Fuel Economy on a GS750

[Anonymous]

What's the average MPG those of you that have 750cc or larger bikes? It's been so long since I've been cruising this bike, and I don't ride it hard, but the last tank only yielded about 33 MPG, which seems low to me. I seem to recall something closer to 50, but I may be dreaming.

Thanks,

Roger

 

[Jethro]

I've figured about 35 - 37 on average for my 1100. I've been told thats pretty average for my bike.

 

[earlfor]

79 GS750E..... Depending on the height I set the floats and the adjustments on the fuel and air screws, my milage varies between
42 and 51 mpg. 42 is running a bit on the rich side and 51 is slightly leaner than I like. Best average is around 48 mpg as a compromise between power and economy.

Earl

 

[Anonymous]

last time i filled up with 4.5 gallons i put 90 something miles on it in town.

 

[earlfor]

Sheesh! Thats only 20 mpg. My truck pulling a 3000 lb boat and trailer does better than that.

Earl

last time i filled up with 4.5 gallons i put 90 something miles on it in town.

 

[chuckycheese]

Mileage

Mileage

'80 GS750L.....I've figured my mileage pretty carefully and it's usually about 46MPG :lol:

 

[Anonymous]

Fuel Economy on a GS750

I've got a '79 GS750L that sucks gas like it is going out of style. I get in the mid 30's, which is worse than my wife's car! By contrast, my '75 Honda CB750 gets in the mid 40's around town, and in the low 50's on the highway. What's worse is that the L model has a small tear-drop tank. I'm lucky to get 100 miles before it won't run anymore.

I've got MAC 4-2 pipes on it, and a K&N filter in the airbox. I cleaned and rebuilt the carbs recently, and unfortunately did not record the position of the FUEL screws before I removed them. When I went to put it back together, I found that Clymer gives me a setting for the AIR screws, but not the fuel screws. Why the carbs have TWO idle adjustments, I'll never know. Anyway, after about a month of tweaking the settings and reading the spark plugs, I got it to a point where it runs pretty well, but I'm not happy with the fuel economy. I had originally changed the main jets, the pilot jets, and raised the needle, but after many trials, I returned to all of the original jets and settings. Any suggestions?

 

[Anonymous]

Re: Fuel Economy on a GS750

I've got a '79 GS750L that sucks gas like it is going out of style. I get in the mid 30's, which is worse than my wife's car! By contrast, my '75 Honda CB750 gets in the mid 40's around town, and in the low 50's on the highway. What's worse is that the L model has a small tear-drop tank. I'm lucky to get 100 miles before it won't run anymore.

I've got MAC 4-2 pipes on it, and a K&N filter in the airbox. I cleaned and rebuilt the carbs recently, and unfortunately did not record the position of the FUEL screws before I removed them. When I went to put it back together, I found that Clymer gives me a setting for the AIR screws, but not the fuel screws. Why the carbs have TWO idle adjustments, I'll never know. Anyway, after about a month of tweaking the settings and reading the spark plugs, I got it to a point where it runs pretty well, but I'm not happy with the fuel economy. I had originally changed the main jets, the pilot jets, and raised the needle, but after many trials, I returned to all of the original jets and settings. Any suggestions?

I BELIEVE IF YOU WANTED BETTER FUEL ECONOMY IN NORMAL DRIVING YOU SHOULD HAVE DROPPED THE NEEDLES

 

[Anonymous]

Re: Fuel Economy on a GS750

I BELIEVE IF YOU WANTED BETTER FUEL ECONOMY IN NORMAL DRIVING YOU SHOULD HAVE DROPPED THE NEEDLES

Well, I don't just want better economy; I want a good compromise between performance and economy. I guess if I had my choice, I'd err on the side of using less gas rather than having more power.

When I initially put the carbs together after cleaning, the Saturday service manager at the dealer said that I should go to 110 mains, 22.5 pilots, and raise the needle three notches. He also recommended that I start with the air screw at 1 turn out and the fuel screw at 2.5 turns out. Either he was on drugs, or he didn't understand what the K&N in the airbox and the MAC pipes would do the the mixture (ie not much). The bike died less than 5 miles from home, but luckily, I was carrying a spare set of plugs on my test drive.

After a lot of trial and error, I ended up back with the stock jets and needle position. It seems to run OK, although it sometimes stalls at stop signs, and other times it idles just fine around 1000 rpm. It pulls pretty strongly through all throttle positions. The plugs aren't really the perfect grey or tan. But they are not carbon black, nor are they oily black. The end of the threaded section is black, but the electrode and insulator are kind of clean and shiny.

So, here are the settings as of now, which match the Clymer spec:
Main Jets: 102.5
Pilot Jets: 15
Needle Groove: 2nd from top
Fuel Screws: 1/2 Out (based on experiments)
Air Screws: 1 Out

I think I had tried to drop the needle one groove, but I seem to recall that the midrange performance went south. But I've been working on this sporadically over the past year, so I don't remember exactly. Since it has been running, I haven't done much lately except complain about the gas mileage. :wink:

Sorry for the long winded posti
ng. Just trying to clarify my trials and tribulations.

