SRS Kart Racing Engines Technical Updates

2001 Honda CR125 Power Unleashed

john@srsengines.com (John Sefcik) — Mon, 27 Feb 2012 06:00:00 GMT

SRS Engines Offers 2001 Honda CR125 Power Valve Plugs

Top performing, precision, investment cast power valve plugs for the 2001 CR125 cylinder are now available from SRS Engines.

The shape of the exhaust duct in the 2001 cylinder is critical to power production. The stock 2001 power valve shape sacrifices peak power to give the engine a broad motocross power band that has good

Stock Honda CR125 Cylinder Comparison

john@srsengines.com (John Sefcik) — Sat, 04 Feb 2012 01:12:02 GMT

Which CR 125 Cylinder Is Faster? That Depends...

SKUSA stock Honda shifter kart rules allow competitors to use either the 1999 or 2000-2002 CR125 cylinders on their engines. The power characteristics of each of the cylinders are different. Deciding on the one that gives the best lap times requires matching the power characteristics of the cylinder to the driver’s technique and the track configuration. Here is a rundown on each cylinder.

SRS Engines Hybrid Float-Twin Pump Carb System

john@srsengines.com (John Sefcik) — Tue, 12 Apr 2011 22:30:35 GMT

Superior Fuel Delivery Unveiled

The All New SRS Engines Hybrid Float-Twin Pump Carb System

Testing is complete and the results are exceptional. Relative to the twin pump fuel re-circulating systems traditionally used today in SKUSA stock CR125 shifter karts, the new SRS Engines Hybrid Float-Twin Pump Re-circulating System performs better in every track test and dyno test we ran.

On the dyno the new SRS Hybrid system with the stock Keihin PWM38

Cooling Stock Honda CR125 Engines

john@srsengines.com (John Sefcik) — Tue, 18 May 2010 21:43:16 GMT

Many racers ask how to limit CR125 shifter kart engine water temp to 120 degrees F in the warm months. The answer is: pass air through the radiator as efficiently as possible and use as large a radiator as required.

The amount of heat removed from the radiator is directly proportional to the amount of air passing through that radiator. Maximizing the air flow with the dirty aerodynamics and average speeds of shifter karts requires a single core radiator positioned straight up. That is because straight up builds the most air pressure in front of the radiator to push

Best Reeds for SKUSA Stock CR125 Shifter Karts

john@srsengines.com (John Sefcik) — Sat, 27 Mar 2010 13:39:31 GMT

There are many small items that go into prepping a powerful reliable stock CR125 engine for shifter kart racing. One item that is optional for stock engines under SKUSA rules is the reeds. There was a favorite reed setup for the 2001 and 2002 reed cages previously allowed by SKUSA, but what about the 1999 reed cages mandated for 2010 competition? Do the type and style of reeds really make a difference on the 1999 reed cage? SRS decided to find out by running dyno tests on a wide range of reed combinations, thicknesses, and shapes. The tests were quite

Honda CR125 Cold Weather Jetting

john@srsengines.com (John Sefcik) — Sat, 13 Mar 2010 18:46:17 GMT

The question of jettijng always comes up whenever the weather changes. That is especially true this winter with the unusually cold temperatures that have surprised racers in the southern USA. In this country kart races usually occur when temperatures are in the 65 to 95 degrees F range. In this range jetting on a CR125 shifter kart engine is proportional to air density. However, if the temperature dips from 70 degrees to 50 or even 40 degrees, experience has shown that the jet

KT100 Clutch Installation and Stall RPM Adjustment

john@srsengines.com (John Sefcik) — Sat, 06 Feb 2010 06:00:00 GMT

Clutch adjustment and operation for a Yamaha KT100 engine is a large factor in lap time improvement. The disk clutches used on KT100 kart engines are designed to allow the engine to operate in an rpm range where overall acceleration is maximized. Here are a few tips to make sure that your clutch performs as well as it can.

Lap the clutch hub to the taper on the crankshaft. This maximizes the contact area between those two parts and reduces the possibility of the clutch hub slipping on the shaft and shearing the key between the two.
Do a trial assembly

Effect of New 2010 SKUSA Stock CR125 Rules

john@srsengines.com (John Sefcik) — Sun, 10 Jan 2010 06:00:00 GMT

The rule changes for the stock CR125 engines to be used in 2010 SKUSA races were formulated to hold down initial purchase costs and maintenance costs while insuring that critical parts are available to all. How this impacts performance is of great concern to all who race these classes. Here is a how each change affects performance.

Modifications to the stock ignition stator to adjust ignition advance are prohibited. When timing advance was set for maximum performance by slotting the stator, frequently a small amount of detonation occurred when using MS98 fuel. The reduced ignition timing advance that is forced

Pump-Around Carb System Installation

john@srsengines.com (John Sefcik) — Tue, 10 Nov 2009 06:00:00 GMT

Most racers in the CR125 stock classes use the Pumparound carb system. The purpose of the system is to stabilize the fuel level above the jets in the carb during high-g turns. This helps keep the fuel mixture constant whether cornering or accelerating in a straight line.

The system has a remote mounted pump assembly consisting of two fuel pumps on a common diaphragm chamber and a Keihin PWK or PWM carb without floats. The pumps are driven by pressure pulses delivered through a fitting attached to the engine crankcase. One pump delivers fuel from the fuel tank to

Why PWK or PWM - Stock Moto CR125 Carbs for SKUSA

john@srsengines.com (John Sefcik) — Sun, 01 Nov 2009 05:00:00 GMT

SKUSA lists two carbs, the PWK with the round screw top and the PWM with 2 screws to retain the top, as legal for the Stock CR125 classes. Each has its advantages and trade offs. The PWK offers very linear part throttle response that helps controllability when exiting slow turns. The PWM gives slightly more mid range power but a more "sudden" part throttle response.

