07 yz450f starts but dies...PLEASE HELP!

Background: bike overheated and dropped a valve in original head and trashed it. So three weeks ago I did a complete to end rebuild. Bike sat for about 6 months while a got all the new parts together. New ported race head, new piston, rings, got cylinder honed, gasktets ect. Did alk the work my self shimmed valves in specs timed ignition started right up. I Broke it in how everyone on here said to do in heat cycles. Ran like a new bike. Did two local races last few weeks bike ran great no problems what so ever. Yesterday took it out for a friday practice. She ran great all afternoon. Then took a break and was gonna do a 5 lap practice race. 4th lap in I went into a turn hot and she started to bog and sputter then stalled. Waited a few minutes then she fired back up but didnt want to keep running. So I kept the rpms up and feathered it back to the truck. Got back let her sit for a few minutes to cool down while I got some water. About 10 mins later got back on started her up rode great for 2 laps then again same symptoms. Bogging then stalled. Frustrated I kicked and kicked then using the hot start she fired back up took her back to the truck and loaded her up. That evening I tore her down and cleaned out the carb and checked valve clearance. Still all in spec. And looking good. Buttoned her back up and fired her up with choke out. Ran good for few minutes then died as if kill switch was hit. Played with fuel screw still same start then die out. Checked gas tank vent hose...all good. Cracked open gas cap still start then die. Could the stator or cdi of gone bad just like that? Is it a bad rod bearing? Im hoping not that after everything ive put into the top end. Please help!!

Check all your wires to make sure they all getting good connection. But this sounds a lot like a stopped up carb maybe your float isn't letting in enough gas and the bowl runs out faster than it gets gas

Check all your wires to make sure they all getting good connection. But this sounds a lot like a stopped up carb maybe your float isn't letting in enough gas and the bowl runs out faster than it gets gas

ok thanks! Do your think that I should re jet it and what should I be looking for with the float? could a passage way in the carb be clogged if so where should I be looking?

Just take it apart and buy a rebuild kit I don't think he cost much just go find one on eBay. Sounds like the jets or the float or maybe both are messed up. It could be some dirt or maybe its got old gas. What's the longest period of time its sat before you took it to the track

Just take it apart and buy a rebuild kit I don't think he cost much just go find one on eBay. Sounds like the jets or the float or maybe both are messed up. It could be some dirt or maybe its got old gas. What's the longest period of time its sat before you took it to the track

oh ok ill try that. I raced last sunday and it ran fine. Then ride on Friday that's when it started acting up.

Well it you never know what it is into the carb is off. When you get it apart tell me if its dirty. Or put some pics up

Well it you never know what it is into the carb is off. When you get it apart tell me if its dirty. Or put some pics up

ok sounds good thanks for the advice man I really appreciate it. Ill put some pics up and let you know what I find.

Okay no problem. I'll check them when you put them up.

Sounds to me like a classic clogged pilot jet. It can be removed by taking off the 17mm drain plug in the float bowl. But in this case id clean every passage in the carb.

Always buy a new pilot jet- you can get oem Keihin jets for $1.50 off Rocky Mountain atv. There's a guy on here who drills them out to clean them ahh! It's a precision sized jet and any enlargement at all will cause more problems.

You will likely need a 45 or 48 pilot jet depending on your temp and altitude.

Ok so I tore the whole carb apart last night used carb cleaner on everything and made sure it was all cleaned thoroughly. Finished at 2am so didnt start it last night. Got up this morning and started it started up fine let run for a few mins to warm up and again died like someone hit the kill switch. Why does it start up perfectly fine then just dies and not want to start again till its cools down little? Is it really just the pilot jet?

Now she will just start for a second then die and if any throttle is givin it dies out.

So I changed the oil and took the carb bowl plug off the bottom and took out the main jet I believe (the long one with the jet on the end that is easily accessible) and cleaned it really good must of had some varnish or something. Reinstalled it and cleaned the bowl plug and she's running good I believe. It was idling high which it wasnt doin that before so I turned down the idle and took it up the street. She ran great parked it and turned it off. Started it back up first kick. Thanks everyone for all the help. Im gonna take her to the track today to make sure everything is back in working order. Will let you know how it goes tonight.

Went to the track yesterday bike ran great no problems. Thanks everyone for all the advice.

There is a great deal of difference between "drilling them out" and using a drill bit of a precise size to clear an orifice of a known size.

Raed: http://www.thumpertalk.com/topic/681801-bike-wont-start-dont-know-what-to-do/#entry6879695

ok so I rode it last weekend and it came back. So I bought a carb rebuild kit and installed it and started it and it ran perfectly took it up the street and around the block ran better than ever. Then pulled it in my garage and put it on the stand and it died. Started it and it sounded like it was misfiring and wanted to die. I think its electrical. Does any one know if it would be the stator or cdi. It seems as when it warms up something starts to fail and kill the engine.

Any way you can test it by substituting a known good CDI? Any of them from an '03 to '09 will run it, they'll just have different power curves.

The stator is usually the culprit, but anything is possible.

Any way you can test it by substituting a known good CDI? Any of them from an '03 to '09 will run it, they'll just have different power curves.

The stator is usually the culprit, but anything is possible.

so what would you try first gray? Stator or cdi? or what other possibilities could it be?

The stator can be tested easily by the checking the resistance. Do it first at room temp, then If the bike acts up when hot- test it while it's hot. Just unplug the connector for testing.

After the stator is ruled out, you can swap CDI's with a known good bike. Unfortunately Yamaha doesn't give any testing for the Cdi and therefore must be swapped out.

I like to start by testing the stator since the connector can be accessed so easily

Testing while the bike is acting up is the only way to definitively catch the culprit, and you should record the readings you get at room temperature for a baseline, as recommended.  But do expect the resistance you read with it hot to be higher, maybe as much as 25%, depending.  The percentage difference you see should be the same for both coils, though.  More than a 10% variance might indicate a problem.

 

If you have an analog meter, or a DVOM with an analog scale in the display, take the butt of a hammer handle and rap around the flywheel cover while you have it hooked up.  Watch for the needle to jump.  Sometimes you can catch it that way.

 

The only thing that can test something like the ECU is a computer system specifically programmed to interact with it.  When available at all, that kind of stuff is just too much money for most people to spend on tools for their hobby.

A pity you can't hook up a multimeter easily to the stator connections and leave it connected whilst running. If the voltage out of the stator suddenly drops and the engine stops that's a pretty good diagnostic of a stator problem.

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