Need help....unknown problem!

[diamond_lady]

First of all...hello everybody!  
I've been reading a lot this forum before buying my GS...a '91, in faboulous conditions.
It's also my first bike, and this is why I need help!  
Ok, I'll try to explain the problem as best as I can (I'm italian so please be patient!!).

The problem is that when the engine is hot (really hot....I'm practicing for the licence, I'm doing hours going round and round at minimum speed   ), when I try to "open the gas" (not slowly.....when I try to open fast) the bike behaves like when the tank is empty. But the tank is full.
The engine "goes down", as if the carburators ar empty.
I thought maybe there's some dirt in the tank, or maybe there's something worng with the carburators...don't know, I'm asking you 'cause I thought that maybe someone had the same problem.
Some hints?? Some ideas??
I don't know if I explained myself properly....hope so!
Thank you all!

[Jake D]

Have your carbs been cleaned?  Have you pulled out a spark plug to look at it (it may have a white appearance to it, blanco).  

(I'm not very smart, but I wanted to try to help).

[scratch]

Welcome!

By your description, the carburetion is too lean. But, I have some questions: Does it bog down, as if it is getting too much gas (flooding)? Or, does it hesitate, but keeps trying to go (kind of like a bucking back and forth)?

[The Buddha]

OK does the bike have a pipe or a filter on it ...
If so ... and
Opening the throttle fast it falls on its face, but it behaves when opening throttle slowly ... that is a slide comming up too fast ... block off 1 of the 2 holes in the bottom of it.
If the bike behaves the same whether you open the throttle fast or slow that may mean a fuel starvation because of a float height set low ...
The Euro bikes had 40 pilots to begin with and I believe 125 mains ... as well as adjustable needles ... I'd think its one of the 2 I described ... as opposed to the characterstic leanness in US bikes ... OK if its a US import ... yea lean ...
Cool.
Srinath.

[pandy]

Welcome, diamond_lady! It's nice to see more and more international representation here!!!  

Welcome also to the world of temperamental GS's!   At least you're in good company, and many of us here have had or are having the same issues.  :mrgreen:

[500rider]

Welcome!

By your description, the carburetion is too lean. But, I have some questions: Does it bog down, as if it is getting too much gas (flooding)? Or, does it hesitate, but keeps trying to go (kind of like a bucking back and forth)?

What does the bucking back and forth problem mean?  I am trying to diagnose my Kat 750.  Plugs are black but not wet.  I could use some help.

[The Buddha]

You open the throttle and it pulls and stops pulling and pulls and stops ... 3-4 times ... = bucking = lean. Its going to be worse on colder days than hot if its a slight lean situation. It will also do it under steady throttle - aka lean surge - yes open the throttle slowly and it will surge too. Open fast and it will almost run normal ... lean bikes make a good bit of power ... they just dont like to maintain the power they make ...  :lol:
If it was rich it will respond almost quite smoothly if you open the throttle fast or slow doesn't matter - but be lacking in power and sound wettish ... like you are riding it under a foot of water ... and will be worse when hot and after the motor gets hot ... Very noticeable ... cos they take a lot longer to warm up ...
If you open throttle fast and it gives off a gasp type noise before falling on it face ... no power and literally will need to have the clutch back in and revv up to keep from dying ... but is normal if you open slow ... slide rising too fast.
Cool.
Srinath.

[500rider]

daimond_Lady:

Sorry for hyjacking your thread.  

Srinath:

You open the throttle and it pulls and stops pulling and pulls and stops ... 3-4 times ... = bucking = lean. Its going to be worse on colder days than hot if its a slight lean situation. It will also do it under steady throttle - aka lean surge - yes open the throttle slowly and it will surge too. Open fast and it will almost run normal ... lean bikes make a good bit of power ... they just dont like to maintain the power they make ...  :lol:

It's not really bucking but more sputtering. Cutting in and out rapidly like not all cylinders firing.   The bike ran pretty good two weeks ago when it was a little warmer.  

