Engine "dies" riding downhill
 

Hello,
I am struggling with EC300 MY2011 of my son.
No way to keep the Engine "alive" while driving downhill at low speed.

Tried:

Main jet : 175
Check carburetor fuel level -> OK
Spark plug -> OK (grade 8)

Idle Jet 40 -> tried 38 useless
Idle Jet 40 -> tried 42 useless

thinking about give a try to Idle 35 ....

Hi, the problem is the stock N1EF needle. RM250 needle will be a good start. Read up suggestions here and will be well on the way to a totally different feeling bike with awesome response. Will fix your issue as a side benefit.

Wot he said!

Plus to the crap needle a misadjusted float height will add. Get this right too, then adjust idle screw a tad (not more!) higher.

Best part is the needles are dirt cheap too
As in $15-20

A mate was sceptical that two things that looked the same could make a difference when I tried one in his bike. Now he'll bore anyone to tears about it.

Did you figure it out?

Could be clutch drag when coming downhill with clutch in, rear brake locking the wheel momentarily causing a stall.

I had the same issue (low idle coming down steep hills). Tried / checked a bunch of different things: needle height, air screw, pilot valve, idle rpm, etc.

Took a while, but finally figured it out to be exactly what you described: clutch drag. Most of the places it was happening, were really steep / technical downhills where you went down as slow as possible. This meant the rear wheel speed was slower than it would have otherwise been at idle. And thus with the clutch dragging, the rpm slowed down.

I've just learned to deal with it. A quick blip of the throttle every 4-5 seconds is plenty to keep it from stalling.