Crappy Gas Mileage

Been averaging about 90 miles to the fuel light for the last month or so.

Havn't had it over 80-90mph, no real hard riding since I've mostly been using it to drive to and from work. Usually keep in the 3000-4000rpm range while cruising, and in a higher gear when possible.

Only thing I've done is a breather reroute, and everything is fine with it.

Plugs, Tire pressure I'd start with

Pressure is good, could be plugs since I haven't changed them in awhile. Will be a weekday project I suppose. Just went and got most of my tools bought today anyways...guess I gotta go buy another socket.

try putting the breather system back to stock

try putting the breather system back to stock

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I cleared 60mpg a number of times on my XB12 with a re-routed breather setup. I truly doubt that's the problem.

O2 or IAT sensor?

I cleared 60mpg a number of times on my XB12 with a re-routed breather setup. I truly doubt that's the problem.

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2 different bikes

I've had the reroute done for about 2 months now, and just in the last 2 weeks is when I noticed a major change in gas mileage. So I'm doubting that's what it is, though I'll play with it.

Had the tail section apart along with the airbox this morning to double check all the connections on the reroute. Everything is connected and setup fine. The filter seems like it's pretty filthy, so I'll probably change it out this week.

Besides that, when the bike is running it almost sounds like it's sucking air somewhere near the top rear of the rear cylinder. Thinking maybe the O2 sensor could have worked loose, and that could be causing it? Or possibly even the header? Not really sure.

Try spraying brake cleaner or similar around where you hear the air "hissing". Sounds like a intake leak to me. If it acts funny, intake leak.

I don't know why I didn't think of this earlier...

The other morning on the way to work I opened the throttle in 2nd to pass a car, hit around 4500rpms, and had the CEL turn on. Pulled over at the gas station about a 1/4 mile down the road, turned the bike off and did a walk around to see if anything was loose.

Found nothing, started bike back up, and havn't had the CEL on since. Just added some oil since it was low the next day.

Also while I had the bike apart today noticed a lot of residue, possibly even carbon buildup, around the right side. On the inside of the tail section, and quite a bit on the inside of the pulley cover.

Probably a loose header than right? Just had them changed about 2 months ago, so maybe it worked loose?

How are you measuring mpg?

You're on a commute with traffic and stop lights on a v-twin?

Wait, opened it up in 2nd?? Well, there's your problem.

Try this, are getting about an hour and a quarter's worth of engine running per tank?

Reset trip meter when I refuel. Check trip meter on the next refuel, and note gallons to fill.

Miles / gallons = mpg

15 mile commute each way. Total of 5 red lights. 2 in the first mile, 2 half way, 1 in the last 1/2 mile. Roughly 13 miles of the trip are highway. About a 20min ride, 30min max. Generally fill up every 3-4 days or so. (2hrs worth of run time on average)

I'm not expecting 80mpg, but I don't think even 45mpg should be out of reach all things considered, especially since I've gotten more than that before.

2 different bikes

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Well, the question was posted in the Firebolt XB12/9 section. I figured my experiance with my XB12R would be pretty relevant [sarcasm].
Just as a side note, I've owned an XB9S as well and it would consistantly get between 50-55mpg on my daily ride and clear 60 on the open road as well. the mielage between differnt XB's is VERY similar in my experiance

To the OP: with that many red lights in that short of a distance, I wouldn't expect more than about 40 from your bike. 45 would be very good for those conditions. Most Japanese sportbikes would be in the mid 30's under similar conditions (in my experiance).
Think of it this way, out of your 20-30min ride you're probably spending about 5-10min sitting at lights getting zero MPG (most lights are 1-3min long ea). Also, red lights and highway are the worst for mileage. You use a lot more fuel getting up to highway speed only to have to stop again in a couple of miles for another red light.

That being said, an air/vacuum leak will definately cause a CEL and poor mileage. Check your hoses closely if your hearing a "sucking sound".
If the O2 came out you have stripped threads and that will be a pain to fix (VERY unlikely though).

If it is any consolation I get anywhere from 65-90 miles before the light comes on. Granted I idle a lot in city traffic and ride 100% stop and go between stop lights with zero freeway riding, but still.

2hrs worth of run time on average

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That's actually pretty good mileage if you were actually getting any miles to measure.

My '03 9R (small tank) might get an hour and a half if I baby it, which doesn't happen.

What's working against you is the short trip, low revs and all the stops.

In order to get a real measurement, you need to get onto a secondary highway so you can cruise at 40-4500 rpm for significant distances. Do a couple of hour long runs and then measure.