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2005 Yz250f Wont Run Off of Choke

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So recently I rebuilt my little brothers Yz250f from the ground up.. literally all the way down to the frame. Replaced a number of things including Crank, Piston and rings (Went from 12.2:1 - 13.5:1 Compression Ratio), Water Pump, Spark plug, Accelerator Pump Diaphragm, Ect, Ect.... You get the picture.

 

So I know the bike needs to be rejetted due to the new piston and compression ratio but I do not know which way I should be going.

 

I cannot get it to run off of choke so I don't know if im getting an accurate reading on the plug to be able to tell which way I need to go.. I'm assuming that because it has to be run on choke that I need to go richer, but how much? If I can get it to run off of choke it back fires really bad, lightly surges, bogs, has very little throttle response, hesitates.. Which are all signs of running lean.. but when I pull the plug its black and sooty?

 

I've been reading every site / blog / explanation / instruction manual i can find but still cant figure out why its acting like this.. It has multiple symptoms for either side... 

 

Any and all help is greatly appreciated! 

 

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No need to change jetting randomly

The ONLY reason to re jet is a drastic change in intake or exhaust flow, or air density.

Your piston won't effect that.

You cannot read a plug for color anymore on pump gas

 

Clean the passage above your pilot jet with fishing line and spray cleaner

Replace the pilot jet with a BRAND NEW one

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Bottom line is that you are very lean on the pilot circuit. That is why you need choke  to richen it up.

 

That means either you have missing jet (main air jet), and clogged jet or passage (pilot) or a stuck open hot start or leaking hot start nut.

 

There is no reason to 're-jet' with the mods you made.

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Alrighty thanks! It has to be the pilot jet then because the entire hot start assembly is brand new! The old cable had a few kinks and would stick wide open / the nut was stripped out so I replaced the whole thing.

I just find it odd that prior to the rebuild the bike ran well (not going to say great because it needed to be jetted in the first place / it's from Pennsylvania and I live in Tx) and now even with completely tearing down the carb and rebuilding twice it is still running like crap.

I'll tear it apart again and see if I can figure out where some blockage or something is.

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