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Yz426f Can't pinpoint problem

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I bought a yz426f a month ago that a shop and it was sitting for 4 months. It is giving me a couple problems but I can't seem to pinpoint it. When I brought it home I drained the tank and cleaned the carb. Also the bike is stock. To start it I have to adjust the idle every time or else it won't start. The plug is very black and the bike already fouled one previously. Also the bike backfires like crazy on decel and shoots 3in. flames. Also when I mash on the throttle at low rpms it tried to bog and die unless I let off. I know I have an exhaust leak and am ordering the gaskets for it tonight. I know the drill to start it and to never twist the throttle when not running because these bikes are temperamental. I figure the backfire is from the exhaust leak and the bike is jetted rich. I can't figure out what is causing the low rpm bog. If anyone could help me out it would be greatly appreciated.

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try cleaning the acc pump on bottom of carb. i wish that was my solution i have simialar issues

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Well I took my carb off a second time and noticed that the plate in the middle of the carb I'm assuming the vacuum plate doesn't close fully. My question is, is it suppose to close fully?

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That is called a slide and it does not close all the way, there should be a small gap at the bottom in the middle. There is a way to measure by using a specified rod size as shown in the manual. It needs to be there so that the engine can idle. If you turn your idle adjuster in and out while you have the carb off, you can see the slide move up and down. Just keep track of where the adjuster is set at now.

You should search for Oring mod on here and set the acc pump cam timing also. That will help eliminate the bogging.

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buy a new pilot jet.it could be clogged or it is starting to varnish.also the flames and popping is from to lean,when it bogs its from it being to rich.

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Well I found the stock jetting settings in the manual and I found the guy before me had a pipe and changed the jetting, put the stock jets in and never moved the clip on the needle to stock setting so I moved that up and it runs 10x better no more bog on hard throttle. The new problem is it will not idle with the choke out, I'm assuming I need to adjust the pilot screw then possible get a bigger pilot jet?

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Well I took my carb off a second time and noticed that the plate in the middle of the carb I'm assuming the vacuum plate doesn't close fully. My question is, is it suppose to close fully?

Be sure you have the plate installed with the "square" side with the hole near the edge down. If you have the rounded side down, it will run, um, badly.

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