Opening the exhaust side of things richens. Opening the intake side leans.

[Shuriken]

"Opening the exhaust side of things richens. Opening the intake side leans."

I picked up that comment from another bike forum. Anyone care to discuss this?

[jjwaller]

I assume we're talking carbs right?
As pertaining to idle mixture or air screws.
Older Keihin carbs for instance had Air screws which are located on the airbox side of the carbs. Opening them leaned the mixture. On later carbs and our Mikunis, the Idle mixture screw is on the engine side of the carb and opening it richens the mixture.
That help?

[trbig]

I can only assume that by opening up the exhaust... say taking out baffles or something... would allow easier/ more air/fuel flow. You haven't changed the MIX of air and fuel going in, but maybe it's letting a bit more of this mix in since there is less restriction trying to get it out. (Okay... this is just a guess? lol.

As for opening up the intake, anything you do to increase air flow without also changing/increasing fuel flow will lean it out.

This is my guess.

Next??


Tod

[81xsproject]

I would also vote that it is referring to idle mixture screws also. Some of the old Mikuni VM26's had idle air mixture screws.

[Shuriken]

That answer was given in response to an exhaust question.

I thought if you improve airflow on an exhaust, you -lean- out the mix. Remove a baffle and you increase airflow and volume and decrease back pressure, right? Cut off a muffler and run your bike with straight pipes and it pops and backfires, a sign of a lean condition?

[skids]

It can be more that that, Ben. If the pressure pulse is not broken by a baffle, it will reflect when it reaches the end of the pipe. As it returns to the head, it can arrive just as the next pulse is trying to exhaust. This is the reverse of "exhaust scavenging" and there is no carb adjustment that will cure that! It will happen in certain rpm bands...

Originally posted by ae7f
Cut off a muffler and run your bike with straight pipes and it pops and backfires, a sign of a lean condition?

[Shuriken]

Right.

So I have a set of mufflers for another bike and the baffle end plate has been removed and drilled. Then I was told using those mufflers would richen the mix.

I thought they would have leaned the mix, like going to a 4-1 system from a 4-2.

[TADracer]

Characteristics of a well tuned exhaust system will take advantage of the intake/exhaust valve overlap event and help draw more fuel/air mixture into the cylinder. If nothing else is touched then a condition (usually) more on the lean side may show up. It is all a balancing act and making one change will usually affect something else down the line. So I think it is not easy to just say doing X will result in condition Y.

You must consider all items between air intake and exhaust tip before making any change (especially one that cannot be reversed). That is why you hear so much of guys that say things like, I put on these headers and my motor runs like C$#p. It probably is not the headers but it is the imbalance caused by installing the headers and not adjusting the other things up the line. Simple as that.

[skids]

It may LOOK like it is running too rich at certain rpms because the exhaust gases are not expelled like they should. A set of plugs that have been installed for a while might look strange with both glazing on the porcelin and carbon on the ring that could occur at slower speeds. Those are my experiences with crummy mufflers, YMMV.

Originally posted by ae7f
Right.

So I have a set of mufflers for another bike and the baffle end plate has been removed and drilled. Then I was told using those mufflers would richen the mix.

[Shuriken]

Well, I should state that I do not plan to use these "modified" mufflers, I was just wondering what would be the result if I did. I believe exhaust systems are designed by engineers who know a heck of a lot more than I do and I would rather start tuning an engine with a non-molested exhaust.