carbs want some advice before pulling them.

[Isotech]

When I bought my bike in Feb is had a horrible flat spot.

This bike had been sitting for five years. So after a new set of plugs, cleaned out the carbs, went up to 40 pilots, and one shim up on the main needle, a carb sync, and  It's rideable now.

Well for the last 4 months I've still had a flat spot at 1/4 throttle opening. Which is somewhat annoying since that is right in the meat of the power band, and my preferred crusing throttle position.

It gets worse in cold wheather, or when the bike is cold, and better in hot wheather, or after the bike has warmed up. But it's always there to some degree or another.

Closed to 1/4 throttle is perfect after putting in my 40 pilots. WFO is fine as well, its just the 1/4 - 1/2 throttle position irregardless of RPM that produces a stumble/flat spot.

The plugs are fine, air filter is clean, carbs have been synched. The bike is all stock except for 40 pilots.

So.....

I think it's the jet needle. Since WFO is fine, its probably not the needle jet. It only happens at 1/4 so I think that the clip on the jet needle needs to be raised another notch. When the shop sync'ed the carbs, they said they raised the clip a notch from stock.

So what do you guys think. Should I try to move the clip another notch?

Has anyone else had this problem on stock GS's?

-Nathan

[chimivee]

First check float levels. Also make sure diaphrams are not torn/pinched under the caps.

[MacDuff]

I have a similar problem.  Lean surge with part throttle between 4 and 5000rpm.  If I ease the choke on it goes away.  My bike is setup the same except for 125 main jets.  I am going to raise the needle to 2 washers and see if it helps.  I will double check the diaphrams and little O-rings on the carb tops also.  

MacDuff

'99 GS500  8000

[dgyver]

It gets worse in cold wheather, or when the bike is cold, and better in hot wheather, or after the bike has warmed up. But it's always there to some degree or another.

Try Raising the needles first. May want to go up a size in the main as well.

http://www.factorypro.com/tech/carbtune,CV,high_rpm_engines.html

[The Buddha]

I think it's the jet needle. Since WFO is fine, its probably not the needle jet. It only happens at 1/4 so I think that the clip on the jet needle needs to be raised another notch. When the shop sync'ed the carbs, they said they raised the clip a notch from stock.

-Nathan

They raised the clip a notch from stock... OK Lovely... They are liars...
Cos there is no way to raise anything on a US spec GS. OK so BTW what is your setup and what mains as you running. If the needle indeed has notches and its an aftermarket needle, you should follow the instructions that pertain to the make of the kit that needle was in.
Cool.
Srinath.

[Isotech]

Here is the setup:

1999 GS00E:
Stock airfilter
40 pilots
stock mains
stock exhaust
stock slides (as far as I know, didnt pull them when I put in new pilots)

So if the jet needle doesn't have notches for clips, then I will have to shim it with washers correct?

I thought some years of the GS came with an adjustable jet needle?

[The Buddha]

A US GS never had adjustable needles... The obvious thing in your case is 1. clean the air filter, the stock paper one can be soaked in gas and sloshed a few times and dried off and re used.
2. 125 mains and maybe 1/2 mm shim up of the needle with a washer.
3. Check and see floats are right. They should fill to the top of the bowl and no more.
Cool.
Srinath.

[Isotech]

Just an update:

Finally found some #4 washers after 3 stores. Pulled the slides out, shimmed up each needle with 1 washer. The air filter was in really good shape so I tapped it out a little and put it back in.

Bike run awesome now my flat spot dissappeared, and now is smooth throttle all the way to redline.

Thanks for the comments, and advice guys. Yeah the dealership had lied... they didnt shim, adjust, anything on the needle, it was stock...

Anyway bike is awesome now.

-Nathan

[i3randon12]

nice dude,,    i have the same problem    but am no way going to havethe time or and money to fix it....     so i just stay above the 5 thousand rpms