MPG, what should I expect?

[orangechicken007]

I have what I believe is basically a basically stock 1982 Suzuki gs650L. Before today been mostly around town and have been pleased with the mileage. Today though I made a 116 round trip. Averaged 75 MPH at 6k rpm?s. According to my calculations I was only getting 32.22 MPG. Also worth noting the full windjetter. Is this normal MPG? I was expecting closer to 40 MPG. What is the best place to start looking to improve MPG? Airbox leaks? Coils?

 

[Brendan W]

75mph average is fast.
Last 650 I owned was a 1980 Z and on 160 mile commutes it returned 57/47 mpg Imp/US regular as clockwork but at average speeds of 50 mph on a naked bike.
I could see a 50% increase in average speed taking a large slice out of that fuel economy and that's before a fairing.
If the bike was burning the fuel properly the plugs should look good. That's where I would start.

 

[tom203]

I get 50+ mpg consistently...the fairing is a big plow.

 

[trevor]

At 75 average you were lucky to get 32mpg

 

[Steve]

On our 850s (see sig), we regularly get 40+. My wife's bike is usually 45+, but we have noted that at speeds over 65, mileage takes a nosedive. We have either a windshield or a full frame-mounted fairing on our bikes, and have not found that they have much effect on mileage. At least not until speeds get over 70.

60-65 seems to be the sweet spot, if you can keep it there, then you should expect 45+.

.

 

[orangechicken007]

I get 50+ mpg consistently...the fairing is a big plow.

when you say 50+ consistently, what is you average speed? I hate the way the fairing looks but I like the windshield, especially at highway speeds. but if its costing that much in MPG then I may have to take if off.

 

[orangechicken007]

On our 850s (see sig), we regularly get 40+. My wife's bike is usually 45+, but we have noted that at speeds over 65, mileage takes a nosedive. We have either a windshield or a full frame-mounted fairing on our bikes, and have not found that they have much effect on mileage. At least not until speeds get over 70.

60-65 seems to be the sweet spot, if you can keep it there, then you should expect 45+.

.

Thanks for your input Steve, always appreciated, Ill take it a little slower next time and Check the difference

 

[Downs]

78 GS1000 here with the VM carbs and get mid 30s pretty consistently. I feel like I have her tuned pretty lean so I'm not sure how I could squeeze much more out of it without causing running problems but I also made the mistake years ago of going to pod filters as well lol

 

[Guest]

Saw this post and thought I'd throw my numbers into the pile. I've got my 78' GS750 that is mostly stock, 4 into 1 and a large rear sprocket. When I bought it I would be lucky to get over 30. After owning it for a while I ended up welding in a wideband O2 sensor. Mostly for my own curiosity but it makes it very easy to dial in the carbs. Afterwards I dropped the main jet 3 sizes and the needles one clip (my bike has VM's). After some fine tuning here and there I managed the best MPG so far. I took about a 1000 mile trip earlier this year. The 750 probably averaged right at 50 mpg. This was mostly cruising between 60-75 the whole time. On one leg I intentionally tried to stretch the mileage with a comfortable but mostly tucked position 65 MPH with a result of about 53 MPG. The very next leg riding as I normally would I managed 58 MPG which has been my highest so far. I typically average high 40's around town and low 40's if I'm doing some spirited riding.

Here's some things I have found that have a big effect on MPG in no particular order:

1. This first one only applies to around town but every time I park my bike I shut the fuel off a mile or so before I get home and let the carbs run mostly dry. When you're making multiple short trips on one tank and parking it in between, the gas evaporates out of the carb bowls. This is work up to about 4-5 mpg.

2. Check that your gas cap is venting properly. When you park your bike the engine has a tendency to get the fuel in the tank very hot. This can cause some evaporation if the cap is not functioning properly which hurts fuel mileage.

3. Check that the float needles in the carburetors are not leaking fuel when you're riding. You will most likely notice it at idle. Pull the vent lines out to the side of the bike one day so you can easily see them.

4. Check that the vacuum line is not pulling fuel from a leaking diaphragm in the petcock.

5. Jetting. Depending on how much you want those extra mpg it may be worth it to pull the carbs and reset them all to factory specs. Float height, sync, jets, etc.

6. Ignition timing. I don't think any of the 80's GS's have points but I thought it would be worth mentioning that having the ignition timing off can drastically affect fuel economy.

7. Last thing I'll mention is simple maintenance: Air filter, valve adjustment, correct oil weight, (in my case) chain maintenance and new plugs. Any of these can make a big difference if they are left unattended for a significant period of time.

 

[londonboards]

Mileage is directly related to throttle opening. On long journeys, I don't stick to one speed. But I do stick to around 1/8th throttle opening.

Mark up your throttle grip with some Tippex (or other white marker) so that you can clearly see Closed, 1/8th, 1/4, 1/2, 3/4 and WOT on the throttle.

If you ride, when you are cruising, around the 1/8th throttle open position, you will achieve your best mileage. If you come to an incline, yes your speed will drop. But if you need to open your throttle to 1/2, just to maintain the same speed, the bike will start drinking fuel like crazy.

Of course, this requires, your pilot jet fuel system to be very finely tuned.

Best way to test this is to do a plug chop after you have been cruising for a good while, on the flat at 1/8th position. Kill the motor and check the plugs.