Hi everyone,

After more than a year of lurking, it's finally my turn to join the community. I've read through the forum posts hundreds of times, but none have helped with my issue.
Now, I'm hoping for a messiah who has any idea that can save me. 

The Issue:
After storing my 2004 GS500F for winter 2023/24, I performed the following maintenance: 
- Replaced spark plugs. 
- Changed oil and oil filter. 
- Replaced the air filter. 

When I took the bike out, it suddenly started bogging down at full throttle and dying when coming to a stop.
It won't hold idle without the choke, and with the choke it's either 0% or 100%, under 100% it simply stalls. With the choke on, it insists on idling at ~4000 RPM. 

Additionally, while riding, it sputters randomly and feels sluggish, refusing to go over 7,000 RPM. 

What I've Tried So Far:

1st Attempt
I assumed the carbs were clogged, so I: 
- Removed and cleaned all jets. 
- Checked float height (measured 11.98 mm) 
- Gapped spark plugs according to the service manual (plugs looked slightly white but nothing extreme) 

After reassembling everything, the same issues persisted. 

2nd Attempt
- Measured valve clearances (~0.04mm / 0.05mm on both intake and exhaust) 
- Replaced fuel lines and installed a translucent fuel filter to monitor fuel flow (seemed fine) 
- Took the carburetor apart again disconnected both carbs from eachother, checked fuel intake between both carbs, and thoroughly cleaned all passages, including those 2 under the butterfly valves. 
- Upsized the main jet to 134. 
- Did control on vacuum lines and boots with start fluid while running no change.
- Tried running on PRI to bypass the vacuum petcock. 

Again, no improvement the same problems persisted. 

3rd Attempt
I suspected electrical issues might be causing misfires, so I: 
- Checked the battery (fully charged) 
- Verified spark on both plugs 
- Measured the coils resistance (both at 19 ohms) 
- Checked ignition caps (4 ohms resistance) 
- Inspected the CDI box (OK) 
- Inspected fuse (OK)

At this point, I noticed the spark plugs were running way too white, indicating a fuel delivery issue. 

Current Symptoms After Startup:
- After 2–4 minutes of warm-up, the bike now holds a reasonably steady idle.
- Still sputters when given gas.
- Feels unusually warm for a short warm-up in cold weather. (8°C / 46°F outside temp) 
- While riding, it randomly kicks hard (like a sudden surge) but then goes back into "limp" mode unpredictably. 

The bike has a slightly larger exhaust, but all other components are stock 

TL:DR
Bike runs rough, sputters, backfires out of carb sometimes, gets warm too easily. Fuel system OK, clearance with valves within spec, electrical for ignition OK. Spark plugs white.
I'm completely out of ideas. The bike ran fine before storage in 2023 to 2024. Has anyone experienced something similar or have any insight? 

Would appreciate any help!

Just I guess here but,  you did not use the OEM air filter for that year?

I'd try that first.

Cv carbs are very sensitive things and rely a lot on the restriction created by the OEM air filter.

Hi Herennow,
Thanks for the reply, I've installed the air filter corresponding to: " Luftfilter, GS500E 88-02/F 03-10", should be correct with partnr.: MCAF3501.

I did try to limit the amount of air allowed in blocking about 60% og the filters Hole with tape. No change.

I would just use till it clears up, carbs could still be clogged. 134mains are maybe too much for stock filter. Spark plug color?
Needle clip can break and the the needle hangs, it will make that binary operation, it happened to me after too much fiddling of the carbs, beware.
Check slides are going up by accelerating without filter

I'll try to look at the slides, but seemed ok. Spark plugs definetly indicate a Fuel problem, I'll get you some pictures later today.

First picture is right cylinder.
Second picture is left cylinder.

It smoked a little from right exhaust header, could this indicate a problem or dust burning off? 

I'll check up on the sliders later.

Assuming you're in the US, four sizes up on the main jet is a lot.

If you search the forum, there have been tons of stories of folks trying to tune their bikes with different exhausts and it's always difficult.
Do you still have the original exhaust or can you borrow one to test?
Post some pictures of your existing setup.
Buddha had done all the testing to have these responses at his fingertips, but he hasn't been around much since his divorce....
I'm guessing a free flow exhaust and a free flow filter might be limiting the slides rise. I remember Buddha used to recommend drilling a second hole somewhere on the slide to allow in more vacuum to lift the slide quicker when different exhausts were fitted, but I don't remember the details.

Nope, located in Europe.

I'd give you that it's a free flow exhaust, but I only exchanged the filter in the original Airbox with one similar to the previous. Also rode normally with that setup before storage.

