Hi all,
I've been riding my GS all over the place since I got it 4 weeks ago now...have over 1000 miles since when i picked it up and it has been a blast every time.

Yesterday I went to meet a friend for breakfast and went on a highway. In 6th going about 80 mph, I rolled the throttle to speed up a little more to get around a construction truck (the ones with the loose rocks that peg you when you ride behind them) and the bike seemed to struggle. Revs did not bounce around, which tells me (I hope) the clutch is correctly adjusted...it just seemed to tremble (for lack of a better description) in a front to back motion...as if trying to accelerate. It did accelerate, but with that light bucking motion....I then backed off and tried it again later in the ride and the same thing happened. Tach was at about 7k or so in 6th at 80.

Is this normal? I'm not not running the bike too hard am I?

PS: I was on a road where the posted speed limit is 75. I am not the racer, but the cruiser with a smile on my face 

At that speed it will accelerate, but 6th just doesn't have a lot of get up and go. You still have a lot of RPM range, so if you really want to get on it just drop to 5th. You could also just check the jetting and such to be sure that everything is where it should be, but...if the response in all the other gears at high revs is good, then don't worry...it's just the bike asking you to downshift.

I could easily get 110-115 on mine but keep in mind, I had new plugs, used non ethanol 93 octane fuel, after market air filter, carbs were jetted and synced, my valves were adjusted correctly

Highest I've ever reached was 178 km/h (111 mph) stock 2004 GS500F, could have got a bit more, but not much more.

When I use to ride with big twin friends I left my GS in 5th on the local freeways, dropped to 4th for passing to match their roll-on speeds.  Both 5th and 6th are overdrive ratios, 5th works nice for passing and 6th is more of a cruising gear. 

Traveling to the mountains to play we did 400-500 mile days on the Interstates at 75-80 mph to get there.  So don't worry about travelling at 80 mph all day long.  It won't harm you bike at all unless you run out of oil.    Most of those trips were on my 97 GS with a 15T front sprocket.

I've mentioned it before, I had my stock 97 GS up to 110 mph indicated with a big Plexi 2 fairing and 240# me on board.  As I recall I ran it up into mid 90s before dropping into 6th, it was back in 02 when I was a kid of 70 riding like a kid of 17.  I don't ride that way anymore, rarely see more than 50-55 now but that's on some local twisties.

Bucking motion sounds like fuel starvation.  Even in 6th, my bike will accelerate slowly but smoothly up through 100.  Were you going uphill?  Was there a strong headwind?  Were you carrying tons of crap?  Do you weigh 300+lbs?  Do you have a giant windshield or bags or something to catch the wind?  All those things can bring your top speed down, but any GS should be able to pull 100 otherwise.

Try putting your petcock in the prime position and see if you get the same results.

Thanks for all the info, guys.
I think the best thing to do first is make sure none of the fuel lines are kinked. Ill look in the fuel tank with a flash light and look for any corrosion that may be blocking those fuel lines.

I will try the fuel tap on prime....what would that isolate?

I will get to the jets and see that they are. The bike has 2 K&N filters, one on each carb, and I just don't know if they are the correct size for those filters and a stock exhaust.

I also notice that after cruising I get a little exhaust pop...at least that's what it sounds like, when I give it a little throttle...this may be wrong jet size?

Sounds like you have pod filters on there...  In that case I would bet its a problem with the jet sizing with too small of main... But do try it on Prime before you dig into anything.  If it 'fixes' it on prime, then there is either a pinched vacuum line, or the vacuum simply can't keep up with the fuel demand with larger jetting (larger jetting than bike originally designed for) and pod filters.  This is common with some of the older petcocks and larger jet sizing which accommodates free flowing intakes.

- Bboy

Thanks for all your help, guys.
I'm going to try and look into this a.s.a.p. as I am afraid to cause damage to the motor...is that possible?

Nah. You won't physically damage anything. Assuming you have plenty of oil, and it's not smoking, or really lurching, and there aren't crazy banging/knocking noises...then you're fine. At the higher speeds you may just be not giving it enough fuel, or too much.

I'd venture that the bike still has the stock jetting.  I bought a GS500F last week and found the peak power band only went up to about 6500 RPM.  On the freeway I got it up to an indicated 95, but it was slow accelerating up to that point.  Last night I put in a K&N drop-in air filter and rejetted it; not it pulls hard all the way up to the red line and has a vastly improved acceleration off the line.  I have yet to try it on the freeway, but in town up to 65MPH it runs so much better.  When I roll on the throttle I can feel the front end get lighter (not to the point of pulling a wheelie), which it didn't come close to with the stock jetting.  FWIW, with stock jetting the acceleration was worse than a 2007 Ninja 250R.

Its probably been jetted, but not properly. If it had stock jetting with K&N pods the bike would be unridable.
Find out what jets you have in there, and then compare to the chart here:

http://wiki.gstwins.com/index.php?n=Upgrades.Rejetting

Bucking, usually is a sign of lean jetting. Let us know! Also, what kind of muffler is on there? stock or improved?

Great video, Funderb. That looks like the guide I will follow.

Exhaust and muffler is all stock...that's getting painted this weekend too!

Im going to try to get to this this weekend.

