|The expansion chamber used on the HPV-4 engine is a lot shorter than the one used on the restricted for kids, HPV-1 engine. The shorted length means that the reflected wave is timed better for high rpm use. Embee Performance coated our chamber with their satin black thermo barrier coating. HPV racing classes do not allow the switching of chambers and all racers must use a spec chamber. This eliminates a lot of expense due to pipe tuning like the Yamaha KT100 classes must have if you want to be competitive. The flexible slip joints and spring mounts keep the pipe from cracking due to fierce two stroke vibrations.|
Getting the kart home we decided to see if it could be made to run. Spinning the engine with the starter proved that we had spark, but looking in the oxidized and crusty fuel tank confirmed that the fuel system was hopelessly gummed up. Opening the master cylinder showed that the brake fluid had also turned into a gummy mess. We did a little research and found that Acceleration Kart Racing in Las Vegas seemed to have the best selection and prices on CRG OEM parts so we gave them a call and found them to be quite friendly and helpful.
|The HPV engine class rules state you must use this spec Horstman clutch. The KT100 rules allow clutch tuning and this is a big part of being competitive. The HPV rules don’t allow this and thus saves a lot of time and expense. We broke the stock chain and ruined the sprockets so we replaced these parts with an Empire Karts sprocket and a more compact and lighter Top Kart sprocket carrier. A gold DID roller chain is long lasting and low friction.|
A few emails and some photo swapping identified our parts and a package with fuel line, a new fuel tank, caliper, master cylinder and carb rebuild parts arrived two days later. We cleaned out, honed and rebuilt our brake system which was really quite easy and carefully cleaned and rebuilt our carb, changing our spark plug for good measure. We bled the brake system with fresh Motul 660, freed the gummy axle bearings by soaking them with tri-flow, and filled the tank with some premix VP MS98 fuel blended with Motul Kart synthetic mixed at 30:1 and gave the starter a whirl.
|The brake is a CRG twin piston with a floating vented iron rotor. We rebuilt the caliper. All of the silver parts on the Kart are billet magnesium and they were badly corroded and frozen to the bolts and bearings. Magnesium is highly reactive and corrodes really easily. We bead blasted them all and sent them to Embee for clear powder coating. The rusted hardware was replaced with stainless allen bolts with trick nut retaining clips from Baller Bolts. We straightened and polished the bent and rusty axle and cleaned, repacked and honed out the bearings. Embee blasted and powder coated the frame which had been painted with latex house paint!|
To our surprise, the HPV started instantly. Blipping the throttle, the engine was sharp and responsive. We put air in the tires and blasted down the street, the thing was fast! Apparently this was a fresh almost new engine and it didn’t run simply because it had sat and the fuel system gummed up with stale pre mix residue, a best case scenario. The brakes also worked well now.
|The master cylinder was full of gummy old brake fluid residue and white corrosion. We cleaned and honed out the bore and rebuilt the old and dry seals. The brakes now work really well. The adjustment rod was rusted solid and had to be replaced as well.|