The bike wants to sputter at 3-4k rpm with 1/8 to 1/4 throttle and seems better in the 5-6K range.  6-8 k range was flat until I moved the stock needle up one notch.  Now it seems better.  WOT @ 10k seems to work good when I can get it up there.  The bike has a Yosh pipe with stock air box, stock needle and pilot jet with Dynojet 120 mains.  It was not bucking at 3-4k before I moved the needle up (but as I say it was a bit warmer then).  Occasionally all cylinders will act normal and there is lots of power but usually it's bucking/sputtering.

Do you think I need larger pilots or just adjust mixture screws?  Float height?  I just replaced the plugs cause one cylinder would not fire.  After replacing plugs all cylinders were firing when I first started the bike and for about the first 2 minutes of riding.  Then the sputtering began with intermittant good operation.

Thanks for your help.

[The Buddha]

daimond_Lady:

Sorry for hyjacking your thread.  

Srinath:

You open the throttle and it pulls and stops pulling and pulls and stops ... 3-4 times ... = bucking = lean. Its going to be worse on colder days than hot if its a slight lean situation. It will also do it under steady throttle - aka lean surge - yes open the throttle slowly and it will surge too. Open fast and it will almost run normal ... lean bikes make a good bit of power ... they just dont like to maintain the power they make ...  :lol:

It's not really bucking but more sputtering. Cutting in and out rapidly like not all cylinders firing.   The bike ran pretty good two weeks ago when it was a little warmer.  

The bike wants to sputter at 3-4k rpm with 1/8 to 1/4 throttle and seems better in the 5-6K range.  6-8 k range was flat until I moved the stock needle up one notch.  Now it seems better.  WOT @ 10k seems to work good when I can get it up there.  The bike has a Yosh pipe with stock air box, stock needle and pilot jet with Dynojet 120 mains.  It was not bucking at 3-4k before I moved the needle up (but as I say it was a bit warmer then).  Occasionally all cylinders will act normal and there is lots of power but usually it's bucking/sputtering.

Do you think I need larger pilots or just adjust mixture screws?  Float height?  I just replaced the plugs cause one cylinder would not fire.  After replacing plugs all cylinders were firing when I first started the bike and for about the first 2 minutes of riding.  Then the sputtering began with intermittant good operation.

Thanks for your help.

Impossible ... you have DJ mains and the stock needle ... BTW you already have 40 pilots - canada ... so no where to go in that area ... 120 DJ ... probably needs to be swapped for 125 mikuni's ... with stock needle ... you lift it 1/2 to 1 mm and you should be fine ... check floats and set to top of bowl. In any case ... you need to get to the numbers that people understand ... DJ puts funky numbers on them ... whihc BTW I suspect are same as Mikuni ... but suspect isn't good enough, and they have done an extraordinary job of speaking in greek when everyone else talking english ... If stock needle ... 125 mains should solve 90% of the problem ... your main jet being 2 sizes off isn't the time to fook with your pilots or air screws ... 125/40/3/1 is what you need.
Cool.
Srinath.

[500rider]

Ok thanks.  I'll check the float height to start since that's the easiest without removing the carbs.

[pandy]

At least you have two sides that run the same...I have one side that's VERY lean and the other that's VERY rich...'splain THAT one to me...  

All of these issues seem pretty inter-related, so it probably wasn't a threadjack.

[diamond_lady]

First of all: thank you!
You all been very kind to answer.
500 rider: you didn't hijack my thread, no problem, it was useful reading your experience.
I think that maybe 'Scratch' said the right thing: my carburetors could be lean.

You open the throttle and it pulls and stops pulling and pulls and stops ... 3-4 times ... = bucking = lean

....this is exactly what happens to me! But I can't understand why it doesn't happen when it's cold (the engine I mean, not the weather!).
Anyways today or tomorrow I'll put my hands on my baby ( :lol: ), to try and understand what's the problem and...to know her a little bit more!
Like pandy said, I need to get in touch with this temperamental world....

