GS550E Doesn't Function Well - Motorcycle shop "Stumped"

[Guest]

Hey All,

Hoping you can help. I have a 1980 GS550E with about 10K original miles on it. Everything from a functionality standpoint is stock (stock airbox, exhaust, jets etc). When I purchased the bike 4 years ago (8K miles on it), it would hold idle well at right about 1,000 RPMs, and operated well except for a lag in power around 3K RPMS. From 4K - 9K RPMs, it wound up great.

After a few years and few thousand miles, the idle started to be inconsistent due to what I presumed was dirty carbs, so I went to rebuild them at the same time I made a lot of positive changes to the bike. I used a carb rebuild kit for my exact carbs and put in replacement needles/jets, which all matched exactly to what was in the carbs previously. I noticed a diaphram was worn and replaced it, so all carbs have good vacuum. Regarding the bike, I checked the valve clearance, ignition advance functionality, compression (about 135 over all cylinders), chain tensioner functionality, cleaned the petcock, checked spark on all cylinders (new plugs) etc. The fuel mixture screw ended up seeming well balanced at about 2.75 turns out.

After I installed the cleaned carbs and vacuum syncing them, I noticed that I still had the inconsistent idle and the same lag at 3K RPMS. I had a newborn at the same time, so I decided to let my friends motorcycle shop spend some time with it to get it dialed in. They pulled the carbs 5 different times and spent about 10 hours on it, with little progress. They were able to get it to idle at 1K after it initially warms up, but once the engine really gets hot, that idle jumps up to 3K RPMs. Sometimes the idle goes from 3K and slowly decreases to 1K, while other times it just sits at 3K. Its inconsistent. The lag at 3K RPMS when accelerating is even worse than before. The bike basically pauses for 1.5 seconds. Otherwise, as always, it pulls hard from 4K RPMS to 9K.

Also if it helps, the bike idles around 4K RPMs when the choke is on, and the choke is needed to start it. With the choke on, it starts immediately everytime.

I am not sure what to do at this point. If the needle jet was adjustable, I would think that moving it could potentially solve my presumed lean condition at 3K RPMs, but it is not adjustable. Regarding the idle, which is most important to me, I am not sure what could be the issue. Maybe the bike is overheating due to the lean condition, which is jumping the idle?

Any ideas on how to proceed would be greatly appreciated. If you live in San Diego and know what you are doing, I would love to swing by with some beer and have you diagnose it.

The bike:

IMG_8444.jpg

[steveb922]

Have you checked/changed the boots, airbox to carbs, and carbs to cylinder head?

[Nessism]

Did you change the intake boot O-rings? http://www.cycleorings.com/intake.html

You may want to check the Newbie Mistakes thread to see if anything else applies...

[Redman]

.........idle at 1K after it initially warms up, but once the engine really gets hot, that idle jumps up to 3K RPMs. Sometimes the idle goes from 3K and slowly decreases to 1K, while other times it just sits at 3K. Its inconsistent. ...............

I was thinking as I was reading:
- I can understand a shop thses days being stumped.
- wonder if he is going to say the idle speed goes wild after it warms/heats up...
- yup, there he said it
- he is going to get a barage of folks saying "intake vacuum leak"
- yup, he is

Is commom knolodge here: erratic or "hanging" idle or increasing idle when engine heats up is a symptom of intake vaccum leak, most common is the o-ring in the intake boot (up against the head). I cant explain the physics of how leaking in more air (making it leaning cuz that air didnt go thru the carbs) makes the idle increase, but enough people have said so , and I have expereinced it myslef.

On one occassion I would adjust the idle when engine warm, then when engine not warm the idle was too low. Then adjust again when not hot and then when was hot the idle was too high. I did not know that black area of the intake boot flange was an o-ring, it was so hard and flat. And boots were stiff and cracked. Changed the boots, clamps and orings out and oh-so-much-better.

On other occassion, years later: when engine warm the idle would raise up and stay there at 2500 to 3000 or even more if real hot, take a long time to come down or maybe not come down. Checked intake boot orings and were okay. Fussed around with a few things. Finally rebuilt the carbs with new orings (see Cycle Orings) including the enricher (choke) body orings and that took care of it.

Do find the Cycle O-Ring web site. A fine GSR member here, not a big bussiness, just a guy doing us all a fine service.

.

[dorkburger]

Definitely agreed on the intakes. My idle fluctuated when my intake boots were on their way out - its a typical tell tale sign.

