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Will an exhaust leak cause a lean condition?

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Guest

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I put on my new Jardine a few weeks ago, and took the bike on a road trip. When I got home, I noticed that pipe #3 had obviously gotten hotter than the rest and had discolored a bit from being lean. I check it's plug and it was white. I took the header off for cleaning, and noticed #2 exhaust port had an extra gasket in it. :oops: So I think maybe pipe #3 wasn't seated properly and leaked. Would that have caused the lean condition on that cylinder? Or should I be looking for something else?
 
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Exhaust is just that. When the engine is at the point of exhausting, it has already burned the mixture and is through with it. Lean or rich is a function of intake.

Earl
 
Not an expert but I think the exhaust leak would draw air into the pipe. Not sure this would cause a lean mixture though as evidence of the white plug. A blue pipe is a likely result.
 
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renobruce said:
I put on my new Jardine a few weeks ago, and took the bike on a road trip. When I got home, I noticed that pipe #3 had obviously gotten hotter than the rest and had discolored a bit from being lean. I check it's plug and it was white. I took the header off for cleaning, and noticed #2 exhaust port had an extra gasket in it. :oops: So I think maybe pipe #3 wasn't seated properly and leaked. Would that have caused the lean condition on that cylinder? Or should I be looking for something else?
Click to expand...

Hi Bruce. The answer is no. As others have correctly pointed out, your lean condition will be on the intake side (lean carb...dirt or change of adjustment etc) or an actual leak between the carb and head (common enough).

Even on a feedback system (a system using an oxygen sensor.....modern electronic fuel injection.....or some carb systems), an exhaust leak might result in a rich mixture (because the O2 sees the lean exhaust and the computer corrects this input by requesting more fuel). Sometimes it isn't even detected ;)
 
doesnt adding additional exhaust flow cause a lean condition cause there is no backpressure or less pressure on the engine???
 
80GS750 said:
doesnt adding additional exhaust flow cause a lean condition cause there is no backpressure or less pressure on the engine???
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That was my thinking as well. If going from a stock pipe to a header leans things out, why wouldn't an exhaust leak?
 
80GS750 said:
doesnt adding additional exhaust flow cause a lean condition cause there is no backpressure or less pressure on the engine???
Click to expand...

Ditto -- it could cause a lean condition back at the plug if it leaked enough.

The question is, how much was it leaking? It seems to me if it was that bad, it would have been really annoyingly noisy, so I'm thinking an experienced rider/wrench such as RB would have noted and tracked down the exhaust leak within about 5 seconds.

It's very hard to tell, though, how much exhaust leak it would take vs. how noisy and noticeable the leak would be.

Guess you'll just have to fix the leak, change the plugs, and see what happens.
 
However, if your Jardine flows better than the VH, it could lean it out just a tad. You have the jetting set up for the best result with the VH, right? You may have to change it SLIGHTLY for the Jardine.
 
renobruce said:
That was my thinking as well. If going from a stock pipe to a header leans things out, why wouldn't an exhaust leak?
Click to expand...

She's a controversial point for sure!

Your new Jardine may be causing it but not likely, as you should have noticed all your plugs showing leaness, not just #3. Have you done any radical mods to your GS ????
Contrary to what some have said, a chronic exhaust flange leak will change the scavenging efficiency of that pot. Lower back pressure does affect torque and cylinder filling especially at lower rpms. If the leak is that bad, you should hear it under load and experience serious backfiring on decel.
 
Didn't you say you'd just finished a ride over near TOM (Who lives at Sea Level) in really cold & wet temps???

Surely Sea level = Lean, Cold air = lean.....

Just a thought. Maybe that one needs a pilot fuel screw tweek...

Dan :)
 
AHH, back to the jetting game. Have fun Bruce. :-D
If it leaked REALLY bad it would be lean. I would be suprised if you couldn't hear it though.
 
salty_monk said:
Didn't you say you'd just finished a ride over near TOM (Who lives at Sea Level) in really cold & wet temps???

Surely Sea level = Lean, Cold air = lean.....

Just a thought. Maybe that one needs a pilot fuel screw tweek...

Dan :)
Click to expand...

I was thinking that, too. But the plug was white when I got home.

chef1366 said:
AHH, back to the jetting game. Have fun Bruce. :-D
If it leaked REALLY bad it would be lean. I would be suprised if you couldn't hear it though.
Click to expand...

I didn't hear any exhaust leaks. If it was leaking, it wasn't leaking much. Maybe this new pipe does flow better, I don't know. But just to be sure, I put on new carb boots, cleaned the carbs, re-adjusted the floats (they were a little high), and adjusted the valves (a few were getting a little tight). I'll get them back on tonight and do a synch and colortune. Then do some chops.
 
Another factor is that the header pipes and their contact with the head help carry excess heat away from the combustion chamber. This happens through the movement of the exhaust gas itself, hence backpressure and velocity concerns, but also through radiation. When there is a leak the heat in in direct contact with the fins of the head. Extra heat in this area is not a good thing, especially on an air cooled engine.

S.
 
renobruce, sorry to hijack but when you use colortune, does it work consistently? what mods have you done to the ignition system?
 
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