This site and board is soooo useful, there's nothing like this in italian; it seems like you all love your bikes in a special way.
And I do love her too, so I feel at home!!   [/quote]

[ballyhoo]

Diamond Lady, you might also want to be sure you hava a fully open fuel shutoff valve on the tank. If it is only partially open, it could starve the carbs when they are pushed hard. Make sure that the fuel supply getting to the carbs is not obstructed in any way.

Sorry for being a dumb Yankee, but what is the translation of "Non plus ultra?"

Best of luck!

[diamond_lady]

Diamond Lady, you might also want to be sure you hava a fully open fuel shutoff valve on the tank. If it is only partially open, it could starve the carbs when they are pushed hard. Make sure that the fuel supply getting to the carbs is not obstructed in any way.

Sorry for being a dumb Yankee, but what is the translation of "Non plus ultra?"

Best of luck!

Hi! Yeah tomorrow morning I'll check if there's something obstructing the fuel supply.
I'll post my conclusions after that. Well...I hope to get to a conclusion!
You don't have to apologize for being a dumb Yankee....I am a dumb Italian, just take a look at my english!  
Anyway, 'Non plus ultra'... I don't know how to translate it...it's an expression to forbid you to go over a limit... sorry, it's the best way I can explain it to you (it's latin, not italian).

[pandy]

"Non Plus Ultra" is a Latin phrase meaning "nothing more beyond" literally, but figuratively it is a descriptive phrase meaning the best or most extreme example of something.

and

Non plus ultra! Nothing above that!

[diamond_lady]

"Non Plus Ultra" is a Latin phrase meaning "nothing more beyond" literally, but figuratively it is a descriptive phrase meaning the best or most extreme example of something.

and

Non plus ultra! Nothing above that!

Great!  
You explained it exactly. But if I can add one thing...as I said, this expression was originally used to warn people not to go over/beyond some given limits (remember Ulysses story? )
Then it was used in a slightly different context and it became a standard phrase to mean that something is 'the best, the most extreme' as you said.

[The Buddha]

At least you have two sides that run the same...I have one side that's VERY lean and the other that's VERY rich...'splain THAT one to me...  

All of these issues seem pretty inter-related, so it probably wasn't a threadjack.

Its the purple gas ...  :lol:  :lol:  :lol:
Anyway ... float height and sucking air in one manifold ... the real reason most likely.
BTW want more purple in your bike ... put in Dot 5 brake fluid. That little round glass will turn purple.
Cool.
Srinath.

[pandy]

Its the purple gas ...  :lol:  :lol:  :lol:

:lol:  :lol:    :lol:

Anyway ... float height and sucking air in one manifold ... the real reason most likely.

Will definitely check this out...thanks!!  

BTW want more purple in your bike ... put in Dot 5 brake fluid. That little round glass will turn purple.

:kiss:

[pandy]

Great!  
You explained it exactly. But if I can add one thing...as I said, this expression was originally used to warn people not to go over/beyond some given limits (remember Ulysses story? )
Then it was used in a slightly different context and it became a standard phrase to mean that something is 'the best, the most extreme' as you said.

Ulysses story...yes...I remember it...barely.... I think it was about 300 years ago when I was in jr. high school.  :lol:  

[diamond_lady]

After a week of using my bike I came up with some considerations:

- never experienced again that 'sputtering'/'bucking' thing, but I noticed that I have to put it on 'res' too early.....I think the tank is half-filled, and I had to put it to res because the bike started to behave strangely. I put it on res and it solved the problem.
Question is: why the hell this happens?

Today I'm gonna check the spark plugs, and tomorrow I'd like to open and clean the carbs (and maybe sync them). I just bought it used (it's a '91 GS) with few kilometers so I think that maybe the guy left it some time unused.
There is something more I can do? Do you suggest something?

Thanks!