2006 YZ450F Running Rough as Hell!

So here is the short story. Bought a 2006 YZ450F few years ago, ran like crap, took it apart and the carb was clogged and the cams were off a lot. FIxed all the issues, got it running well. From there it was also determined that it needed the valves and their seats redone, so the head was rebuilt. Get that back and tada! it runs amazing. Well about 2 months ago we go to put it on the market(it only got about 15-20 hours on the motor the 4 years we have owned it), and it will not idle and it skips and misses and just does all the nasty things 4-strokes love to do. So naturally we take the carb off, pull ALL the jets out and clean them all real well and also give the carb a wash job. That did not fix it, so we checked all the electrical on it with a good tester. Everything seemed fine except that we could not check the CDI unit cause there is no spec to check on it. So we buy a replacement, and that did not fix it. So I pulled the valve cover off to check the valves and the cam timing. All seemed fine except for one tight valve, I reset the clearance to tolerance and put it back together, start it up and no dice. It is still popping and high revving and just being a bad bike. Does anyone have any idea what to check now? I am at a complete loss of words and any help would be MUCH appreciated.

Nobody made the mistake of assembling the release plate to the slide upside down, did they?

We have never disassembled the carb down that far. The slide has always remained intact with the carb. I guess it could be worth a wag to take that apart and check it for wear. Also a note that I forgot to include is that the thing gets INSANELY hot very quickly, im talking within a minute the header and the head and everything is just boiling hot. Which tells me 1 thing specifically, it is lean. But the thing is, the jetting is at 48pilot, and FS out about 2 turns. The main is irrelevant because thats not what is wrong with the engine(i cant remember what it is, so now I am making excuses). However it is correct according to JD settings. So either it is an air leak, or something is wrong with the carb. Unfortunately for me I dont have another FCR to just throw on there to check it with. However the airbox cant be the source of the leak because that is upstream of the carb. So that tells me that the intake manifold part leaks, BUT I checked that when I had the bike down yesterday and It seemed in fine shape. As you can tell, I am in a bit of a pinch and a dilemma. Thanks for any input.

Have you only sprayed/blown out the pilot jet? If so, it may still be partially blocked.  A dried film of varnish .002" thick will resist most cleanings and reduce the effective jet size to a #37.  Try "rodding" out the jet with the shank of a number drill:




If you cannot find anything else in the carb, it may be wise to order a main carb body gasket from JD Jetting (the only one supplying them to my knowledge) and then open it up to see if something has set up house in one of the concealed passageways that lie between the upper and lower body.

We always clean all the jets with a torch tip cleaner. But I guess I will need to actually blow the passages out with the compressor to make sure that the passages themselves are in good shape. We have had to deal with clogged jets in the past by the dozen but have since mostly remedied that issue and thats why this is so troubling. I do not understand how a bike just gets like this sitting there with NO gas in the carb, we always drain the carbs on our 4 strokes now. The only time I ever ponder life is when I work on a 4 stroke. Can someone stupid on craigslist just please buy it??

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