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Rebuilt my xr400 carb and now it's stalling when snapping throttle

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It wasn't doing this before but I rebuild my carby because my float needle was stuffed so the float wasn't stopping the fuel and at idle the fuel was gushing out the over flow , but now that's all fixed and I changed the slide needle , new main jet and pilot jet , and now it runs fine reving it but when I snap the throttle open quickly it stalls ? Have set the fuel screw to 2.5 turns , 1999 xr400 standard carby standard jetting

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Changed the slide needle to what? Changed it how?

What are the standard jets on an Aussie bike?

With Standard jetting and fuel screw setting, the carb is tuned in only the grossest sense. What's your elevation? I'm guessing its hot there.

A stumble when snapping the throttle open quickly on the stock carb is normal. But with careful tuning can be somewhat diminished. Being a 4 stroke engine, its not going to have the instant response like a 2 stroke when doing that.

I don't buy that it never did this before, or at least not as bad. More likely, you didn't notice it because you hadn't just rebuilt the carb and hadn't been whacking the throttle open in an unnatural way conducive to real world riding, in an effort to guage response.

Is that 2.5 turns out on the fuel screw just your initial setting, or is that where it has ended up after tuning for best idle and throttle response off idle, on the rich side? I'm guessing, with the major stumble off idle you seem to be having, its just your initial setting and you haven't spent any time fine tuning. Probably set it back to where it was before the rebuild.

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27 May 2014

It wasn't doing this before but I rebuild my carby because my float needle was stuffed so the float wasn't stopping the fuel and at idle the fuel was gushing out the over flow , but now that's all fixed and I changed the slide needle , new main jet and pilot jet , and now it runs fine reving it but when I snap the throttle open quickly it stalls ? Have set the fuel screw to 2.5 turns , 1999 xr400 standard carby standard jetting

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OK, so it was extra rich with the leaky needle and that gave it better throttle response on snap but the spark plug is probably black under that condition .  The hesitation on snap is normal with the stock carb and doesn't happen in normal riding conditions because you don't normally snap the throttle.   

 

What number jets and what intake/exhaust mods?  Also, which needle position?  The hesitation can be reduced with the stock carb but not eliminated.  A pumper carb can eliminate the hesitation.

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Ohk so took the jets back out that unchanged , they told me they were stock jets so I didn't even look but found out stock pilot I had was 162 and the kit had 140 and main jet I had 56 and in the kit it has 52... No idea if my jetting is wrong or the kit was wrong they seem like big differences

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We can't advise on jet sizes without knowing exhaust mods and intake mods.  A 162 main would be for a free flowing exhaust and intake.  A 56 pilot would be for a fully restricted exhaust and intake.

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As BR hinted at, your 162 is your "main" and the "56" is your pilot. Actually, there is no 56. It has to be a 55.

I agree with BR that the 162 is a size usually used with intake and exhaust mods at around sea level. And with that size main and those conditions, you usually need to run a 60-62 pilot jet.

Intake and exhaust mods from stock configuration, elevation, temp and humidity all play a factor in being able to recommend jetting.

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It's standard exhaust with no baffle in it and no idea if it has any air box mods ... Doesn't have a top on the air box lid under the seat ? Might have to order a 62 pilot then

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27 May 2014

It wasn't doing this before but I rebuild my carby because my float needle was stuffed so the float wasn't stopping the fuel and at idle the fuel was gushing out the over flow , but now that's all fixed and I changed the slide needle , new main jet and pilot jet , and now it runs fine reving it but when I snap the throttle open quickly it stalls ? Have set the fuel screw to 2.5 turns , 1999 xr400 standard carby standard jetting

Open your fuel screw another turn.  Your overfilled bowl was making the pilot circuit extra-rich.  You may want to go up to a 58 pilot too.

Edited by jayc250x

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Righto might order some pilots , would the float min and max setting change any of this ? I set them just making sure but

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Righto might order some pilots , would the float min and max setting change any of this ? I set them just making sure but

The min spec setting could, if it was off, but if you set it properly to the stock spec of 14.5mm, i wouldn't suggest altering it just for the sake of trying to clean up an off idle whack hesitation, when altering the spec would most likely cause issues in throttle response and engine running in areas that really matter.

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I actually went for a ride yesterday and didn't notice the bog once , when your riding it's fine doesn't miss once so I'm quite happy , seems to be leaking fuel out the overflow at idle though , just a little bit but might have to set float heights again , would this be a min or max problem

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Leaking out the overflow is a min spec height problem. Min spec sets how high the fuel level is allowed to rise in the bowl before the float and inlet needle shut off flow. Don't discount the possibilty of a worn inlet needle tip and/ or seat too, so give them a good look. If you can see an indented ring in the needle tip, it needs replaced.

Check the seat and needle bore for corrosion / pitting. Needle might be getting hung up in its bore, or you could just have a piece of trash preventing the needle from seating.

If you're not sure you're settingnthe float level properly, take a look at my carb video on Youtube or search for link to it in the forum here.

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My buddy recently appeared to have the leaking-out-the-overflow-hose problem on his xr4.  We took the carb apart and the float was adjusted properly and the needle looked fine.  When I removed the fuel screw,  the o-ring looked like this "C".  I think fuel was actually running out the bottom of the screw and down the outside of the overflow hose.  I replaced the o-ring and it solved the problem.  

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