In the past month, I have noticed I am getting 30-40 miles LESS per tank than I used to. The story behind my GS 500 2001 model is that I put it in storage for 3 months while I was in China. Everything went well but lately I have had a slew of problems. First off, would adjusting the idle have anything to do with decreased performance? Do you need to rejet if you adjust the idle? The bike was idling at 900 rpm so adjusted it to 1200. Also, I have noticed I only have maybe 2-3 mm of clearance between my rear tire (yes, it IS too big) and the swing arm. At first, I thought it was rubbing against it. We tried to adjust the rear tire, but to no avail. I painted the tire and it does not seem to be rubbing. How can you tell if your tire is rubbing against the swing arm while you ride? Anyway, that is all I can think of. I have not changed my riding style or my routes. Everything is the same except getting crappy mileage. Let me know what you tihnk.

Quote from: Kaizer on November 02, 2007, 08:46:46 PM
First off, would adjusting the idle have anything to do with decreased performance? Do you need to rejet if you adjust the idle?

No and no.  On the pre-'01 models, adjusting the idle up was exactly like twisting the throttle grip a little bit.  Anytime you rev higher than idle, the idle adjustment screw loses contact with the butterfly assembly and it's as though it (the screw) isn't there.

I can only assume that the same (or similar) is true of the '01+ models...?

Quote from: Kaizer on November 02, 2007, 08:46:46 PMHow can you tell if your tire is rubbing against the swing arm while you ride?

Hmmm.  You could temporarily paint a thin layer of mud (or something similarly innocuous) on the inside of the swingarm and see if it gets rubbed clean. 

Quote from: Kaizer on November 02, 2007, 08:46:46 PMI have not changed my riding style or my routes. Everything is the same except getting crappy mileage. Let me know what you tihnk.

How many miles on the bike?  Was the decrease in mileage kinda gradual, or did it seem to happen "all at once"?  Lurking behind both of those questions is a suspicion that your valves may be out of adjustment, particularly the exhaust valves.  After I sold the black '96 on my home page to a neighbor kid, he went through the same thing.  I don't know how suddenly it came on, but I do know that he was stranded out in the desert once because of it.  (Well, and because he didn't know that using the "full throttle" position of the grip would consume a disproportionate amount of fuel. )

When we finally checked his exhaust valves one of them was 4 (!) shim sizes too tight.  Got him fixed up, and both his fuel efficiency and his uphill power came back.

To answer your question, it has about 10570 miles on it. Not bad for a 2001. The problem is definitely sudden. I am not sure what would knock the valves out of place. She has plenty of power, and acceleration is smooth. My shifting still sucks but that should not have that much impact on fuel economy, right? How can i check the valves? Can I adjust them myself?

Quote from: Kaizer on November 03, 2007, 12:35:13 AM
To answer your question, it has about 10570 miles on it.

If the valve clearances haven't been looked at (supposed to be done every 4,000 miles) then they're certainly overdue to be checked.

Quote from: Kaizer on November 03, 2007, 12:35:13 AM
The problem is definitely sudden. I am not sure what would knock the valves out of place.

Hmmm ... that makes diagnosis more problematic; I wouldn't expect a valve clearance change to happen suddenly.  (It's not that the valves get "knocked out of place" ... it's that the shims that provide clearance become out-of-spec.  More accurately, the valve seats may wear down, or carbon deposits may build up, either of which would change the valve clearance and require the shim to be replaced ... with one that is thicker or thinner ... to bring the clearance back within spec.)

Quote from: Kaizer on November 03, 2007, 12:35:13 AMHow can i check the valves? Can I adjust them myself?

Yes - you can definitely check the valves (with a few tools) and adjust them (with the necessary replacement shims in hand) yourself.

Modesty almost forbids but since no one else is awake I guess I can direct you to my [Valve Adjustment video on Google Video].

Alternately, you can download a similarly "low-res" WMV version of the video from my website (along with the files that I used to ship on the CD) at
   http://bbburma.net/Videos/GS500_ValveAdjustment.zip

The additional files include photos of the first and second incarnations of the valve adjustment toolkit that I sent out a few years ago and then upgraded a couple years ago.  Those pictures will give you an idea of the tools needed for the job.  Ah - I found the photo of the [Valve Adjustment toolkit - Version 2].  The 3 screws, one of the screwdrivers, and one of the Allen wrenches are actually "extra" ... they were items that were in the kit when it came back to me, so I sent them back out with the "upgrade".

Also included is a chart that helps you determine which replacement shim is needed for a given set of measurements.  You can get the chart separately [HERE].

Again, I can't say for sure that your valve clearances need adjusting ... but they should be checked to (hopefully) eliminate that as the root cause of your fuel efficiency problem.

PS: I'm uploading the new, lower-res version of that ZIP file as I type.  If you decide to grab it, you should wait another 35 minutes or so.  (WARNING -- the file is 222MB in size!  But for a 1 hour, 19 minute video I guess that's not TOO bad....)

