Carb ports and rev issues.

[babalouj]

This is my first post guys so take it easy on me.  I have been working on fuel injected cars for ~10 years but my friend recently acquired a 98 gs500e with around 2000 miles for free from a friend. I have been forced into the world of carbs and I can honestly say that I am pretty stupified by the problems the bike is having. The bike initially had an idle problem where it would never idle lower than 3000rpms + some idiot decided to use vacuum hose as fuel line... He already had a replacement carb so we installed it and now it idles around 1200 with some idle screw adjustment but when rev'd the rpms stay high for a few seconds before coming down and when in gear it is slow to increase rpms. Giving the new carb a once over I found two ports on the carb that are just sitting there open to the air. They seem like vacuum ports and when covered rev the bike to 3000rpms. These ports were open to air on the last carb too but leaving them open without knowing what they are just leaves a bad taste in my mouth. Attached is the best picture my friend could take of the port with the tank still on. The other port is in the exact same location on the other carb. Please shed some light on the issues I am having and what these carb ports do and what they are supposed to be connected to. Thanks in advance!

[ohgood]

that looks like the right side carb, shot from the front of the bike. if so, it's the non-used port for the frame mounted petcock. the petcock is vacuum operated, and usually a cause for much grief. do a search on the forum for 'fuel starvation' and you'll see what i mean.

the LEFT side carb has a line that should run directly to the smallest port on the frame mounted petcock. if that hose isn't putting a decent vacuum, the petcock with cause starvation issues without even being ridden at high speed.

the RIGHT side carb on mine isn't drilled for the vacuum line, it's just a dummy boss on the casting.

usually, hanging after rev = vacuum leak, and a lean mixture condition

the gs's are known to be lean from the factory, and you may want to (OR NOT) re jet the bike to richen it up a little. there is a 'rejetting matrix' here on the forum, it's a nice starting point. check the float heights too, there is a tutorial on either kerrys or sanjay's pages.

welcome to the fun fun world of carbs friend

[babalouj]

Ok, so the port not pictured should be running to the petcock to help with fuel supply and the port circled in the picture should be capped off?

[ben2go]

Check out these threads to lend a hand.Remember bikes are different than auto's.The GS idles at 1200 rpm.

This will help with deciding rich/lean condition.
http://cgi.stanford.edu/~sanjayd/gs500/Upgrades/Rejetting-LeanOrRich?

Diagrams to help with hose routing and carb
http://cgi.stanford.edu/~sanjayd/gs500/Main/HoseRouting

http://cgi.stanford.edu/~sanjayd/gs500/Main/1989-2000

If the petcock is causing fuel starvation try these.
http://gstwins.com/gsboard/index.php?topic=19363.0

http://gstwins.com/gsboard/index.php?topic=36958.0

[babalouj]

Wow, those diagrams really help. Thanks for posting the links. I bet alot of the problems will go away once I plug the right carb vacuum port and route the left carb vacuum port to the petcock.

[beRto]

Wow, those diagrams really help. Thanks for posting the links. I bet alot of the problems will go away once I plug the right carb vacuum port and route the left carb vacuum port to the petcock.

Don't forget to let us know how it turns out! 


p.s. that photo is so large; perhaps you can reduce the size a little?

[Ry_Guy]

I bet alot of the problems will go away once I plug the right carb vacuum port and route the left carb vacuum port to the petcock.

It recently just solved my idling problem 

[ben2go]

Wow, those diagrams really help. Thanks for posting the links. I bet alot of the problems will go away once I plug the right carb vacuum port and route the left carb vacuum port to the petcock.

You're welcome.

[babalouj]

Well I am starting to hate this bike. We routed the hoses correctly and capped the right carb vacuum line. There is no difference in the throttle response. When the throttle is held open it takes a couple of seconds to react and when released it takes a couple of seconds to come back down to idle.

