Suddenly idle seems lean ... help!!
 

My bike has been fine and the only recent change has been from mogul 710 to belray h1r 2t oil - both mixed 40:1.

The last two rides the bike has shown v lean tendencies at idle and low rpm (where it used to chug previously) it is reving higher and surging and the chugging up climbs became more like riding a yz125 than an ec300.

The last ride (it was colder) i eventually stopped and lifted the needle (although running open road the bike seemed to run fine) and this helped a bit. I suspected that since nothin had been changed maybe the pilot jet had become partially blocked so took the carb off yesterday to clean it and all looks fine (the float pin fell off while removing the carb but not sure if this was from all the jiggling or if it had previously worked loose if that is possible)

Everything seemed fine but the float height seemed a bit high - float was angled downwards when the fuel closed - but I could ride the bike flat out on the way home without any issues and I am sure this could not change by itself?

Not sure where to look next if the cleanout doesn't help? Plug?

I will check the rubber boot between carb and reeds for leaks but surely that would affect all areas?

Any ideas?

Running 38 as2
Nedj on second clip (changed to 3rd on the ride but this made open Richie)
Main 170
Pilot 40
Altitude 700-1000m (ride 3 weeks ago -before the issue appeared - in warm weather with no complaints was from 600m to 1800m)

I am by no means a jetting guru, but if I were you I would try adjusting the air screw as it has much more effect on idle than the needle position. It could be that it has been colder lately and you were border line lean before but now it is too lean. There also could be a slight viscosity difference with your new oil, or it could also be a combination of both things. The jetting 101 sticky in this section of the forum has some great information too. Good luck!

A crank seal starting to go bad, probably on the mag side.

RB

that is the strange thing. on the ride 2 weeks ago (when i first noticed the issue) the day started cool and got hot (28?C) but was at lower altitude (400-800m) and it got worse later on the ride (slow riverbed at about 400m and the hottest part of the ride). the last 10km was on the road and i wound it up to clean out the pipes and it ran perfectly there wide open (this has been a bit rich at higher altitudes where i normally ride so i expected it to be better down there) until i ran out of gas 100m from my van

then when i got home and warmed the bike up and idled it the air screw seemed right and it didn't have the lean idle, everything was fine, but i didn't take it for a ride.
when i rode this weekend it initially idled fine in the parking lot (and every now and again out on the ride) but once i started riding it had the same hanging/surging idle (but worse than the weekend before - possibly because it was much cooler 11?C)

I was thinking this, but the bottom end was done about 10 months ago, and when i took the magneto cover off I could not smell any fuel or anything like that in there (if this is a check??), just a few drops of water from the deep river we crossed i suspect

Also regarding a leaking crank seal, surely this would affect all jetting circuits?



Last night i also checked my coolant and the water pump because ithe bike was overheating. most likely from the lean jetting, but just wanted to make sure it wasnt the other way round. Impeller was fine and the gear was holding it and turning with the kickstarter. But the strange thing is that the coolant was under pressure - when i released the radiator cap it sprayed all over the place, maybe i overfilled the radiator or the chinese radiators have higher pressure caps that didn't allow it to equalize, but i did boil a little out there so i would have expected it to suck rather than blow.

Also checked the plug after the first problem ride and it was perfect (last few km were flat out so above 1/4 throttle it was running sweet) and then again last night and it was much darker and a bit wet - probably the richer 1/4 up from lifting the needle (PS we lifted the needle because it was the only option at the time - although you are right we should have screwed in the air screw first)

I've seen a couple get debris in the pilot jet and seem ok when checking.
Might want to try a new one, especially if your not using a inline filter.

Stator side seal pulling air past, air leak elsewhere (carb boot/intake manifold/reed gaskets/cylinder base gasket).

Or a blocked pilot circuit. Don't forget to blow out the passages in the carb as well, and I'd either have a very close look at the pilot or replace entirely.

Pressurized cooling system with bike cold means something else is getting in there. Does it smell of exhaust down the radiator fill hole? Cracked head or orings gone bad?

things are sounding worse and worse. lol thanks for the input, it looks like this weekend is going to be heavy maintenace. If it is any of the serious items i will be missing my extreme ride i have paid for in 2 weeks www.theimpi.co.za


I will check the radiator this weekend when i start up the bike. could this have an impact on the jetting though?

@jakobi surely any leak would be noticed throughout the entire jetting circuits? not just the pilot.