 mm of preload is allowed.

»To decrease the engagement RPM point remove a 0.5 mm preload shim or if no shims are installed, rearrange the original stack to eliminate one set of doubled disc springs. Be sure to maintain the same overall original stack height by facing the concaved sides together.

»Here is the basic disc spring layout, laid on its side, starting with the base disc springs, in the clutch shoe well, and working toward the hex head (HH) of the bolt; Base ( ) (( )) (( )) (( )) HH

In summary;

· Keep the oil/fluid clean and fresh.

· Check the engagement RPM on a regular basis.

· Clean and check the “Belleville” disc springs on a regular basis.

· Measure the clutch shoes and clutch drum and maintain a 1.5mm – 2.0mm clearance.

· Rule of thumb; 0.5mm of preload under the stack with increase the engagement RPM by 500 RPM and vice versa.

· Don‘t overlook the clutch set-up when dealing with engine performance issues.

» A well maintained and set-up automatic clutch system delivers the most performance your engine provides.

Jetting made easy!

One of the most frustrating topics in a bike shop is jetting. On current model year bikes we can give recommendations; but when a bike is over a year old you just have to stone up and go through the process of jetting your bike yourself - or pay a qualified shop to do it. The fuel density at your local station, just how worn your carb and engine are at the moment, your altitude and even your skill level all have an effect. The older the bike gets the bigger the variables become; just how fresh is your muffler packing? It has an effect on flow!

The good news is jetting is easier than invading Lebanon. All you need to do is note the steady state throttle position in relation to the way the engine runs. Please take a look at the chart below:

Zone 1 is the pilot/slow jet and fuel/air correction screw. 2 is the slide cutaway. 3 is the needle jet or diameter. Zone 4 is the needle position and 5 is the main jet. 1, 4 and 5 are the biggies.

1.1 Air or fuel correction screw; This is how the bike idles. Air screws are common on 2 strokes and are always toward the air filter side of the carb. Out is leaner, in is richer. Fuel screws are common on 4 strokes and in is leaner, out is richer. Adjust the screw in and out until the bike idles equally bad in both directions (with good somewhere in the middle), count the turns and split the difference. You're done. If you're less than 1/4 turn out or more than 3 turns out you may need to change the...

1.2 Pilot Jet; This is the jet that controls the fuel up to 1/4 throttle and is the major culprit in plug fouling on 2 strokes. As with all jets little numbers are leaner.

Zone 2 is the slide cutaway. If you look at your slide (its the air valve that moves up and down with the throttle) you'll see that the lower edge has been beveled on the air filter side. The more of it that's been trimmed away the leaner the bike runs in the area of the chart above. This is a fine tuning adjustment and usually the last one done. Most of the time you can tune around the slide with the other, more cost effective adjustments.

Zone 3 is the needle jet. This term is used to describe the clearance between the straight untapered part of the needle and the female fitting it slides into on the floor of the carb. You have to buy a new needle (on modern carbs) to change this and the numbering systems could confuse a Physicist so always try to adjust the needle position first. A lot of times you can balance the pilot (zone 1) and needle position (zone4) to cover this adaquately.

Zone 4 is the needle position. It's adjusted by moving a circlip into different grooves cut into the top of it. Moving the clip up makes the bike run leaner at mid-throttle. Don't be afraid to experiment! Move it up and down and notice how different the bike runs.

Zone 5 is the Misunderstood Main Jet. It determines how the bike runs when the throttle is wide open. It's all but impossible to foul a plug because of this jet. Go out riding and find a place where you really have some space; get into a higher gear, hold the throttle open to the stops and see how it runs when it's revved out against the load. That's all the main jet does. Once you have it and the zone 1 adjustments made the rest falls into place pretty easily.

Some very general rules to keep in mind;

If your bike runs bad always start with a good thorough "tune up" before you dig into the carb. Clean and properly oil the air filter, change your oil, pop in a new spark plug, maybe some fresh gas and check your valve clearance or compression. A lot of running problems blamed on jetting can be cured by this.

Jetting changes gradually over time with normal wear. If your bike has a sudden negative change in the way it runs then it's very likely that you have a mechanical or ignition problem and not a jetting issue.

If you start jetting the bike following the instructions above and it doesn't run any different; STOP. Put the original jets back in and look elsewhere for your problem. You also won't have to pay a mechanic to figure out and undo your jetting adjustments before he can diagnose the real culprit.

Backfires on four strokes are almost always caused by air leaks in the exhaust and not jetting. It could be jetting caused but 90% of the time it isn't.

Special circumstances;

If you have a modern 4 stroke race bike with a "pumper" carb please again note that jetting should be done at constant throttle only. Every time you open the throttle the accelerator pump squirts more gas into the engine than all of the jets combined! Play with it on the bench and see what I mean...

Two strokes are load sensitive when it comes to jetting; an expert needs richer jetting than a novice. Also realize that as a two stroke piston wears the blow by goes into the crankcase and is picked up as a second additional load of fuel. Is your ten year old 250 running rich? If so suspect the piston and not the carb.

A big time two stroke jetting myth; The icky goo oozing out of the pipe and onto your swingarm is caused by rich jetting or too much oil - WRONG! The reason it resembles tar is because that's what it is; tar (oil that has been cooked but not burned). The trick is to ride fast enough to burn the oil that you're using, or to use an oil that burns at the temperature that you are generating in the engine. If you go slow enough long enough a little drool is inevitable. If you get your jetting so lean that the engine is running super hot (and clean) at low speeds and then finally get it wide open in a fast sand wash the next sound you hear might be your crankshaft asking for a divorce.

If you can hear the intake as if it's louder than the exhaust, your bike is popping while under load or your reeds are fraying then your jetting is too lean. It costs power on a four stroke and engines on a two stroke.

  More to come