[beRto]

Well I am starting to hate this bike. We routed the hoses correctly and capped the right carb vacuum line. There is no difference in the throttle response. When the throttle is held open it takes a couple of seconds to react and when released it takes a couple of seconds to come back down to idle.

"Hanging idle" is a common problem. See here for some troubleshooting steps: http://gstwins.com/gsboard/index.php?topic=41199.0

Your bike may also be in need of a valve adjustment.

We'd be happy to expand on any of the points that may be unclear. Good luck!

[ohgood]

Well I am starting to hate this bike. We routed the hoses correctly and capped the right carb vacuum line. There is no difference in the throttle response. When the throttle is held open it takes a couple of seconds to react and when released it takes a couple of seconds to come back down to idle.

yep, it's always hate until the carbs are finally sorted. once they're set (FINALLY!) it's allot of fun. hang in there.

you can spray WD-40 carefully around the intake boots (rubber flanges between the carbs and the head) to see if there is a vacuum leak. your vacuum slides in the carbs may be worn also, and it may have tons of junk in the carbs. i'm betting on a air leak somewhere, possibly the vacuum tops are cracked, or the caps on the vacuum take offs ?

there are lots of little things it can be, along with low compression, poor air sealing, all that jazz.

the bike will be a blast once it's done, and your sense of accomplishment will be great.

[ben2go]

Once you have your bike running properly,a little maintence a few times a year, and she'll never let you down.   

[babalouj]

We sprayed wd40 around all intake related parts (carb, intake manifold, vac lines, etc.) and no idle change so its not a leak. The carb that we put on did have a cracked vacuum top but I swapped it with the old carbs top so thats all fixed. I think I am going to do the float adjustment and clean the carb this weekend. Supposedly the carb that we put in only had 900 miles on it.

Are there any people in Atlanta that might be able to give me a hand?

[ohgood]

sorry man, i'm 8 hours or so away in tampa... but....

if you get some nice clear macros of the carbs, and the bits inside, someone might notice something that is really really off. like the float height (a big deal), the condition of the needles, condition of the jets, condition of the o-rings, condition of the slides, condition of the vacuum boots, it all plays together. there is always something working it's way right into uh-oh condition on carbs

slow and methodical, you'll find the main cause for now

[babalouj]

Today we will be doing the float height check, hopefully we will find that the float heights need to be readjusted. I will report back.

[The Buddha]

OK you have delayed throttle response ... OK what makes you think it may be the carbs ... anyway float height does play a part when throttle is being opened especially under load.
However I have never seen floats go too low ... ever, always too high, and that will not cause your problem.
But check it and you will know.
If it fails, send the carbs to me. I can sort out and send back.
$45 for a rejet, $25 max for fixing stuff without rejet. Other parts will be on a needed basis.
Cool.
Bddha.

[babalouj]

I totally forgot to post the progress we have made. The idle has been adjusted to around 1000rpms per the suggestion of a thread around here and the throttle response is fine and the rpms come down fine. The problem now is that there is no power underload. We might just end up sending the carb to you buddha.

[The Buddha]

Its playing cat and mouse with ya  ...
Yea send it over if you need to, I will get the 3 + the numerous weird requests out by this weekend ... so I should be good by next week. 
Cool.
Buddha.

[babalouj]

Did the float height tube test and both came back perfect so we adjusted the idle to 1100rpms to test and it seems to be working well. It bogs under 3K in gear but I guess thats managable. Its fine above 3k. We are leaning on sending the carb to you buddha.

[clango]

THE BIKE WORKS! 

I'm "the friend" whose bike this post is about.  After sending the carb to Buddah for a re-jet & cleaning and de-rusting the gas tank the bike loves life again!  Idles fine doesn't hang, makes lost of power in the low end.  Turns out the carb was really gunked up in addition to having just the stock jets.  That may have been due to the rusty gas tank which is now rust-free... All in all, problem solved and +1 happy GS500 rider!

Thanks for all the help guys!   

next project: handlebars.