Poor mileage

[copeina]

Hi folks,

Been lurking on here for a few years and gotten a pile of support by reading, reading, reading. Love my bike!

Ran into a situation late last fall where my mileage suddenly dropped from 500+ km/tank to dry at 405km. Any suggestions are most welcomed!

2002 ST1100 no ABS. Purchased late 2019 with 52000km on it. Averaged 4.8L/100km or 49 US MPG or better. At 77000km on the odometer, I very suddenly started getting 6.0L/100km or 39 US MPG.

At 76000km last fall

• Fuel shutoff thing removed because it left me stranded on the highway. Easy fix to get home, and vacuum line now properly sealed.
• New fuel filter.
• K&N Filter cleaned and re-oiled.
• Coolant flush.

At 80000km this spring (yes, I rode all Winter, just not as much)

• Needles changed from 120's to 118's.
• Carbs balanced. One was way off.
• Valves checked. No adjustments required.
• New plugs, just because.
• K&N Filter cleaned again, very lightly oiled.
• New tires. Bridgestone T31's
• New front wheel bearing, just because.

• Performance hasn't changed at all, riding style hasn't changed at all.
• Mostly long distance at legal(ish) highway speeds.
• Tire pressures always 36/42.
• No puddles or obvious fuel issues when I park.
• Took it up over 200km/hr the other day to see if there was a power drop, and it was flawless right up to redline in 5th, so probably not an airflow issue.
• I almost always run 91 octane, and am not loyal to any specific station, so bad gas is probably ruled out.

The extra fuel cost is secondary to the lost range. I really don't like having to think about gas stations at 300km!!

Thanks very much for all your help, past, present and future!
/Kris

 

[Uncle Phil]

Brakes dragging perhaps?

 

[Al st1100]

49 is a bit high but fuel is always being blended differently. Summer, winter, city and rural all make a difference how it's blended (at least here in the US) seehttps://www.fuelly.com/motorcycle/honda/st1100

 

[dwalby]

check the right rear spark plug for fouling, and while you're at it, check them all.

the right rear is the cylinder that draws the vacuum for the fuel shutoff valve you removed. If the diaphragm got a tear or hole in it, that allows raw fuel to enter that cylinder and run rich, resulting in a fouled plug. I wouldn't expect it to drop your fuel economy by that much though, but give it a look anyway.

 

[copeina]

check the right rear spark plug for fouling, and while you're at it, check them all.

the right rear is the cylinder that draws the vacuum for the fuel shutoff valve you removed. If the diaphragm got a tear or hole in it, that allows raw fuel to enter that cylinder and run rich, resulting in a fouled plug. I wouldn't expect it to drop your fuel economy by that much though, but give it a look anyway.

Forgot to mention - "changed the plugs" this spring as well. Strongly suspect that's why one carb was way out when the shop balanced them.

Thanks!

 

[dwalby]

why did you change the needles, was that after the fuel consumption went up, or might that be a contributor?

 

[copeina]

why did you change the needles, was that after the fuel consumption went up, or might that be a contributor?

Changed the needles this spring after about 3000km of increased consumption. 2000km later, no improvement unfortunately. Power band changed a little though. Still not sold on that so may swap back.

/Kris

 

[kiltman]

I blame mine on winter fuel. Here are my stats. Premium Shell was the fuel when I put the bike away in November...look at my March stats, that the fuel from November....then it slowly gets better after a few fill ups. That has been the case with each of the previous STs I’ve owned.

 

[copeina]

Thanks folks. Dug in and stripped off the plastics tonight, and did the carb cleaner test for vacuum leaks. Seems like there may be an issue on cylinder 2 (left front), so I will try to get in there and inspect the boot or whatever goodness is hiding under there. Hopefully it won't need an intake gasket.

I'll post more with what I find. Thanks again!
/Kris

 

[kiltman]

Also if you heat the intake rubbers with a hair dryer, the carbs will be easier to insert along with the rubber friendly lubricant.....law of nature....um I’m getting into dangerous territory

 

[rwthomas1]

If you're going in and pulling the carbs, do all the intake rubber carb insulators, $10 each. While your there, if you already haven't, replace the coolant hoses, elbows (or at least the O-rings) and delete the PAIR system. I don't like having to go into areas like that twice if I can avoid it and its cheap insurance.

RT

 

[dwalby]

A little tip for you. When re-seating the carbs. Especially with new boots or boot. It can be a bit tricky. Allot of people recommend using a special non petroleum based rubber lubricant to get them on there.

I however, like to use my brain. And dip my finger in some fully synthetic engine oil or some fork oil. Seeing as how I keep engine and fork oil handy in my garage..... I don't keep non petroleum rubber lubricant handy!

From the Internet:

Vaseline or other petroleum products should never be used on rubber or neoprene objects. It can deteriorate the rubber or neoprene very rapidly. The correct lube to use is a silicone based lubricant, which comes with or without Teflon.

