Crykie, need some advice Weird things afoot

[EvilScooby]

ERRRRR!!!

Just when things were going sooooo good.

When I start my bike it starts rough, then it revs to 5k and then back down again and then back up to 5k, it will do this over and over all by itself.
Also when I tried to start it with the choke on no go. I had to start by turning the throttle at the same time with the start button
When I put the choke on it stalls the engine.


NOW for the Weird thing, When I remove my tank it starts and runs beautifully, but when I put it back on, same problem
Any ideas?

:dunno:

[CasiUSA]

Check your vac lines. Also, if You're recently dismantled the carb. check for the little o ring that sits between the body and the plastic top on the vacuum line. Good luck, hope this helps

[EvilScooby]

When I hook the tank back up, it does not bend any hoses or block anything

HELP!!!!

[cummuterguy]

i don't know a lot about these bikes, but i know a lot about cars,(fix them every day) and you just described a large vacuum leak... I'd look at that o-ring casi was talking about

[EvilScooby]

I did that, the carbs are fine and they are clean, its only when the gas tank is hooked up does this happen

All hoses are properly installed per Kerry's hose routing page, and they were like that all week and ran fine. now all of a sudden this started happening

[Ed_in_Az]

Tank vent  maybe ? :dunno:

[Kerry]

Good idea, Ed!  Scooby, how well does it run with the tank on and the filler cap propped open?  

With the petcock on PRI?

Have you tried the WD-40 test on the carburetor boots, to see if the RPMS change (in a different way than they're changing on their own)?

Let's see, what else ... Is that "fat" hose connected in between the airbox and the valve cover?

Oh, one last question.  When the tank is off, what method are you using to supply fuel to the system?

EDIT: Changed link from sisna.com to bbburma.net

[EvilScooby]

When I take the take off I use the fuel thats left in the lines and it will run for about 8-10 mins.
But I also propped the tank up and turned the tank petcock off and get good results. It runs great
but when I turn it back on it goes all crazy again

The Fat hose is connected to the air box

Have you tried the WD-40 test on the carburetor boots, to see if the RPMS change (in a different way than they're changing on their own)?

What will that test tell me?


I wil ltry running it with the tank cap open right now and see

[Kerry]

]Have you tried the WD-40 test on the carburetor boots, to see if the RPMS change (in a different way than they're changing on their own)?

What will that test tell me?

Good question!    Actually, I don't expect you to find anything there.  But if you do.... let me know?

(Ahem...may I be excused?  I think I left my air-cooled motor running.)

[EvilScooby]

OK, I tried running with the cap open and no change.

I also now have fuel leaking out of the left carb, I removed the tank and airbox. start her up and runs fine with leftover fuel in the lines.

I do notice when I rev the engine air comes out of the 2 little holes on the left carb. is that normal?
Its the 2 holes like in this image



Could something be clogged in the carbs still?  I cleaned the crap out of them 2 weeks ago, rode her all this week with no probs!

Why does it run great when I turn the tank petcock off but crappy when its on?   :dunno:  

[Kerry]

You haven't mentioned what position the frame-mounted petcock is set to.  I'm asking because, if you're using one of the vacuum-actuated positions, then the symptom may mean something different than if you're using the PRI position.

While we're at it, does it act differently in the ON position versus the RES position?

Just searching for clues....

[EvilScooby]

They are acting the same on all positions,
With the tank off I can feel suction on the fuel lines wether its on, res or pri

I was goint to remove the carbs today and pull them apart. not sure why but thats the only thing I can think of

:dunno:

[EvilScooby]

I am officially in GS500 hell!!!!!!

OK I pulled off the carbs again, nothing wrong checked the floats all the jets, everything looks great.

now runs at 5k steady when the tank is hooked up, and of course again when I turn the tank petcock off it runs perfect.
I put the frame petcock on any setting with the tank on and it runs and revs at 5k, remove tank runs great on any setting.

While the tank is removed I can run the bike for about 8 minutes with the fuel still in the lines, I can feel suction on the hoses.
example:
when the petcock is in the on position I can feel suction on the on hose, when it is in the res and pri position I can feel suction on the res hose.

It seems like too much fuel is flowing into the carbs with the tank connected, maybe I am getting too much of a vacum effect.

Anyone have any ideas, I am lost in GS hell
:dunno:

[EvilScooby]

Does anyone think its the fuel mixture screws?

I know what to do to adjust them, but how?

