I've got a fuel economy question (yes, I know...it's a bike, who cares?). My 15 Street Glide Special has gotten strange on range and economy--I only noticed due to riding to/from work. On a 75-80 degree day, normal highway riding at 70-75 mph it gets about 44 mpg(per gps). 70-75 degree night, running same speed it's getting 38 mpg on average(per gps). Always start and let it warm up, stock bike other than SVT Boneshakers slip-on exhaust(been on there for about 5-6 years). Fresh 3 hole service, new plugs and air filter at 35k, currently sitting at 37.5k. Not so much bothered by the mileage as much as wondering if there's something wrong with the bike that I'm missing. Display typically shows range being about 225 at fill-up, used to run 250-260. Just curious what the great minds here think or have seen. Sorry if this is posted in wrong place, wasn't sure where to post.

 

If engine is running well, how about checking your fuel filter? They can get glogged and may be part of your problem.

 

sooooooooo many factors
the only way to hone in is to do data logging, looking at short term and long term fuel corrections. the long term will be more insightful, the short term gives an idea of how well the system is working at present point.
an engine responds diff to a lot of things like temp and humidity and such.
for starters, look at O2 sensor data and at dwell times, a lazy sensor will increase fuel usage. next i would look at the map sensor. most newer systems have the map ported into the manifold but if yours is connected via hose, look for leaks.
also do not forget fuel quality and road conditions.
also of note is that GPS is relative just like radar.

 

Change gas stations? Winter to summer/summer to winter fuel blend changes? Just some other things to think sbout

 

That is a valid point that had completely slipped my mind. Just took over doing maintenace myself on the bike (had dealer servicing since I had an ESP--less headache if something happened) and it hadn't occurred to me to go there. I know they have one, and I know the service interval is some insane mileage for a fuel filter, IMO. Thanks!

 

I'm a heavy equipment tech by trade, so I understand your point of so many factors to consider. I know the GPS is just relative, and I have always taken that into account--I'm also one that manually does the math when I fill the tank(do that with everything I own, weird tick) and have noticed slow declines in the past year. Thus the reason I did air filter and plugs at 35k even though plugs were done at 30k. I didn't ride frequently in that timeframe--Covid, kids, life getting in the way---so just wanted to freshen everything up. Just seems to be getting a little worse, so I figured I'd pose the question here and get y'all's input.
Thanks!

 

Always get gas at the same station near the house--$0.30-$0.40 cheaper than the other stations will do that. All national chain truck stops. I suppose depending on when they switch their blends, it's possible--not sure how much they do that in the Carolinas but who knows. Also, as I just told bustert as well, its been slowly falling off for the past year and it's finally gotten to the point that I thought I'd check with the wealth of knowledge here and see what others thought.
Thanks!

 

I run top tier. Hoping of course they added some detergents like they are supposed to. I also each oil change add fuel system cleaner like Lucas or what have you.

 

Top tier, as in high test? That is all mine gets, ever. I've wondered about running fuel system cleaner as it's good for any EFI system, just wasn't sure if it needed to be anyting special. I'm sure the MoCo has their own recommendation.
Thanks!

 

On the riding conditions that give poor economy, gas up and do the math, and make sure it is not something to do with the internal calculator. After awhile I don't trust them. Though odd it is night and day based. Maybe something you are missing, on how you ride night and day. Maybe collect more data to be sure.

Also I am up on how the MAP sensor works, could it be giving different values at night and day, skewing the calculator? Again, I have not idea about the MAP.

Myself, I would collect more data, filling up the tank, and doing the math myself, before I got to worried.