The best gas mileage on my ST1100 has been 43 mpg, is something wrong?

The best gas mileage on my ST1100 has been 43 mpg, is something wrong?

I often read and hear about people getting over 50 mpg from their ST1100's but the best mileage I've gotten out of either one of my ST1100's is 43mpg. I often give a good effort to get the best gas mileage from my ST1100's keeping the revs down to no more than 4000 rpm on road trips, no stop lights on the interstate, my brakes are not dragging. I've tried new air filters and plugs, synched the carbs, and check the valves. (I bought the 2[SUP]nd[/SUP] bike from a friend who told me he was getting 50 mpg out of this bike but still it is only 43mpg – we talked about this after I put about 3 thousand miles on the bike - and he said that it did get 50mpg but it had been sometime since he checked and something must have changed- he is a good friend and good mechanic and a straight shooter)

Often the bike smells of gas when parked but no drips on the ground. I think the next step is to take the carbs apart and see if I spot anything like miss adjusted floats or stuck enrichers.

I talked to one ST1100 owner I met on a road trip a few days ago and he told me that it seemed like there where two motor set-ups and one of these batches of motors would get 42-43 mpg and the other 48 to 50 mpg. (This was a new one to me and I'll take that with a grain of salt but he did seem to believe what he was saying)

Has anyone had this issue where they had a ST1100 that was getting 50 mpg when taking it easy and then have the best mileage drop down to around 43 ……if so what was the cure?

Thanks in advance.

I'm sure the 1100 guys will speak up here soon.. I'm a 1300 guy.. however 43 mpg sounds good to me. If your using your bike for fuel economy/budget reasons then maybe there is some effort to put into it for better mpg.
Me, I ride it to have fun and not concerned about fuel mileage unless its excessive. Getting 300 miles @ 40mpg out of a tank of gas of 7 1/2 gallon @ $16 a fill up is good enough for me. I'm not concerned enough to squeeze out more.

Do you have a higher than stock windshield ? How much do you weigh ? How much gear are you carrying ?

At about 4,000 RPM you are doing almost 80 mph. I think 43 mpg is very reasonable at that speed. It's about what I get at 77 mph. At 58 mph , I got 56 mpg. So, wind drag is a big factor as far as mpg is concerned.

I've had two ST1100's and both have given me close to the same mileage. I measure in Imperial gallons which is larger than a US gallon. (4.6 litres compared to 3.8 litres) The highest was 54mpg most of the time I get between 47-49 mpg on the highway low 40's running around town. In theory we are suppose to get close to 300 miles on a tank of fuel. I usually fill up around the 240-260 range and I have about 6 litres left in the tank. I think 43mpg (US gallon) is about what one should expect. contrary to what others have said they get above 50 mpg for a US gallon, frankly I think that's crock! YMMV

The smell of gas after shutting off sounds like your fuel shutoff valve may have a bad diaphragm. A bypass of the valve will cure that problem. It may or may not improve fuel economy though. As it starts leaking really bad you may notice the #3 cylinder developing a fouled plug (the gas seeps through the diaphragm leak and into the #3 cylinder through the vacuum hose that is supposed to actuate the diaphragm).

I routinely get 50mpg on mine at about 75MPH steady cruising, but I've ridden with others who got fewer MPG on the same run. I don't know if there's such a thing as light/heavy throttle hand, but over the years whenever I rode with people with the same bike as mine, I typically got 10% or so better gas mileage than they did, for no apparent reason.

I wouldn't tear into the carbs, I'd first try a little lighter throttle control and see if it makes any difference. If your plugs look normal I doubt there's anything significant worth tearing into the carbs to sort out. But I've never had the problem, so can't say for sure.

My 1991 gets mid 40's at highway speeds, 75-80, two up and loaded.

kiltman said:

contrary to what others have said they get above 50 mpg for a US gallon, frankly I think that's crock! YMMV

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yeah, I've got nothing better to do than hang around here and lie about my gas mileage, you caught me.

Doug - I'm not trying to be cheap but rather get the range of 300 miles on a tank without gas stops - the way it is now I need to be looking for gas at around 240 miles or sooner if I'm pushing hard on the interstate.


