I found out my 97 GS is starved at highway speeds. Here is everything that has happened to me (all with a full tank):
Rode GS on freeway to work. When crossing, the bike did the classic fuel starve around a steady 75mph. Got to the shoulder and switched to RES. After a minute I was able to start up and go. On the way home I had no troubles, I even drove another 10 miles extra of freeway for fun. The next day I go again to work, but this time I keep it in reserve the entire time. Once I reach the same spot on my route the bike starves again. I was able to get it started after a few minutes and took it on the backroads home to get my car. This is strange because when I'm going the opposite way of the freeway I never have troubles. If it helps, every time it has starved on the freeway I was going slightly uphill in hot weather with high wind.
Here's a list of the short key points:
-Bike starves 'usually' on a gradual uphill climb in heat with lots of wind
-Tank was full the entire time
-Bike starves on both ON and RES
-I have not attempted riding to work on PRIME yet
-I have noticed the gas cap is a bit gunky, I will be cleaning this tomorrow morning
I have been scanning through multiple threads on how to resolve this issue, but I understand there is not a "cure all". But what I am interested in is compiling a list in this thread of everything we can check from the gas cap all the way to the carbs. If anybody can post different possible fixes (especially with guides/links on how to perform them) that would be greatly appreciated! I really do not feel like selling my bike after two months. I was planning on taking it on a 250 mile ride at the end of the month!
Thank you all!
The fuel cap is a good place to start, there is a vent there that may be blocked and restrict fuel flow.
it might not be fuel starvation, you might be having a problem with your ignition coils. Several members here have had coils go bad where they would lose spark when the coil got hot and were able to continue riding after waiting by the side of the road 5/10 minutes.
There are a couple recent threads where they had similar symptoms to yours and they found a fix. .I'd search for you but I'm feeling lazy. Edit: Just kidding, I went back and read the two recent similar threads and the OPs did not post what the fix was. Don't be like those guys.
Here's some links
http://gstwins.com/gsboard/index.php?topic=67733.msg815533#msg815533
http://gstwins.com/gsboard/index.php?topic=63468.msg752530#msg752530
http://gstwins.com/gsboard/index.php?topic=63885.msg759336#msg759336
http://gstwins.com/gsboard/index.php?topic=8080.msg67169#msg67169
Any kind of add on AUTOMOTIVE fuel filter could cause fuel starvation, MC type add on fuel filters, NOT a problem, unless fouled.
After the gas cap is cleaned (like this (http://gstwins.com/gsboard/index.php?topic=41061.0)), this is what I would do:
Make sure your carbs are spotless (here (http://gstwin.com/carb_work.htm), and here (http://gstwins.com/gsboard/index.php?topic=56601.0)). If the bike has sat for any considerable time the jets will be a dull yellow/brown. If so, replace them. I soaked mine in carb cleaner and reamed them out with guitar string and could still visually tell a difference in the hole diameter between old and new.
Replace all fuel lines and vent hoses and make sure everything is routed correctly (like this (http://gstwin.com/fuel_hose_routing.htm))
You can clean your petcock as many here have done but I would just replace it, especially if the bike has sat (ebay (http://www.ebay.com/itm/NEW-89-00-SUZUKI-GS500-GS500E-PETCOCK-SECONDARY-/201565055015?fits=Model%3AGS500E) is your friend).
Get the tank as rust free as possible. There's several ways to do it so I'll let you figure that out. When I first drained my tank, I could shake it around and it sounded like it was full of gravel and sand. This is not good. All i did was rinsed it with a hose and got all the loose mess out then shook some wd 40 around in it. I plan on completely de-rusting it this winter with something like this (http://www.evapo-rust.com/).
Just so you know, my 2000 GS has stock jets, 2.5 turns on the mixture screws (stock), and no extra washers on the needle and runs all day on the highway. Well, that might be a lie because the longest I ride on the highway at one time is about 40 minutes and I am a fair weather rider but it runs flawlessly nevertheless.
On a side note, make sure to get your valves in spec if they aren't already. If you get slight stumbles on acceleration when the engine is cold or the idle hangs a little high after running on the highway, definitely check your valves.
I agree with all of this above comment from afatrat, mainly because I had the exact same problem you are describing, I however took mine to my mate to sort he's a well know mechanic in my area, and he did all the above new fuel lines cleaned the carbs and new jets in cleaned the fuel tank out best he could and fitted a fuel filter to the pipes ran a dream ever since never missed a beat 👍 I done a 3 hour ride down our motorway totalling 180 miles and it was fine all the way and I don't think I went under 80mph once
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Don't forget to check the actual superfine mesh on the pickup in the fuel tank. In the GS it has a very small surface area and wouldn't take much gunk to clog it enough to slow the flow. Easy to check but requires fuel removal and fuel tank turned up side down.
Also check the vacuum hose for the shutoff valve isn't leaking and not allowing full open.
... another also... check your tank petcock! .. it needs to have the screw slot completely vertical, if you turn it till the stopper cam bumps the stop you are actually slightly closing the valve again.. 90 deg from off is good, 100 deg is not good!