[LRussoPhoto]

I just picked up an 06 crf80 for my daughter. When I purchased it, it wasn't running. It had been sitting for a long time and i could smell that the fuel was bad. I drained and cleaned the tank, took apart and cleaned the carb, put some fresh fuel and and it started right up. Im having an issue with the idle. I can't seem to get it right. I first started by raising the idle slightly so it was a slight high idle, I then tried to adjust the fuel screw by turning it in until the engine almost stalled then raising it till the the idle went high then leveled and then backed off slightly. Problem there was even when I turned the screw all the way in the engine still ran. SO I just backed it out one and a half turns and left it there. So now when I try to start it cold, I turn the choke on and it fires right up but the choke doesn't hold the idle up, if i let go of the throttle it stalls. If i turn the choke off its better but still won't idle till warmed up. If I raise the idle to keep it running the idle will be too high when warmed up. What am I missing?????

Also anyone know where I can download a free repair manual?

[JimDirt]

Check the carb boot where it connects from the carb to the head , it may have cracks in it causing a vacuum/air leak , which would allow it to still idle with the screw turned in all the way

You can try something , just be real careful , with the engine cold/cooled down where the exhaust is cool to the touch , take some carb cleaner spray and start the bike , then spray directly at the carb , and the intake boot and see if it changes the RPM , avoid hitting or spraying near the exhaust header , and only do this for the first minute at most , before the exhaust temps get high , if it does change the RPM then you will find the source of the air leak , because when the spray hits the leak the RPM will change

[LRussoPhoto]

Yes, I think I have an air leak. The idle does sage every now and then. I was just outside messing around and spraying carb cleaner around the carb area. Seems like the rpms change when I spray around the top o the carb, where the slide cover screws to the top of the carb but the gasket LOOKS ok. Could it be that?

[JimDirt]

It could be also around the choke , try hitting the choke directly with the spray and see if it changes , also it could be that the Needle Jet (the long tube that the main jet goes in and the the needle goes in as well) could be worn , it will cause erratic idle and make setting the fuel mixture a pain because what it does is allow fuel to bypass the needle when the throttle is closed causing the idle to not keep consistent , as well as making the mixture , rich , then lean

You could rev the engine and it will then idle high , then adjust the idle screw , then rev the engine and the engine will die or try to , then you rev it again and it idles normally again , as well as affecting the mixture screw , it makes tuning a pain because the Needle Jet being worn allows the needle to bounce around inside and it gives it the same input as raising and lowering the slide , allowing more fuel or less fuel , but its doing it at a idle

You will not be able to see the wear , unless you happen to notice a discoloration like some of the coating is worn off the needle itself from it rubbing on the inside of the Needle Jet , the Needle Jet is cheap , you can replace it and see if it cures the issue , they are a "Wear Part" , and the engines are very reliable and trouble free , so it is most likely a vacuum leak , or something is worn causing the issue

[LRussoPhoto]

So is the the needle jet what the main jet actually screws into? The main uses a flat head to install and the needle jet uses a hex head to install and actually screws into the carb casting then the needle rests on it?

[JimDirt]

Correct

Think of it this way , you stick your finger (which is tapered like a carb needle) in a round tapered opening , when your finger as all the way to the bottom of the tapered hole , the hole is sealed , as you raise your finger it allows fluid to flow , the more you raise it the more fluid flows , now take the hole and oval it out (the needle jet is softer than the jet itself) , now when the needle/finger is all the way in the hole , there is still areas that allow fluid to flow thru because they are worn oval instead of round , then as it wears , the space allows more and more fluid , so now , no matter how you set the needle/finger , it allows fluid to flow

So your needle is bouncing around in the ovaled out hole , and creating lean and rich conditions continuously at a idle when it should not be allowing hardly any , not saying 100% this is the issue , but it will affect tuning , but is usually confirmed by a inconsistent idle (idle is normal , then you blip the throttle and the idle is high , or too low , then you blip the throttle and the idle is normal , next time its high , then you adjust the idle and its normal , then you blip the throttle and its way too high , this is the most common scenario for a worn needle) , along with the mixture screw is always off no matter how you adjust it

I am far from a carb expert , but it is something that needs to be checked if the symptoms continue after replacing jets and fresh fuel and cleanings do nothing , along with verifying the above mentioned vacuum leak , is or is not the issue