YZ400F.... makin headway. Finally.

1 reply to this topic
  • Vanquish66

Posted October 17, 2010 - 09:11 PM


SO.... last post was 8 months ago. About a bike that wouldn't start or run at all. Fixed that, somewhat.

My carb still will leak gas with fuel flow on and bike off (not a flow, but a steady drip) out of the overflow even though i have the float level at 11mm instead of the stock 9mm. Thinking this is due to a poor needle valve, so next time i get in there im gonna replace that and probably just grab a new set of jets for my 11 year old bike.

Next, out of the vent hose coming out of the cylinder head, i find oil dripping after the bike has been running. A real nice drip. Doesn't smell like gas or anything, but I'm suspicious I overfilled the oil last time i was in there. Would that explain it?

Also, the bike runs super rough in the low RPM range, and if I don't twist the throttle just right from closed it will pretty much die instantly, as if it were too rich.

So, i'm open to any ideas or suggestions about this you guys have got. The thing kicks over and starts now, so i've felt like a champ haha.... but now i want my bike to run like a champ too. Right now.... well.... i need some help. Lemme know what you guys think. :excuseme:

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  • grayracer513

Posted October 17, 2010 - 09:51 PM


There are a couple of things to check. Look at the plate, #12 in this illustration:


Be sure it is oriented as shown, and that it isn't cracked or missing a corner.

See if the idle mixture can be adjusted so as to cause a change in rpm and overall smoothness as you close it up and open it back out again. You might have a partially blocked pilot jet.

The oil drip from the breather is pretty normal. If you overfilled by a fairly large amount, that will make it somewhat worse, yes.

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