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Old 04-26-2010, 11:01 AM   #15
The Griz
North Forest Rider
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Joined: Nov 2008
Location: Minnesota
Oddometer: 3,787
Originally Posted by MookieBlaylock
if you open up the intake and exhaust you will need more fuel also, so you will take a mpg hit. I am really surprised there are no tuning options for this motor.
Sorry, man, this simply is not the case. I've rejetted two KLR650's that I was running UNI air filters and Two Brothers exhaust on. If you open up air intake and open up exhaust flow without increasing fuel intake then you'll be running extremely lean: loss of power, overheating, pop-pop-pop, etc.... Now, if you open up air intake, open up exhaust flow, and also increase fuel intake to match, then what you've effectively done is improved power AND fuel economy. The engine will only burn what you provide it or allow it to have. It's not like we're forcing or pushing more air into the cylinder, rather allowing more air to come in. If you're allowing too much air to come in and not enough fuel: LEAN. If you're allowing too much fuel to come in and not enough air: RICH. If you're providing the correct mixture of air and fuel to the cylinder: IT WILL RUN PERFECT - regardless of exhausts and air filter. As long as the mixture is at the stoichiometric ratio of 14.7:1. The engine will only burn what you allow it or provide it. On both of my KLR650's, after I properly tuned the fuel air mixture to match what the cylinder needed, I noticed improved power and throttle response while maintaining the highest fuel economy, if not improving that as well.

Now, regarding the F800GS. I am running a UNI USA air filter and Leo Vince carbon exhaust. I am only assuming that the engine management computer increased the amount of fuel being injected into the mixture in order to compensate, but who knows? There is no hard evidence that the computer on this bike will do this. I do know that I'm pop-pop-popping down the road, which indicates a lean condition. This is due to the increased heat build-up in the exhaust system that the lean condition creates. This increased heat in the exhaust manifold causes some of the gases in there to ignite: POP POP!

The Griz screwed with this post 04-26-2010 at 11:18 AM
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