Low MPG puzzle

5thMLC

5thMLC

Joined
Jul 2, 2025
Messages
25
Age
69
Location
Oakley, CA
Bike
05 ST1300
Hi everyone, my name is Vic, I have a "new to me" 2005 ST1300, with 90,000 miles on the clock at the time of purchase. Bike starts on a dime, runs strong, well-equipped with mods by PO.
This was right in line with the money I wanted to spend, and I am happy with it, but now comes the usual dilemma: did I get a killer deal at $3000 or a bag of issues that will drive me nuts?
After the 1981 GL 1100, 1983 GL 1200, and 1987 GL 1200 Gold Wings, I wanted something in a similar arrangement, younger, lighter, but just as tough, so I have no regrets.
I changed the oil and oil filter, air filter, and final drive oil. Next, I pulled the plugs out; the color was uniform, dark brown/black, no oily deposits. The display showed 27 MPG average.
So I figured something is out of whack when I read a few posts where other riders are getting upwards of 40 MPG, and my 2004 Toyota Rav4 5-speed manual does better than that.
Plugs I pulled out were NGK CR8EHIX-9 Iridium. I replaced them with a new set of the same P#.
After putting on 500 miles in mixed city/freeway rides display showed a consistent 33.7 MPG, which coincided with manual calculation using 5 gallons of 93 octane gas twice.
There was no noticeable difference in the bike's performance that I could detect.
I then pulled out the plugs and replaced them with OEM CR7EH-9; the display now shows 33.6 MPG, closely repeating rides between city and freeway.
Bike warms up to 3 bars and stays there no matter what, so now I am looking at a set of Iridium plugs I pulled out and see that dark coating is already forming on them.
I am not a mechanic, was a machinist for 40 years, have no in-depth knowledge of fuel combustion specifics, but it seems that, despite flawless performance, the bike is running a rich air/fuel mixture.
So the question here is, how much trouble is it to have that checked and adjusted by a qualified mechanic, assuming my guess is correct.
The alternative is just dishing out more at the pump and disregarding the cost and trouble of correcting it.
My rides are mostly around town, with about 1/3 freeway riding. Am I way off target on MPG, or is this acceptable for mostly city riding?
 

Attachments

  • red.jpg
    red.jpg
    144.4 KB · Views: 11
Welcome to the forum from Coquitlam BC Nice color.
I would read up on some of the articles here about what to look at when you first buy one of these bikes you could also post a pic of the plugs
There's a lot to these bikes just to dismantle / reassemble the components to reach critical parts for inspection and evaluation which not every mechanic will be familiar or proficient in doing
If you see an invitation to call a white courtesy phone would be your best place to start
 
I doubt plugs are the problem. As @billow suggested, what's the temp gage on the bike show? You should get 1 bar in a minute or so of idling (from a cold start) and 3 bars w/in a couple of miles of riding, or maybe another 4 min of idling. There are a number of threads on low mileage, you might do a search (blue band atop this page, right end) for that.

This article won't address your problem, but might help you prevent other problems. I'd suggest a full fluid change with your used bike purchase and pay special attention to a full brake flush with new DOT4 juice.

You can also hover your cursor over @Igofar's name, click on start conversation, and send him a private message asking for help. Give him your phone number and he'll call you back when he has time.

Article - Maintenance Items Needed for a New (old) Bike | Articles

This article is the result of collaboration by Andrew Shadow, CYYJ, jfheath, Max Pete, SMSW, and SupraSabre. Igofar’s list was copied from the first link listed above. Click on the attached file. This one is V.11; in the future, any changes will be noted in the title on the first page as the...
www.st-owners.com www.st-owners.com
 
Vic,

Poor fuel mileage can be the result of brake drag. I can attest, as I own an '05 myself, that rear brake drag is often caused by a malfunctioning secondary master cylinder. The SMC is part of the left, front brake caliper. When functioning normally, the linked braking system on the ST13 is fantastic. However, the SMC is one the bike's week points.

While I don't want to alarm you, a malfunctioning SMC could cause the rear wheel to lockup. If your SMC is not functioning properly, the recommended fix is replace the whole unit. I can attest that rebuilding the SMC will fix the problem for a while, but the malfunction will resume fairly quickly. Replacing the whole unit will solve the problem. That, and correctly bleeding the linked brake system is about the only way to ensure your SMC remains in good working order.

Welcome to the forum, and good luck with your diagnosis.

Chris
 
My experience agrees that's too low, as my non-old-man riding style typically returns 41mpg, or 38mpg if pulling a trailer.
Also agree that Larry / @Igofar , or John / @aniwack are your best bets to run this down, and run your mpg up.
EDIT: also concur with @Buckeyechris but if thats the case, your rear disc will be hot to the touch after a short ride. After a medium ride, the rear rotor will be too hot to touch.
That's easy to determine.
For a better idea, had your bike sat for months or years before you brought it home?
 