I checked the slides and vacuum diaphragm again, no luck. Suction was good, E-ring placed in lowest setting, getting the needle as high up as possible. I've put in 130 mains, no difference.
It is still struggling to get fuel as it has delayed throttle response and seems bogged down until the rpm then lights up, hangs, drops and stalls.

Any other guesses? Because I'm running out.. 

Fuel tank breathing ok? How fast is fuel coming out of carb drains? (Petcock/ inside of the tank ok?)

Fuel tank good, no dirt inside, petcock in tank serviced not so long ago with new o-rings.
OK steady fuel flow as I did empty the tank to get a look at the diaphragms on the carb.

Did look like there was a slightly higher pressure on the reserve drain than the ON drain, but still flowing.

Only 10 ml in left carb, nothing much, was started before test.
First picture is right carb and second is left. I've taken pictures of the tubes height to the bowl before fuel was dripping out. Seems particular low, flow height set to service manual.

Are you still running on the tank of fuel from storage. If so drain and replace, it could be stale gas or water in the gas from ethanol.

Quote from: chris900f on March 05, 2025, 04:42:18 PMAre you still running on the tank of fuel from storage. If so drain and replace, it could be stale gas or water in the gas from ethanol.

Hi Chris,

Yes it's new fuel. 

Could these be the culprits?
Both seals are cracked where the fuel enters to both carbs? 

At worse it would leak, I would check the oring of the carb boots, they sit between the cylinder head and the boot, after the carbs

Quote from: Armandorf on March 06, 2025, 11:03:06 PMAt worse it would leak, I would check the oring of the carb boots, they sit between the cylinder head and the boot, after the carbs

I pulled 'em off, the o-rings were completely flat. Reinstalled normal jet, as to eliminate some variables.
Do you have any other suggestions, before I put it all together again?

New fuel filter

Hello again,

Did a couple of tests since last.

Added new fuel filter, put it back together still ran rough.
TPS was set wrong to 1,33V at closed throttle, so put it back to 0,6V. Did at compression test and both cylinders were 150 PSI, this also indicates OK valve seats, battery was drained to 12,2V so put it on charger no change with fully charged battery. Spark plugs had 1 side on both which were now black with sod, does this indicate anything?

so you have compression,clean fuel , spark, changed the oring valve boot, is the fuel getting through the bowls, maybe float are stuck, have you cked carbis actually squirting fuel?
it seems you just need fuel, dont really know.
i would check the needles are not hanging on the diaphragm slides.

If it's carburetion, it can be very frustrating, they need to be really clean! I had two late model GS500 like yours and spent quite a bit of time working on both sets of carbs, though I was tempted to buy a replacement set. Finally got both sorted, so maybe some of my actions can help you sort yours.

1. the value of pictures, surprising how many times a member chimes in with, what's that thing in picture #1? mine doesn't have that, and problem gets solved. close ups of carb internals and snapshots of entire bike showing exhaust and the installed carbs with airbox and connections.

2. Consider replacing replaced parts, especially air filter. the one you bought was 149 on the website, but they list another for 249, wonder about quality difference. Covering intake is clever troubleshoot strategy, I usually wrap some plastic piece around half of the body of the air filter assembly. Also, suspect the fuel filter, some are junk and too restrictive, even though "new"!

3. 10 ml in bowl. That's not right, should be more like 45-55 cc in each bowl, plus what's in the fuel line. Take a close look at the physical operation of the float. I had one where the tang actually got stuck at the screw that holds the float pin. I had to grind down the head of the screw to solve the interference.

4. Was it difficult to replace the slides/diaphragms? This is a trick question! Anyone who says no problem is suspect; it should be difficult to re-install, difficult not impossible. Once installed you test by pushing them up and watch/listen for the "whoosh" sound as they come down.

5. Replace both pilot jets one size up; if you had 38, use 40's.

6. in #12 above the first picture shows the rubber piece/seal, but look where it goes, looks like a lot of corrosion. If it's corroded there, it's corroded throughout the carbs. It might need soaking in an ultrasonic cleaner to clean out passages, especially pilot jet passage. test by shooting carb cleaner into where pilot jet screws in and it should come out one of the holes in the venturi near the throttle plates. If not, blow compressed air same place and see if it comes through. It must be clear to run properly!

7. With throttle plates completely closed, turn throttle screw clockwise until plates clear about 1/2 half of the hole in the venturi. Set mixture screws around 3 turns out. Adjust idle as necessary after total warmup.

8. Here's a Youtube video that has some good ideas too: https://www.youtube.com/watch?v=AJh1hxNf7BA

Cheers!

Correction: replace #17.5 pilot jet with #20.

2 different carb sets around 2002,2003, which carbs do you have, picture please?

Check to see if #13, called jet needle in parts diagram, fell out of carb body? It's a little chrome guide that the actual needle glides down and up.
https://imgur.com/a/Anax9xM
carbs