The upload of [the new ZIP file] is complete.

If anyone downloads it, and encounters a problem of any kind, please let me know!

Have a look at the air-filter, if its very dirty and clogged-up it could be a factor relating to the reduction in your mpg.

hey Kerry, I noticed that's a pretty hefty file. maybe we should make a torrent to relieve your server( s ) ?

let me know, i know the bandwidth is expensive.

Kerry, That video is excellent! I haven't downloaded it, but I've watched it a couple of times.
It made the process very understandable. Thanks for all you do for us.

Kaiser, I had a slight reduction in mileage also. My bike went from an avg. of 52 MPG to 48. I change the plugs and it came back to 52, Then I decided to put half a can of sea foam in the tank. Last time I checked the mileage, I got 55.47 MPG.

PJ.

Quote from: ohgood on November 03, 2007, 05:01:24 AM
hey Kerry, I noticed that's a pretty hefty file. maybe we should make a torrent to relieve your server( s ) ?

let me know, i know the bandwidth is expensive.

I guess you could say that bandwidth is expensive, but somehow it feels even more expensive when it's not being used....

Here's the deal:  A friend and I are sharing a business-level hosting account, with GOBS of webspace and GOBS of monthly data transfer. Our usage is barely scratching the surface of either capacity. (Between the two of us, after a year we have filled a whopping 3GB out of 100GB of space. And we're seeing about 2.5GB of data transfer a month ... out of 2,500GB available!)

Let's see ... 2,500,000MB/month divided by 222MB = ~10,000 downloads a month.  The Google Video version has "only" been watched 14,000 times in a couple years, so I think I'm safe.  (Fingers crossed.)

Anyway, thanks for thinking of me! 

Wow! Thanks Kerry! Out of curiosity, my bike was re-jetted last year. Would the valves be adjusted during that time? I will check with the last owner to make sure he did that. Also, I will check the air filter. The spark plugs are a little over a year old. How long do spark plugs last? I put sea foam in it initially and still the mileage went down. It is just pretty weird. Thanks for all your help. And the video zip file is hard to download. Very slow. Thanks though anyway. You are all very kind.

Quote from: Kaizer on November 03, 2007, 11:35:51 PM
my bike was re-jetted last year. Would the valves be adjusted during that time?

They could have been, but I wouldn't consider the two to be related.  Pulling the carbs to do a rejet is entirely different from pulling the valve cover to check/adjust the clearances.  About the only steps they have in common are removing the seat and turning off the tank-mounted petcock.

Quote from: Kaizer on November 03, 2007, 11:35:51 PMThe spark plugs are a little over a year old. How long do spark plugs last?

A lot longer than that - unless something very strange is going on.  It might be more useful to ask how many miles a spark plug should last, but even that could vary depending on conditions.  In 7 years and 39,000 miles I have replaced my plugs twice at the most, and I have no proof that either change was necessary.  Having said that, don't be afraid to try a different pair of plugs if you "suspect" your current set ... they're pretty cheap!

Quote from: Kaizer on November 03, 2007, 11:35:51 PM[...]the video zip file is hard to download. Very slow.

Hmmm ... sorry to hear that.  Can you quantify "very slow"?  It took nearly 40 minutes to upload it to the server, but I would expect download times to be somewhat shorter.  Just remember -- watching the video online takes the full hour and 19 minutes, and at the end you're left without a local copy to review "at will".   

 Just some FYI, I had recently used some Sea-Foam, it was the first time I've used any additive in my 05' (at 20,000mi) and noticed about a 4 to 5 mpg increase. But I'm not sure if it was the Sea-Foam or that the Weather here in Florida has finally cooled off some from our average 90'+ daytime temps. , or could be a combination of both.   
  But a  + one on ether cleaning or try some new plugs, and has the Weather in your area changed much in the last month to have any effect on performance, if its a lot colder some times a thinner grade oil may be needed. 

I will take your comments into consideration and take it into consideration. The weather has been funky. Up and down in temperature. At least a 30 degree difference. But it didn't do that last year. hmmmm. Can you guys think of anything else I should check? I put only a little over 2000 miles on the bike over a 9 month period. That is not much. Let me know.

I checked my air filter. Clean as a whistle except for a couple of small pine needles. I didn't take the entire filter out, just peeked in there with a flashlight. So...would those pine needles be causing all my problems?

Quote from: Kaizer on November 05, 2007, 12:47:22 PM
I checked my air filter. Clean as a whistle except for a couple of small pine needles. I didn't take the entire filter out, just peeked in there with a flashlight. So...would those pine needles be causing all my problems?

The visible stuff is rarely what clogs an air filter -- it's the dirt which lodges in the open "pores" of the filter material that does that.  Try cleaning it using compressed air blowing from the outside of the filter IN.  Hold it upside down as you do this (opening to the ground) and see what comes out.