Might be the PAIR? Passing air in route is out the exhaust port. That means the unspent gas is reignited with fresh air sent via the PAIR system... if manifold means like a car's exhaust manifold?
That's a header pipe in bike nomenclature. It goes; exhaust headers are the first set of pipes out of the cylinder head. The middle part is where all 4 pipes run into a 'collector.' The pipe out to muffler is the next section, then the muffler itself. Or, say the pipe and muffler are one; so then you are down to 3 parts of the exhaust system.
That's where you have a few choices is the PAIR system.
1. You can let it ride and no harm no foul.
2. You can just disconnect the sensor that has the two hoses in the middle of the top cam cover. This throws a code, but who cares.
3. You can remove everything and buy some cap off aftermarket part to close the top cam cover inlets.
4. You can keep the OE top cam cover L pipe in place and find a rubber plug and cover over the hose diameter nipple end. Cork it with a zip-tie.
Back to... leave it alone until inspection. Then decide. The quick and dirty is to run the pipe and feel it out. Then reach in there, disconnect the sensor, ride it again and that's the difference seat of the pants, take your pick.
Say the air to fuel ratio (AFR) w/PAIR is 16.5a. Once that goes thru the cat, that's even more spent and out the pipe is more plain old oxygen [ideal AFR] we can breath. But there are parts of other gases not breathable, etc.
So if no PAIR, the real AFR number is about 14.1a. That's a number some NASCAR tuner used for his race engines.
Therefore, the lower the AFR number, the richer the fuel in ratio. And that is the PRE number all day long. That says rich on the overlap [reversion], not sucking back in 16a say.
... for every action, there is an opposite and equal pulse me back and forth, some spent, some unspent, some money not spent on the richer [more for performance] tune up.
And I do not recall [the name but] someone asked if it was OK to just run the header only. I said go ahead. Maybe he came back months later and said it was just too loud. Not one word of; HUB you shit-0-piece of shit my bike is in. It's all burnt to a crisp... FU turtle. Just it being too neighborly noisy was all he wrote.
Signed,
So how did that PRE work out for you?
By doing that, you have a little unspent back into the cylinder, and this will richen up the bike a little this way. Have to remember what I call the 'PRE'... which means, all sensor input has been 'predetermined' and is clueless to the exhaust reversion as who cares... Pre calls the ball and you don't need to mess with this so as to add piggy/flash/etc.
It's not more air going in the engine if say we remove the air cleaner. The vac sensor still reads said vacuum for said condition, as if it will hurt the engine, no. The air speed just stepped up the speed of the same air being sucked in, not more air, no. Just a faster event is how you have to think of the air, the pre being the stock setting; as if you changed the vac signal, no.
Make sense?
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