idling erratic and higher rpm buck

[Anonymous]

I just got this bike a month ago its a 83 gs550LD and have been having running problems ever since. The guy i bought it off of told me he had cleaned the carbs about 3 months before he sold it to me. Here is what i have done so far new plugs new inline fuel filter, new air filter, rebuilt fuel petcock, running high octane fuel in it per talking to suzuki dealer, tried to adjust carbs, does anybody know what the base setting is on these is. I about at wits end with this thing. please help.

[KEITH KRAUSE]

Erratic idling and higher rpm "buck"(?) Do you mean missing or a stutter/hesitation?
Could be a lot of things. Is the bike completely stock or are there ANY intake/exhaust changes? Dark/blackish exhaust fumes? Burning any oil (white). Any fuel leaks from the carbs or airbox? Does the idle increase a lot from cold to hot? Cold-blooded?
What did you try to adjust on the carbs? Mixture screws? If stock, they're generally about 2 to 2 1/2 turns out. Do you know how to vacuum synch the carbs, check/adjust floats, etc?
Is the spark good and whitish/blue to all 4 plugs?

[Anonymous]

stutter

Yeah its more like a hesitation at about 5 to 6 thousand rpms in and out of the rpms just feels like its bucking like getting fuel then not getting fuel.The bike is completely stock no mods at all except a k&n air filter.exhaust fumes are good no apparent white or black. No leaks from carbs or airbox. The idle does increase from cold to hot and races sometimes. And yes IT is cold blooded. The mixture screws are the ones that i adjusted. The plugs are burning real good so i aliminated a spark problem. I did talk to a repair shop and he told me especially with the age of the bike that the intake boots are probably the main culprit. I ordered two new ones and orings. And after i do this project then im going to take it to a repair shop and have them sync the carbs. When i have the carbs off to do the int boots im going to pull the bowls off and check float height. Because im not sure that the guy that had it before me really knew what he was doing or not.

[KEITH KRAUSE]

Allright. The rpm's rising when hot is a classic intake leak symptom.
Replacing the manifolds and any o-rings with them, along with a good synch and float check/adjustment, will hopefully fix your problem. Apply some hi-temp bearing grease to those o-rings and don't over-tighten them. If you replace any Phillips screws with some Allens, you can torque them to about 6 ft/lb.
Be sure any float bowl venting tubes you have are clear and not kinked too. Also, make sure the gas cap vent is cleaned out.
If you still have questions, let us know.

[Anonymous]

The erratic idle is indeed a lean air draw in the pilot system. If there is an o-ring on the mixture screws, these should be checked/replaced and also check the vacuum caps on any unused vacuum ports to see if they are in place and if they are, if any are cracked. After installing your new intake manifolds, I suggest you allow bike to warm up and at idle, spray WD40 around them to see if idle speed changes. If it does, there is a seating problem (air is leaking in).

[Anonymous]

cap vent

Ok keith this is for you im going to be stupid here and ask you were in the world is the cap vent and how do oyu go about cleaning it. Thanks

[KEITH KRAUSE]

Re: cap vent

Ok keith this is for you im going to be stupid here and ask you were in the world is the cap vent and how do oyu go about cleaning it. Thanks

Gas caps differ a little, but your cap DOES have a vent.
If similar to mine, you should be able to shake the cap and hear a ball rattling around, unless it's stuck. That's where your vent is. I once took the 2 screws off and the plastic cover on my cap and shot the whole thing with carb cleaner with a spray tube. All kinds of reddish sediment came out, even though I didn't have any venting problem. I just mention this because a clean vent is necesary for proper fuel flow. Your previous reply suggests your biggest problem is an intake leak. (high/racing idle)

[Anonymous]

still idling funny

Ok guys I replaced the intake manifolds today and while i had the carbs off i checked float height and one was off acording to specs so i adjusted it and also while i had the bowls off i cleaned the jets and carbs. I dont think the guy that had it before me knew exactly what he was doing as far as mechanics. but thats beside the point. All the pilot screw o rings were fine and i adjusted them all to 2 1/2 turns out from bottom. Got everything back together and ran the bike and it runs like a raped ape now going down the road but i still have an idle problem where it changes from hot to cold running. What i did was just adjust it at a hot idle for now and it seems to be ok. But still throws fits cold and during the warm up period. Any suggestions. Everything else looks fine and i did spray around the carbs and intake boots and carb box boots. oh i also cleaned the gas cap vent out to it had the normal old fuel brown to it. Let me know what ya think. Thanks Howard

[KEITH KRAUSE]

Glad the bike's running better, but if your idle rpm's are still rising significantly from cold to hot, this suggests you still have an intake leak. If you replaced the manifolds with new ones, did you check for any o-rings your manifolds may have? The o-rings sit in a groove and can be rock hard and flattened and hard to see sometimes on old manifolds. But the o-ring groove would be easy to see on new manifolds.
The carbs on some models "pop" into place and the manifold clamps need to be tight also. So be sure of this too.
After any intake leaks are repaired, a good carb vacuum synch is necessary for the bike to idle well. The vacuum levels may be way off. Fine tuning of the mixture screws should be done at the time of synch too. My 2 1/2 turns out is just a general setting suggestion, and fine tuning will probably be necessary. Even a 1/2 turn can matter a lot.
Another reason CV carbs can have idle problems is if the rubber plugs that go over the pilot jets are damaged/missing.

