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Dr350 idle problems

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My 99dr350se fires right up and idles fine when cold, but when it gets hot i can not get it to idle at all, however it runs fine at throttle. i have adjusted the idle screw and it helps a little, but it just causes it to die slower. Any advice on fixing this? The bike has an exhaust, a modded airbox, and i am unsure if it has been rejetted or not.

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My 99dr350se fires right up and idles fine when cold, but when it gets hot i can not get it to idle at all, however it runs fine at throttle. i have adjusted the idle screw and it helps a little, but it just causes it to die slower. Any advice on fixing this? The bike has an exhaust, a modded airbox, and i am unsure if it has been rejetted or not.

Your pilot circuit is way too rich. Excess unatomized fuel is building up in your intake tract when you are idling (low velocity). Sounds like someone installed a pilot jet that is much too large if you've already messed with the pilot screw... or are you saying you just adjusted the idle stop screw? If that's the case you can try adjusting the pilot screw. Get the bike fully warmed up then let it idle and begin turning the pilot screw inwards.... there should be a point that the engine begins to surge (the idle becomes erratic). From there back the screw out slowly until the engine just smooths out. Add an additional 108 turn out. Readjust your idle stop screw to get the idle speed you want. If the PO put a bigger than necessary pilot jet in the carb you won't find the surge spot until the pilot screw is about closed. It's an extremely rare case that a larger pilot jet is required with air box mods. Even the highly restrictive air box of the DR650 puts up no flow restriction to the tiny bit of flow required at idle.....

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If it starts up without any choke and then runs rough and dies when hot then likely your idle pilot screw is out way too far.

Try screwing it in all the way and run the bike from warm. Alter the idle speed to keep it running at 1500. Now blip the throttle and see how it returns to idle. If it just drops down and maybe goes low for a moment and then comes back up then it's still rich and there's something big time wrong with your carb internals. What it SHOULD do is hang at about 2500 for a moment or two and then slowly fall back to the 1500 rpm set idle speed. That little hang time in the revs is what says it's slightly lean. So turn the pilot screw out about a 1/2 turn at a time until it drops smoothly down to the idle speed with no lean hang. At this point you can play with it in 1/8 turns to a max of about 1/2 a turn away from this setting to achieve the best pull away response that doesn't have any sign of hesitation. But don't stray more than a 1/2 turn from this point. Or at least make sure you counted how far out the screw is to get rid of the lean hang without running into a rich sag and return.

If you can't get it to operate like this then you've got some grunge in the carb or it was previously given a ham fisted jetting kit job. To fix that you'll need to play or have someone knowledgable play with the jetting and needle positions to fix first the top end, then the mid range and finally with those two points fixed you can play around with the idle mix screw. But they all interact. So the main jet/full throttle operation needs to be spot on before you can work with the needle position and size for the midrange and that has to be good before you play with the idle.

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old post, yes.

but my 99sex is doing the same thing.

all stock except extended screw & clarke gas tank. was running perfect for months then noticed fuel dripping from air boot.

found stock petcock leaking a bit & carb inlet valve o-ring was dried out. replaced petcock with new raptor. replaced carb valve seat o-ring & float o-ring. also new pilot jet (stock).

motor will idle normal when cold with choke, runs & accelerates normal off-idle. when warm, motor stalls at idle. adjust idle speed to make it idle, it will idle fast over 2k, then still will drop and stall if no throttle is used.

could an intake leak cause this ?

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