Choke (enricher) function sounds normal, although there no need to let it fly up to 4k. Just enough to to keep it running is fine

[Tenshots1]

Have you checked/changed the boots, airbox to carbs, and carbs to cylinder head?

Thanks all for the quick replies. I think i tried spraying carb cleaner around the intake boots previously to see if it leaked and they did not, but I will look back at these regardless. I'm glad to have something else to check. I will mention that I have not taken these off since ownership, and so I havent renewed the o-rings. I have noticed that the boots themselves are still pretty soft and hold into the carbs tight.

Just ordered some O-rings from Robert at cycle O-ring. I will go ahead and replace these regardless

[Skinner]

Thanks all for the quick replies. I think i tried spraying carb cleaner around the intake boots previously to see if it leaked and they did not, but I will look back at these regardless. I'm glad to have something else to check. I will mention that I have not taken these off since ownership, and so I havent renewed the o-rings. I have noticed that the boots themselves are still pretty soft and hold into the carbs tight.

Expect the o-rings to be like hard spaghetti. www.cycleorings.com is your first stop.

[Tenshots1]

Expect the o-rings to be like hard spaghetti. www.cycleorings.com is your first stop.

Just ordered! This will be my next plan of action.

[Nessism]

Those O-rings leaking is one of the most common of all GS problems.

[Tenshots1]

Those O-rings leaking is one of the most common of all GS problems.

Good to know. Could it be leading to the lag I have when accelerating under load around 3K RPMS? My thinking is that it will held the idle issue, but not the running.

[Steve]

The o-rings on the intake boots will certainly help. However, if they don't eliminate the problem, you might want to consider CLEANING the carbs, not "rebuilding" them.

Even though your carb kits were "for [your] exact carbs", they likely included parts of questionable quality that were likely not needed in the first place. CLEANING the carbs by soaking the bare bodies overnight in carb cleaner dip will clean out the small passages between the jets, which could be causing your erratic operation, especially at low speeds and low-throttle conditions.

.

[gsrick]

Hey All,


I am not sure what to do at this point. If the needle jet was adjustable, I would think that moving it could potentially solve my presumed lean condition at 3K RPMs, but it is not adjustable. Regarding the idle, which is most important to me, I am not sure what could be the issue. Maybe the bike is overheating due to the lean condition, which is jumping the idle?

Any ideas on how to proceed would be greatly appreciated. If you live in San Diego and know what you are doing, I would love to swing by with some beer and have you diagnose it.

Everybody has already addressed the intake o rings, so I'll tackle the non adjustable jet needle. It may not have slots and a clip that you can move into different positions, but you can raise the needle up by placing small washers under or over the plastic doughnut. This is just an example.

On top on the doughnut.

[scratch]

Everybody has already addressed the intake o rings, so I'll tackle the non adjustable jet needle. It may not have slots and a clip that you can move into different positions, but you can raise the needle up by placing small washers under or over the plastic doughnut. This is just an example.

On top on the doughnut.

Consider this a thought question more than a critique... considering the precise weight of the slides, spring calculated resistance all in relation to vacuum lifting said slide ... would adding wieght to that slide nulify or at least dull the intended effect? Perhaps nylon washers might be a better choice?

[Steve]

You are overthinking the process a bit, the weight of a couple of washers won't be noticed.

By the way, that picture is actually a rather poor example, as there are no GS carbs that have needles that look like that.

All the needles in GS carbs (VM series and BS series) have a metal circlip that fits in a groove on the needle. There is a metal washer below the clip, then a spring. Above the clip is the nylon spacer. When "shimming the needles", you need to remove the nylon spacer and replace it with a stack of washers that is thinner than the spacer. Most of the washers I have seen take five washers to equal the thickness of the nylon spacer, so a stack of three washers is a good start.

.

[Tenshots1]

The o-rings on the intake boots will certainly help. However, if they don't eliminate the problem, you might want to consider CLEANING the carbs, not "rebuilding" them.

Even though your carb kits were "for [your] exact carbs", they likely included parts of questionable quality that were likely not needed in the first place. CLEANING the carbs by soaking the bare bodies overnight in carb cleaner dip will clean out the small passages between the jets, which could be causing your erratic operation, especially at low speeds and low-throttle conditions.

.

In addition to swapping out the jets for new ones, I did soak the bare carbs in the big bucket of carb cleaner and scrubbed everything with a brush, using a needle to clean out the small holes. So these should be very clean carbs at this point.

Regarding the washers, this looks like it could definitely work and I will see if it is necessary once the intake o-rings are in. Thanks all for your help!