Suddenly idle seems lean ... help!!

[RBrider]

Originally Posted by swazi_matt

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

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

[swazi_matt]

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)

[Neil E.]

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.

[Jakobi]

Originally Posted by swazi_matt

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)

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.

[swazi_matt]

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

[swazi_matt]

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

[Neil E.]

Originally Posted by swazi_matt

are any special tools needed to remove the magneto to replace the seal - what other bikes have the same size?

You need a flywheel puller for the 2K3 flywheel. Left hand thread M27 x 1.0 pitch. Same as used on KTMs.

[swazi_matt]

Originally Posted by Neil E.

You need a flywheel puller for the 2K3 flywheel. Left hand thread M27 x 1.0 pitch. Same as used on KTMs.

thanks, that shouldn't be too hard to find

[swazi_matt]

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