Tight twisty tracks that require strict throttle discipline tend to favor the PWK, while tracks with

Summer Tunes

john@srsengines.com (John Sefcik) — Wed, 05 Aug 2009 06:00:00 GMT

SRS stock CR125 shifter packages are supplied with carbs jetted slightly rich for density altitudes about 1000ft and ambient temperatures around 75 degrees. The main jet will usually need to be reduced about 5 points to attain the best lap times. Variances in temperature up to about 15 degrees will require only a main jet change. However, drastic variances in temperature and or density altitude from the 1000ft/75 degree range will require slide needle position and air screw/pilot jet changes to

TAG Crankshaft Tips

john@srsengines.com (John Sefcik) — Fri, 29 May 2009 06:00:00 GMT

Tag engines have been developed and refined over the years to a high level of performance and reliability. But to keep that high performance and reliability, the crankshaft demands respect. The crank rod assembly is one of the most highly stressed components in the engine.

It is asked to spin at up to 17000 rpm while exerting huge acceleration and combustion forces on the rod bearing and main bearings. Surprisingly it survives this bedlam, but only if it is well aligned and not wobbling. Wobbling is called crankshaft runout in technical terms. Runout occurs when the two crank halves

VolksKart - Stock Honda Shifter - The People's Class

john@srsengines.com (John Sefcik) — Thu, 23 Apr 2009 06:00:00 GMT

The performance of the latest tuning generation of SRS stock 125 shifters is incredible, relative to the stock engines of the past. Anyone considering running a shifter kart should seriously evaluate the the Stock 125 classes offered by IKF and SKUSA. This applies not only to new shifter drivers but also the experienced racer.

Beginning shifter drivers will like the stock 125 because of the ease of tuning, mistake-masking broad power band, and relatively low maintenance. The veterans, even those who have enjoyed the surge of a modified Honda, will like the near-modified level of performance without the fear

IAME Gazelle Horsepower O-Pinion

john@srsengines.com (John Sefcik) — Thu, 19 Feb 2009 06:00:00 GMT

One day while dynoing to extract the last little bit of power from a Gazelle 60 TAG engine, a surprising power increase was noted when one simple change was made...

The dyno session was started with a 10 tooth driver whose teeth had that tell-tale hook shape that indicates tooth wear. After a few runs to stabilize temperatures, a few more runs were made to gather data for changes made one at a time to gauge relative performance of each. When that was all done there was some time left before the mandatory dyno noise curfew. So on a

SRS Parilla Leopard Carb Settings

john@srsengines.com (John Sefcik) — Wed, 11 Feb 2009 06:00:00 GMT

(By Mike Jones John Sefcik)

The factory recommended carb settings for the Parilla Leopard TAG 125cc kart racing engine are very safe and user friendly. The manual gives a starting point of 1-1/4 turns open for both the low and high speed needles. These are settings that allow for clean throttle response and idle and cool engine operation.

These settings in a race with experienced tuners will leave you in the dust. Assuming you adhere to the factory recommended pop-off settings of 9-1/2 to 10-1/2 psi and you're running close to the Senior Class race weight, SRS

Best Stock Honda CR125 Shift Points

john@srsengines.com (John Sefcik) — Sat, 31 Jan 2009 06:00:00 GMT

Knowing how much rpm will drop when shifting gears will help you to hit a shift point just right. This requires that the gear ratios of the gears being shifted between is known. Below is the ratio of each transmission gear for late model CR125’s that use the 1997 gear set.

1st 2.357
2nd 1.867
3rd 1.526
4th 1.286
5th 1.130
6th 1.000

The percent change in rpm when up shifting from one gear to the next is proportional to the ratio of ratios

Shift Happens

john@srsengines.com (John Sefcik) — Thu, 22 Jan 2009 06:00:00 GMT

When SHOULD you shift gears?

Experienced drivers feel it, beginners don’t. If you are beginning shifter kart racing and are wondering what is the best rpm to shift gears, this article is an explanation that may help you.

When you open the throttle to accelerate off a turn, you feel the effect of engine horsepower pushing you forward. The more horsepower the engine produces at a given rpm the more force is created to push the kart forward with you sitting in it.

Octane Requirements for Spec Honda 125 Shifter Kart Engines

john@srsengines.com (John Sefcik) — Mon, 19 Jan 2009 06:00:00 GMT

Recently, I have noticed a non catastrophic, although damaging, amount of detonation in S3 engines using the required VP MS98 fuel at the 2008 Supernationals. We (customers and SRS) haven't experienced that problem here using VP C12 or Tracktek 111 fuel. So it seems that the spec Hondas are tuned so well now that they will detonate if octane levels are lowered to the MS98 level.

On the dyno and the track VP MS98 fuel (96 motor octane) and VP

Why Dyno Test Your Kart Racing Engines?

john@srsengines.com (John Sefcik) — Sat, 17 Jan 2009 06:00:00 GMT

Peak horsepower numbers are impressive for "bench racing", but the area under the horsepower curve over the usable rpm range at real world temperatures actually wins races.

Engine power is highly dependent on atmospheric conditions especially temperature. SRS engine packages are tuned to give their best performance at the temperatures and track conditions they will actually encounter. An engine can be tuned to make an impressive dyno “trophy pull” for bragging rights by running the engine at less than operating temperature on