Suzuki GS500 Fuel Economy

[redyaris]

low&slow
I would recomend the size and shape that Allan Smith used on his Kawasaki Ninja 250. My behinde the rider cargo box is longer than it needs to be at 36" long. mine is also to wide at the front at 18". the other recomendation I have is make the sides curved. my calculations suggest a length of 24" and a width of 14" to 16" at the front. I have found a way to do mine in Aluminium with curved sides, but what ever works for you. My results are also slow in comeing but I suspect that after correcting my mistakes I will get better and better. I have made slow but stady progress, just not as fast as I would like. What I am finding is that the only way to make progress is to make mistakes and then find better ways after the trial & error. I think in terms of how many years/trials did it take to get the modern super bike? It would seem that even with the best of everything, it take time and effort to make progress.

[redyaris]

so far on this trip I have gone 803 miles and used 11.7 galons for a consumption rate of 68.6 mpg. What I have noticed is that at 110 km/hr at 4200rpm on the highway I use only 20% or less throatle,which is barley off idle. the light black deposit on the exhaust pipe suggests over fueling, I will have to install the O2 readout system to check and adjust the carb if that is true. I think I may be very close to the limit for this size engine & camshaft. I don't think I can lower the rpm without a change of cam profile to move the power/torque curve around. the engine is probably miles away from it's BSFC optimum at less than 20% thoatle at 110km/hr [68mph]. an other idea would be to find and install smaller carbs.

[low&slow]

Hi Redyaris, Thanks for the suggestions. I started working on my tail section and will finish it soon.

It sounds like you are starting to reach some of the inherent limits of a motorcycle with a larger engine. What you have achieved with a 500cc gasoline-powered motorcycle is amazing but to be competitive with the top motorcycling hypermilers you will probably have to go to a smaller engine machine. I love my Vision but its doubtful I'll ever break into the 80mpg territory as you have done due to its shaft drive, relative low gearing and larger motor . I agree with Craig Vetter that a 15-17 hp motor would be optimal for an 80 mph / 100 mpg capability in an efficient aero-enhanced package. The new Honda 250cc fuel-injected single would be a great starting point. I'll probably start shopping for a 250cc this winter for my enxt hypermiling project.
all the best L&S

[redyaris]

Low&slow
I believe you are right although I still see some room for improvement. All the low hanging fruit is gone. The next faze is redo the tail section with curves and other improvements, and install the O2-fuel/air guage and adjust the carb jetting if nessisary and I think I may get well into the 70 - 80 mpg range but not any higher without radical changes and even then...? I am thinking in terms of a used Kawasaki ninja 250 myself, for an ultimat high mpg with some highway cruisability.

[alvaro84]

Bad that I can't directly compare Gray's results with Teresa, because that 110km/h that's a typical speed for you counts as a rather high speed pulse for me (my normal speed is more like 80km/h or 50mph at 3200rpm, or even a bit lower) - but based on that I can do better than 80mpg with a 650 I'd still say there is room for improvement. With really good aero at those speeds, though.

[redyaris]

Originally Posted by alvaro84

Bad that I can't directly compare Gray's results with Teresa, because that 110km/h that's a typical speed for you counts as a rather high speed pulse for me (my normal speed is more like 80km/h or 50mph at 3200rpm, or even a bit lower) - but based on that I can do better than 80mpg with a 650 I'd still say there is room for improvement. With really good aero at those speeds, though.

I have been meaning to ask you some questions about how you get the FE you get with such a large engine. Although BMW's have always got better than average fuel economy, than other bikes.

