Tuning Advice
  • How to race /ride CHEAP .
  • 2023 KTM sx 125 Electronic fuel injection
  • Synthetic , Caster oils and ratio,s
  • Porting of Modern Cylinders.
  • Spark Plugs
  • Summer versus Winter Jetting
  • Crankshaft Balance
  • Fuels
  • Engine Cryogenic Treatment (Controlled Freezing of Parts)
  • SX150
  • exhausts choices
  • Mazzoochi Forks
  • Pistons types , changes, when to replace & why ?
  • Scalvini Exhausts
  • EHR HGS Exhausts
  • EHR Products
  • High Performance Super Finishing (Gearbox Gear Tumbling)
  • Wheel Bearings (all bikes)
  • COBRA CX50 and COBRA CX65
  • Kawasaki KX65 / RM65 / KX85

How to race /ride CHEAP .

There are some things that cost riders, or parents alot of money,   1.   dirt passing into the engine.    2.  water passing into the engine.     3.  Forgetting to change the transmission oil.      4.  Items coming loose.

Water and or Dirt will destr0y inside the   modern 2 stroke.   Past the air filter, into the CRANKCASE, cranksgaft, bearings,  then into the cylinder and piston area.   Airfilters, claen and reoil but also double check fitted and sealed back in place.

Over pressure washing-     water in the carby?   water in the transmission?   water in electrical connectors?    Always cover the sparkplug when washing, ( cable tie on plug connector is great too)  use a air filter cover too.    Dont over wash with high pressure, just enough and stop.

Dirt track bikes vibrate alot, things come loose, keep rechecking.

Chains-    dry or wet ?      If you clean your chain , get dirt off , then lube it, it will last longer, less friction, faster bike!    WD40 first, as it will soak in , then a thicker lube on the out side works well.

Clutch adjustment-   cable type or hydraulic,   it must have FREEPLAY or it will get hot and burn out.

The small auto clutches KTM   sx50  – you really need a Tacho to check the engagement speed, remembering if the slip speed drops, they are very hard to tune, many dads spend hours with bog,s and hesitation, only later to find its clutch speed.

Mod engines, pipes heads etc-   When learning, there is no point really!   Until the rider is flat out, no power increase will help anyway!    More time riding is all thats needed, until there reving it flat out.

Buy in BULK-  engine oil, transmission oil, brake fluid, carby cleaner, chain lube, brake cleaner, air cleaner oil and washes.    Some cheap brands are available from auto shops.

Parents-   riding/racing bikes starts is FUN.  If you have a Champion in your family , your rider will prove to you how they are a Champion.  If your rider is not ever to be a Champion, well this is still a wonderfull sport to do.  Most young people who ride or race, learn skills that help them in all parts of their life, sometimes much later in life.   Sometimes, working on bikes, travelling, camping , the social side is fantasic.   The  coaching events available  , to gain skills not only in riding/racing, but other skills needed like food, exercise, education etc are fantasic.    If your rider doesnt become a Champion, chances are he will meet a Champion and become friends with him, life long friends.     Its a wonderfull sport and you will enjoy the ride.  The kids grow FAST,  i hope you enjoy the time in the sport.

2023 KTM sx 125 Electronic fuel injection

The 2023 model , the first KTM 125 using fuel injection has arrived. The Efi system has been on other size engines for years and works quite well. Inside the engine has not changed very much at all. On the Dyno, compared to  the older carby version  2022 ,  the 2023 doesnt rev as hard, so basically the midrange power has increased a small amount, but the top end power has been reduced, as well as the top end revs.   A better exhaust chamber, better cylinder head and a better ignition map  will give   good power  gains, as well as modified fueling maps.  The 2024 and 2025 will only get better.

Synthetic , Caster oils and ratio,s

Synthetic 2 stroke engine oils are today the best oils .  All lubricate very well.  Some do not burn as well and leave exhaust deposits, some are very clean and have little deposits or smoke.   Penrite full ester synthetic , Silkolene comp 2  are great oils for slower riders learning, as they are clean.   Smaller engines with low volume crankcases now are using 60 to 1 ratio,  and this works very well.   Caster synthetic type oil smells great,  lubricates well, but is quite dirty inside the engine, dirty,sticky exhaust deposits, not ideal for powervalve engines, and the oil can separate from the fuel in the fuel tank and carby, if not used with in 2-3 weeks.  The fuel oil goes stale very quickly.  Will one oil make the difference of winning or loosing a race?   Using Caster, take care to regularly clean fuel and exhaust and inside engine parts, and drain and use fresh fuel and oil.

Porting of Modern Cylinders.

