The great debate lives on in the eWorld of karting.

What is the best fuel system to use on my Keihin carburetor?

Well, I am not going to tackle that argument, instead, I will explain to you how to hook up a single rectangle Mikuni fuel pump to your Keihin carburetor.

What you will need:

• carburetor of your choice.  Read your rulebook carefully
• Mikuni Round Fuel pump (http://www.shopswedetech.com/Mikuni_Pump_Round_DF_52_21_D_p/mikuni%20pump%20-%20round.htm)
• OR Mikuni Rectangle Fuel Pump (https://www.shopswedetech.com/ProductDetails.asp?ProductCode=DF44-211D).  We offer both on our shopping cart.
• Plastic Y Fitting – http://www.shopswedetech.com/product_p/y%20fuel%20line.htm
• Pulse Line – http://www.shopswedetech.com/Pulse_Line_braided_p/pulse%20line%20-%20braided.htm
• Fuel Line – http://www.shopswedetech.com/Blue_fuel_line_1_4_ID_for_use_on_most_karting_p/fuel%20line%20-%201-fslash-4%20blue.htm
• Fuel Filter – Always run a filter before the pump – http://www.shopswedetech.com/Filter_Fuel_1_4_p/filter%20-%20fuel.htm
• Rubber Mount – Optional – http://www.shopswedetech.com/18355_KS6_000_fuel_pump_mount_p/18355-ks6-000.htm

Step 1 – Make sure you have a pulse line installed on your engine.  If you do not, install one.  If you do not know how, call a qualified engine shop to do this for you.

Step 2 – Decide where you want to mount the fuel pump.  Try to keep the pulse line as short as possible, while not interfering with any other components of the engine or chassis.  The above optional rubber mount is a great way to secure the pump to the side of the engine.

Step 3 – Measure the length of your pulse line for ordering.

Step 4 – Measure the length of the fuel line needed to go from:

• the go kart fuel tank,
• to the filter
• to the fuel pump
• to the Y fitting
• to the carburetor
• AND from the Y fitting back to the return fitting on the gas tank.

Our explanation requires 1 supply line from the gas tank and 1 return line back to the gas tank.  When you route the fuel line, you need to make sure that you have enough fuel line to allow for a free flowing route.  You do not want tight bends or kinks in the fuel line.  You do not want to pinch the fuel line when securing it.

Step 5 – Once you have the fuel line routed and connected to the carburetor, make sure you have enough fuel line from the Y fitting and to the carburetor to allow for easy removal of the carburetor for jet changes.

Step 6 – Make sure your carburetor is vented properly.  The lower overflow nipple in the bottom of the float bowl must have a piece of fuel line long enough to allow for an upward route above the carburetor.

Step 7 – Run the engine and take the kart on the track.  You may need to adjust float levels for proper performance.

*** WE DO NOT OFFER TECH SUPPORT FOR THIS TYPE OF FUEL SYSTEM PLAN.  SwedeTech recommends the GFS.  http://www.shopswedetech.com/Speed_Concepts_GFS_p/gfs.htm *** We have done ample testing and at this time this is the best fuel system for the current rule structure.

Last month, I highlighted some of the important areas of the Honda CR125 Stock Moto engine and racing program.  This month I am going to focus on our approach to running the Stock Moto.  Some topics in this article will be specific to SwedeTech Racing, but I will try to make this a broad as possible.

Let us make the assumption that you have a brand new engine that is properly installed on your chassis.  If you do not own a data system that, at minimum, records water temperature and r.p.m.’s, stop reading NOW, call SwedeTech or your favorite parts supplier to purchase one now.  YOU NEED DATA!!!!!

All your nuts and bolts are double checked and you have properly secured loose lines, wires, and cables with tape, zip ties, or other means.  You have primed your fuel system and double checked that the fuel is flowing in the proper directions.  The radiator water lines are filled with distilled water and you have checked all connections, routing, and have burped the water system.  Make sure the temperature sensor is between the water outlet(s) on the head and the inlet on the radiator.  If any of this sounds Greek and you live near some great restaurants, I am available for hire.

