81 gs850 gas consumption PUZZLER, HELP!

[TallBoy]

I have a 81 gs850gx with stock everything. have brought the bike up to speed with all the routine manuevers (oil, plugs, new air filter, fuel filter). however i seem to get about 30-34 mpg. have done a total cleaning of the carbs, replaced both the main jets (115) and pilot jets (40) (i suspected that someone bore them out). was blowing black smoke, ie running rich. mechanic has adjusted the carbs and done compression tests on the cylinders. it seems like the carbs are running fine. my mechanic put some "6" spark plugs in, the idle sounds a lot better and its performs great, however, im still getting bad fuel economy. everyone that ive heard from has claimed they are getting 45 mpg+ on their 850's. has anyone had similiar problems with their bike? whats the solution. my mechanic has over 30 years of expirience (more like an advisor, because as he works in his shop i work on the bike outside) thinks i should go down on the jet size to a 110/35. im not opposed but im looking for a miracle cure, ive already taken the tank/carbs/airbox off and on a good 20 times and spent hours trying to solve this problem for the past three weeks and im pretty fed up
thanks,
tb

[DanTheMan]

I've never gotten better than 42mpg on mine. Generally, depending on wind, riding speed/style, and other factors, my mileage has been between 35-42. Who told you 45+?????
Maybe in ideal conditions, flat ground, (tailwind would help), speed below 60 mph as indicated on the 5mph fast speedometer that might happen. (Oh, and drafting a truck or RV might work too..........)Sounds like you're chasing your tail............:-D

[TallBoy]

also, after i put in the "6" spark plugs and drove it around for a few hours my plugs where coated with black soot so its still running rich. i think im going to drop down the jets, id rather save money than go fast, i like to cruise at 50 anyway.

[SqDancerLynn1]

PUT THE CORRECT PLUGS IN THE ENGINE unless you want to burn a piston ???? I have gotten as low as 20 when running very hard
GS850 (80) the specs are for the CV's

idle.................... 1050 +/- 100 r/min
carb................... mik BS32SS
id no................... 45120
bore size ............ 32 (1.26)
float height ......... 22.4 +/- 1.0 (0.88 +/- 0.04)
fuel level ............ 5.0 +/- 0.5 (0.20" +/-0.02")
VALVE SEAT........ 2.0
STARTER JET....... 32.5
PILOT SCREW ..... 3.5
PILOT AIR JET ..... #200
pilot jet............... #42.5
jet needle........... 5D57-3 (the -3 3rd notch)
needle jet .......... X - 6
pilot outlet........... 0.7
BY PASS............. 1.0, 0.8, 0.8
MAIN AIR JET...... 1.7
main jet............. #115

[marvinsc]

My 850 Refuses to Cruise at 50 but at 60 plus I average around 38-42 mpg.

[rkubik]

a factor

how much do you weigh?

[chiphead]

how much do you weigh?

That was my first question after reading the original post.

My other questions:
Is the float level set properly?
Are the needle and seats for the float sealing?
Do the choke plungers completely seal off the choke circuit when in the down position?
Do you ride WFO all the time? This really doesn't apply if your blowing black smoke.

If by "6" plugs you mean B6ES plugs, get them out of there.

[Steve]

... my mileage has been between 35-42. Who told you 45+?????

He might have seen a post I made about our trip to West Virginia last week.

The first two tanks were at a rather constant 70 mph on the freeway, into a headwind. We normally keep to a max of 65, but were with a group intent on getting to the twisties. Here are the mileage readings for the entire 4-day trip:

31.98
30.63
40.91
42.41
39.85
46.32
53.74
53.65
58.78
49.69
50.58

That's right, almost 59 mpg in the mountains of WV. \\/ We only went 86 miles on that fill, but the next stop was uncertain, so we filled early. Only took 1.47 gallons. Overall, the trip was 1175 miles. Her bike took 26.6 gallons for an average of 44.42 mpg. If you ignore the first two tanks that were so bad, that covers 986 miles at an average of 48.5 mpg.

Maybe in ideal conditions, flat ground, (tailwind would help), speed below 60 mph as indicated on the 5mph fast speedometer that might happen.

I know that bike speedos are quite often rather optimistic, but ours happen to be rather close, according to GPS. On my Wing, an indicated 70 mph on the speedo shows as about 70.4 on the GPS. On her 850, an indicated 70 shows as 69.2. \\/
Odometers are also rather close. For our trip to WV (most of which is hardly considered flat), I did an extra trip on my bike to visit the rest of the group at the other motel, so I went about 2.5-3 miles farther than she did. Other than that, we were riding together everywhere. Her bike odometer: 1184. My bike odometer: 1178. GPS: 1174. Her bike is off 10 miles in almost 1200, which is only 0.99% error. I think I can live with that. My Wing's error is 0.34%. Yeah, I can live with that, too. 8-[


.

[slugsride]

That was my first question after reading the original post.

My other questions:
Is the float level set properly?
Are the needle and seats for the float sealing?
Do the choke plungers completely seal off the choke circuit when in the down position?
Do you ride WFO all the time? This really doesn't apply if your blowing black smoke.

If by "6" plugs you mean B6ES plugs, get them out of there.

would like to add:
Is the air filter over oiled?
Is the petcock vacuum line leaking gas?

My 700 has averaged 45 mpg since new, 45+ on a 850 seems high.

[BassCliff]

Your mileage may vary

Hi,

For comparison...

Most of my miles are during my daily commute and I average 36mpg. If I go for a long ride, don't twist my wrist too much, I've gotten a little over 38mpg. But I never "cruise" on the freeway at less than 75mph. My bike is all stock. Perhaps if I "cruised" at 65 I might get 40mpg. When I have time I'll experiment. Or perhaps rebuilding my carbs would help.

Thank you for your indulgence,

BassCliff

[Go Mifune]

Would a different rear sprocket help get more Miles Per Gallon?

[focus frenzy]

what needle and needle jet do you have in it? if the needles have been changed to a thinner one this will make it rich.

[focus frenzy]

Would a different rear sprocket help get more Miles Per Gallon?

not on a shaft driven bike!
it can depending on the bike. generally going to a tooth or two smaller on the rear will improve mileage, but it is Dependant on the bike and what it came with stock.

[dpep]

36 - 40 usual range on my 850s. The red one, the one I got from Redman, seems to get the best, up into the low 40's on some stretches.

[bwringer]

I'd suspect a clogged or over-oiled air filter. It doesn't take much extra oil to mess this up -- you only need a VERY light coating. Usually, if you wash an over-oiled air filter with lots of dish soap and warm water, the light film of oil that remains after drying overnight is about perfect. Make sure every bit of the water is gone before reinstalling.

I've also seen old air filter elements get gummy -- they can sort of stick together internally and restrict airflow too much.

Another possibility is that the choke mechanism is getting stuck open, or if you've totally misunderstood which way the choke lever should go once the bike a warmed up a bit (yes, I saw this once.)