Over the years most manufacturers have made lots of improvements to Cylinder port shapes.  Most cylinders can actually flow worse, if you grind /polish the area,s from under the cylinder. If you take material away, you may decrease bottom to mid power, as this effects the primary compression ratio. This can be corrected with case stuffing.  Without a good  small Dyno, you may not realise whats happened.  The curves in the transfer ports have now a more tighter curve, increasing the slug volume speed into the cylinder, KTM have pioneered this design which works really well, and yet the ports look small! High air speed is gained. Most surface finnishes on modern cylinders cannot be changed, to gain power. Even the exhaust expansion chamber inlet is now smaller than ever, on late model pipes, keeping air speed high.    However, there is still work that can be done, port windows, chrome rough edges, and the whole exhaust port can be changed that yields good power improvements over most of the rev range.  Cutting through the chrome is tricky, most engine porters now using some lubrication/cooling method, so as the chrome plating is not being effected by heat and vibration.   Dyno testing with many cylinder port shapes, sizes, heights etc is done to make sure the power is gained.  So before you grab that file, or porting tool, call and have a chat, we can hopefully save you some time.

Spark Plugs

Some engines 85cc 125cc 150cc 250cc need to use more stronger/robust type spark plugs.

If the engine has higher internal pressures, excessive crankcase stuffing, too high compression ratios, incorrect crankshaft balance factor, Detonation, engine frequency type vibrations/pulses can harden and weaken the earth electrode and it will FALL OFF causing expensive damage.  Always try to use a ECM type spark plug.   Meaning NGK  BR9ECM   or BR9ECMIX   IX is just a fine wire iridium type .  The IX lasts longer if it stays clean,  less energy is used to fire the spark from the coil.  The std type plug BR9ECM can be better for slower riders, as it keeps firing even if dirty.

Some modern engines are already made high performance from the factory and pressures are really high and they need better spark plugs. Some 85cc and most larger 2 strokes will need these plugs. part number NGK R6918B-9 is one of the best choices. $60.00 each. Replaces BR9EIX or BR9EG or BR9EV or BR9ES etc. ( 9 ) is the heat range ,so you can buy 8,9,10 heat ranges normally.  Detonation is normally the cause of sparkplug earth electrodes breaking off, high compression presures and internation high frequency vibrations.

Be careful, if the bike comes from the factory with a R6918 type plug,(like the current model Suzuki RM125) dont put a cheaper plug in as you will reduce performance and damage the engine.

Summer versus Winter Jetting

In winter you always need to increase fuel supply. Approximately 5% richer.

Crankshaft Balance

Balance factor is different from sizes of engines. Change of the factor will change the power curve.


The new VP Roo Fueld makes combusion and mixing temperatures cooler. Good for 2 strokes! Must change jetting approx 6% richer. Best to increase compression too. Good for 4 strokes too.

Note: Race Fuel Above 100 – No point using it. Fuel testing will be done at Australian and FIM Wold Championships.

Engine Cryogenic Treatment (Controlled Freezing of Parts)

The benefits you can achieve by having components treated include:

  • Increased wear resistance to rotating and friction bearing parts
  • Increased time between rebuilds
  • More consistent engine compression figures over time
  • Better heat dissipation du eto increasing temperature coefficients
  • An overall performance increase. HP, Torque and Revs.
  • Reduced warping/cracking of susceptible components
  • Should be done to Piston & Barrell as a minimum task


HGS Exhaust. VHM Cylinder Head. 185-190 main jet. Ignition timing 1.1mm BTDC.

exhausts choices

The European exhausts are the best tested on the dyno and at the track.   The scalvini produced good power in the top end, and the engine needs to be tuned for this type of power, the pipe is thin and will get damaged easily , the damaged pipe will have a loss of power.  Van Hasselt exhaust is specially designed for MX, best mid range power and easy to race , and the construction is good.  the HGS has the best top end power out of all the pipes, but engine must be tuned to suit this for the rider.  All pipes have more power than the stock pipe. USA pipes, euro pipes included.  USA pipes crack alot. Euro pipes are stronger and make more power, but are not coated and rust easily.  Most of the power increase comes form the pipe, not the silencer .  The silencer does change the engine noise alot, but the dyno tests show no big power changes are made.

Mazzoochi Forks

Some pistons on the compression side do not have a wear band-ring. You can order one from the rebound side and machine the piston to fit it so you have smoothness on compression (as it should be). Common SX65. Shivers have this as standard.

Note: Only use Mazzoochi Seals (a lot less drag).

Pistons types , changes, when to replace & why ?

