2006 GS500F Running Rough (at highway speeds)

[jbmazda6]

Hi all,

Making my first post on another forum is always fun (maybe not too much right now since I'm coming to the experts with a problem).

Anyways, some background information:

I bought my gs500 a few weeks ago with 12000 miles on it. The body was in very good shape and it ran well, at least to my knowledge, at the time of purchase. The previous owner installed an in-line fuel filter because the tank has rust in it and it was getting to the carbs. He also took out the vacuum operated portion of the petcock. I personally watched him clean the carbs and they looked good afterwards.

On to the problem:

About two weeks after my purchase I was cruising at about 60mph on some back roads when the bike suddenly lost power and started bucking. I tried giving it more gas and it would rev up but eventually the throttle would get no response at all and the bike would die as I came to a stop. I let it sit for a few minutes and it started up just as it normally would. I began riding again and encountered the same problem a couple miles down the road. I was able to get the bike home by not going to fast and keeping the revs moving. After this I let the bike sit over night and went for a ride the next day and didn't have any issues. Most of my driving is less than 40mph as I just drive around campus. I did take it out on a few rides and it cruised at highway speeds without issue for a few days. The problem then presented itself again a few days ago after about 5 miles on the highway. I was able to limp the bike home again that time but decided I wouldn't stray far from home until I could get the problem fixed. I decided to test the bike the next day on a very short stretch of outer road and encountered the bucking and stalling problem after about a half mile of going 60mph. At this point I was VERY frustrated and decided to just tear into the bike to see what I could find.

What I've found so far:

Lots of rust in the tank. The rust was getting through the fuel system because there was no filter element on the in tank petcock. Not sure how this happened. A crappy picture of inside the tank and the plastic piece without the filter element are attached. I also decided to open up the carbs to see how they look. Both were still very clean and all the jets were free of rust or anything else that could clog them.

The in-tank petcock wasn't blocked by junk but definitely had some gunk inside of it.

I also checked the spark plugs a while back when I completed an oil change and they looked a little grey so the bike is running a little lean most likely.

What I think the issue is:

It feels like the engine is starving for fuel (like you're running out of fuel) at highway speeds. I know many people say that the vacuum operated system has issues at high speeds because of low manifold pressure but my vacuum system has been deleted so that couldn't be the cause. It then made me think that the float bowls are still getting low somehow. Could it possibly be that I'm just not getting enough fuel to the carbs fast enough because of a possible blockage in the fuel system or because of the in-line fuel filter that was installed? The fuel filter is installed the correct way so that is not the issue. Also, when this has happened I look down at the fuel filter and both sides are full of fuel which makes me believe that it's not a fuel starvation issue.

Could it possibly be a carb-syncing issue? I'm very new to carburetors and am trying my best to learn as fast as I can (On a side note, I come from the direct injected turbo world. If anyone wants to chat shoot me a pm).

I just haven't read of somebody having the same issue as me after they figured out the issue with the vacuum operated petcock.

Final thoughts:

If anybody has an extra in-tank petcock I will buy it from you! Need one ASAP because I am not putting everything back together until I get one with a filter on it. My plan was to seal the tank as well while I have everything apart. I did clean the frame mounted petcock as well while I have it off. Need to find an o-ring that will fit the circular knob piece to finish that "rebuild".

Wow, longest first post ever for me. Hopefully I'll be lucky enough to get a few responses from you guys! Thank you for taking the time out of your day to read my wall of text. If I can be of any assistance to somebody in the NW Arkansas area please let me know.

Thanks,
Justin

[Big Rich]

Hmmm.... I have to ask: have the valves been checked recently? I don't think it's the root of your problem, but it is important. Since the vacuum petcock has been deleted (mind explaining how exactly?) that does take one part of the equation out. But if you're getting high rpm fuel starvation issues, it could leave either the gas tank vent or the carb vent line. Do you have the stock airbox or a K&N lunchbox? Oh, and if there's no vacuum line going from the carb to the petcock, is the line properly capped off at the carbs?

[jbmazda6]

Thanks for the response.

I am not sure when the valves where checked last. I looked into doing that myself but do not want to spend the money to buy a whole shim kit as I'm just planning on owning the bike until next summer and then upgrading. I will probably break open the valve cover and at least check the gaps while I have everything apart. If it is way out of spec then I guess that could be the issue.

The little plunger and diaphragm were removed out of the frame mounted petcock and a new gasket was placed there instead. I do not see how it could cause any flow issues. It should flow more than stock if anything.

The carb vent line is clear and the vacuum line coming off the carbs is capped. I opened up and cleaned the gas tank cap right after I took the tank off because I was having trouble turning the key to get the cap  open. All is smooth now and I didn't see anything blocking the vent.

