Loss of power at high rpm | GTAMotorcycle.com

Loss of power at high rpm

jcbarnar

Well-known member
Hey GTAM,

I have a problem with my bike and am hoping for some guidance on where to start looking so I don't waste too much time/money troubleshooting.

I've got a 2001 CBR600F4i with 30,000km, purchased used, the only known history being a new CCT and valve adjustment both of which were done since purchasing.
The motor sounds great and the valve train is very quiet. Until yesterday, midrange power felt excellent to me!

The issue is a complete loss of power at WOT anywhere over 10k rpm. At partial throttle the bike will rev freely, but at 3/4+ throttle it will simply stop revving above 10k. It is not a jerky loss of power like a rev limiter, but very smooth and it will just maintain that rpm until I back off the throttle halfway then it will continue to rev. It is not just a temporary dip in power delivery, it will maintain that rpm indefinitely. If I gear down to bring rpm anywhere in the upper range, as soon as I twist the throttle it stops making power, so it's not right at 10k but anywhere above. The issue is also getting worse, yesterday it started happening at a lower rpm to the point of affecting the midrange for the first time, and then on my final route home it wouldn't make any power over 6k, highway riding was nearly impossible! I will add that in neutral with no load it would always rev freely, but yesterday when I got home it would not even do that anymore stopping around 8k or so.

My first suspicion is fueling or fuel pump. I will be pulling plugs for inspection and measuring exhaust temp on each cylinder as well. I will be checking the airbox etc. for blockage, pinched hoses, since it's easy to do. Bad timing is a suspicion, but not my first, that would result in poor performance but not a complete lack of. I also think this issue was happening before I had the work done. The reason I don't know for sure is because I never pushed the bike hard prior, but the one time I did I felt hesitation at high rpm but didn't think much of it since the bike was going to the shop in a couple days.

Thanks for any tips.
Jeff
 
I think you are on the right track. I would definitely focus on fueling restrictions. Second line would be air or spark problems.

What other bikes have you ridden? Can you compare your bike to another 600ss to know if it is down on power everywhere or just up top?
 
My friends have similar bikes and the midrange was comparable for sure (for the past week), only ran out of juice up top right when it should start making the most power (and thus require the most air and fuel). I started it up again today and the issue persists, does not have enough power to make it past 6k just like when I parked it yesterday.

I downloaded the service manual. My fear is just throwing parts at it, things like the fuel pump are very expensive so I'm hoping there are tests that can be performed.

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Don't throw parts at it, try to test the parts you have. You were on the right track with checking the headers for heat and things like that (you don't need a temp gun, a wet rag will sizzle on the header if the cylinder is firing).

How long ago did you get the service done? It could be crossed plug wires or a missed lead to a coil. If this happened immediately after the service, there is a chance it was reassembled incorrectly.
 
Test the fuel pump out. They are known issue.
 
How do you test a fuel pump?
 
My guess is line from the pump into a jar, run it for a minute, measure the fuel and see if the rate is close to spec.

I would be interested in hearing from someone that knows more though to see if I'm way off.

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My guess is line from the pump into a jar, run it for a minute, measure the fuel and see if the rate is close to spec.

I would be interested in hearing from someone that knows more though to see if I'm way off.
I know to test the fuel pump on my R6S I had to take the line from the return feed from the fuel pressure regulator, then measure the quantity put out over xx seconds. I guess taking the line right from the pump wouldn't be accurate because the pump isn't pumping against any back pressure. I believe it was the service manual that had the fuel pump test procedure in it.
 
My guess is line from the pump into a jar, run it for a minute, measure the fuel and see if the rate is close to spec.

I would be interested in hearing from someone that knows more though to see if I'm way off.

Sent from my Nexus 7 using Tapatalk

They usually list the flow / per min. I'd run the fuel pump for 30 seconds into a big jug and measure how much it flows out. If a fuel pump is not flowing enough - the amount that comes out would be quite a lot less. I'd say only about a 1/3" would come out....

Generally speaking - when a pump starts to fail - it will prime weak. And will flow / trickle only a marginal amount of fuel. As the consumption of the motor rises with RPM/Load - the amount/fuel pressure isn't enough to supply the motor.
 
Thanks guys. Trying to find the time. I will test the pump and report back

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I think it's just a pinched fuel line. It looks like the main hose to the fuel rail was installed backwards and its not long enough :p with the tank propped up slightly it runs a lot better. I'll rotate it tomorrow and see. I hope no damage was done from running ultra lean..

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