Hmmm... I must learn about this.... something new and intriguing. So you drill out the actual idle jet, rather than swap it for a bigger one or is there a starter jet I'm just not aware of? Now I'm confused, teach me wise one. Is there a post with pics of this adjustment?

 

Wise one?...what you been smokin'?

The starter jet is a pressed-in brass jet, not replaceable. It only operates when you pull the choke plunger out, and it lets more fuel mix to aid in cold starting. There's another post or two here on the forum that even has a pic of this jet. Though not common, this has been the fix for the occasional hard cold starting problem on some bikes in the past. Kawasaki wouldn't publicly admit this back in the '70s, but when I worked part time at a Kaw shop, that was the way we were told to fix hard cold starting KZ650's...had to drill all four carb's starter jets on some bikes. I did this on my '06 KLX, and I can barely get my finger off the starter button now on a cold start before the bike fires. It's not a secret thing or magic by any means...just getting more fuel into the carb on cold start. It makes no difference when you turn the choke off, as the circuit is then plugged off. Of course it has no bearing on hot starts.

I'm leaning more toward Brewster's suggestion on the valves right now. There's a multi-page post on ADV where a similar hot starting problem was traced down to valve adjustment. This is more common than one might think. The valves clearance closes down which I believe cuts down the engine's vacuum draw to a level that affects pulling fuel into the engine...more problematic when hot. Does that sound right, Brewster? If the valves won't stay closed or at least stay closed long enough, engine vacuum drops and no or little fuel is pulled into the motor. I'm no engineer, just using the dangerously small amount of engine knowledge I have to muddy the water.

 

Hot start problems on modern 4stroke mx bikes have been addressed with a hot start valve that allows a sip of fresh air. So one could make the assumption it's a rich mix issue. Without a hot start valve you might want to try a leaner air screw mix.

My experience with my old XR's was a pilot/mix screw setting that gave good cold start, usually didn't hot start well. So you had to find a compromise setting.

Experience with bikes with zero'd intake valves has been hard cold starting, followed by nasty sounding backfires during warm up if revved, then they usually start and run ok the rest of the day.

 

Great input. I have never adjusted the valves on this bike, and I now have 3,200 miles on it. This may be the issue. Question, I assume this bike has the cams directly on the valve stems. So are the shims onto of buckets, or below them? Do I have to remove the cams to change shims?

 

Oh, I forgot, what are the valve specs for intake/exhaust on a cold engine?

 

Yeah, you have to pull the cams when replacing shims. Clearance is .15-.24 mm on the exhaust and .10-.19 on the intake.

 

I have a new 2009 model and have to choke it when it's cold as well as when it's warm/hot. I just assumed that was normal. No?

 

Shouldn't be "normal" when hot, but these bikes are super lean as delivered and heavily choked up by airbox and exhaust design.

 

Quick update.

I started to adjust the valves last night. I found a problem. One of the exhaust valves appears to not be closing 100%. I measured it to be about .025", way out of spec. The other valves were close to spec. If this valve is stuck open, I'm sure it is burned by now. It looks like I've got to pull the head to see what is wrong. Will update later.

 

The reason why the one exhaust valve was reading the .025, is because that is the compression release doing its thing. All valves were within spec. I now have ordered a 37.5 pilot jet to see if that helps. On a positive note, I had a both .40mm (.0157") and .45mm (.0177") drill bits in the shop from a previous jet drill project years ago. I drilled out the cold start jet on my KLX with the .45mm. It seems to have solved the cold start problem. Great! Will update with results from the pilot jet change.