 

[Anonymous]

if your plugs are that color i would be thinking of where else the fuel is going- i have no other ideas at this point. Has any one fooled with the sprockets . the mack pipe should have no effect whatsoever from what most of the guys say about cosmetic only mods- the k&N filters should also be non functional with a non performance exhaust--did you say that you are totally back to the stock settings and maybe you should compare your jetting with Earls 750 His bike ran perfectly and got good mileage even with 50 pounds of bugs stuck to it. Again has any one fooled with the gears--how much do you weigh --what sort of routine driving do you do- and are you a stoplight warrior???

 

[Anonymous]

Fuel Economy on a GS750

Sprockets is a good question. :idea: I'll have to check and see what's on the bike versus what's in the manual. As far as my other stats... I'm not a stoplight warrior; I'm a smooth rider. I spend about half of my time in town and half on the highway. At 180 pounds, I'm hardly taxing the motor. Doing exactly the same type of riding, my CB750 gets 45 mpg or better.

I noticed in another string that someone recommended the fuel screw to be set 3/4 to 1-1/2 out, and the air screw be set to 2 to 3-1/2 out. That's richer on the fuel screw, but a lot leaner on the air screw. I may have to try that setup and she how she flies.

Earl: What ARE your carb settings?

 

[Anonymous]

and read your plugs after you make a change

 

[Anonymous]

earl

earl

i have constant running rich problems, compression is good, spark is great its those carbs man im at a loss, i need a exhaust gas analizer to really know whats going on...actually i have a mac ega but it dont work

 

[Anonymous]

Re: earl

Re: earl

i have constant running rich problems, compression is good, spark is great its those carbs man im at a loss, i need a exhaust gas analizer to really know whats going on...actually i have a mac ega but it dont work

Rick you louisiana swamper
are all of your plugs reading rich whats the reading on all 4 separate plugs

 

[earlfor]

Re: Fuel Economy on a GS750

I'm running 7/8ths of a turn out on the fuel screw and 1 3/4 turn on the air screw. Plugs run a very light brown. I could probably run it a little leaner, but with these settings, the bike starts so easily it criminal.

Earl

I noticed in another string that someone recommended the fuel screw to be set 3/4 to 1-1/2 out, and the air screw be set to 2 to 3-1/2 out. That's richer on the fuel screw, but a lot leaner on the air screw. I may have to try that setup and she how she flies.

Earl: What ARE your carb settings?

 

[TheNose]

Earl,

What kind of screwdriver do you use to adjust the fuel screws so accurately? (7/8 of a turn) I have a heck of a time getting a screwdriver in and trying to turn it while counting the revolutions. It always seems to slip off the head when I'm turning and then I've got to start over. Got to be an easy way to do it, I just haven't figured it out yet.

Terry

 

[earlfor]

Terry
It takes me about 5 minutes to disconnect the fuel lines, remove the airbox, undo the clamps and take the carb stack off. Maybe 5 minutes to reset fuel and air screws and another five to reinstall everything. I find its much easier and more precise to do it this way rather than standing on your head, mirror under the carbs, trying to shine a light in the right place and set everything with the carbs installed.
I just use a medium size jewlers swiveling screwdriver.

Earl

Earl,

What kind of screwdriver do you use to adjust the fuel screws so accurately? (7/8 of a turn) I have a heck of a time getting a screwdriver in and trying to turn it while counting the revolutions. It always seems to slip off the head when I'm turning and then I've got to start over. Got to be an easy way to do it, I just haven't figured it out yet.

Terry

 

[Anonymous]

Dom

Dom

yes after a 100 miles are so all plugs turn sooty black.....my carb setup at the moment is.......pilot air screw 3 turns out, fuel screw( the screw under the carb next to float bowl) 2 turns out...stock pilot jets, needle jet clip is 2nd from bottom clip, 102.7 mains....i had 100`s but it still ran rich but that was with the old coils......from 1/4 throttle to half throttle it hesitates, top end is great, i pulled the front wheel yesterday a few inches of the pavement

 

[TheNose]

Earl,

It takes me a bit longer than 5 minutes. I have been removing the gas tank. I guess that isn't really necessary. I may try removing the carbs like you suggest. Mine runs great and starts instantly, but the mileage is only about 33 mpg. Plugs are a little sooty. Thanks for the advice.

Terry

 

[Anonymous]

Re: Dom

Re: Dom

yes after a 100 miles are so all plugs turn sooty black.....my carb setup at the moment is.......pilot air screw 3 turns out, fuel screw( the screw under the carb next to float bowl) 2 turns out...stock pilot jets, needle jet clip is 2nd from bottom clip, 102.7 mains....i had 100`s but it still ran rich but that was with the old coils......from 1/4 throttle to half throttle it hesitates, top end is great, i pulled the front wheel yesterday a few inches of the pavement

Could i talk you into experimenting with the needled--if all of your plugs get black then drop the needle 1 notch-i cured a similar problem by doing the same thing on my bike(i had to use washers--no notches you lucky dog) if it works the result may leave a lean spot when the carbs are coming totally off the idle jets and it will also go a bit lean when you slack off the throttle at cruise--((i like the soung and by watching my plugs i see no problem with heat from the temporary lean condition.