Many different production types. Example: KTM Vertex is not the same piston as Vertex after-market type. Check weights! But both are quite good.  Some brand pistons are different heights, so your squish clearance can change.    VHM billet pistons do actually have a run in coating!     The 12 degree pistons change the port timing and also are flat , increasing the top end power .  Most manufacturers say to replace small size high rev pistons at 10 hours.  Most riders do them at 20-25 hours.     Using the dyno to test, most engines see more power made if a piston is replaced after  about 12 hours.   After about 12 hours some exhaust gas pass the compression rings, and enters the crankcases , this reduces the power of the engine a small ammount.   Using a new piston before an important race meeting is well worth while.  Modern hard coated cylinders with light alluminium pistons dont take long to run in at all.  Do not add more oil for run in.  Deglasing the cylinder when replacing the piston is worth doing, using only a soft scouring pad.  Adding a thin layer of oil or grease on your base gasket, will allow you to reuse it.  Cylinder head orings must be changed each year at least.   Always replace exhaust orings each piston change as well.  The KTM sx65 powervalve operates on exhaust pressure, its different, like the kart engines, so any change in the pressure-compression, changes the power curve of the engine. A new piston or even  Silencer repacking changes this too .  On the dyno, a new silencer fitted to a sx65 with reduce the power, for about 20 minutes!   Never fit a new silencer before a race to a sx65 !

Scalvini Exhausts

This Italian company is spending more time and money making and testing Exhausts than others. Some of the 2 stroke systems add a lot of power. After installing a Scalvini on a SX85, the engine feels like it has had large modifications made. Expensive pipes. Some pipes are hard to fit (SX65). They can get damaged easy, and power losses result.  look great.

EHR HGS Exhausts

Development changes to expansion chamber and mufflers. Each exhaust is exactly the same from 1st stamping to the 50th stamping.

EHR Products

EHR products for making racing bikes go faster, but also the engines are easier to race as the power band becomes wider. The power doesn’t have a hard hit, so the kids like the set up. All the race parts have been tested on the dyno, then on bikes in Holland and we test them here. You can still make some mods yourself to improve the set ups too.

High Performance Super Finishing (Gearbox Gear Tumbling)

Treatment of gears for low friction and better shifting, done with a Tumbler/Vibration machine.

H.P.S.F Victoria Ph 03 9775 0898.

Wheel Bearings (all bikes)

Make sure to use good quality wheel bearings with the extra clearance rating of C3 in the part number. They have less friction, especially when hot and particles like dirt and water etc get in, will not cause as much friction in them.

Also check your chain for any drag from guides, rollers, etc. Especially small sixe bikes as this robs power.



Cobra CX50 (KING) Senior bike

What a ripper! The fastest 50 made for racing so far.

The suspension is extremely good and the handing of this bike is great.

The bike comes std with Vforce reeds, a full circle racing type performance crankshaft and a insert type 2 piece cylinder head and adjustable ignition timing. The cooling system on this engine is very well designed, engine works well in sand as well as long tracks and also the ignition stator and housing is cooled really well to stop failures.

Best mods- HGS exhaust, reduce squish clearance, adjust slipper clutch tighter (70-80) use a good engine tachometer and adjust clutch engagement speed 8500rpm to 9500 for racing.

Cobra CX65

The suspension and handling is very good. The engine needs more power to compete in racing. The primary compression ratio needs to be changed, using stuffing to enhance the flow from the crankcases into the cylinder. The engine needs a better crankshaft , a full circle type race crankshaft. The powervalve is not adjustable in any way, except modifiying it , trial and error. The Carby is old fashioned round slide, and is not close to the engine induction. Comes std with Vforce reeds which is great.

Best mods – HGS exhaust works well. Crankcase stuffing required. Use the KTM type 24mm carby, and best to bore to 26mm, need to modify intake rubber boots and air cleaner boot.

Kawasaki KX65 / RM65 / KX85


The engine power is too high in the rev range for MX, ok for flat track.

Suspension,linkage change required as well as revalve and springs required for racing MX. The bike is now well out dated for racing, although very reliable and cheap to race. A great club level bike to learn skills , power needs to moved to get more bottom end for MX. Cylinder and head work required. The KTM sx65 is alot faster as the bike has a powervalve and better suspension. HGS exhaust and a vforce reed valve are the best mods for the engine, and with cylinder and head work the engine is very good for mx or flat track.

KX85 2016-2016

The basic bike is still a little behind the KTM sx85 in stock form but mods are easy to do on the bike.

Fitting the HGS or VH exhaust with the VHM cylinder head and special insert developed by BUD racing, the engine really performs well. Some jetting and needle changes are required for racing. Vforce reeds work better then the boysen rad valve.

Changing the suspension springs, a new linkage, and revalve to suit rider weight, the bike performs very well. The conrod weight is very heavy and needs to be reduced for top level racing. After the mods are done for racing you have a very solid bike that gives very little trouble. Overall this is probably the best mx or flat track bike as the performance is good and ongoing costs for racing can be low. This bike has much better brakes,throttle set up, rear suspension than the Ktm sx85.

Things to watch- run oil ratio at 30-1 for racing. Crankshaft oil seals wear if using some race fuels and you have to split the cases to replace them. The 2 ring piston is only good for trail riding or enduro but you can remove 1 ring for racing. The Vertex coated piston is better for racing. Overall bike weight is higher than the ktm, the gearbox is heavier than the ktm. There are areas on the bike you can reduce weight. ( gear tumbling works well for racing on the kx85) long term we will see more of KX85 on the racing seen.

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