Can bad exhaust gaskets cause lean conditions?

[Incubus]

My carbs are clean. They've been off three times now, so I'm finally confident of that. My air filter is a K&N. It is pink, not dusty. I have a 4-1 exhaust. Jetting is stock. The bike ran fine with this set up before, and it has a real smooth idle now. But it sputters off the line and again over 5000 rpm. Runs great in its limited range. The plugs tell me it's running lean.

The exhaust headers on this bike have to be removed to pull off the oil filter. When I changed the filter last week I discovered that my exhaust gaskets are more notions than barriers. There is not much material left.

I knew the exhaust gaskets were pretty much gone from the increasing popping coming from the pipes on deceleration. My question: can bad exhaust gaskets be so bad that they cause the lean running conditions I described?

Thanks.

Patrick

[TopCatGr58]

YES, yes, yes. Not being facetious, just needed at least 10 characters for the site to submit the reply.

[Incubus]

Thanks, TC.

[donebysunday]

Imho

you would be so annoyed at the noise your leaking exhaust would make, you would fix it ASAP.
Now if your running old stock pipes and mufflers you could have blockage inside from rust. Tell tale sign is the rings/bulges seen in the chrome of the muffs where the baffling is like rings swelled inside the muffs showing on the outside.
It can also happen to have blockage that does not show.
Another blockage I've seen is where somehow the head pipes got water in them, froze in the cold temps and collapsed the inner pipe on the double wall system. This water inside the pipes does not seem possible so maybe factory flaw ? On the bike I found this on it was impossible to tune so if it was like this from Yamaha it would never have run right and most likely would never be accepted by a buyer .

[TADracer]

The technical answer is yes.

All things being the same in each cylinder, the one with any significant exhaust leak would show lean because the leak affects that illusive back pressure in the pipe. That would affect the overlap event in the cam timing which is important to moving fuel/air into the cylinder. Intake valve opens slightly before the exhaust valve reaches the seat to promote scavenging and help accelerate the fresh intake charge. Upset this balance and a lean condition can occur.

Sorry, it's been a long time since I posted anything technical and I felt the need

[skids]

The technical answer is yes.

All things being the same in each cylinder, the one with any significant exhaust leak would show lean because the leak affects that illusive back pressure in the pipe. That would affect the overlap event in the cam timing which is important to moving fuel/air into the cylinder. Intake valve opens slightly before the exhaust valve reaches the seat to promote scavenging and help accelerate the fresh intake charge. Upset this balance and a lean condition can occur.

Sorry, it's been a long time since I posted anything technical and I felt the need

Excellent explanation!