 

[Smudgemo]

Mission Automotive Silicone Paste gets a lot of use in my projects.

 

[paulcb]

Thanks folks. Dug in and stripped off the plastics tonight, and did the carb cleaner test for vacuum leaks. Seems like there may be an issue on cylinder 2 (left front), so I will try to get in there and inspect the boot or whatever goodness is hiding under there. Hopefully it won't need an intake gasket.

I'll post more with what I find. Thanks again!
/Kris

Try tightening the clamp screws on the boots before pulling everything apart. There's a clamp at the top and bottom of each boot. If you do go in there, replace the boots, hoses and aluminum elbows while you're in there. Tip: replace the boot clamp screws with allen head screws... makes tightening the without rotating them much easier.

 

[rwthomas1]

From the Internet:

Vaseline or other petroleum products should never be used on rubber or neoprene objects. It can deteriorate the rubber or neoprene very rapidly. The correct lube to use is a silicone based lubricant, which comes with or without Teflon.

The internet is never wrong, correct? I don't know if this is an old wives tale or not. Maybe back when there was still natural rubber used automotive stuff, but now? Seals and hoses of all kinds are used with petroleum products all the time. There are multiple rubber seals in our motorcycles that are in contact with petroleum. They appear no worse for wear, and give in some cases, hundreds of thousands of trouble-free miles. Everything today is synthetic rubber, its highly unlikely that any of it will be affected by common petroleum products. Granted, there is no harm in using a water based glycerin type lubricant or silicone but I'm not sure an iron-clad ban on petroleum is warranted.

RT

 

[dwalby]

The internet is never wrong, correct? I don't know if this is an old wives tale or not. Maybe back when there was still natural rubber used automotive stuff, but now? Seals and hoses of all kinds are used with petroleum products all the time. There are multiple rubber seals in our motorcycles that are in contact with petroleum. They appear no worse for wear, and give in some cases, hundreds of thousands of trouble-free miles. Everything today is synthetic rubber, its highly unlikely that any of it will be affected by common petroleum products. Granted, there is no harm in using a water based glycerin type lubricant or silicone but I'm not sure an iron-clad ban on petroleum is warranted.

RT

yeah, just more of a word of caution than an absolute rule.

But some types of rubber are adversely affected by petroleum based products, look at any seal guide under the "motor oils" category and there are a few types of O-rings that are considered unacceptable with motor oils. So it all depends on which type of rubber is being used, and its not just natural rubber, its synthetics as well.

I'm sure that seals made specifically for contact with oil and other petroleum based products are designed with synthetic materials that resist them, such as fork seals. But I don't know that the carb boots would necessarily fall into that category, since they're not expecting to be in contact with oil. They are in contact with gasoline vapor though to some extent, and there's a lot of O-ring materials that are unacceptable with liquid gasoline, so maybe the carb boots are made of a fairly chemical resistant rubber that doesn't need any special cautions. Its your call as to what the carb boots are made of, I won't claim to know.

The only practical experience I have with this topic is the O-ring in my pool filter. Its pretty well understood that using Vaseline or other petroleum based lubricants on that O-ring isn't good for the material its made of. So, I happen to have a tube of silicone lubricant sitting in my garage for the filter O-ring, and used that on the carb boots when I replaced them a few years ago.

 

[dwalby]

But synthetic oils are not really solvents, for that matter they're not really petroleum based either.

most synthetics still use a refined petroleum base stock, and even those that have a pure synthetic base, like the Group V synthetics, have hydrocarbon chains like regular petroleum.

 

[rwthomas1]

I can see vehicle body mounts, suspension bushings, etc. as things that might react poorly with petroleum products as they are not really designed to be exposed to it with any regularity. But anything on an engine, particularly a modern engine, should be entirely compatible with petroleum products. The engines run on and are lubricated by them. Exposure is guaranteed.

RT

 

[copeina]

Well, the thread took a detour, but the bike is now back together. Carb cleaner trick sniffed a vacuum leak under the carb bank, so ordered and installed new boots. Pulled the bowls while things were up and they were nasty after only 30,000km, so that was probably the mileage issue more than anything. Also discovered the shop (that I will no longer be taking my bike to) had completely bunged up the fuel settings when they claim to have gone through everything, "balanced" the carbs and put in the 118 jets. Put the original jets back in and she's good to go again.

Lost a drag race with a streetglide last week. That was the last straw.

Not entirely sure why it gummed up so quickly, but that's the joy of quad carbs in Canada.

Thanks again to everyone for your help.
/K

 

[copeina]

Last update for this thread. Just got back from a little road trip. 1356km, 63.955L of fuel.

That means 4.716L/100KM, 49.88 US MPG, 59.9 UK MPG.

I'm happy again.