[Swift-Rider]

I have a 2007 crf250r that I’ve been working on for quite a while. I’m now tweaking with the bikes carb and have had a few problems.

PROBLEM 1: When giving about half throttle the bike seems hesitant. Like it’s not sure if it wants to go or not. I’m assuming it is too rich, but I’m not sure what jet I would change? I have changed the main jet because at full throttle the same thing was happening.

Problem 2: When gunning it on a straight road, then letting off the throttle, the bike dies out of nowhere immediately. Could this be due to too low of idle or also another jetting problem?

Any help would be much appreciated as I have been struggling with this bike for what feels like forever. Thank you.

[JimDirt]

Welcome to the site !!

You need to give some more detail on what is currently in the bike for jetting , whether you have checked to see if the accelerator pump is squirting , and what elevation you are riding ...

Also , was the bike running fine then just started running bad ??? , does it run the same when it is cold (the temperature outside) ?? ..... Have you checked the spark plug to see if it is black and sooted or golden and white ?? , this would give you a good indication if it is actually lean or rich

The more detail leading up to this , and during this will help diagnose if this is a fuel or electrical or valve , or compression/piston issue

Did you buy the bike used and it was doing this from the start ?? , or you have had it a long time and it ran fine then did not ?? ..... was the bike sitting for more than a couple months ??? , was the gas drained from the tank and carb before storing ???

All this matters in trying to figure out what is going on .... I am posting the jetting specs for it , pay attention to the elevation (left side) , and air temperature(top) and that is where your jetting should be

[Swift-Rider]

Yes Jim so everything works carburetor wise. There is fresh fuel, new air filter, the piston had been replaced about 5 hours ago. Valves have not been done. I put the jetting for the carb back to stock setting for my elevation and temperature (About 500ft and 80F). The only thing I did change was the main jet because it jet sputtering and lurching forward when giving it full throttle.

When I pulled the spark plug I did notice it was turning a little white. I don’t think that has to do with the main jet change because before I changed out the fuel screw it looked healthy.

It idles almost perfectly. Starts up on first kick (when cold). I’ve only had this bike since I rebuilt it so I’m not too sure if it ran fine before or not. It is bored out to a 270 and I’ve never really messed with carburetors before this so I’m kind of learning as I go.

[JimDirt]

What about the needle position and accelerator pump squirt ?? , have those been checked ??

Also , you mentioned the fuel screw change ... could you have perhaps left the old possibly damaged O-ring in ?? , or accidently left out the new O-ring or put the washer on the screw last instead of right after the spring ?? , also , is the screw adjusted to spec ??

The fact that you mentioned the plug "was" darker , leads me to think it is now lean , not rich , and you are going the wrong way with settings , maybe try richening the circuit back up and see what it does , like go to where you were then 1 step richer and see if it improves , or worsens .... since you do not have a prior example of how it ran to go by , it is possible that there is a internal blockage in the carb or even something else wrong you are not catching , maybe even a bad ECM or a coil breaking down , but work on 1 issue at a time .... eliminate the fuel system completely before moving on to electrical ... , or possibly the hot start is stuck in a open position (pulled out allowing more air into the system)

If all that is eliminated , then do a quick valve lash check , then move on to ignition ......

Basically you need to 100% eliminate any fuel issue , and it sounds like you have missed a few things , or just did not mention them here ...... Also is it possible that the air filter is over oiled ?? , this would cause lurching , sputtering , etc. , since it would be starving for air ... A big Bore is wanting more air , so a restriction could cause the issues you are having ... but any lean or rich condition would as well ... , the filter would have to be really heavily oiled , like dripping oiled to do this

One last thing to check ... remove the vent line for the gas cap (not sure if you have a aftermarket rattle cap , or the OEM hose that goes into the triple clamp) but make sure the hose is clear and not blocked , blow on the line , if it is the small cap , then blow and then suck on it , it should allow air each way and you should hear the ball bearing rattle or click from end to end when you either suck , or blow on it , if you don't hear it rattle or click , then you need to either spray some carb cleaner or WD-40 into it , and try to get it to rattle when you shake it , or replace it , if it is just the long hose , then just blow thru it , if it is blocked , stick a long Philips screwdriver , or if you have a air compressor , then put the nozzle to it and blow it out till its clear ...

I am so happy I went to a EFI bike , just get on it and ride , it does not care what the elevation or temperature is , you just hit the button and it starts ..... I ride anywhere from 5,000 ft to 300 ft , and when I had a carb bike , it was always needing the jetting changed or the fuel screw messed with , or both ........... I went from a 02 450R to a 2020 450R , HUGE difference , and so far (66 hours) no issues at all