Engine problems

[galadrium]

Hello. I recently purchased a 1999 GS500E. I am having some engine problems I cannot seem to figure out. The engine runs rough throughout the RPM range, frequently hesitating. The idle is set correctly, but sometimes after operating around 4-5K RPMs the engine will remain at those RPMs for 30-40 seconds then will gradually return to the correct idle setting. Upon pulling the spark plugs I have noticed that the plug on the left side of the engine was extremely fouled, the spark plug on the right side of the engine appeared normal.

Some of the things I have done so far to this bike to hopefully fix the problem are:
Installed a repair kit on both carburetors (new gaskets, seals)
Cleaned both carburetors, twice.
Synced the carburetors
Drained and cleaned out the fuel tank
Cleaned and recharged the K&N air filter
Replaced both spark plugs (the plug on the left side fouled up again after 20 minutes of use)

I am still at a loss for what could be causing this. Does anyone have any thoughts about what my problem could be? Thank you in advance for any help you might have.

[bigfatcat]

Hello. I recently purchased a 1999 GS500E. I am having some engine problems I cannot seem to figure out. The engine runs rough throughout the RPM range, frequently hesitating. The idle is set correctly, but sometimes after operating around 4-5K RPMs the engine will remain at those RPMs for 30-40 seconds then will gradually return to the correct idle setting. Upon pulling the spark plugs I have noticed that the plug on the left side of the engine was extremely fouled, the spark plug on the right side of the engine appeared normal.

Some of the things I have done so far to this bike to hopefully fix the problem are:
Installed a repair kit on both carburetors (new gaskets, seals)
Cleaned both carburetors, twice.
Synced the carburetors
Drained and cleaned out the fuel tank
Cleaned and recharged the K&N air filter
Replaced both spark plugs (the plug on the left side fouled up again after 20 minutes of use)

I am still at a loss for what could be causing this. Does anyone have any thoughts about what my problem could be? Thank you in advance for any help you might have.

Assuming the left plug fouled with carbon, I'd guess the left carb is flooding - even if you set the float level by the book, if the float needle valve assembly is worn it will leak. Use the clear tube method to see the actual fuel level in the float bowl.

[salamander]

Welcome!  You'll find there's a great bunch of folks around here that know the GS5's inside and out -- unfortunately, I'm still learning and I'm not one of them. 

Have you checked if you're getting a good spark, especially in the left cylinder?

Can you be a little more specific in what you did when you cleaned the carbs?  Getting the gunk out of the bowls is good, but there are lots of small passages that need to be cleared, too.  For example, did you clean the jets (a good soak in carb cleaner works wonders).  Also, what size jets are you currently running?

[galadrium]

Thanks for all the responses.

When I cleaned the carbs, I took everything apart i could and cleaned it. Jets included. I also replaced the float needle valves, they came with the carb repair kit.

I tried to check to see if I was getting a good spark from the plugs. According to the repair manual I am supposed to take a plug out and and hook it to the plug wire and let the spark jump across the engine case. I couldn't get either plug to do that, although I could see the spark clearly between the gaps on the plugs.

[salamander]

That's where you'd expect to see the spark -- you're just holding the threaded part of the plug against the engine to make the ground connection.  The sparks were strong and blue in color (not orange)?

On the carbs, like I said, there a lot of small passages -- were those cleaned as well?  There are two small openings in the mouth of the carb that feed air into the main and pilot circuits.  Do you know how the pilot air screws are set (ie, turns out)?

With the K&N filters, the bike may have needed different than stock jet sizes -- do you know what sizes are currently in there?

[gsJack]

Mmmmm, sounds familiar.  I was waiting in line at the bank drive-up last month and my 02 GS idle slowed and then it died.  Had to hold the throttle open to restart so it was flooding out and not starving out.  Repeated a couple times.  No problem above idle while riding it home and after it was parked a while  there was the tell tale little puddle of gas below the air box drain hose.  Open and shut case, carb float needle valve was leaking and I searched ebay and found some new ones at a good price and ordered.

While waiting for parts and dreading taking those old carbs with 97k miles on them apart I decided to check further.  Discovered the left plug wire was loose in the coil and snipped it off, put a big dab of diaelectric grease on the end, and screwed it back into the coil tight.  Problem solved, bike running good as new again and the carbs with 97k miles on them remain untouched.     And I have a couple new needle valves available now if I ever need them.