Suddenly idle seems lean ... help!!

S

swazi_matt

Active member
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!
 
Halcon said:
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!
Click to expand...
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)
 
RBrider said:
A crank seal starting to go bad, probably on the mag side.

RB
Click to expand...
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.
 
swazi_matt said:
@jakobi surely any leak would be noticed throughout the entire jetting circuits? not just the pilot.
Click to expand...

Not at first, in my experience. but it'll show up every where in the range as it gets worse.

Also regards the pilot jet. On my EXC 450, I thought it was lean at idle, but the pilot looked good (I thought). I bought a new one same size and compared it with the old and found the opening in the old to be about 1/2 the size of the new. The old had just been slowly corroding closed like an old rusty plumbing pipe.

However,I'm still betting on the leaky mag side crank seal.

RB
 
to replace that seal means splitting the cases?

It is fairly new. was replaced when they did the bottom end less than a year ago, could it fail so quickly? (considering the previous one lasted 6 years without failing)
 
If your engine guy installed it without any grease on the lip, it could be wearing prematurely. I think it's more likely you have a crack in the rubber boot between the carb and reeds. Any air leak will always affect the pilot circuit first and only show up in other circuits when it gets worse.
 
swazi_matt said:
to replace that seal means splitting the cases?

It is fairly new. was replaced when they did the bottom end less than a year ago, could it fail so quickly? (considering the previous one lasted 6 years without failing)
Click to expand...

I put something like 260hrs on my stock 2010 one without fault and only changed it due to the bottom end period maintenance.

On the other hand I found my 2013 model weeping at the first top end around 65hrs (from memory).

You don't need to split the cases. Can't remember if yours is an e-start or not.. but pull lhs engine cover, pull flywheel and stator. Access to the seal directly.

With mine, I could see that it has been blowing oil past the seal with the flywheel and stator still in tact. Oily residue across the bottom of the cases. I didn't have any significant lean symptoms showing at that stage, but figured if it's blowing some oil out past the lip under compression it'll likely be able to pull some back past on the opposite stroke.

Also as Neil has said, intake manifold/rubber boot can definitely do the same. I had replaced one at some point on my 2010 as well. Like most rubber items they tend to harden and perish a bit, and given that the carb fitment is a bit less than perfect it does tend to carry a bit of load on it.
 
ok that is a relief. (found this nifty video https://www.youtube.com/watch?v=iQwulUnPxew )

I checked the rubber boot between the carb and engine and while it has some cracks on the outside they do not appear to go right the way through - i have a spare boot so may just replace it to be safe

I also checked the pilot thoroughly and it is clear and the hole is round and comparable to the 38 i have. I did find some small bits of grass or similar in the float sump, so i am praying this is the where it all is - any one of those pieces would block or obstruct the jet for sure

would a leaking LHS crank seal leak in both directions? If so i should be able to see something in the magneto area?

I will take off the head and have a look to see if the o-rings are fine since i have the coolant drained and the tank off
 
now 2 questions. are any special tools needed to remove the magneto to replace the seal - what other bikes have the same size? What pitfalls to look out for?

and when setting the float height is this the measurement i need to get at 8.5mm when the float is just resting on the needle. The pick below is how i adjusted it, it was much lower (ie the measurement shown was larger) but i doubt it would have changed by itself so i am assuming it was set like that and jetted like that

 
So i cleaned out the carb and all seems fine.

I fitted an inline filter as well.

It is running a bit rich but that may be a result of raising the float level to about 9mm.
I also discovered that the needle had been dropped on its point. I am not sure when this happened (i have 2 small boys who like to fiddle so i suspect it happened while it was on the bench), I took some jewellers files to it and it looks ok, a bit of a blunt end but the sides of the point seem uniform now, but i will be ordering a new, slightly leaner one, soon
 
You must log in or register to reply here.

Similar threads

Wbdisco
Needle Testing
Replies
15
Views
2K
Wbdisco
Wbdisco
V
Carb dumps gas into the crankcase
Replies
4
Views
2K
(F5)
(F5)
M
Engine surge/runaway?
Replies
4
Views
134
Mustyeddie
M
S
2011 EC200 6days
Replies
2
Views
2K
(F5)
(F5)
C
2009 gas gas EC jetting
Replies
5
Views
3K
cofl1001
C
Back
Top