650sx won't go past 50% throttle

[bumperlt]

At the very end of last summer it started bogging down and not going full throttle. I thought maybe I didn't mix it at the right ratio, but I drained the gas and filled it with 40:1. No change after riding it for 30 minutes on the lake. I know there's a lot of things that can cause this sort of thing, but i don't really know where to start. I did find the reserve fuel line was detached, so I'll fix that but I don't think that's the culprit. Current plan is to check the fuel system, and blow come compressed air through everything. I think it might be worthwhile to pull the carb and clean it up good. I haven't done a compression check as of yet, I should have... So i'll do that as well.

Any other input to help me track down the problem before summer is over would be much appreciated!.

I should note that it's not stock, I'm not sure what's all been done.

 

[kswiatk]

I've had this issue before.. I ran some sea foam fuel system cleaner in the fuel and it was back to normal..


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[Pro-pulsion]

There are a few little things that can cause this too, start with the easiest things first. There is a little one way check valve on the fuel tank vent hose. Make sure it only allows air into the tank and both ways. I have even had them fail preventing air from going in. You get 20 minutes run time then nothing until the tank gets air again.

Next you can look into the fuel valve. These are a very commonly over looked area on the good ol 650's. They can be disassembled and there is an o-ring inside that wears out. Usually what will happen is water gets into the fuel system through there and then droplets get into the carb killing delivery.

The carb may be due for a cleaning and rebuild, those Keihin carbs are quite finicky when they need a rebuilding. And then there are possible broken reeds, that will cause this too, but finally would be the CDI when all else fails. If the CDI fails it will run like garbage and frequently stall sounding like it's a carb issue.