[baronduff]

I could be very wrong, so hopefully someone else will chime in, but I was under the impression you could buy single shims. It would mean cracking it open, taking measurements and then replacing the shims at a later date, but avoids having to get a full kit?

[Big Rich]

Yeah Baron, you are correct. The entire shim kit is way over priced (unless you are opening up a bike shop....). Single shims are anywhere from $7 to $10 each.

[lucas]

Hey you mentioned that there was an in line fuel filter at one point.  Is that still the case?  I have heard of other people having fuel starvation at highway speeds due to in line filters.  I guess the float bowls don't fill up fast enough due to the restriction in the filter element.

That might explain why it worked ok at first.  It took some time for the rust to migrate down from the tank and into the fuel filter.

Some fuel filters are more restrictive than others and are for applications where a fuel pump will force the fuel through the element.  We only have gravity to move our fuel.

[lucas]

Ps, no pictures are attached.  I don't know if this forum allows new members to post photos...

[1034am]

the inline fuel filters are very polarizing. some guys swear by them, others insist they're the cause of all troubles.
try it both ways....

[jbmazda6]

I have not tried it without the in-line filter because of the rust problems. As soon as I clear all the rust out and get the proper in-tank filter/petcock in I will see what happens.

I am going to measure the valve clearance but pass on completing that because I want to tackle one problem at a time so I know what the solution is.

I tried attaching two pictures to my first post but they were too large because I took them with my smart phone.

Has anyone tried the Tourmax replacement? The OEM one is crazy expensive.

Link to the Tourmax petcock: http://www.ebay.com/itm/New-Fuel-Petcock-Gas-Petrol-Valve-Tap-chicken-GS500-GS-500-E-F-See-Notes-Z55-/361392699261

[lucas]

Well how does the fuel filter look, is it dirty?

If you suspect that the fuel filter is starving your carbs you can try using a funnel and fuel hose pieces and pour gas through the filter and see if it runs through easily.  The fuel should run through the fuel very easily with very very little resistance.

Unfortunately since we only have gravity to move gas from the tank to the carbs almost any resistance can be a problem.

[Suzuki Stevo]

the inline fuel filters are very polarizing. some guys swear by them, others insist they're the cause of all troubles.
try it both ways....

If it's a Automotive Filter like the one in my photo, you will probably have problems, if it's an Inline Motorcycle Filter you will probably be Ok, you just have to have a filter that works with a gravity feed system. The Fram in my photo is an Automotive Filter that worked fine until around 3/4 of a tank (see photo) it needs a fuel pump and my garden tractor and the GS500 does not have one.

Regardless if it's the right kind or not, I would bypass it and see, if only to rule it out...as you already mentioned

[jbmazda6]

The in-line fuel filter was not extremely dirty. There were some rust pieces in it but nothing extreme. I believe it is a motorcycle fuel filter so it shouldn't have had a flow problem. Could have though, which is why I'm getting rid of it. I ordered the Tourmax fuel petcock today so once I get that I am going to put everything back together with new fuel line and see how she runs. If I'm still having an issue then I'm going to move on to checking the valve clearance. It doesn't look like it would be too much trouble to replace the shims but I'd rather not.

[lucas]

Hey just want to encourage you to check your valve clearance even if your bike starts running alright again.

It takes far less time than you might imagine and it is something you need to do periodically to keep your bike running in to form.

Seriously, once you have the tank off it is trivial to get at the cams.  As long as you have a set of shims down to say .002 or .003 you are good to go.

[jbmazda6]

Yeah, I'm definitely going to check the clearance. I just want to tackle one thing at a time for now. I also need to get another measuring tool because the one I have now only goes down to .004.

[1034am]

and clean out that tank! a good (strong) rust neutralizer followed by a epoxy tank lining will get rid of any of that nasty stuff. just remember to clear out your holes w/the epoxy or you will be drilling out new ones. (my fuel line holes were epoxied over and i had to drill out.) good luck.

[jbmazda6]

I've been working on cleaning the tank with vinegar. Two 24 hour baths and it looks much better!

Before:


After:

[lucas]

Huge improvement!  What steps did you follow for the vinegar soaks, I'd like the inside of my tank to look as nice as yours.

[1034am]

regarding the tank, my personal experience: everytime i got it rust free, I'd start planning my next move, and by that time it would be rusted again!  Someone recommended an epoxy coating to prevent the rust from returning. I really didn't want to do it, but w/it rusting after just a few days, I did it and seems good. Got a tank liner kit on Amazon, not the mess I thought it was going to be. Just don't epoxy over your holes or you'll have to drill them out.