Signs off around 8k rpm

[pucksdown]

I owned a GS450 thirty years ago and it came on strong around 8k but I bought a 2006 for my son and it gets weaker after 8k and feels barely faster than a Ninja 250.  It has 26k miles and I was about to pull the plugs and look at them..  It idles fine just feels weak after 8k rpm.  I will check the air filter after that.  Not a great mechanic, so I plan to change the oil and plugs and air filter if needed then take it to a shop after that... Any ideas?

[Atesz792]

Fun should begin somewhere around that, not end... maybe you got a restricted version?

[NYNJ8]

I find my GS powerband completely different than my Ninja.  The ninja never really gets any real power, but what power it does have runs from 8k to 12k.  My GS has good power from 4k to 6k and very good power from 7k to 8k.  I don't find much power after that.  But then again I don't spend much time in that rev range and haven't had my bike very long. 

Keep in mind you are comparing one bike with a 14k redline to one with an 11k redline.  Everything happens much sooner.  But if you feel like the power is comparable then you probably do need to do some tuning.  I'd say that my stock GS is twice as powerful as my stock ninja.  My 2c

[pucksdown]

I pulled off the side fairings just now and will pull the plugs Sunday and see how they look. I'll check the fuel filter, air filter, and oil.  If none of those solve it, then I will take it to the local shop.

[gsJack]

The GS500 hits max HP at about 8500 rpm and power on a stock GS drops off quickly after that.  I found my stock 97 ran strongest between 7-9k rpm and I would keep it in that range for hours when running fast in the mountain twisties years ago.  When the 97 was totalled at 80k miles back in 03 I replaced it with my current 02 GS.  The 02 with the 3 circuit carbs felt stronger thru the mid range than the 97 and was better in every day riding about but after I bought the 97 back and fixed it I ran them both back to back the same day a couple times and while the 02 was much better running thru the mid range the old 97 with 80k on the clock still felt stronger on the top end. 

Always felt there was a cam change too when the 3 circuit carbs replaced the 2 circuit ones from 01 on but never confirmed it.  Anyway pucksdown, I can see where your GS450 might have felt stronger than your sons 06 does on the top end but you should still be pulling strong at least to 9k or so on the 06, my 02 did until I got old.   

A good job of intake, exhaust, and jetting mods will extend the power past 10k or so but I always felt my GSs were too much fun as they were without modding them.

[gsJack]

Typical stock dyno run:


Typical modified dyno run:

[Ron888]

Always felt there was a cam change too when the 3 circuit carbs replaced the 2 circuit ones from 01 on but never confirmed it

An interesting thought.My workshop manual contains listings of which cams are different.As far as i can tell there was only some build differences, that is- the cam lift,overlap and profile were the same for all years?
I wonder if the three jet carbs had different flow characteristics?
Could it have been a change to the ignition advance curve?

[gsJack]

Just the addition of the mid jets makes a big difference in mid range flexibility I think but shouldn't affect top end like a cam change would.    The ignition modules are quite different and not directly interchangeable between 89-02 and 04-09 models.  Ignition advance for the 01-02 models is the same as the E33 (California) models were for the 89-00 models and remained the same thru the 04-09 F models I think.



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[MeeLee]

Have you checked/replaced the air filter?
I notice barely any decrease of power from 8 to 9.5k RPM on my 2004 GS.
At 10k RPM it feels like it pulls about the same as at ~7k RPM

[Janx101]

I noticed same thing, but dyno sheets from others say it does. ..

I suppose it all happens quite quickly with most of the gearing... shows a little in 5th and more in 6th when up in the high rpm. ...

Goes to show what 'feel' can trick us all with!

Plus with as little torque as a GS has compared to big power bikes. .. the decrease in torque wouldn't exactly be a jolt!

[Kijona]

Does it have an aftermarket exhaust? Is it louder than the stock exhaust?

On my 2007 GS I noticed it seemed unusually gutless towards the top-end after I removed the baffle from the aftermarket exhaust it had. Less backpressure = less top-end power.

[Atesz792]

Wouldn't less back-pressure mean less low-end power?

[Ron888]

Does it have an aftermarket exhaust? Is it louder than the stock exhaust?

On my 2007 GS I noticed it seemed unusually gutless towards the top-end after I removed the baffle from the aftermarket exhaust it had. Less backpressure = less top-end power.

Ive read that the concept of backpressure is a complete myth.That makes sense,because it goes against almost everything else that IS proven.
What you've probably done is alter timing of the reflected wave,thus losing power