So you have taken all of your photos of the new package and posted them on Facebook to read all the comments from your jealous friends.  Your face is permeated with a huge smile and you can’t wait to hear that first ping of the exhaust pipe.  You can’t wait to fill the garage with two-stroke fumes and have a swig of beer.

As with any racing engine, it is the end users responsibility for tuning.  When breaking in your engine, it is encouraged to richen your jetting by 1-2 sizes on the main jet.  Do not add more oil to the gas for break in, this will only change your jetting and not properly increase the lubrication.

SwedeTech does not recommend heat cycling your engine on the kart stand, as this will do nothing for your engine.  To properly break in the piston and ring, the engine requires a load that is similar to your application.  Holding the brake pedal, while winding the shit out of your engine is not a proper load.  At best, it pisses off everyone within a 3 mile radius.  This also will not make your KT100 or Comer engine faster.

We do however recommend that you warm the engine before heading out on the track for your break in sessions, practice, or timed events.  While the engine is warming up, double check your work.  After about 15 -20 seconds of running, place your hand in a safe spot on the cylinder.  If it is hot or warm to the touch, shut the engine down and double check your water plumbing and make sure you burp the system.

Warm the engine water temperature up to 115 degrees Fahrenheit.  Make sure the temperature sensor is between the water outlet(s) on the head and the inlet on the radiator.  Once the engine is at 115 degrees, strap on your helmet and hit the track.  For break in, your engine water temperature should reach 150 -155 degrees during the first couple of laps.  If it is not, come in the pits and add tape to the radiator.

On a 30 second track, slow the pace 4-5 seconds per lap.  Run the engine at full throttle on the track, keeping rpm’s low by short shifting.  Allow the engine to cycle through the RPM range from 6,500 – 10,500 for the first five laps.  At 5 lap intervals, increase the rpm’s by 750 – 1000.  Continue until maximum rpm’s are achieved.  Run the engine at full throttle on the track, keeping rpm’s low by short shifting.

For the last couple of laps, your engine is ready to be flogged.  Once the engine is properly broken in, it is time to tune for best conditions.  At this time, you will want to keep the water temperature between 125 – 135 degrees.

If you find that you are driving the engine at 100% and it is not creating the proper water temperatures, double check the water circulation.  If the water is circulating properly, lean your main jet down 1 size.

Now let’s fast forward a couple of race weekends and three cases of beer.  Being a racer, you probably have A.D.H.D. and just have to work on something, and your preference is to screw with the kart.  And since you have A.D.H.D., your track notes are flawless and you know that your engine now has exactly 4hrs:17min:32sec of run time on it.  Perfect, now it is time to think about a top end rebuild.  If you can properly use a wrench and have basic mechanical aptitude, you should be able to do your own top end.

SwedeTech recommends replacing the piston, ring, wrist pin, bearing, circlips, head gasket, and base gasket.  If you are using a SwedeTech CR125 O-ringed exhaust manifold, we recommend inspecting the o-rings every hour of run time.  When it is time for a lower end rebuild, we recommend that you send your engine to SwedeTech.  If you do not like our recommendation, please send the engine to a trusted and reputable engine builder that is familiar with the CR125 and the Stock Moto rules.

Here are some quick notes that you will find helpful for your Honda CR125 Stock Moto engine package.

Break-in water temperature should be 150° – 155°

Normal running condition water temperature between 125° – 135° (Take the reading anywhere between the cyl. head outlets and the radiator) (Engine will lose performance after 135° water temp.  Overheating can occur with temperatures past 160°)

New engine break-in 15-20 laps, New Top End break-in 12-15 laps, Increase main jet 1-2 sizes for break-in

Usable RPM Range – 7,000 – 12,400

Spark Plug – NGK BR10EG or R7376-10 Spark Plug Gap – 0.024” – 0.028”

Oil – Motul Kart Grand Prix or Maxima 927 – mixed at 24:1

Fuel – VP MS98 – Do Not Use Pump Fuel

Transmission Oil – Motul Trans Oil 10w30 or Motul Trans Oil Expert 10w40

New engine-650ml (21.9 oz)

Use 50ml less for routine oil changes (20.0 oz )

We recommend changing the gearbox oil every 4 hours.  Oil is cheap compared to the cost of replacing clutch or gearbox parts.  If possible, change the oil while the engine is warm.

