I am having a couple problems with my 1989 GS500E.  I am planning on riding it for another season (next summer) so I really want to fix them cause this is becomming a real problem for my highway riding (of which I do alot).  I will list the problems and what I think I have to do to fix them and I would love any advice on how to fix these this winter.

1. Fuel Starvation
So...this used to only manifest on the Highway, in 6th gear, when over 120km/h (6000RPM) for more then 10-15km.  A Pingle has been recommended on several occasions but I found, up until recently, that putting the bike in Prime would resolve the problem (even on the fly).  However, lately, that has not been the case.  The problem seems to manifest in ON, RES or PRIME.  Nothing I do aside from pulling over on the side of the Highway seems to fix the problem.  Gas cap has been checked out and does not appear to be the problem.  Have recently thought about going to a Pingle but I am worried that, that won't fix my problem.  Especially since this appears to happen when I am in Prime.  City riding seems to be fine.  Any thoughts on what I can check or do to resolve this is GREATLY APPRECIATED.

2. Flooding
This has only ever happened about a half dozen times since I got the bike (May 2005), the last time being early on in the summer.  I will be riding (doesn't matter how long I have been riding it has happened quickly after leaving the apt or after being on the highway for an hour) and my bike really starts to bog down.  Stopping at a light or something will immediately cause a stall.  Gas is coming out of my Air Filter.  Last couple times it happened I determined that it only appears to happen when the Gas tank is low but I am not 100% certain on that fact.  Only thing I can do to fix the problem is to pull over, drain my floats, and then start going again.  Once I fill up...problem seems to not manifest again (hence the low tank comment).  Once again...any advice is GREATLY APPRECIATED.

3. Flat Spot (for a lack of better words)
Happens often when the bike is cold and is easily re-created if shifting or giving gas in the 3000/4000 RPM range.  Now I can power through 3000-4000RPM but to get caught shifting or giving gas in that range can cause the problem.  Especially when cold.  All that happens is it really bogs down.  Local shop has given impression it could be my K&N Air Filter but they also appear to very much dislike them (especially on a GS500).  Have considered replacing the K&N with a Stock Air Filter and getting my Carbs re-jetted.  Thoughts?

Any help with these problems is greatly appreciated.

If you can wait a few days, I can let you know if my attempted fix for the last 2 issues on my '89 worked.  Also, driving in prime on the freeway will cause fuel starvation since it flows too little fuel.

Things I did: 

1.  Had buddha clean the carbs, rejet and replace any old seals on the carbs. ~$100 with round trip shipping

2.  Bought a used 2004+ frame petcock on ebay.  The old petcocks tend to fail, which can cause all 3 of these issues.  They were brilliantly redisigned in '04, but will require thicker fuel lines.  ~$30 shipped on ebay + $10 for new fuel lines and clamps.

These symptoms aren't uncommon, and I plan to first replace the carb, and then the petcock to isolate the problem.

Hi Juan,

Thanks for the info...
I can definitely wait a few days to hear back from you regarding your attempted fix.
(I will also send you a PM).

Little bit of bumpage just in case someone else has some ideas...
So far it looks like I am going to try replacing my Pet chicken/Fuel Lines with ones from a 2004+.

New petcock won't change your overflowing carbs though. Stuck floats maybe? Clean out those carbs. New petcock is still a good idea.

I agree that a carb cleaning/inspection is required at this point. A cleaning will probably help the bogging problem and an inspection will determine if the float valves are damaged. I'm not sure what kind of K&N filter you have. It is possible that this requires a rejet. I suggest posting a picture of your setup.

Regarding fuel starvation, I my first thought was that you should replace the tank-mounted petcock. My only reservation is that the problem also occurs on PRI. In that case, you may want to take a look at the tank-mounted petcock. There is a filter screen in there that could be clogged. Maybe also a blockage in one of the fuel lines, or rust particles blocking a carb passage?

Good luck!

+1 for cleaning/inspecting the petcock(s) and adjusting float height.  I was having the same problems as you a few weeks back and I did this and worked great after.

good luck

Buuuuuuuudhhaaaa!