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2006 Suzuki GS 500f
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Discussion Starter #1 (Edited)
Hi All,

I have an '06 Suzuki GS500F ~28k miles. I bought it through a private sale earlier this year (it is my first bike). Since owning the bike it has idled at 4-5000 RPM. In doing some of my own research the hanging idle is a very common problem with this model. In an effort to get it running good and an idle around 12-1500 rpm I have performed some routine maintenance to try and alleviate the problem.

I cleaned the carbs, found dirty jets on one side during this.
Changed the oil and oil filter
Changed the air filter
replaced any brittle looking rubber that could give me air/vacuum issues.
Replaced the battery
Replaced the spark plugs
The air fuel mixture screws are covered with a brass cap from the factory, reading forums the bikes tend to run lean. the belief is that this is an emissions thing. recommendations stated to remove caps and unscrew 1 and a half turns for both carbs, thats what I did.


The bike used to get closer to 40 mpg, last few fill ups have been around 26-27 mpg. In addition if I am flat out in 6th gear on the highway I maintain speed or very slightly accelerate at best. I generally have to downshift into 5th for hills and to get to 70 mph. leads me to believe I am not burning efficiently. (need to check the plugs)

The exhaust pops a lot both when I turn on the bike and after it has been running for a while.

If I take the choke off 100%, even if I have been riding the bike for 1-2 hrs, the engine dies when coming to a stop.
When starting the bike up it will idle at 12-1400 rpm for 20-30 seconds and then die (full choke). I have to rev and hold the throttle to warm the bike up or it will just die.

See images below for my spark plugs

Right Plug
64032


Left Plug
64033


Thanks!
Mike
 

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The choke situation is a dead giveaway that the engine is starving for fuel and the choke cutting off AIR will allow more fuel in, in proportion (Fuel/ air ratio) or it may actually be enrichening the Fuel ratio squirted into the air stream, as there are 2 different types of choke systems on modern Carbed bikes, not like completely flooding the float bowl like on earlier bikes!!!!!!!!!!!!

If a rich mixture from you leaving the choke on is allowed for even a short time, the excess fuel will 'Wash' the valves and seats, Guides, valve stem seals, Pistons and rings, the Cylinder and absolutely ruin them! I know from experience:(

Re-do the Carbs yourself or take them off and have them fixed by a Pro, is my best advice.

Sam:)
 

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Sounds like you have clogged pilot circuits in the carbs. Maybe not the actual jet if you cleaned those well, but the circuit within the carb body leading to the pilot jets. And maybe a vacuum leak to boot.
 

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Your plugs look OK but I see some ash and the side electrode looks like it has gotten really hot. The ash is usually from poor fuel quality, I would drain the tank, replace with good new fuel (any grade) and use some type of cleaner like Lucas Fuel System Cleaner. Second double check the carbs. This screams clogged jets or circuits all over the place. The pilot jet is responsible for the idle, but doesn't do much while you are riding, the main jet and needle do that. If you have diaphragm type carbs check to make sure that the diaphragms are not torn and that they seal up at the housing, and also that they move freely. These are what pulls the throttle valve up and the needle out of the jet, both are critical for getting fuel into the engine. I usually soak carbs in a carb cleaner bath in an ultrasonic cleaner. I heat the solvent up to about 100°F and run the cleaner for around 30 to 45 minutes for really nasty carbs. Clean off the solvent with a quality carb and choke cleaner as the carb bath doesnt evaporate cleanly. Lastly in order to get your bike to idle correctly the carbs need to be sync'd. If they are not in sync the bike will never idle correctly, it will either need to be too high to compensate for the cylinder that is trying to die or it will surge as the bike tries to stay running. There are plenty of sync vids on youtube, with professional tools and with DIY tools. I have done both and actually prefer the DIY water gauge over a professional vacuum setup.
 

