Fuel/Air management systems

[Adirondack Bill]

Just wanted to get some opinions on when you need to get an air/fuel  controller when doing modifications. I know that whenever you open up your Air-box or change your exhaust to a more free flowing system, you need to think about  the possibility of some type of fuel modulator.  In the past, if I just opened up the air box via a different set-up or a better flowing filter, it was not necessary to fool around with your air/fuel mixture- am I correct??  However, if you open up both the intake and exhaust, you would need a fuel modulator correct??  Our options are very limited with our Valks, but I have a scrambler I am  playing around with. Please forgive me as this is not a Valkyrie modication, but I greatly value your opinions.

[Bill Havins]

Bill,

Oh boy, have you opened a can of worms!  I will share the very short version of my opinion with you.  If you want to tinker with air intake -> exhaust you really need a way of measuring the effect of what you do.  Too much air through the system and things lean out very rapidly, causing all kinds of "rideability" issues, deceleration popping/backfiring, and potential damage to the engine.  On the other side, too much fuel in the system and you get incomplete combustion AND (this is what often gets overlooked) overheating of the engine and gas in the oil (which quickly ruins your main bearings).

I have always used a fuel/air monitor when tuning engines of the modern era.  Just before I bought my Valkyrie I bought an Innovate LM-2 to tune my Moto Guzzi (http://www.innovatemotorsports.com/products/lm1.php).  These systems are often used by race crews to "tweak" air/fuel mixtures to match weather and track conditions, etc.  It is in perfect condition (about ten hours of use).  I'd be glad to sell it if you decide you want to do some serious tuning.

On Moto Guzzis the O2 Sensor is active in the lower RPM range.  It is not part of the MAP at "cruising" speeds (appx. 3000 RPM and up).  I think I'm remembering that right - lots of water under the bridge.

But back to your question.  "Closed loop" systems (ECU adjusts Air/Fuel Mixture based on O2 Sensor input) can handle some increase of air input, but not too much.  They can also manage a change in the exhaust, if the back pressure from the exhaust is not altered significantly.  But, when you change either a great deal, or when you change both, you are liable to overwhelm the Air/Fuel "MAP" in the ECU - it just doesn't accommodate the dramatic change.  Then you have to "re-MAP" your ECU or run the potential of damaging engine parts. HD riders are notorious for doing such things and then wonder why their scooters run so poorly.

If your scrambler has carburetors you're in luck.  They can be easily re-jetted to accommodate the changed air intake/exhaust.  If it has an ECU then you are likely to need a re-MAP.

Hope this helps a bit.  If you pursue things be sure to get an air/fuel meter of some sort so you can tell what is really going on.

Good luck!

Bill

[bscrive]

I changed the exhaust on my bike and had no issues.  I put on a Rush exhaust with Torq Loopz.   They sound awesome together, I must say.  The computer will compensate quite a bit.  I did follow the instructions I found on the F6B site to set up the computer.  It was real easy and the bike does run better IMO.
There are no other sensors on the exhaust, other than the O2 sensors

Sorry, I can't help you with the Scrambler.   

[Robert]

The assumption here is the mod is for the Scrambler and if you would be so kind as to tell the model and if it has carbs or fuel injection and is it air cooled, it would go a long way to a proper answer. I tried to look on line and found some but didnt know if it was the bike you are referring to.

Our bikes (the 1800) does not need any sort of compensation since the O2 sensor that is before the cat would more than likely be able to compensate since the maps on the factory fuel injection should allow enough variance to compensate. If there was a problem you would get a check engine light that would tell you the system is not able to compensate for the mods. In that case you could correct the system in a few ways. As mods go the more I look into our Valks the more I see a very balanced system that would be a bit hard to get more out of.

As for general carb rule of thumb while 98 is correct about the gas analyzer being the best check there is a way for a simpler check. Its also understood that any newer motorcycle will run in the lean range to accommodate newer pollution standards, so any form of enriching the system should add some seat of the pants feeling to the positive.

Part of the problem with the 1500 as an example is the air box is calibrated into the system to richen it on full acceleration. At a certain point there is a vacuum in the air box that draws more gas out of the carb into the engine. To design this into a system is pretty amazing  and a example of why its not so cut and dry to determine the correct mixture. The old rules still apply if there is a flat spot you more than likely need more fuel if the bike feels free and easy and accelerates smoothly and without hesitation then its probably ok. If the plugs on a normal run come out white its lean they really should be a light tan.

Go ahead and do the mods look on line for others who have done some mods and see what they have to say and proceed from there. I dont know if its air cooled either in that case it would need to be a bit richer since if it runs lean it can run hotter and destroy the cylinders.

Just as a bit of information the newer designed O2 sensors are digital and can compensate for fuel mixture extremely quickly and sample extremely fast and back pressure does not seem to effect them that much. I have run cars with the exhaust off and still not had a problem with the fuel mixtures.

[Bill Havins]

I hope I didn't introduce confusion into this topic by using the term "back pressure" as a type of shorthand.  My use of the term referred to errors I have seen people make, including "oversizing" an exhaust system too close to the exhaust port(s) of the engine head(s).  When this is done, exhaust "pulses" fail to develop, and combustion gases are not efficiently expelled from the engine.  This leads to poor running and can sometimes lead to overheating of the exhaust port and valve (or worse).

So, my reference to "back pressure" was a caution against making the exhaust system too large and, additionally, too close to the exhaust port.  Hope that makes sense.

Bill

[Robert]

Its ok Bill we Forgive you 

[Adirondack Bill]

Robert, the scrambler I am referring to is a 2017  Yamaha SCR 950. It is air cooled and fuel injected. I bought it new last fall as I missed riding in the dirt. It is basically a somewhat stripped down Yamaha Star C-spec. It is a V-twin with an external air filter completely enclosed in an air box. I could tell the bike was crying for air, so I purchased a  Cobra  exposed air filter to try out in the spring.  I feel that just allowing the engine to breath a little easier would not require any fuel mapping changes since I am leaving the exhaust alone. I just don't want it to be running too lean. What do you think?

[bscrive]

Bill, If the bike is fuel injected then the computer will compensate. 
Just start the bike and let it idle for 10 mins. then turn it off.  Do that again and turn it off.  Then take the bike for a 20 min ride and the computer will have compensated for the new exhaust.  More than likely it is the same if the breather is changed.  This is what I did with my bike.
The other thing you can do is disconnect the battery to put the values to base numbers and just ride the bike for 30 mins to reprogram the computer.

[Robert]

Wow nice bike someone has themselves a new toy 

The bike has a catalytic converter that is built into the muffler and an O2 sensor so there is not a problem with just changing the air filter. I would think that you would want to change the exhaust sometime maybe after the warranty expires and also put on a power commander. Just looking around the internet at the bike and Vance and Hines makes a loud but cool exhaust that makes it sound like the old school scramblers and removes the cat. Even if you do this I doubt you would need to do anything about fuel mixture either. But the power commander is not even expensive for the bike and it would more than likely make it just a bit more fun to ride. Same idea as our Valks but not like the Valk in price that is at around 550.00 compared to around 200.00 for the Yamaha.


Seems like a perfect bike for your area since you could do some off roading or dirt road exploring.
There is alot of accessories for the bike and its a cool looking bike and got some really great reviews, enjoy.

[Adirondack Bill]

Thanks for the input guys. You have confirmed my thoughts on this issue. I appreciate  you taking the time to  chime in  on my questions.