Hello All,

I am Aron from Hungary. First of all I'd like to say thank you to the members of this community because I found here a lot of good specifications about GS500 maintenance.

I have a GS500F (2006) and unfortunately I have faced to a strange problem which still could not be solved. (9900 miles in the bike)

The symptoms are the following: If I accelerate (e.g. in second gear) to 9k rpm and that time I close the throttle the bike jumps (I mean speed up). Of course I feel that the engine lost its power at all rpm range but mainly at high rpm I feel it is weaker than before. At acceleration sometimes the bike twitches above 5k rpm as well. So it is far from the "smooth acceleration".

My idea was it will be air/fuel mixture problem or firing problem.

I have checked the following things:
- spark plugs; the color of them are ok; I changed them to new ones, but no improvement
- try to run on PRI; no improvement
- I have checked all of the fuel hoses and in-line fuel filter, they are fine
- I cleaned and rebuilt the carburetor (stock jets, stock exhaust, stock air filter) however when I opened it was absolutely clean. I synched the carburetor by eyeball. Air/Fuel mixture screw is at 2,75 turn.
- I checked all of the air hoses; they were clean
- the float level is OK; I used Kerry's instructions
- the air filter (Hiflo HFA3503) seemed to me clean
- choke and throttle cable are OK

So I have not found the source of the problem yet. I would be glad if you can write down any tips where to continue the fault finding. I run out of ideas. ( Maybe an electrical issue? )

Thank you for your answer in advance,
Aron

Ps.: I am sorry about my poor English

Your english is better than most of ours' so I wouldnt worry about it.  as for your problem did it start all at once or get worse over time?  How does it act at lower rpms?

Hello Jeremy,

At low rpm I think it is OK. The idle is not as stable as a rock there are small patches but as I remember it was the same in the past when the bike was OK.

"Did it start all at once or get worse over time?"
It is a difficult question because I can not give you a clear answer. At the end of last year I changed the spark plugs, oil, air filter (12000km regular maintenance) and it was OK for a while (500km) and at one time I felt something is not OK when I accelerate. From that moment I have recorded the problem.

Today I went a longer trip and I readjusted the idle to 1200rpm (today the weather was hot) and I felt the acceleration is little bit smoother, but the "jumping effect" is still exist. An other new experience: when I accelerate slowly (not with full gas) there is no jumping effect at 9K rpm when I close the throttle.

Tomorrow I am going to try out 3 things:
-   adjust air/mix screw 3 turns
-   carb balancing by the aquarium hose balancer
-   add two #3 washer to the needles
Let's see what happen after these adjustments:)

New updates

So I adjusted the air/fuel mixture screw to 3 turns – no improvement

I did carb balancing and after it the bike has became much powerful. The acceleration is smoother now but the "jumping effect" is still exists when I close the throttle at high rpm. What can be the reason? I still do not know

I added one washer on the needle and the acceleration became much linear on full rpm range but I feel the bike lost her power at high rpm range. There is no gap at 5,5K rpm but I can not feel that I get some additional power above 7K rpm. So I can assume that this cheap carb mod does not work to me.

Now I am at loss I do not know what can be the next step.
Any idea?

it sounds to me that you might be running a bit on the rich side you said your plug color is ok but i take that as there not glow in the dark white.  are they coco brown or more of a black color?

Check carb diaphram boots for holes 

Just a thought... That was my problem w/ the throttle jumping. 

I checked the diaphragms once again and unfortunately I did not find any holes on them (I say unfortunately because now I still do not know what the problem is .). What I realized that one side of a diaphragm was a little bit damaged. The other has been damaged as well at the same place but not as much as the other.

Here are some photos of them:




Can it be the problem?  I do not think so but it is strange to me how it was damaged.

I have checked the spark plugs once again and they seemed to me brown as I can see on the reference pictures. Tomorrow I will take some photos of them as well.

looks like someone took a grinder or file to the slide to make it lighter in hopes of getting better throttle responce.

Before I opened the carb the screws on the top of that were untouched. I think I was the first man who opened it.   It is funy because once I payed to a bike mechanic team for carb cleaning. Maybe they just used seafoam or something similar...

Should I change the diaphragm or they are OK and can not cause the reported problem?

The filed sides look scary ... but they may not affect much.
I will read your first and other posts and respond. Usually if the post has a lot of replies I tend to leave it alone, or that I got no concrete theory.
Cool.
Buddha.

OK I know why I didn't respond to this post.
On a GS there are 2 carburetion problems I have not solved. I have had this happen on 1 of mine ... it was very much minor and I still own it. Could be the slide comming up too fast, could be a foat that is set higher than it should be ... no idea.

The second problem is much more uncommon. From 3/4 or even 7/8th throttle if you open the throttle ... it will deecelerate. Never had it happen, but I know of someone who did.

Fortunately these are both very very rare.
Sorry man, I am clueless. Let me know how it pans out.

Cool.
Buddha.

Thank you for everybody who tried  to help me  

So as my last idea I have changed all of the fuel hoses and I have removed the inline fuel filter as well.  I cleaned air hoses and the air filter with compressed air. After these adjustments now the bike runs much better. The acceleration is smooth except around 6k rpm where a gap is but I think it is normal at a stock GS500. The "jumping effect" has not disappeared totally but I can feel it very rarely and it is not as drastic as previously. 

Now I am quite satisfied how the bike runs. Maybe later I will add a new K&N filter and I will rejet it. I hope after it both the "jumping effect" and the hesitation around 6krpm will disappear. 

Aron, welcome to the board!   

While you still have it in stock condition, return the mixture screws to the stock setting, which I think is 2 1/4 turns.  As I read this thread I was thinking you had a fuel starvation problem, but I see you solved it before I read it.

I see you like riding around at full throttle and 9,000 rpms.  Be careful, you're riding in public roads!

Hi Aron!
I think I know where the problem is. It is to my opinion the hiflo airfilter you installed responsible for all the symptoms. After I installed it in my GS500f had exactly the same problem as you have described them and exactly the same thoughts with you, but I came to the conclusion that it is an 'artificially made' fuel starvation problem.

I solved it by installing an original Suzuki air filter, so I dropped the carb sub pressure back to normal levels and I do not have any more problems.  I suggest you do the same and leave all setting screws of the carburetor as they used to be.

I am, also, almost certain that if you want a hiflo air filter on your GS, you will have to rejet the carbs. If you do not want to through away your hiflo airfilter you can slightly block the air flow of it by either spraying it very gently with color (to block a bit of  the air passage) or place some cotton 2-3 cm in the bottom of it (also to block the air flow a bit).

I hope this helps.

Hey sorry to revive a dead thread but I am also suffering from hiflo filtro syndrome.  Does the cotton trick work?  I was just thinking about exactly the same trick with a crumpled grocery bag or something like that.  I foolishly left my stock filter at my parents house and have not run the bike hard until just now but I am going to the track this weekend, so I am willing to try something.  I was liking the stuffing idea better than the spraying idea because you can always take stuffing our to get it just right.

If you need a filter RIGHT NOW, you can go to any hardware store and get a foam filter for a shop vac. Layer it up a little and maybe a thin coat of oil on it.

I do want to point out- this will stop insects from getting in your carbs, but not much else.

I am going to drive to my parents house and get my old stock one today.  I have the Hiflo Filtro brand drop in one in right now and it runs but has hesitation at a couple of rpms (5 and 9-10) under hard driving.  Does not seem like a good drop in to me.  I tried sticking plastic bags in it to cut off some of the area but it did not noticably help.  Could be too much restriction also, but there is not much I can do to make it higher flow.  Going back to stock seems like the best solution.