Thanks all for the quick replies. I'll try to filter out a few things to start with. The PO rode the bike as a commuter and in parking lot practice sessions.
He installed aftermarket fork springs and rear suspension, LED lights all around, a Sargent seat, front and back cameras, GPS, and new tires before sale. It seems he took real good care of it.
I had it sit in storage for about a month while working on regaining my M1 license that was lost after 15 years of not riding.
Initially, I managed to do some maintenance in 5' x 9' storage unit as mentioned before, only after riding for a while, I started paying attention to the digital display regarding fuel consumption.
Because nothing jumped at me as "defective," I just went through a few 2-hour rides a week before looking into it.
As always, I am prone to do something stupid even in the midst of trying to do the right thing, so I trashed old plugs after a few days of comparing them to online pictures of diagnostics.
All I can say now is they were all uniformly dark brown or black in spots, with no physical damage to electrodes and no clue as to how long they were in.

So far, both wheels are spinning freely while on the center stand, rotors show some wear but no gouging, the master cylinder window of the clutch and brake reservoirs show clear fluid.
Braking is buttery smooth, pads look good, recently installed.
As for temperature, I missed any sign of a gradual warm-up progress, so I'll pay attention to that on the next ride.
I read comments about "excessive heat" being produced by ST1300 in a few threads. I ride mostly in the morning hours when the temperature is around 70 degrees, by the time it goes to 80 and over, I am back home wiping smiles off of my face near AC.
I have no evidence of excessive heat on my legs, as some have complained about. Is that a good thing or a sign of trouble?

Looking back on all responses, I realise there may be an issue with a few things that I am not equipped to deal with due to a lack of space and expertise. I've done some routine work, but anything requiring the removal of fairing is out for me; time to see the local shop and get the estimate on the overhaul of critical systems.
I was looking for some thrill, a test of "do I still have it," perhaps, at the age of almost 69, I have no complaints, but I don't need a can of warms either, especially if a snake is hidden within.

Going to test the time it takes to reach 3 bars on the temperature gauge and report back later.
 
I experienced low fuel mileage when I first got my 2005 ST1300. At the time it was 10 years old with 61k miles. It turned out to be a stuck thermostat which is fairly common for the ST1300. It might be worth your while to get the factory service manual and learn how to work on the bike. It's not that big of a job if you remove the radiator and go in from the front. Not many shops are familiar with this bike, and many won't work on bikes that old. Plus you'll save a lot of money :thumb:
 
Dragging brakes, defective thermostat, and plugged or partially plugged 5-way TEE vacuum hoses are the most common causes of high fuel consumption next to the most obvious, which is an overactive throttle hand.

Black spots on the spark plugs is an indication of a rich mixture.
Do not neglect checking to see if there are any fault codes stored in the computer as they can give an indication of a cause.

See below for how to check for codes and for how to clear them, as well as a list of fault codes and their descriptions.
ECM Check and Reset Quick Guide
ECM Fault Codes
 
In order to get the correct mpg I reset the trip when I fill the tank. The other thing to do is fill the tank, reset the trip and do the math to see if the mpg readout is correct.
 
ASPC said:
In order to get the correct mpg I reset the trip when I fill the tank. The other thing to do is fill the tank, reset the trip and do the math to see if the mpg readout is correct
Click to expand...
Always the best place to start, it can be a tough job to fix. If it isn't broken. The mileage figures that I hear are all probably accurate I am sure.
I know my mileage isn't that great and I have myself to blame. I tend to use the throttle more than I should. I am a bad man!
 
Back from a short ride, and here is what I learned:
Bike on the center stand, used the left hand to lift the front wheel off the ground by the fender, then span the wheel with my right hand.
It made about 3/4 of a turn and stopped.
Using my right foot, I spun the rear wheel and observed about the same 3/4 of a turn.
Not what I would call free spinning if bearings are good and breaks are not binding, but there were no weird noises like clicking or scraping.

Started the bike and stopwatch on phone, took 2 minutes and 18 seconds for the first bar to appear on the gauge.
3 minutes and 15 seconds for the second bar to appear, and darn close to 5 minutes for the third bar to appear on the gauge, conclusion ...... CRAP.

Went for a ride around town, did normal traffic stuff, then went to an empty parking lot, did some low-speed maneuvering while dragging the rear brake, not sure if it also drags the front
due to being a linked system.
Sped up to 50 MPH and applied hard progressive braking and repeated the same one more time.

Stopped at the pump to top off the tank and rode back home, put the bike on the center stand, and repeated the wheel spinning test.
This time, each wheel rolled about half a turn and stopped; there was a hint of hissing noise that I didn't observe on the cold bike test.
Operatively, there is some brake dragging as the rotors heat up.
All rotors were hot to the touch but not so hot as to cause a burn.

Soooo, no more freeway rides until there is a resolution to these issues. I have a factory service manual, but the problem is I don't have space to work in, which leaves the local shop as an option.
Time to make a phone call and see what can be done and at what cost.
 
