Chasing Problems on Game Day

Memorial Day weekend 2005 at VIR – karts everywhere, perfect weather, and a top class racetrack. What’s not to like?

Friday morning practice presents something I was, for a change, anticipating that my kart would be too loose for VIR’s road surface. But I wasn’t sure how I was going to tackle the problem, since most of the time I am attempting to make my kart more loose, not less. And sure enough, after two practice sessions I was convinced that no amount of change in tire pressures was going to get my Coyote laydown to stick the way I wanted. The kart was going more “east-west” than north-south through the turns, but if I lowered the pressures much more, I ran the risk of having the tires “tuck under” during hard cornering. Some consultation with colleagues confirms a strategy ? a change to smaller front wheels and tires. I dragged out an old pair, put them on the kart, and instantly the kart settled down. The increase tire wall flex kept the rubber on the ground longer, and though now the kart had become a touch tighter than I preferred, with some additional air pressure, I was easily able to get it to handle within my comfort zone. Small victory number one.

But some trouble arises near the end of Friday practice. Suddenly, the motor starts doing something totally new ? that is, my trigger (remote high speed adjuster) suddenly stopped working altogether. Pulling it in or out seems to make no difference to the engine. The engine does run, but won?t twist high at all. Odd. Nothing was clearly wrong with the carb, but we pulled it off the engine, and ran a pressure check, which showed no internal leaks. I quickly bolted the carb back on (remember this), and more group consulting leads to the conclusion that the problem is probably in the ignition system. Perhaps a bad magneto coil, but the TCI module and spark plug cannot be ruled out. Friday practice had just concluded, and I was in the second race on Saturday, my first race in a new class, so how to isolate the problem by the next day? I didn’t want to change everything in the ignition system. While that might have been the most effective route, still I would be left wondering which of the three components I had removed from the motor actually was functioning improperly.

Since the magneto coil was most difficult component to swap out, that was the first thing to do before Saturday?s first practice session. We decide that I will know within one lap whether the coil replacement fixed the problem ? if it did not, then I would come in, swap out the spark plug, and go back out. In one session, I would have eliminated two out of the three potential culprits in the ignition. If neither of those changes cured the engine, then between Saturday?s two practice rounds, I will replace the TCI module, and then hit the track for the last session.

As it turns out, the magneto coil was bad. No need to look any further. Small victory number two the weekend’s last.

Flash forward to the next day, Sunday’s race. At this stage, I am dangerously behind schedule. Chasing these problems has gobbled up most of my testing time for the weekend, and switching back from Sporstman to PPCan Medium, I cannot decide if I have set up the kart correctly. I might still be a second or two slower than I expect to be, so following Sunday?s practice session, I dig into the clutch to make some changes. The maneuver goes against my instincts, but I do it anyway. At the last minute, I am trying to recreate a setup from last year, based on notes, without actually having a chance to test it.

The race soon proves the changes wrong ? the leaders are pulling away fast, and no amount of tuning or hell-bent driving can keep them in reach. The lap timer?s first reading shows me to be a staggering five seconds off pace. I curse the decision to make the clutch change, and worse yet, the kart is again behaving strangely. I?ve had to lean the carburetor down beyond any previously known level to get heat in the engine, and still, the kart feels like it?s lugging badly. I chalk it up to the Yamaha gods, and half-heartedly finish the race.

A post race inspection reveals the real problem. The carburetor is loose! Dangling, almost, from its two long bolts. It seems that my earlier haste in tightening the Walbro bolts finally “paid off,” leaving the motor sucking air, and not much else. Was the clutch also a factor in the kart?s poor performance? Because of the dangling carburetor, the relative success of the clutch change is lost as well.

There’s some old saying about living and learning. As soon as I remember it, I’ll pass it along.