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Discussion Starter · #1 ·
Alright so for like the last month or so my bike doesnt have any top end power for the first 20 mins while im riding. If i just jump on the bike and try and go full throttle when i hit 10k rpms with %100 percent throttle it just stops accelerating. The engine is still going but the rpms dont go up however if i give it like 75% throttle then it accelerates. Eventually this becomes less and less of a problem as i "warm up" the bike however this has never happened before and there has to be something causing it. Anyone have similar problems or any idea what it might be? Anything would be greatly appreciated.
 

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Discussion Starter · #4 ·
or a few minutes to warm up?
Maybe but i dont think so. I let my bike get to around 100 degrees everytime before i ride and then even when its at operating tempurature around 180 degrees it still doesnt have full power. It takes around 20-30 mins of riding before it starts to get the power back.
 

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Check that the the fuel cap and it's vent pipe are not clogged. They have been known to cause a partial vacuum in the fuel tank restricting the fuel flow under load causing your synptoms.

Also a bad spark plug or spark plug cap




can cause the same problem as can porous or damaged fuel line.
 
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It never, ever hurts to check the valve clearances.....if you've read any of my past posts I'm normally the one stressing that they should at least be checked because tight valves can for sure cause weird running behavior as well as possible damage. However the tip-off on your problem here is that when the problem is present if you back off on the throttle a bit the power comes back on....this normally indicates a fueling issue which I think statistically is the highest probability issue with the SV's. The inlet screen to the pump can and will get clogged with muck as well as the tiny internal fuel filter will only hold so much dirt before becoming restricted.

Before pulling the tank to access the pump....perhaps doing the 'fuel volume' test would be in order. A quick search here will give you more than enough help to do it and what the results should look like. Or just jump in and remove the pump....money has it that the inlet screen could be cleaner and if you back-flush (carefully) the filter you'll get a bunch of nastyness out of it. Then reassemble and I'm wagering that your problem will be gone. :)

If cleaning/inspection of the pump doesn't do the trick....there are a couple other things involved here: TPS and STV's. The ECU only knows how much throttle you're giving it via the TPS reading and they...like anything...can and have gotten flaky on some bikes. It would be a bit weird that the 75%+ portion of the TPS is causing a problem..normally down around idle and low openings where it spends most of its' time....but never say never. The other possibility would be the STV's not opening fully or doing something odd. I'd start by verifying the whole tune....valve adjustment, plugs, air filter and all settings just so you know where you're starting from. I can tell you from experience it's a bad feeling when you chase a weird problem for a while and finally find that it would have been fixed with a basic tune-up so for many years now that's my starting point. If nothing has been found that needed adjusting....then move to the fuel system, and lastly the TPS and STV's if no joy has been found. Good luck!
 

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Discussion Starter · #8 ·
It never, ever hurts to check the valve clearances.....if you've read any of my past posts I'm normally the one stressing that they should at least be checked because tight valves can for sure cause weird running behavior as well as possible damage. However the tip-off on your problem here is that when the problem is present if you back off on the throttle a bit the power comes back on....this normally indicates a fueling issue which I think statistically is the highest probability issue with the SV's. The inlet screen to the pump can and will get clogged with muck as well as the tiny internal fuel filter will only hold so much dirt before becoming restricted.

Before pulling the tank to access the pump....perhaps doing the 'fuel volume' test would be in order. A quick search here will give you more than enough help to do it and what the results should look like. Or just jump in and remove the pump....money has it that the inlet screen could be cleaner and if you back-flush (carefully) the filter you'll get a bunch of nastyness out of it. Then reassemble and I'm wagering that your problem will be gone. :)

If cleaning/inspection of the pump doesn't do the trick....there are a couple other things involved here: TPS and STV's. The ECU only knows how much throttle you're giving it via the TPS reading and they...like anything...can and have gotten flaky on some bikes. It would be a bit weird that the 75%+ portion of the TPS is causing a problem..normally down around idle and low openings where it spends most of its' time....but never say never. The other possibility would be the STV's not opening fully or doing something odd. I'd start by verifying the whole tune....valve adjustment, plugs, air filter and all settings just so you know where you're starting from. I can tell you from experience it's a bad feeling when you chase a weird problem for a while and finally find that it would have been fixed with a basic tune-up so for many years now that's my starting point. If nothing has been found that needed adjusting....then move to the fuel system, and lastly the TPS and STV's if no joy has been found. Good luck!
Wow thanks for all the information this type of help is so useful. I will be going down the checklist sometime soon just been real busy as of late. I would not be suprised if it was the filter/inlet screen as I am now realizing the bike starts running full capacity again not after 30 minutes but after a couple pulls where i keep the throttle pinned. Even though im not accelerating i think its like clearing out the gunk cause right after a couple pulls it runs perfect. I just thought it was 30 minutes of run time cause thats how long it would take for me to do that. Def going to open her up and clean out the gunk if thats the problem tho. Again thanks for all your help
 

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I had a similar issue on my old GS500. What I found was: a gallon of water in the tank. Not pure water: it had a lot of ethanol etc. in it, but the story was: I looked for fuel system issues and found none. I had the gas drained into clear jugs, and just as I Was about to give up and pour the gas back in, I realized that it separated into two layers. I decided to pour only the top layer into the tank and after a little while, after the carbs ran out of the old fuel, the bike started responding to throttle like never before.

So yeah, there may be fuel system issues, but there also can be a fuel issue. It never hurts to start diagnosis with the easiest items first :)
 
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