I just looked at the chart for the 01+ bikes (mine is a 2001) and it states this:

pilot 20

main 142.5

washers 1

turns 3

people 1

I think this is missing a jet...I understand the 01+ bikes have 3 jets.
What is the 1 washer and 3 turn info for?

Quote from: nico on September 19, 2013, 04:32:15 AM
I just looked at the chart for the 01+ bikes (mine is a 2001) and it states this:

pilot 20

main 142.5

washers 1

turns 3

people 1

I think this is missing a jet...I understand the 01+ bikes have 3 jets.
What is the 1 washer and 3 turn info for?

The washers/turns refers to raising the needles and adjusting the idle mixture screw respectively.
The idle/mixture screws are on the bottom-front of the carbs under brass plugs.

I'm guessing that guy didn't change the mid-main jet (60 stock) and this didn't list a jet used.  I just put in 20/62.5/142.5 jet sizes with about 1 washer and 3 turns of the mixture screw and it's made a huge difference; just need to fine tune it, probably needs another washer and only 2 turns of the idle screw.

QuoteExhaust and muffler is all stock...that's getting painted this weekend too!

Good stuff! You may just need to re jet and you will be fine.
I would recommend a new muffler, if you can get your hands on a slip on or have a performance muffler adapted to the bike, like I did, Those K&N filters let in A LOT of air, and you're making the engine wheeze it out through a tiny hole with the stock exhaust. Its like breathing in big gulps of air and blowing all that out through a straw. It can make the engine difficult to tune properly.

If you have time and a little welding ability you can make any muffler attach to the bike!
This is my akrapovic on mine just before I totally rebuilt the bike:

That thing sounded great.

Quote from: radodrill on September 18, 2013, 08:46:23 PM
I'd venture that the bike still has the stock jetting.  I bought a GS500F last week and found the peak power band only went up to about 6500 RPM.  On the freeway I got it up to an indicated 95, but it was slow accelerating up to that point.  Last night I put in a K&N drop-in air filter and rejetted it; not it pulls hard all the way up to the red line and has a vastly improved acceleration off the line.  I have yet to try it on the freeway, but in town up to 65MPH it runs so much better.  When I roll on the throttle I can feel the front end get lighter (not to the point of pulling a wheelie), which it didn't come close to with the stock jetting.  FWIW, with stock jetting the acceleration was worse than a 2007 Ninja 250R.

I suspect it is something other than stock jetting.
On my 2009, all stock, no problem even getting up to 100. On 2 bikes I built (see threads on them), both have 2006 motors and the carbs have stock jets. Once I rode Phenix with the liter bikes and got over 100 with no problem. Sure when accelereating from 70 to 90 I was a little behind them, but didn't take long to catch up.

I think it is wrong to think you need to re-jet to get to 100mph. I'd look more at:
1. Inadequate fuel flow (dirt, pinched lines, etc.)
2. Electrical: low voltage will be a weak spark and less power
3. Air: Air leaks or restricted air from dirty air filter
4. Dirty carbs: lots of passages in them - more than just the jets. Everything needs to be clean. Clogged ports will reduce performance
5. Bad plugs: yes, they make a difference. I now use Brisk performance plugs and get a little more power and more linear power band. Even regular plugs need to be clean.
6. carb sync: if carbs are out of sync, you can be running on one cylinder which will really impact your top speed (ok it may be 75% on one and only 25% on the other, but you know what I mean)
7. Valves: proper valve clearances will improve performance.

My bikes with older 2 jet carbs are stock except I change the pilots from 37's to 40's (which is what the rest of the world uses) and  that only helps the low end. I can still hit 100 with no problems on any of my bikes.


I would suspect your jets were dirty. When you re-jetted, one thing you did was put in clean jets and probably cleaned out some of the other passages as well. New stock jets and the same cleaning would have produced a dramatic improvement, I suspect.

Interesting you mention the Ninja 250. A neighbor has a new 2012 250 with only 6000 miles, and I can beat him on any of my bikes. Then all my carbs are pretty clean and engines have proper valve clearances.


Not to put down what you did, but I wish to make it known that stock jetting does not keep you from going 100+mph. Other things are the cause of poor performance and less than stellar speed.

Quote from: adidasguy on September 20, 2013, 11:42:55 PM
I would suspect your jets were dirty. When you re-jetted, one thing you did was put in clean jets and probably cleaned out some of the other passages as well. New stock jets and the same cleaning would have produced a dramatic improvement, I suspect.

I got the 500 with 2678 mi on it.  The stock jets did have a little bit of discoloration (from oxidation) but other than that they were clean and all the passageways were clear.

Quote from: adidasguy on September 20, 2013, 11:42:55 PM
Not to put down what you did, but I wish to make it known that stock jetting does not keep you from going 100+mph. Other things are the cause of poor performance and less than stellar speed.

I never said the stock jetting wouldn't do 100+  Before I did the rejet I had it up to 95 @7500rpm and it was still picking up speed, just took a bit longer to get there than I wanted; in my case rejetting made a huge difference.

In re-reading the OP I see he mentions not only slow acceleration, but also light "bucking" motion.  I agree that the "bucking" is likely due to one of the other possibilities you listed.

Thank you for all of the info guys. I will be diving deeper and deeper into this as time permits.