ASPC said:
In order to get the correct mpg I reset the trip when I fill the tank. The other thing to do is fill the tank, reset the trip and do the math to see if the mpg readout is correct.
Click to expand...

On my 2012, resetting the trip meter is not resetting the AVG MPG.

Even after resetting the trip meter, I was getting AVG not matching calculated actual until resetting AVG......don't remember the procedure though, but it also involved holding a button down for over 2 sec.

Looks like AVG is based on a fairly long MPG history (in my case, included a PO who had never changed his Air Filter...!). May be a good idea to reset AVG from time to time, to get a better picture of the current ST health.
 
MidLife said:
On my 2012, resetting the trip meter is not resetting the AVG MPG.

Even after resetting the trip meter, I was getting AVG not matching calculated actual until resetting AVG......don't remember the procedure though, but it also involved holding a button down for over 2 sec.

Looks like AVG is based on a fairly long MPG history (in my case, included a PO who had never changed his Air Filter...!). May be a good idea to reset AVG from time to time, to get a better picture of the current ST health.
Click to expand...

I thought holding the button for the 2 seconds was resetting everything, which is what I do. I didn’t know you could just reset the trip on its own.
 
5thMLC said:
Back from a short ride, and here is what I learned:
Bike on the center stand, used the left hand to lift the front wheel off the ground by the fender, then span the wheel with my right hand.
It made about 3/4 of a turn and stopped.
Using my right foot, I spun the rear wheel and observed about the same 3/4 of a turn.
Not what I would call free spinning if bearings are good and breaks are not binding, but there were no weird noises like clicking or scraping.

Started the bike and stopwatch on phone, took 2 minutes and 18 seconds for the first bar to appear on the gauge.
3 minutes and 15 seconds for the second bar to appear, and darn close to 5 minutes for the third bar to appear on the gauge, conclusion ...... CRAP.

Went for a ride around town, did normal traffic stuff, then went to an empty parking lot, did some low-speed maneuvering while dragging the rear brake, not sure if it also drags the front
due to being a linked system.
Sped up to 50 MPH and applied hard progressive braking and repeated the same one more time.

Stopped at the pump to top off the tank and rode back home, put the bike on the center stand, and repeated the wheel spinning test.
This time, each wheel rolled about half a turn and stopped; there was a hint of hissing noise that I didn't observe on the cold bike test.
Operatively, there is some brake dragging as the rotors heat up.
All rotors were hot to the touch but not so hot as to cause a burn.

Soooo, no more freeway rides until there is a resolution to these issues. I have a factory service manual, but the problem is I don't have space to work in, which leaves the local shop as an option.
Time to make a phone call and see what can be done and at what cost.
Click to expand...

I got a better idea….
Call me on the white courtesy phone (free)
And I can explain to you how to check/inspect/test things.
The shop will charge an hourly rate which is in the triple digits, and more than likely their guys won’t have a clue how to work on it.
And most shops won’t work on a bike over ten years old.
I’m on the RAN list under Arizona.
 
There are a LOT of complaints in other threads about Honda Dealers and even independent shops providing poor to awful service on these bikes. Fact: These bikes are very reliable when serviced according to Honda's suggested preventative maintenance. Fact: Comparatively few were sold in the USA. Fact: It will take any mechanic some time to get up to speed servicing any model bike - if he gets to work on a number of them. My first two listed 'facts' mean that few service techs have seen many of these bikes, and the last means that experienced techs are few and far between. I too was screwed by my local Honda dealer, and their chief mechanic had no idea about proper troubleshooting procedures but preferred to shoot from the hip. That cost me $650. (I did agree to him trying to fix the problem.)

When I last visited California (c. 50+ yrs ago), I found a work-on-your-car-yourself shop that rented bays by the hour/day. Here in Cleveland, we have the Skidmark Garage. Google it, they rent space with more tools* than you can imagine for bikes by the day, week, or month. Surely Skidmark does not have a lock on the idea of you-rent-it-shop-space and maybe you can find something similar near you.

When I had a real problem w/ my 1300, a friend in MGNOC suggested a guy named Kevin. This mechanic serviced mostly Harleys, but he owned and had fixed up his Goldwing. I took my ST to him with the manual. He later told me he read the appropriate chapters the night before servicing my bike. Kevin also went over my machine w/ a stethoscope while I was there to pinpoint the noise. Long story short, he was a very good mechanic and was willing to learn...and his prices were very reasonable. This guy cannot be the only one out there. You just have to find yours.

Paying someone to work on an old ST (all of them are old now) is going to be expensive at best and very disappointing and expensive at worst.

*In addition to ratchets and the usual hand tools, tire machine, vapor blasting, sand blasting, spray paint area, welding (Tig, Mig, Stick), even a milling machine and a lathe, etc. The environs are not spiffy, and some individual spaces are immaculate and others look like the guy's philosophy is when the dirt gets thick enough it will fall off of its own accord. Some guys even rent space to store bikes that look like they have been there for years.
 
You must log in or register to reply here.
Back
Top Bottom