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Stock Moto Parts |
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Over the years karting has seen a several classes come & go. 125 Shifters are a unique breed of their own as they seem to have gone a full circle due to the extreme durability and fun factor they offer. A properly assembled and tuned 125 Stock will produce in the range of 35 HP and offer a good usable powerband from 9500 RPM to 12,200 RPM. Comparing the Stocker to a fully blueprinted/Modified S1 spec 125 producing 41 HP on the same Kart with the same driver would be about 1.2 seconds faster on the typical Sprint track. The S1 Spec motor will have a much wider powerband and require 4-6 less shifts per lap. The 125 Stock will emphasize Carb Tuning, Gearing, chassis set up, and most of all driving. Basic parts list
CR125 Motor Kit Honda supplies motors in Kit Form to Honda dealers as a big box of 343 parts. While this package is available to all their dealers, only a few of them have chosen to fully support the karting market by keeping inventories and low margin pricing. Some even assemble the motors which is probably the best option for most karters. If you know what you’re doing to put one together, plan on about 3 hours to open the bagged parts and sort them out, and another 3 hours to assemble. It’s probably best to buy a motor already assembled. Honda motors are constructed such that a “blueprinted” assembly is pretty much limited to getting the exhaust plugs correctly shaped, base gasket thickness correct and advancing the stator timing. Motor Kit prices vary from about $2400 in unassembled form to as much as $3000 in assembled form. In addition to Motor Kits are the accessories to consider. What to know about Performance and Parts selections Motors won’t make a much difference in the bottom end assembly if it comes from one of the above sources. There may be several other great sources they just haven’t yet been identified to us, so this list will probably grow. Air Filters will perform slightly better then Air Boxes without foam filters, and much better then Airboxes with Foam Filters. The noise output of a 125 Stock with an Air Filter is comparable to a CIK legal ICC so Airboxes should avoided where CIK Legal ICC’s are allowed to operate. If you have to use an Airbox, look for a 3X28mm hole size with Mesh Filters fitted to the intake horns. Carburetors have been limited to the Keihn PWM or PWK with 38mm bore. The PWM is a shorter body and works a little better in road racing where drafting passes are vital. Otherwise the longer body PWK will be a better choice. All Keihn carbs are intended for motorcycle use running about 5% of the fuel pressure you'll have with a fuel pump. Its strongly recommended to convert to a Pump-Around style to avoid flooding and starvation issues. Pump-Around Mods are relatively easy to do but still require a twin fuel pump. Instructions for Pump-Around conversions are available in the Kartweb Subscriber Service or can be updated commercially for about $250. Fuel Pumps are a diaphragm type powered by the intake pressure pulse. The Mikuni Round Pump is pretty much standard and produces about 3-5 PSI. If you convert to a Pumparound it will take two pumps and it's best to have a custom made centerpiece to join the pumps. Power Valve Plugs are required for 98-99 model cylinders. There are two types; one has an O-Ring seal and the other doesn't. The O-Ring is strongly recommended. These plugs will need some minor grinding as instructed in the Stock Moto Tuner's Guide. Exhaust Flanges are available from several sources, although we tend to prefer the Shockwave version for the durability and tight fit on Pipes. Flanges will need O-Ring replacements and these are available at most local Bearing Shops. Look for a Viton O-Ring and order 50 of them at a time to save money through the year. Pipe & Silencers are the most controversial component of the pick. The RCE T3 and Leary Hi-Tech generally offer the best choices while the RLV T4, and RLV B4 have been proven to work very well also. By limiting the port timing, compression, and ignition, any of these pipes can be tuned with header spacers to achieve relatively equal performance on the track. 12” minimum Silencer length is specified, although a 14” may actually be a better choice to build backpressure at higher revs. There may be a spec pipe & silencer coming in the future although there will be a minimum 6-month warning to the requirement of a spec pipe. Most pipes tend to lose their “tune” after a full season of racing anyway. Motor Mounts are more important then they look. Rule #1 is that the mount is straight and perfectly aligned to avoid sprocket/chain binding. There are some that are offset to move the motor a little to the right for more driver room. The clamps need to sized to fit the chassis - distance between tubes as well as tube diameter. J-Arm Levers replace the kickshift lever from the bike. They may be offset to clear the seat brace. Drive Sprockets may range from 14 -19 teeth. At about 19 teeth the chain begins to come dangerously close to the case. There are some 20 tooth and larger sizes that are offset by welding 2 sprockets together. Axle Sprockets are split and come in sizes from 21-29 teeth. Higher priced aluminum versions are available but they tend to have limited life and really won't lower your lap times. The Gearmaster will give you a clear understanding of all the possible gear ratios. Radiators may range from “Heater Core” sized units up the “Barn Door” size. Generally a radiator that measures 150 square inches will give a Delta T of about 40° on a Sprint track for a 125 Stock – so at 95° ambient, the water temp will run about 135°. The 125 Stock is a little more tolerant of higher temps then a fully modified Moto so take that into account on sizing a radiator.
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