2011 EC 300 Jetting/Carb Troubleshooting
 

38mm Carb, #7 slide, JD Blue needle, #4 Clip,170 Main, 38 Pilot (JD's Specs except 1 richer on the clip), manual choke installed, air screw set per JD guidelines, idle screw: (still trying to adjust correctly...when I got the bike it was screwed in to the stop).

I have owned this bike just a couple of months, very little seat time yet. Note that the jetting on the bike was "off" when we purchased it. It idled high and uneven. Upon inspection it had some goofy settings and based on past experiences, ordered up the JD Kit.

The bike seems to run good everywhere but at idle (No WFO tests). But the idle remains uneven; sometimes it will run a little high, but blip the throttle and it will rev down and die if I don't keep it running. Return to idle after a throttle blip is slower than I would expect. After a quick up and back on a straight-away (3rd-4th gear) at 1/4-1/2-3/4 (maybe) throttle, chop the throttle and come to a stop, it may keep idling high or it may rev down and die.

Scratching my head...feel like I'm missing something. Maybe gummed up air circuit? Maybe some mysterious air leak somewhere (actually found a slice in the old air filter and found that it had been haphazardly installed so I replaced it with a new one...the mating surface/shape does not give one a high degree of confidence when fitting!).

Any thoughts are appreciated.
GW

Until I went to the 42 pilot jet, I always had the throttle stop screw in too far in order to get my bike to idle (raised my slide and needle above the normal idle circuit positions), and it didn't idle well; none of them.

The 42 will give you a pilot jet rich enough for the other adjustments to work together for a desirable idle.

Check the squish. A lot of people who didn't have the proper amount had an idle issue.

+1
Instant steady idle
Did my head recently and remembered why is so essential mod. (had on a previous bike)
jetting is on the track again

Thanks Jim. I'll give that a shot.

So you're switching the base gasket to get proper squish?

There's a lot of information on here about cylinder Port timing and squish settings. But just a quick overview, you can use different size base gaskets to change where your power is coming on. But afterwards you have to adjust your squish accordingly as cylinder height affects it.

A lot of guys were getting good results by aligning the exhaust port at bottom dead center with the piston and then adjusting their head squish to 1.5 millimeters

I have 1 mm of "squish" on my bike.
Note: If anyone uses the Athena gaskets, the base gaskets are a different "color to thickness" than the stock GasGas base gaskets. Always measure your base gasket thickness when doing a top end job to make sure you get what you started with, or at least get what you expect.

Update: So I did not have a 42 (amazing due to the amount of brass in my jet collection!), so I used a 40, took the JD Red needle back down to #3, up to the 175 main. Air Screw 1-1/2 out. MUCH better. I also blew things out pretty good with carb cleaner while I was in there just to be safe. Now just a bit of a bobble off idle, which I will try to tweak when it warms up again. Little more spooge at the pipe but honestly that doesn't bother me too much as long as I'm not fouling plugs. Rode 2-3 hours Sunday and never loaded up too bad. So thanks for the help!

What gearing are you woods riders running on your 300's? Not sure what counter sprocket tooth count is, but it has a 52 on the back. Still seems a bit of a beast in the tight stuff.

That's great news. I'm glad I could help.
It will be smoother with a 42 pilot jet, but may spooge a little worse out the silencer.
Play with the needle clip position to fine tune what you currently have, before you try a different pilot jet. Then, try one of the Suzuki or Yamaha jet needles suggested in this thread to make it "more better".

Reading your update above, I had another thought concerning "Still seems a bit of a beast in the tight stuff".
Which ignition setting are you using in the tight woods, rainy or sunny? The rainy setting is abrupt "down low" on the 300, and shuts down early when compared to the sunny setting. I've found that I use the rainy setting a lot more on the 250 than I did on the 300. It really helps the 250 "pick up" and climb the hills from a low rpm start.
With the 300cc engine, the extra torque will be smoothed out in the tight stuff by the sunny setting, yet there will still be plenty of power to do anything I need during trail riding. Plus, the power keeps up at higher rpms, letting me carry the front wheel further on long mud holes, etc.
On the 300, I most of the time I only used the rainy setting when I was in full "race mode" in the tight woods, and when I was in a line of riders going up a steep hill, where I couldn't "break loose" and had to stay at more sedate speed while lugging up the hill.

On the 250, I use the rainy mode a lot, and normally only go to sunny mode when I'm in a hurry in the open stuff.
It really amazed me at the difference in the effect that the ignition settings had on the 250 and 300.

I've found that the 49t rear and the 52t rear have very similar feel; only a gear different. (49t 2nd feels like 52t third, 3rd feels like 4th). Those are my favorite race gearings. The 52 will give you a "granny" low first gear, and bring your gears marginally closer together. The 49 will still have plenty of power to climb anything you want to tackle, unless one is using an auto-clutch. With an auto-clutch, the lower first gear is needed to keep the front wheel on the ground when the auto-clutch engages while taking off from a dead stop on a very steep incline. (Like when you are following someone up a steep hill and they don't make it, so you have to stop, too. The manual clutch lets one modulate the drive with more finesse in those situations.)

Lug that torque monster 300cc engine for the most fun.

Good luck and Good Riding to You!
Jim

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