'80 GS550 Idle Issues

[brickredroux]

Hi all,

I am having issues with my idle and trying to figure out a few options. At the moment the bike starts up with a little encouragement and choke, however it will not stay idle for long before dying. Even after riding for a bit I still have have to continually throttle slightly or pull the choke to keep from stalling out at a stop. There is no issue with backfires and the bike runs well without choke once its moving.

I had the local shop do a once over at the beginning of the season and they did a carb clean. Speaking to a few people I've heard everything form needing to adjust the idle screw to needing to check the filter on the petcock.(still need to research how to do these)

Has anyone had similar issues or suggestions?

Thanks

[Big T]

Tight valves are the most common cause of idle problems.

[scratch]

Has anyone had similar issues or suggestions?

Anyone?I think everyone here has had to work out some sort of similar issueat one time recently or in the deep past....
Pickedyour post because I have, have had and have worked on a good numberof ‘80 GS550s… I’m quite fond of these bikes.

Let's start at the beginning.

You are trying to nail down a malfunction ina complex system so, more info is needed. It’slike you just left a message for a doctor on an answering machinethat says… “I was born in 1980 and I don’t feel so good” andare asking for a diagnosis.

Tight valves indeed can cause idle issues, so can a bad petcock, a pinch in the vacuum line, a clog in the fueling side, an improperly set idle, poor carb sync, mixture screws to far in, air leaks (in the boots, tubes, mounts, chamber or airbox, even in the cylinder head) exhaust leaks, torn or improperly installed diaphragms. Then there are the electrical possibilities… is your battery good, is it charging? Etc etc etc…
In other words, it could be anything… some things are easier to check and fix than others, some things are more difficult to isolate.

Cleaned carbs by a shop unfortunately means nothing at this stage. Discount that till it is proven that were indeed done correct (I have rebuilt a dozen of recently shop or dealership cleaned carburetors for friends. I could tell you horror stories of bikes that have burst into flames from fuel leaks straight out of the shop to carbs that were reassembled improperly for a $750 service bill)
Finding a good shop for old bikes is… it’s a hunt. They exist, they are not all bad but, they are not all good either.
For now, forget that it happened.

Let’s get some more history.

When was the last time you had the bike running properly and what changed since then?
Is the bike stock with factory air-boxand pipes? Any other modifications?
When you first start it, with full choke, what are the rpms? Does it start to rise from there before you put the choke back in? Where does it settle before it starts to die out… does it settle at all?

Do you have a work space and tools?

Let’s get the story and try to figure this out. Don’t get discouraged,that bike will go dang near forever once you get it back to a good running state and keep up the maintenance and care from there.
Once we know if you have a factory air-box, pipes and some other basic info I’ll do what I can to help you work through it.

[Nessism]

The newbie mistakes thread linked in my signature may help.

[brickredroux]

Thank you for reply, as you have picked up on I am a newcomer to the forum/motorcycles/and mechanic work in general. I will do my best to give the back story as far as i know it!

I picked the bike up at the end of last season. Was told it had a once over by a shop the month prior. It ran well enough, no idle issues and cold start with choke was ok. Got it home to find a battery issue. Replaced the battery and that seemed to fix that. It sat during the winter months and then I had a local place do a carb clean at the beginning of this season. During the evaluation they mentioned "If customer is looking for best performance we should order new (larger) jets. He is running k/n pods and a more open exhaust."

-Went for a ride this morning and with full choke, the bike starts around 3000 and then rises to about 4000. When putting the choke in the bike sits at about 2000 before slowly dying.
-The exhaust looks like it has been frankenstiened a bit. It is still 4 in to 2.
-K/N pods. Each pod connects to two carbs, so not individual.
-I live in the city but do have an underground parking spot that I keep the bike in and have been using as a staging area. I have basic tools and am collecting as they are needed. (if there is a suggested tool kit list on this forum i'd love to be pointed towards it)

Again, I really thank everyone for all the help. Please let me know if I am missing something or not explaining anything well. My motorcycle vocabulary is still progressing. I have gone through all emotions with this so far, excited, frustrated, embarrassed and back to being hopeful!

Thank you again.

[brickredroux]

The newbie thread looks like it has a lot of information that could/does fit my situation. Thank you

[scratch]

If I understand you, the bike was in a running state before winter, then after a carb clean & change in jets… it began to behave erratically?

This is possibly a direct cause-and-effectrelationship.

Did the shop return your old jets? Swapping the original jets back in for the new ones makes sense. If you or they don’t still have them, did they at least record the sizes of the old jets? How did they determine what jets to change to? Did they set the mixture screws and vacuum synchronize the carbs after reinstalling? There should be some sort of accountability and explanation for this. Find out exactly what they did.

Part 2
Did you get the original air-box with the bike? The absolute best course of action imo would be to restore the factory air-box & jetting. If you have a factory airbox, sealed correctly and properly cleaned & tunned carbs, working out other issues becomes less complicated. If not, for now lets focus on the jetting change that occurred.

Part3
Working with what you have. Your carb installation may have been incomplete. Idle may have been set before the bike ever got warm (set to low) and your mixture screws set to far in. There is a dial between the back of the 2 and 3 carburetors. Turn it about an 1/8 turn clockwise facing front. Start the bike and see if it will settle to a running state after the choke is off and the bike is warm. If there is improvement but, dies out again...try another 1/8
(If the dial is real loose and then seems to make contact give it an a tiny nudge into the resistance range and try again)

If you can achieve an idle, report back and then we’ll set the mixture screws… (important)


Part 4
Your battery may not be charging. Do you have a basic electrical tester? You are going to need one if you want to own a vintage motorcycle.

