Desflurane's Romaniacs Blog

Chronicle of My Participation in the World's Toughest Enduro Rally – Again…

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I never claimed to be the sharpest tool in the shed…

Posted by desflurane on March 23, 2011

I was out for a nice two-hour afternoon workout ride the day before yesterday. We had a little snow in the morning followed by sunshine and above-freezing temperatures, so the snow vanished below about 5,500ft elevation. The dirt ranged from nice and tacky to slime-ball mud, it was fun.

I got into one nice sandy section with a long straightaway, perfect for a little wide-open-throttle drill. I was dismayed when my engine bogged and almost died every time I twisted the grip all the way. Clearly something was amiss. I decided a little jetting attention was warranted.

The next day I tore into the project. A quick check of the plug confirmed my suspicions that I have been running a little rich for a long time – the insulator and electrodes were coated with black, oily gook. I swapped in a fresh plug and turned my attention to the carburetor. I had swapped out the stock 165 main for a 162 last fall and installed the needle that the local KTM dealer recommended. Being that I was still a bit rich, I planned to swap in a 160 main and raise the needle clip one position.

The needle clip change was swift – I only moved the clip in the wrong direction once and it was BEFORE I reinstalled the slide in the carb! Clip correctly positioned, I unscrewed the plug at the bottom of the float bowl to get at the main jet and immediately discovered the source of my open-throttle woes: the main jet had come loose, fallen out of its bore and was lying flat at the bottom of the float bowl! I have been running with NO main jet for who knows how long! (Thus my title for this post – I am definitely a newbie at jetting the two-smokers!)

I installed the 160 main, as per my plan, put it all back together and went out for a test run to see what I had accomplished. With the first spirited twist of the throttle from a rolling start in second gear, I nearly looped out when the power valve opened! I couldn’t believe the difference! Tons of screaming, snarling power! No sputtering, no bogging – just power! The engine rebuild did the same sort of thing for the low-end, and the jetting I had wasn’t too bad up to the 3/4 throttle range – but at 3/4 and up I had no idea how much power I was missing out on!

I’m now wondering how much of the trouble I’ve had climbing steep hills has been due to a main jet that was rattling around at the bottom of my carb instead of doing its job. Repeatedly, I have had the engine bog and die on steep climbs when I try to get on the gas – no wonder!

So I ripped a bunch of wheel-spinning trenches with my rear tire across the vacant lots next to my house before retiring to the garage before somebody called the police. A quick check of the plug showed an insulator toasted to a lovely golden-brown perfection. Good enough to eat!

I then twiddled a little with the air screw and got a bit better off-idle throttle response. Now she doesn’t cough or sputter when I attempt throttle wheelies. Rolling on the gas – power just builds smoothly until the exhaust valve opens and Satan himself takes over my motor, extracting from my naive piston and gears unholy gobs of devilish horsepower! OK, I’m exaggerating… a lot – but the power increase is significant! I’m pleased.


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