Whats the proper way to freshly start out turning them. Do I turn them all the way closed them count turns to open them?

IS turning them in allow more fuel/air or is it the opposite?

[Kerry]

Does anyone think its the fuel mixture screws?

I honestly couldn't say, but you're welcome to experiment!

Whats the proper way to freshly start out turning them. Do I turn them all the way closed them count turns to open them?

Yep, that's the proper method.  If your screws are still at the factory setting, make sure to count as you turn them all the way in, so you can restore the setting later.


From the old Ok, whats the diagnosis now? Srinath? ANYone? thread:

The idle mixture screw is only effective at idle, and up to 1/8th throttle.
[...]
Note that the GS does not have idle air screws [...]. They are idle fuel screws, and so in is leaner, out is richer.

Read Kevin's other posts in that thread for some good info on tuning the carbs.


PS - Are you SURE you're not missing any of the rubbery parts?  Not even the tiny O-rings just under the top cover of each carb?


Also, no tiny rips or tears in either diaphragm?

One last thought.  I wonder if it would be worth the effort to bypass the ON/RES/PRI petcock altogether and run a hose straight from the RES (front) outlet on the fuel tank to the lower T-fitting between the carbs?  You would have to either cap off the ON outlet from the tank, or connect both hoses to a T-connector or something.  And don't forget to cap off the vacuum line from the left carb to the ON/RES/PRI petcock.

EDIT: Changed link from sisna.com to bbburma.net

[EvilScooby]

This is so weird, I played with the mixture screws abit and now it seems to be working,
The carbs I purchased last month were used and I purchased the same kit you list on Kerr'y's last post. and they are clean and look really good

I am not sure if that is going to work but I hope it stays. I am now afraid to go too far from home   I will give it a week before I attempt it.

I am also thinking about bypassing the frame petcock as you suggest.
Do I cap off the vacum outlet on the left carb itself?

It just seems like too much fuel was getting in the carbs

[Rema1000]

Something sounds fishy there.  If it runs fine without the tank, it seems a stretch for the problem to be within the carbs.

I have had the hoses look fine when I set the tank down, but then when I push the tank forward to insert the tank screws, the hoses kink right below the tank-mounted petcock.

But also, the throttle cable runs through there, too.  If it were somehow getting pinched, then that my apply some throttle.  Be sure that the idle is even when you rotate the handlebars... if not, then the cable is binding somewhere.

[Kerry]

Something sounds fishy there.  If it runs fine without the tank, it seems a stretch for the problem to be within the carbs.

Agreed!  But given the following statements, what can ya do?

When I hook the tank back up, it does not bend any hoses or block anything

But I also propped the tank up and turned the tank petcock off and get good results.
It runs great but when I turn it back on it goes all crazy again

=======================================

I am also thinking about bypassing the frame petcock as you suggest.
Do I cap off the vacum outlet on the left carb itself?

Yep.  I'm not sure about the best to do it, though.  I mean, a purpose-built vacuum cap would be ideal, but where are you gonna find one of those?  :dunno:

It seems to me that a short length of (extra, not original) vacuum hose with a screw or bolt (or silcone?) inserted in the open end should work.  

[Greg Gabis]

I have bypassed the stock poopcock...er...petcock on a few bikes.

I fill a valve stem cap wit a little silicone and use that to pluf the vacuum port on the left carb. You'll want to give it time to dry so you don't suck any goo into the carb, but it doesnt take long.

I have a strong suspicion that it is the petcock.

[Hi-T]

I bypassed my petcock... you can buy official, honest to goodness, vaccumm caps from checkers or Autozone or Napa.  They come in various sizes and are cheap.  Plug it and use a hose clip to keep it in place.

If the hose on the carb that attaches to the top 'T' gets clogged or pinched, you will spit gas back through those holes you mentioned.  That tube must be free to breath.  Try taking that tube completely of the bike and replacing the tank.  I actually got rid of that hose and topped it with a filter.

It is possible ( i guess) that when you replace the tank that it sits funny on the airbox or carbs.  that might create a slight leak in the boot seals and may be a problem.  The wd 40 test would let you know if there is a leak- If you spray around a boot and there is a leak- the RPMS will shoot up.

Remember- KEEP IT SIMPLE.  Do one fix at a time.  I'd even recommend ordering a pod filter and doing a slight rejet.  That would free up some space in the bike and take some weight of the carbs.  

Anyways...