1. What is the bore size of your carb. or fuel injector?

At 80km/hr the GS500 is turning at 3000rpm in 6th gear, I find I have to gear down to 5th gear if I want to accelerate smoothly. I do suspect that I may be running rich but I will only make changes after installing a O2 sensor and readout. At 110km/hr I use less than 20% throatle, which is just off idle, at 4200rpm. The GS500 has 2, 34mm mikuni carbs, which may be way to big for good fuel economy. The Kawasaki Ninja 250 has 30mm carbs 22% smaller. I may look into getting smaller carbs maybe as low as 28mm, if mikuni makes ones that will fit in the place of the stock carbs. I do agree that there is room for impruvement, although I dought that at 110km/hr I will get better than 70 -80 mpg. I will keep going to see at what level it ends...
If you look at the 82.5mpg I got at Lacey averaging 40mph, between 30mph and 55mph, it is clear that under the conditions you face I to would get much better than the 68mpg I get now.

[alvaro84]

Originally Posted by redyaris

I have been meaning to ask you some questions about how you get the FE you get with such a large engine. Although BMW's have always got better than average fuel economy, than other bikes.

1. What is the bore size of your carb. or fuel injector?

At 80km/hr the GS500 is turning at 3000rpm in 6th gear, I find I have to gear down to 5th gear if I want to accelerate smoothly. I do suspect that I may be running rich but I will only make changes after installing a O2 sensor and readout. At 110km/hr I use less than 20% throatle, which is just off idle, at 4200rpm. The GS500 has 2, 34mm mikuni carbs, which may be way to big for good fuel economy. The Kawasaki Ninja 250 has 30mm carbs 22% smaller. I may look into getting smaller carbs maybe as low as 28mm, if mikuni makes ones that will fit in the place of the stock carbs. I do agree that there is room for impruvement, although I dought that at 110km/hr I will get better than 70 -80 mpg. I will keep going to see at what level it ends...
If you look at the 82.5mpg I got at Lacey averaging 40mph, between 30mph and 55mph, it is clear that under the conditions you face I to would get much better than the 68mpg I get now.

1. I must admit that after an hour of googling I don't have the faintest idea about the injector diameter. I can tell you the cylinder bore*stroke (100*83mm), the compression ratio (11.5), I even found the Bosch part number for the injector, but nothing about the intake size

Rpms: it's 2800 at 70km/h and that's about the bottom of 5th with Teresa. Of course acceleration is quite weak here, but it doesn't hurt anything when I'm cruising. At ~3500rpm it's much better, but if you have power for a brisk acceleration the engine is too strong to work efficiently I try to keep the engine at somewhat higher rpms on inclines, especially with a passenger. And I usually glide the declines. It's not rare that I P&G on flat either (with 90-110km/h pulses then glides down to 70).

In 4th the bottom is ~2500rpm, though she likes ~2700-2800 better. It seems the most efficient gear to me, even a bit better than 5th, given that I really use it at <3000rpm (~60km/h) - I think aero drag kicks in at the speeds where I can shift to 5th. I cruised pretty much in 4th in the winter, I was simply cold in 5th and didn't feel lively enough to P&G

In lower gears I practically always P&G (except for steep inclines), and if I have at least ~500-600m to glide I like to FAS.

Redline is at 7000rpm anyway. I never see it, I shift as soon as possible.

[redyaris]

I looked as well and had the same result. I did look in my KLR650 service manual and it has a 40mm carb. bore. When I do the math for the ratio bore area/displacement 1256.6mm^2/651cc = 1.93mm^2/1cc so for one cylinder at 250cc the carb bore area would be 482.5mm^2 so the bore would be 25mm. yet the GS500 has 34mm bore carbs. great for max power and rpm, but not so good for fuel economy. what I have not found is the intake port area/diameter for the intake port.

[redyaris]

My GS500 gets horible FE after I drop it on its sides, and then have to Uhaul it 150km home due to damage to the drive chain and clutch lever, resulting from slow speed fall. I filled it up after I replaced the brocken clutch lever, and it came out at 4.1L/100km [57 mpg], a number I haven't seen since I was bracking in the new motorcycle. I suspect that some of the fuel leaked out when the bike was on it's side for a minute or two. the section of road had been rained on that day and it was muddy with almost no traction. without traction motorcycles have a hard time standing up.

[alvaro84]

Huh. Are you okay?

I hope Gray will be in working order soon enough.