[Anonymous]

idle

The rpms are only rising from cold about 6 to 7 hundred rpms. When i put the new manifolds on i installed new o rings on both manifolds. But i did find that when i took the choke cables off the carbs to remove the carbs from the bike the plastic threads were stipped so i have new ones coming that surely would give me an air leak at that point. i double and triple checked the tightness of the clamps and sprayed around everything with wd40 no apparent rise or drop off of rpms. Now one thing these rubber plugs you re talking about do they cover the pilot adjustment screws and if they are the ones all of mine are gone. And were do you get them i looked on bike bandit and alpha sport and they are not in the picture as a replacement part. I do have a carb synch tool coming from mac tools. Please let me know a rough idea how to do this and were to adjust according to my book you adjust a screw between the carbs that has a lock nut on it is this right?

[KEITH KRAUSE]

I'm not familiar with your carbs, but I hope the "plastic threads" involved with your choke cable is causing an intake leak. I say this because a rise of 6-700 rpm from cold to hot isn't acceptable and suggests you still have an intake leak. There's a small chance a throttle plate(s) could be sticking and causing trouble after it heats up but more common reason for that much rpm gain is an intake leak.
We'll see. The carbs need a synch anyway, so between repairing that possible intake leak and THEN a good carb synch, your problem should go away and the bike should idle about 1,100 rpm's once warmed up.
The rubber plugs I mentioned are above the pilot jets inside. They're meant to hinder tampering.
As for synch instructions, I'm not familiar with your model. Your brief description of the synch adjustment screw sounds right. There's a screw held by a nut and a spring under that. You have to adjust it so the top of the throttle plates meet a specific point. Even with only 2 carbs, there may be a synch order too. Your model may require a slightly different synch procedure. You need a manual or ask someone here who knows how to synch your model. It's very important to get it right.
Be sure to use two large fans to keep the motor cooler while doing the synch. Don't over-heat. Plug the vacuum port if you use a vented fuel reservoir instead of the tank with extended fuel/vacuum lines.

[Anonymous]

about ready to sell my bike and get a good one

Another problem my lag at 5 to 6000 rpms is gone but now if im cruising and go to give it more throttle it stutters and bogs for a couple of seconds and then takes off and runs good. Ive about had it with this bike its benn nothing but problems since ive had it. And then of course there is the idle problem oh boy. i got a synch tool today so im going to synch the carbs when i get the right adapters for my carbs. I dont think that i have any air leaks that i can find i sprayed with carb cleaner and wd40 and nothing seems to change. But then it wont idle long enough sometimes to check but when it does cant find anything. Please help or im gonna burn it and collect the insurance money. Thanks

[KEITH KRAUSE]

Well, like I said, the cold to hot rpm's shouldn't rise that much. Something's wrong. The spray test doesn't always expose a leak. I use fine water mist by the way. It's cleaner than WD40 or others. The rpm's will drop a moment using water, if you hit the spot.
The carb synch should be done, but it can't be done right with an intake leak. If you feel there's no intake leak, then try the synch and see how it runs after.

[Anonymous]

hallelujah

Its finally fixed guys! Pulled the carbs off and really cleaned them and in talking to a guy who owns a bike repair shop, he told me that the #95 main jet is to be in the middle and the #105 main jet is to be on the outside the dumd*@%^$*@%^$*@%^$*@%^$ that had them apart before i got the bike had them SWITCHED. Put the best ngk plugs in it and checked the head torque and valve adjustment and mechanically synched the carbs and put it back together and walla will miracles never stop happening. Thanks for your help.

[KEITH KRAUSE]

Re: hallelujah

Its finally fixed guys! Pulled the carbs off and really cleaned them and in talking to a guy who owns a bike repair shop, he told me that the #95 main jet is to be in the middle and the #105 main jet is to be on the outside the #### that had them apart before i got the bike had them SWITCHED. Put the best ngk plugs in it and checked the head torque and valve adjustment and mechanically synched the carbs and put it back together and walla will miracles never stop happening. Thanks for your help.

Glad you got it running better.
The improvement must have been a combination of cleaning/synching the carbs, valve adjustment, etc.
As for the correct main jet placement, the bike repair guy you mentioned has it backwards. On some models, the 2/3 (middle) carbs use a larger main jet to compensate for the middle cylinders running hotter and that models exhaust design. On these stock bikes, the middle cylinders also are supposed to be synched with less vacuum through the carbs. Though there's a little less vacuum at 2/3, the same amount of fuel is drawn (compared to 1/4) because the mains are larger. The benefits of this set up are for 3/4 to fully opened throttle positions.
At less than 3/4 throttle position, a little less vacuum is needed at 2/3 because there's more back pressure because of the exhaust design. 2/3 headers first flow into a cross tube and then out the exhaust. I think the back pressure is more of an issue at lower/moderate speeds. A little more back pressure means a little less flow so a little less vacuum balances things out.
So I don't know how the bike runs 3/4 throttle and above, but you do have the jetting backwards now. Also, are you sure of the main jet difference in size? 95 and 105 is quite an increase. I'm more familiar with a smaller increase, like 2.5 or 5 larger. Example: using 95 and 97.5 or 95 and 100.