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70 CB 18 Wolf 19 San Gabriel
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Choke on but plugs not covered in black soot are contradictory. I suspect that you are not getting fuel flow as noted in the post directly above.
If you have CV carbs, the diaphragm has to be positioned correctly to insure the slide is rotated to the proper orientation. If the diaphragm is not sealed tightly, but is 'off', vacuum won't operate the slide properly, and will choke off airflow into the engine. Because the slide is 'down', it won't expose more of the main jet, nor open it up to flow more fuel. Result is the engine will be starved, for both fuel and air.
If you have a cylindrical slide, operated by a diaphragm, it may not move down as far as it should if not oriented properly. In the manually operated slide, round ones, it has to be oriented to make the idle speed adjustment 'hit' at the proper point on the slide. If not, the slide may not go down as far as needed, and you will have a very unstable idle with a lot of stumble and chugging as you attempt to accelerate. There is a slot on the round slide to make sure it is in place, but you can put it back together improperly, but it won't work right. It does look like time for a couple new spark plugs, or at least take a file to the side and center electrodes to 'square off' them both. Spark plugs work better when the electrodes are both 'sharp edged'. The electrons gather together, and don't like to be near their neighbors, and are looking for a way to jump and get away from them. If you give them a 'sharp corner' or a point, as is used by TIG/MIG welders, the spark can jump more readily as the electrons can gather nearby to each other without being crowded as much as they can with a rounded electrode.
Look at the electrodes on a new plug. Squared off, and sharp cornered. Make that happen, on your old plugs, and they'll work close to new(until the side electrode becomes so thing...)
In short(after all this verbiage) you need to go over your carbs again. You can get pretty close on synching without any sort of manifold/vacuum gauge by setting the butterfly on each to being fully closed. Make note of the idle screw mechanical stop on each(where the slot points), and the install. While watching the throttle arms where the cables are attached, work the throttle from full close(you left them fully closed, right?) and adjust the slack in each cable so they BOTH come off the idle spot at the same time. That should get the butterfly in synch with the other. Now you can adjust the mechanical idle stop to 1-1.5 turns from fully closed. Start the engine, and adjust the idle rpms as desired, trying to adjust both the same amount so they stay synchronized. This 'mechanical' synch will work pretty well if you are careful.
tom
 

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The air fuel mixture screws are covered with a brass cap from the factory, reading forums the bikes tend to run lean. the belief is that this is an emissions thing. recommendations stated to remove caps and unscrew 1 and a half turns for both carbs, thats what I did.
Are you saying you turned them 1 1/2 turns out more? (In addition to the factory setting / added to the original setting).

S F
 

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2006 Suzuki GS 500f
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Discussion Starter #7
Hi Everyone, thanks for the responses so far. @SemiFast the factory setting was all the way screwed in. I unscrewed 1 and 1/2 turns from that. I am surprised that I need to do more work on the carbs after cleaning them. Does this mean that I put them back together incorrectly?

Also I synced my carbs, forgot to add that to the list. From what I understand a carb sync is a fine tune, should not be the source of my issue.

Thanks
 

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The air fuel mixture screws are covered with a brass cap from the factory
(About fuel mixture screws): the factory setting was all the way screwed in. I unscrewed 1 and 1/2 turns from that.
Hum... Never found one maladjusted that way from the factory.
However, on some carburetors I have seen the caps over fuel mixture screws VERY close to the head of the screw. It is easy to touch the head of the screw with the drill while drilling the cap out, spinning the screw in. Not saying that is what happened but there is that. BTW, A limiter on the drill helps to prevent over-drilling.
Anyway...
Unfortunately I don't remember if I've ever done carburetors on a GS500F or what setting would be the bench setting for the fuel mixture screws. I would expect 1 1/2 turns out to be too lean as most of the Japanese machines end up in with fuel screws more in the range of 3 ~ 4 turns out. Back when they used air screws 1 1/2 turns out was a common bench setting but not for fuel screws.
As for the way the bike has acted up for as long as you've owned it I'm thinking you may still have an air leak somewhere or a carburetor problem, maybe both.
Have you checked the vacuum petcock to be sure the diaphragm is not leaking air?

S F
 

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2006 Suzuki GS 500f
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Discussion Starter #9
Hi,

The bike had good mpgs when I had it and did not spit or sputter as much before cleaning the carb. The diaphragms inside the carb were in good health. I have not inspected my petcock.

With the drilling out I made a small hole then used a screw to pull out the caps. Did not go deep at all.

I believe there is something I can get from an auto parts store to spray around the carbs to look for an air leak, right?

Raining where I am today and tomorrow so I won't be able to do any work till Sunday

Thanks again for the responses
 

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70 CB 18 Wolf 19 San Gabriel
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You can use 'carb cleaner' or 'brake cleaner' that is flammable as a spray that will richen the mixture when its near a leak. You can also use a bernz-o-maitc type propane torch, along with a length of tubing attached to the outlet nozzle. Open the spigot a bit, and wander the end of the tubing around the areas you suspect. The gas will/can get sucked into the air leak, and make the mix more burnable and smooth the engine out. Not as messy as sprays, but still flammable. Propane is heavier than air(I think) so do not use in a closed space where it could gather. Wear eye protection.
tom
 
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