Inconsistent idle/off throttle surging
 

Looking for help on two (maybe related, maybe not) issues with an '11 300 ec.

First issue is the engine is stalling (while throttle is shut off) during hard riding especially on uphills/downhills. The idle works fine at rest although I have had to turn the idle screw in nearly all the way. My first thought was float height, but it looks to be ok. I have had this issue since the bike was new.

The second issue just started last weekend: the bike surges while the throttle is shut. Just quick short blips that while coasting with the throttle closed cause the bike to accelerate every so slightly. This started (I think)after I backed the the air screw out to 2 turns to try and get a higher idle to fix problem #1. I have enough slack in the throttle cable so I can't figure out what's happening here.

Carb set up:
175 Main
38 pilot
stock needle ???
air screw 2 turns out
not sure which model carb, but the bike is an e-start with ohlins/marz.

That sounds like a lean surge issue. Since I like a really crisp off-idle acceleration, I tried going as low as a 35 on the pilot and got similar symptoms. I tried a 40 pilot with as many as 2.5 turns out and the bike got blubbery off-idle. I ended up going to a 38 pilot at 1 3/4 turns and bumped the idle up a tad. I also swapped the 48 tooth rear with a 50 which enables me to ride a gear high in most situations and lug around in 2nd. This keeps you into the throttle a bit more and avoids the worst of the gurgling/blubbery part just off-idle. I'm using a JD blue needle (GasGas kit) in #3 clip, 175 main. Typical elevation is 500 ft and temps are anywhere from 45 to 65 degrees F. I think the 38 pilot is probably marginally lean and I still get a minor surge every now and then, but my plug tip is fine and anything bigger on the pilot will cause the off-idle to blubber too much for my liking.

Thanks for the info. I forgot to mention the bike ran pretty close to spot on back when temps were in the 40's, but now that its been in the sixties here lately, these issues have come up. That makes me think it may be running too rich at the higher temps, but I'm just speculating. Need to do a plug chop to verify the main, but my seat of the pants check says it's real close.

My bike started surging when I stopped during a ride once. When I got home I removed the carb and cleaned it out. The problem went away. Never hurts to start with a simple solution.

Update - surging is gone, but the stalling issue is worse. Anytime I come to a hard stop, the bike quits running. You can keep it running by holding the throttle open. When you do that, it seems to be loaded up, like somehow the sudden stop caused the carb to go rich.

I'm bumfuzzled. It's nearly unridable. I've cleaned the carb and tried all kinds of jetting combinations but the bike still stalls just the same.

I don't know why, but I have to have the idle screw turned nearly all the way in to get the bike to idle (with a 35/38/or 40 pilot, doesn't matter -air screw position either). Is is possible that the slide is raised enough for fuel to dump into the intake on a closed throttle on hard decel?

I'm bolting on a 38mm AS1 tomorrow as a last resort.

If you're running the stock needle and position, try moving the clip higher. The stock needles seem to be way too rich right off idle, I think mines in the top groove now on my ASII with a 38 pilot and somewhere around 175 main. It runs good, no blubbering or hesitations and idles nice, but I think it could be made crisper with a different needle. I'm going to pick up a YZ250 needle to try, seems to be a lot of guys who like them.

Wes.

I've tried stock and JD red & blue needles in variuos positions.

This isn't a blubbering issue - this is the bike shutting off at every corner.

Just a guess, have you checked the float height? I'm wondering if you have a fuel level issue.

Not sure if it will help but try safety wiring the throttle cable where it enters the carb. The GasGas cable is different than other bikes the way the cable end is made. On mine I could not get the idle set consistently and this was the problem.

Do the reeds look ok?