Jim - With no luggage and windshield in lowest position and only hauling my 160 lbs around with speed not exceeding 60 mph 43mpg is the best I can get. I have the Mad-Stad adjustable windshield it does not matter if I have it in the lowest position I still get no better than 43 mpg. I've also tried no windshield at all - just to test and that did not help either. The 4K rpm would be max such as accelerating in lower gears upto speed - if I take the back hiways and stay between 55 to 60 that is the only time I get as good as the 43 mpg. At a sustained 80mph with windshield up to tallest position and loaded with camping gear - I've done as bad as 30 mpg which required a gas stop before reaching 200 miles.

Thanks for the input.

Dwalby - Thanks I'll by pass the fuel diaphragm and see if that helps. It should get rid of the gas stench in the garage if nothing more. I'll report back on the results.

PhotoDoctor said:

Dwalby - Thanks I'll by pass the fuel diaphragm and see if that helps. It should get rid of the gas stench in the garage if nothing more. I'll report back on the results.

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yeah, if you've got gas stench in the garage its definitely bypass time. When I bypassed mine I did a plug check and #3 was very black and sooty. I had noticed that it seemed like I was getting 2-3 MPG less than I remembered in years past, and since bypassing it I think I've recovered those, but your mileage is way lower than what mine was. I have a stock windshield, and even at 80MPH (85 indicated on speedo, might be a little less than 80, never checked it against GPS) I can't recall ever getting less than 45MPG for steady freeway riding.

you might also check for brakes dragging, bad wheel bearings, or other mechanical resistance, your figures do sound lower than normal.

I always figure about 40 mpg....sometimes better...seldom worse...

Yes, the brakes on both bikes are fine and don't drag. I'll do the bypass on the fuel diaphragm and see what happens.

Then the next thing that comes to mind is the air-cut-off valves in the carbs.



Cheers

On my 1992 with no fuel diaphragm, clean and intact carbs and new plugs, clean filter, no draggy brakes and standard tire pressures, standard windshield, light pannier load and 190 lbs of me, I usually get 40-42mpUSG at around 70-75mph. That is about 50 mp imperial gallon.

I do very little freeway riding, mostly twisty roads with a reasonable amount of braking and relaxed acceleration. On my VTR1000F ( a bike noted for thirst) at a similar pace on the same roads I get 37mpg, and my VFR800 does 39mpg. I love the bigger fuel tank on the ST.

Idle mixtures and sync CORRECTLY done(CORRECTLY means done with air filter and housing all in place like it is normally ridden), at constant 75-80mph on LD rides, fully loaded, one-up riding, 48-52mpg. Lowest mileage ever was local riding with a lot of heavy right hand....44mpg.

I own a ST1300, but some other ideas are tire pressure and maybe the wheel bearings are going bad or excessively worn. From what I read they should be replaced about every 40/60,000 miles (?). My ST1300 uses premium fuel, I have noticed that I get slightly better gas mileage with premium (not sure if the ST1100 takes premium). Good luck

dwalby said:

yeah, I've got nothing better to do than hang around here and lie about my gas mileage, you caught me.

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I admire you for fessing-up, Doug.

I had three st1100's. On my '92 and '98, I always got right around 42 mpg loaded and at legal speeds. That's around 325 miles from full to empty tank. My '96 for some reason got a bit better economy - usually around 44. So in my opinion, if you're getting around 42 that's about normal. YMMV - literally.

I have always wondered if you really get better mileage from a lower windshield? Wouldn’t the human form be less aerodynamic than a windshield and result in higher fuel use? No proof one way or the other but to me it just seems to make sense.

Gerhard

PhotoDoctor said:

Dwalby - Thanks I'll by pass the fuel diaphragm and see if that helps. It should get rid of the gas stench in the garage if nothing more. I'll report back on the results.

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A quick check for a diaphragm failure is: 1) is there fuel leaking from the vent hole at the bottom of the vacuum petcock? 2) Is there just a slight amount of air movement coming from the vent hole due to the diaphragm pulsing back & forth, or is there a significant amount of vacuum. Put your finger over the hole. If you have either fuel or a vacuum leak, then that's a problem.