Surging R80GS

**gsworkshop** · #1 8 Sep 2005

HELP ! ! !
Maybe someone have had this problem before and can help with good information.
I have a broplem with terrable surging on a GS. The carbs have been rebuilt, meaning repacing of all rubber parts, floats, needles etc.
The problem only starts to hapen when you accelerate past 4000rpm in any gear. Below 4000rpm the bike pull very well with loads of power and is in fact very light on feul, but when you hit 4000rpm it just stop accelerating and surges voilently. When you have a bit of down hill and can push the revs up to 5000rpm it will start running smooth again.
Sofar I have replaced the needle nozzle with a 2.64 versus the 2.68 that was in there and have dropped the main needles with one notch to the 2nd possition.
The main jet is 135 and I am going to install a 145 but the main jet should influence the rev range for the last 1000 or so rpm to full throttle.

[This message has been edited by gsworkshop (edited 08 September 2005).]

**Sean Kelly** · #2 9 Sep 2005

Hi

I had a 'similar' problem once after fitting a K&N air filter in place of a standard one to an R80GS with Y-piece (no re-jetting required apparently). Bike went fine below 3500rpm but nuts after - then ran perfect with the OE filter back in. You could well be on the right track with the air intake side of things.

**simmo** · #3 9 Sep 2005

Your tank bag straps arn't being sucked into the airbox snorkles are they....dont ask how I could even suggest such a thing.

**yngveer** · #4 11 Sep 2005

Hi, do you use any fuelfilter?? If so, maybe thet gives too much resistance, and it dosent get enough fuel??
Just a sugestion.. Hav e just fitted K&N on my 91mod R80GS with no problems.

-yngve-
Down under
www.gravelseekers.com

**Frank Warner** · #5 12 Sep 2005

Is the fuel tank vented correctly? If the vent is blocked then fuel will not flow out of the tank quickly. Open the fuel filler and see if the problem goes away (leave the cap on, but loose ... and don't do it with a full tank of fuel).

**gsworkshop** · #6 13 Sep 2005

Thanks for the reply, these are all valed pionts.
The problem was first a needle nozzle to large at 2.68 and then I replaced them with old 2.64's which were worn. After replacing them with new 2.64's sudenly she was going like a rocket.
If you feel you loose a bit of power around 110km/h this should be the first thing to check after cheking the other more obviouse things you guys refered to in this forum.
Needle nozzles tend to wear causing an over rich mixture the moment the taper on the main needle start to emerge from the needle nozzle or needle jet.
This will hapen at almost exacly 4000rpm or 110km/h if in 5th gear.