Surging

[maxfli11]

Got the beast out yesterday for it's first breakin ride, and after a short fairly fast run it wants to surge two or three times before it comes down off the pipe. Keep in mind this is the first time I've really ridden this bike since i got it, rebuilt it and broke it in. I've read some of the posts on carb tuning, and I haven't checked plugs or anything yet. I did notice this morning that a little fuel had leaked out of the carb from somewhere onto the crank case. I'll find that tomorrow. Just need a good starting point to get her tuned up. She idles like a new one, and mid range seems good. Not sure about top end, I haven't got anywhere i can open it up like that where I'm at. I wouldn't bet I got it out of third gear. Wasn't counting.

[reklessj]

U don't need it to idle. Alot of the surge will go away at least it did on my new motor but they all surge a bit

[Foxx4Beaver]

The fuel leaking on the motor is most likely due to a worn out float needle valve and/or float valve seat. You can try replacing the float needle...what happens is the rubber tip gets worn, and no longer gives a good seal...same with the "seat" it rests in.
I went through this with mine for a few months, replacing float needles, only for it to be a temporary fix, because the seat was also badly played out, being the original carb. So I just opted to buy a brand new carb from Sudco...problem solved.
As for the surging...you want to get that leak fixed/figured out 1st....then get it jetted as precisely as you can(making sure the float height is set correctly first).
There's lots of threads on here concerning surging, most of them are old threads, but still very useful...do a search on surging and you'll find plenty. As rekklesj mentioned, you don't need it to idle...I myself don't have my bikes set to idle...I find it annoys me...but, you'll also find that in some of the surging threads, that some members found that setting the bike to NOT idle, actually helped reduce the surging considerably....whereas some members found no difference at all....so it could go either way for you, but worth a try.

[Foxx4Beaver]

You never mentioned if you've done a leak down test to that motor either...that could be crucial to your surging issues "if" it has an air leak....somethin to think about.

[maxfli11]

Yeah. I have no idea how to pull off an accurate leak down test, and I'm afraid of what it's going to tell me. I think everything in it is original. I really don't want to tear this thing completely down and go through every seal and bearing. Might be the right thing to do, but it's riding weather! The surge isn't a big deal. Just not used to seeing it. How do you test for leak down?

[maxfli11]

Just read an article on leak testing. So it's primarily testing the combustion chamber, and intake for leaks? Some pressure pass by the rings into the crankcase. Your crankcase has a case vent. Won't this psi pass through at this point?

[maxfli11]

Also the exhaust doesn't BOLT on the KX. How are you going to block off the exhaust 100%

[Foxx4Beaver]

Also the exhaust doesn't BOLT on the KX. How are you going to block off the exhaust 100%

https://youtu.be/zdq7NRcUIp8

[maxfli11]

Sweet! Thanks!

[Foxx4Beaver]

Sweet! Thanks!

Just so you're aware, the reason I suggest doing a leak test...is because "IF" you do have an air leak, it'll be impossible to jet it....you'll be just going in circles. This is a case of better safe than sorry.

[maxfli11]

Sweet! Thanks!

Just so you're aware, the reason I suggest doing a leak test...is because "IF" you do have an air leak, it'll be impossible to jet it....you'll be just going in circles. This is a case of better safe than sorry.

Well I don't want to get caught in a lean situation and seize either. The previous owner did seize it. It's bored .5mm over and nicsill plated i believe. I don't have a warm and fuzzy about it.

[Foxx4Beaver]

Alot of times surging can mean it's getting extremely hot, and ready to seize...not always, but sometimes. I had a CR125 do that to me once years ago...and just a couple years ago my sled did the same thing...the mag side crank seal went whilst I was out riding, and by the time I knew it, it was too late.

[Polar-Bus]

Got the beast out yesterday for it's first breakin ride, and after a short fairly fast run it wants to surge two or three times before it comes down off the pipe. Keep in mind this is the first time I've really ridden this bike since i got it, rebuilt it and broke it in. I've read some of the posts on carb tuning, and I haven't checked plugs or anything yet. I did notice this morning that a little fuel had leaked out of the carb from somewhere onto the crank case. I'll find that tomorrow. Just need a good starting point to get her tuned up. She idles like a new one, and mid range seems good. Not sure about top end, I haven't got anywhere i can open it up like that where I'm at. I wouldn't bet I got it out of third gear. Wasn't counting.

What were the ambient temps when you ran your bike ? Do you know what the current jetting is ? All KX500's do have a small amount of "decell surging". It's just the nature of the engine. If you have a sound fresh top end there is no way you can sieze a fresh engine from just light acceleration as you described. Like Foxx commented it is possible you have an air leak. You can check for a mag side crank seal leak by removing the mag cover, start the engine and spray some carb cleaner behind the flywheel, if you hear an abrupt change in engine rpm you have a bad mag side crank seal. Another tell tale sign of a bad PTO side crank seal is if the engine uses a lot of trans fluid, but you have no external leaks. The crankcase pulses suck trans oil through the seal and burn off your trans fluid.

[maxfli11]

Got the beast out yesterday for it's first breakin ride, and after a short fairly fast run it wants to surge two or three times before it comes down off the pipe. Keep in mind this is the first time I've really ridden this bike since i got it, rebuilt it and broke it in. I've read some of the posts on carb tuning, and I haven't checked plugs or anything yet. I did notice this morning that a little fuel had leaked out of the carb from somewhere onto the crank case. I'll find that tomorrow. Just need a good starting point to get her tuned up. She idles like a new one, and mid range seems good. Not sure about top end, I haven't got anywhere i can open it up like that where I'm at. I wouldn't bet I got it out of third gear. Wasn't counting.

What were the ambient temps when you ran your bike ? Do you know what the current jetting is ? All KX500's do have a small amount of "decell surging". It's just the nature of the engine. If you have a sound fresh top end there is no way you can sieze a fresh engine from just light acceleration as you described. Like Foxx commented it is possible you have an air leak. You can check for a mag side crank seal leak by removing the mag cover, start the engine and spray some carb cleaner behind the flywheel, if you hear an abrupt change in engine rpm you have a bad mag side crank seal. Another tell tale sign of a bad PTO side crank seal is if the engine uses a lot of trans fluid, but you have no external leaks. The crankcase pulses suck trans oil through the seal and burn off your trans fluid.

So i think i found an air leak source. My fault. The intake clamp was left loose after i installed the subframe last, and it was not over the intake completely. found the fuel leak also. The overflow tube had come off and was missing, a well as some fuel coming from the bad connection on the intake boot. All sealed up now. Ready for next shake down ride. Still looking for a slight antifreeze leak. Had some antifreeze on the cylinder on top of the kips valve linkage cover. Noticed possibly some moisture around the head gasket. I checked all torque and they were fine. I did dump it over on that side while i was riding, so it may be from that and the radiator over flow. I hope!

[Foxx4Beaver]

Glad ya got it figured out...but it sounds like you should really take some, and go over that thing completely, to be sure you don't have any more unpleasant surprises, that could potentially end your riding season temporarily.