Jetting

Keihin 38mm PWM

160-180 main (center of the carb, 6mm hex )      Main jet supplies fuel from ½ throttle to full throttle

48-62 pilot (next to main jet, use 5mm flat screwdriver to remove)          Pilot jet supplies fuel from 0 – ¼ throttle

DGK,DGJ, or DGH needle – 3^rd from top.  Experiment with 4^th & 2^nd clip from top.               Needle regulates fuel from 1/8 throttle to ¾ throttle

Air Screw (side of carburetor body, above fuel inlet) – 1 Turn      Air Screw regulates air from 0 – 1/8 throttle.  Turning the air screw in will reduce air through circuit, effectively, increasing the fuel to air ratio.

Top End Maintenance /Top End Kit – Piston, ring, circlips, wrist pin, bearing, head gasket, exhaust o-rings, and base gasket.

For normal use – 6 – 8 hours

For optimum performance – 4 – 6 hours

Normal use – for the recreational racer that is looking for longevity and cost effectiveness.  Typical normal use includes jetting the engine on the richer side.

Optimum Performance – for the avid racer that is looking for every performance advantage.  Optimum performance includes jetting the engine for best performance.

Note that the above schedule of maintenance is based on our experience.  You may find that these times may be adjusted based on your needs, driving conditions, and overall engine maintenance.  Many factors affect wear and tear on components.

Clutch adjustment- you need about 3/8-½ inch free play at the end of the lever. You shouldn’t have more than 1 inch of travel when you engage the clutch. Any more than that and the outer plate could jump out of the basket. Make sure your cables have the nylon inner housing and keep them straight and well lubricated. You should not need more than two fingers to engage the clutch.

When viewing your Dyno Sheet from SwedeTech Racing Engines, the first question you might ask yourself, “Where Are My Dynamometers Horsepower Numbers?”

Great question!  We don’t supply dyno numbers.  We do not want to understate the importance of having the proper tools and equipment to build a racing engine and the dynamometer is a huge asset.  However, we want to educate our customers on when the dyno numbers are important.

Like any quality measuring device, Dynamometers provide extremely useful data that can be very difficult to measure in a working environment.  Dynamometers help bring a standard while testing many different components.  There are many variables that will affect the actual numbers that are given by a dynamometer.  Weather, humidity, air temperature, changing dynamometer parts, changing software settings, process used during a power pull, timing of software sampling, load applied by dynamometer, belt or chain tension, and many other variables.

SwedeTech does not try to hide our Horsepower numbers.  We do however want to minimize as much confusion as possible when it comes to the information we provide.  The only accurate way to compare horsepower is to minimize as many variables as possible.

For example, when we compare our dyno numbers, we run multiple test runs in succession, in the shortest time frame possible.  This minimizes many variables.  We have seen horsepower variances from one day to the next, with no changes made to the engine or the dyno.  Many times this is due to atmospheric conditions, but this is an added variable.

When reading your dyno Sheet, we provide you with the essential information.  We provide you with RPM’s and the power curve.  From this information, you can properly assess the best operation range for your engine.  Depending on different tracks and air conditions, you may have to run your engine in different rpm ranges to maximize on track performance.

Some tracks or some sections of a track may require you to use a lower rpm range to maximize the time you spend in the sweet spot or the power band.  Other times, you may have to gear the engine to run at the upper RPM range to take full advantage of the gearing and power band.

Keep in mind that there is never a perfect rpm range for all racing conditions.  Every track will have its own unique characteristic that will affect the engines optimum performance.  An often over looked aspect of the engines rpm range is how it can affect the handling of a chassis, or vice versa.  When you are driving your kart, it is very physical and mental, and at the same time it is a delicate dance between the driver, chassis and engine.