Notes:
Evenif you get an idle. There is probably long way to go before this isa reliable bike in healthy condition. You will have to get your valves in spec. The electric will need attention and you may have to change jets again… this is going to be a process. If lucky, you may mask a symptom but the overall cause or causes are still most likely not going to get sorted out right away. You should be hunting for a factory airbox set up as of right now. Pods on your type of carburetor are for people with good knowledge of their motorcycle or someone with a lot of dough and a good mechanic or a dependable friend/family member with the correct skills and knowledge. In experienced owner’s love of the pod aesthetic putsthem in a state of cognitive dissonance about their drawbacks on this type of carburetor.

The newbie mistakes thread is great, it's absolutely great! But, if you have no idea what you are doing it may be a bit overwhelming so, just remember to take things step by step slow & steady.

[brickredroux]

Starting again with a thank you for your time and feedback:

Part 1: I did not explain the jet issues well enough, we did NOT go through with the changing of the jets but it was suggested as the next step. The jets right now are the original to the bike as far as I know.

Part 2: I did not received the original air box when I purchased the bike. I see you can purchase them online so that could be an option. I am not trying to have a speed demon here, just a reliable machine. Are there specific models I should be looking at or is it categorized by year?

Part 3: I am familiar with the idle adjust screw but had been weary of playing with it until I had further information. That looks like my first step.

Part 4: I do have a electrical tester. The battery is reading between 12.3 and 12.6

I am going to include the original blurb from the ad from when I got the bike encase it gives you any further insight into what has been done:

"TRi Sports did the following to get the bike running properly:
Replaced carb intake boots
Replaced spark plugs
Cleaned and synchronized carbs
Replaced battery

The previous owner of the bike also made the following updates. The bike was only ridden for ~200 miles after those updates were made
New seat
New lights
New tires
New shock absorbers
New rear wheel bearings
New front brake pads"

Thank you again- step by step slow & steady

[Big T]

Did TRi fully strip the carbs when they "cleaned" then? Did they replace carb O rings and O rings at intake boots?

[brickredroux]

So the blurb regarding Tri was from when I first purchased the bike so I am not sure what exactly they did but I am assuming they didn't not replace O rings. The carb clean I had done by a local shop here this season was supposedly a "full tear down and soak" but no ring replacements.

[scratch]

So the blurb regarding Tri was from when I first purchased the bike so I am not sure what exactly they did but I am assuming they didn't not replace O rings. The carb clean I had done by a local shop here this season was supposedly a "full tear down and soak" but no ring replacements.

Ok... "full tear down and soak", even if done correctly and even if o-rings were replaced doesn't change the fact that you can't acheive a steady idle. The rest of the forensic investigation will fill itself in as you fix it.

Best case, your mixture screws need to be turned in to lean out the mixture.
If idle sags dramaticly, it's very often because your fuel to air ratio is to far to the fuel side. Because the K&N's create a leaner condition than a stock airbox, someone may have cranked out the air screws to compensate and done it to far...

I was proposing you crank the idle a little to see if you could get it to stay running long enough to adjust the mixtures and to get your feet wet with the a basic carburetor adjustment: the idle screw. From there, was going to encourage you move you on to the mixture screws... It's a lot easier to chase down other possibilities if the bike will run.

If manipulating the mixture screws does not do it, we'll move on.

As for the airbox, 0-rings, proper cleaning, vacuum sync, valves, electrics etc... lets move on to that later. But, take note, getting your bike to a good running state is a process. This is just just the first page of the story.

Part 3: I am familiar with the idle adjust screw but had been weary of playing with it until I had further information. That looks like my first step.

It's not going to fix itself... nothing bad will happen, turn it. If it doesn't work, it can always get turned back.
Give it a whirl and then we'll move on to the mixture screws.
Tomorrow, I'll be syncing a '80 GS550 so I can I'll take a picture or two of where the mixture screws are and how to manipulate them.

[brickredroux]

I was able to get the bike out this weekend and played with the idle adjust screw. It definitely made a difference. At the moment the bike is idling high (after running for about 15min it sits just under 2000) but it does not die. So the idle holds, I just need to tweak the idle screw to get it where it needs to be. What is the range I should be shooting for and what is the best time to play with it, meaning how long should the bike be warmed up before diving in?

Thank you!

[scratch]

Congrats! Have a box fan ready then drive it arround for 15 mins, get it right to that place where it has settled to that just under 2K zone. While still running, park it, put it on the centerstand, reach back in there and move the idle knob counterclockwise a a little bit to you hear the idle drop a bit. Go slowly, and note the idle. You will want it to settle at 1100 ish...
If it takes longer than a few mins, get that box fan blowing on the motor so it stays cool.

Then go for a ride and report back if you can with results

I was able to get the bike out this weekend and played with the idle adjust screw. It definitely made a difference. At the moment the bike is idling high (after running for about 15min it sits just under 2000) but it does not die. So the idle holds, I just need to tweak the idle screw to get it where it needs to be. What is the range I should be shooting for and what is the best time to play with it, meaning how long should the bike be warmed up before diving in?

Thank you!

[brickredroux]

Perfect! I will try this and report back.