Severe MPG Drop-off

[RodPlunger]

Hi All,
'99 R1100S ABS 52K, Remus Exhaust, No Cat, Booster Plug, 35 mile commute daily...

I recently did my 48k tune up. I replaced the spark plugs, fuel filter, oil filter and air filter. I had adjusted my valves a little while before hand. I have not balanced my carbs, as I don't have the right tool. So, as the post title suggests, I have experienced severe mileage drop-off. My mpg has gone from 36 to an unbearable 30mpg. This needs to be remedied. I have read through other posts regarding mpg, but am not entirely sure where to start. I have a Remus exhaust system, no cat, and a booster plug connected to the bike. (All of which was done by a previous owner.) During the tune up, I replaced the K/N air filter with a Mahle paper air filter, as I didn't have the time to clean, dry, replace the K/N. Otherwise, everything went back to being the same as before the tune up. So, what could be causing the 20% fall in gas mileage? What have I not done? I have not "reset" or "remapped" the Mototronic computer, because I guess I don't quite know how. But, would this cause that big of a drop? I have been riding with this for over a month, so I would guess it has had enough time to correct itself? Could the breather tubes for the tank be pinched, and would that change mpg? I could see how it would create a potential vacuum in the tank (seen before on my R1100RS) but...? Wrong plugs?

Any suggestions would be great. I love the bike, but hate the MPG. I owned a '99 RS for a long time, and never got below 42 MPG riding two up and fully loaded. However, that bike was fully stock. I was just hoping for something close with the S, as you are already short with the smaller tank... Below are the parts used bought as a kit from Beemer Boneyard. Thanks Y'all...

[2wheelmike]

Have you looked for an exhaust leak that might throw off the O2 sensor? A buddy had a K1200 that suffered from this problem. Exhaust had a leak that burned through the clutch line (which is why he discovered the leak). Fixing the leak solved his poor mileage.

[2BGJGZ]

How about a vacuum leak. Another possibility might be a suck or dirty injector with a bad spray or leaking. What do plugs look like after a good hard run?

[RodPlunger]

Originally Posted by 2wheelmike

Have you looked for an exhaust leak that might throw off the O2 sensor? A buddy had a K1200 that suffered from this problem. Exhaust had a leak that burned through the clutch line (which is why he discovered the leak). Fixing the leak solved his poor mileage.

Do you have a trick for finding it?

What do plugs look like after a good hard run?

I'll pull them tomorrow...

[brentw1]

check the air temp sensor

[Chris Canning]

Originally Posted by brentw1

check the air temp sensor

On the fuelling spoofer.

[RodPlunger]

Originally Posted by Chris Canning

On the fuelling spoofer.

Any idea on how to check it?

[Chris Canning]

As I’ve no idea if you understand how these fuel spoofers work,but I’ll start at the beginning.

When you change exhuasts air filter etc you end up with an imbalance between air and fuel,these 1100s’s are Stone Age the only way to alter fuelling is either with a chip or third party add on the normal route is a Power Commander so you can add or take fuel out of the map depending on what it needs.

The problem they ain’t cheap so there’s been surge in after market fuel spoofers that lash extra fuel in regardless and they work on the basis that you will notice the extra fuel in the places you need it rather than extra fuel where you don’t.

These spoofers fool the ECU into thinking the air temp is lower that it so the ECU puts more fuel in to go with the extra air,some where on you spoofer their will be an air temp lead??? Where is it have you move it??.

But if your looking for a quick fix and a bit of a learning curve about what they do just unplug it,I rode my 1100s with Lennies/SJ/open exhaust for 4 years without any 3rd party fuelling mod.

[N41EF]

Did you unplug the air temperature sensor when you replaced the air filter? And plug it back in?

[RodPlunger]

Originally Posted by N41EF

Did you unplug the air temperature sensor when you replaced the air filter? And plug it back in?

No. I didn't... Are you referring to the booster plug air temp sensor? Do I do this with key on? Thanks

[RodPlunger]

Originally Posted by Chris Canning

As I’ve no idea if you understand how these fuel spoofers work,but I’ll start at the beginning.

When you change exhuasts air filter etc you end up with an imbalance between air and fuel,these 1100s’s are Stone Age the only way to alter fuelling is either with a chip or third party add on the normal route is a Power Commander so you can add or take fuel out of the map depending on what it needs.

The problem they ain’t cheap so there’s been surge in after market fuel spoofers that lash extra fuel in regardless and they work on the basis that you will notice the extra fuel in the places you need it rather than extra fuel where you don’t.

These spoofers fool the ECU into thinking the air temp is lower that it so the ECU puts more fuel in to go with the extra air,some where on you spoofer their will be an air temp lead??? Where is it have you move it??.

But if your looking for a quick fix and a bit of a learning curve about what they do just unplug it,I rode my 1100s with Lennies/SJ/open exhaust for 4 years without any 3rd party fuelling mod.

Thanks. I do know how they work... I guess, all things being equal, I'm looking for what would be a quick fix. Not necessarily a part breaking at the exact time I am doing my tune up. It just seems too coincidental. I feel like I might have missed a step. But, I'm definitely going to check the exhaust for leaks as that might explain the 36 mpg I've been getting since I bought the bike.

[Chris Canning]

You have to go back to basics,you need to buy a device for balancing the injectors and disconnect the spoofer and go ride the bike.

[N41EF]

The air temp sensor is under the seat just behind where the air goes down into the air filter. You said you replaced the filter, and depending on wiring you might of unplugged it for access. Just take a peak and make sure it's plugged in. Its a two wire connector that is straight up and down with a wire loop to press in to disconnect.

[RodPlunger]

Minor UPDATE: So, last night I finally got around to replacing the air filter with the K&N. Which, if someone has a way to remove the tank before the snorkel or the snorkel before the tank, I'm all ears, but that's another post?... Anyway, as I looked into syncing the throttle bodies, I found that my left side "vacuum nipple" was missing the rubber cap. I have ordered the part, but put a clamped rubber tubing over it to seal it off in the mean time. On my ride into work, the bike immediately felt more stable at 4k RPM with considerable less surging. I will run through a full tank of gas by the end of the week and get to see if there has been any improvement in gas consumption... But, can anyone tell me empirically what not having a cap on the vacuum tube would do? Seems to me it's been sucking air for God knows how long. Thanks...