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bog after wheelie or hill climb

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had an issue past 2 rides

when I wheelie over something or just loft the front wheel, right after the front comes up, the motor bogs/sputters just for a second.

this also happens during a hill climb, motor seems to bog or like its out of gas for just a split second, but is really affecting my safety as I go up some rocky texas hill climbs. ideas? carb?

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You need to set your float levels to 14.5mm minimum drop and 19mm max drop. Each setting has different effects on engine performance if not set right. Right now your max drop is probably around 25mm. That's too much. It allows the float to bounce between the 2 stops too much when on technical/rough terrain. Without going into specifics, that displaces fuel in undesirable ways and causes the stumble.

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is it normal for this to have just begin unaltered? the bike has been fine for a year now, this just started...that normal?

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A 9 year old XR, sure, it's possible. Like I said, check/set the float levels and take a look at the inlet needle tip to for wear. Blow out the jets while you're in there. Make sure the white slosh baffle is on the main jet tower when you remove the bowl. If it's not, it could have come off and was interfering with the float. You bend the little tangs that hold it to the jet tower to make it grip it firmer.

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For setting the float levels and getting them as spot on as possible, removal is best.

To check the float drop:

With the bowl off, hold the carb so the float is oriented hanging down and swinging from it's pivot pin. Rotate the carb in your hand so that the float swings toward shutting off the fuel flow/closing the inlet needle. You want the float to "just contact" that little nub in the tip of the inlet needle, not compress it any. Hold it in that orientation and measure from the bowl mating surface of the carb to the flat bottom edge of the float "in-line" with the main jet, which is going to be at about the mid point of the floats length. Should be 14.5mm. That's minimum drop. You adjust, if needed, by bending the tang that the inlet needle hangs from.

For max drop:

orient the carb so the float swings the other direction, contacting its stop. Measure same way. Should be 19mm. To adjust, if needed, bend the small tang at the side of the silver float arm.

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Great answers TR42!

Also, something that no one thinks of (and I never really did until three years ago when I learned it) is overhauling the carburetor. If the jetting is stock, or even jetted and 4 or more hard years old, a lot of parts should be replaced, The taper on the needle jet wears, the slides can wear (there are specs for that), cable wear, and float needle wear. There was a rash of that in the 90's with inline fours with aftermarket jet kits from a manufacturer that would wear out in as little at 4000 street miles! Our crap takes a huge beating compared to that.

Even a beginner could do a carb. There was a video floating around the internet and with no super special tools (very new tipped phillips driver size 1 and 3, gallon of carb dip, can of cleaner and compressed air). If you are not a patient, careful worker with your hands you really should find a friend or shop who is!

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Make sure the white slosh baffle is on the main jet tower when you remove the bowl. If it's not, it could have come off and was interfering with the float.

+1 on that. That stupid baffle gave me loads of trouble. Doesn't take much for it to interfere with the float.

I had money burning a hole in my pocket so I replaced the stock carb with an Edelbrock pumper from barnumspro.com

Expensive, but worth it to me for many reasons. A lot of people here swear by a properly tuned stock carb, but I never did get along with it. My frustrations sit in a box now & my bike has never run better.

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I am experiencing the exact same problems on mine 280

My mechanic has suggested an old "secret" where they extend the pick up with a piece of hose so it sucks up juice from down lower in the fuel bowl..

Anyone heard of that? does it work?

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Yes, I did it to mine. It's just a 10mm length of fuel tubing. Shove half of it onto the end of the pilot jet That extends the reach of the pilot into a bowl a little more, keeping it in fuel when the bike is at extreme angles. Good mod, do it.

I had forgotten this mod, as I don't run the stock carb any more.

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Had a horrendous bog/hesitation when jumping or running hard over extreme terrain a couple of years ago. Float level was good but drop was excessive. Setting the float drop as described by Trailryder42 above, along with extending the pilot, completely solved the problem.

-B

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ok, so I removed the carb and I am trying to measure. It seems that if I hold the carb so that the float is all the way "inside" the carb and resting "closed" it seems to be a 14mm measurement. But when I tilt the carb so that the float falls towards the "bowl" side of the carb, it doesnt appear that the float tab ever leaves contact from the needle/pin. So I measure it all the way open (or tilting all the way towards the bowl side) and its 25mm

is that right to measure...it just doesnt look like the float tab ever seperates from the piece that it depresses..

thnks

oh, and still do the hose mod? will some airline tubing from my aquarium work...

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The inlet needle hangs from the float tab, so as the float swings toward the max drop stop the inlet needle will be pulled out of its bore. You just want to make sure that when you check for the 14.5mm spec(when the needle is seated in its bore) you hold the carb so that the tab doesn't compress that little tit in the end of the needle, just want it to contact it. If you were doing it correct, then your 14mm measurement means you're still .5mm too high.

Your 25mm max drop measurement is exactly what I thought it would be. Bend the max drop stop tab on the side of the float arm so that you get 19mm.

Don't use your aquarium tubing. It needs to be fuel impervious. If you can't get or find anything else, cut a 1/2" off your carb vent drain line and use that. And yes, you should still do the mod.

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attaching pics to get a better understanding.

which tab do i bend, and which direction?

where does the carb vent hose go?

just dont want to F it up and have to take the bike back apart to fix it. And when I measure my float drop, i still say the "nipple" never leaves contact from the tab...i could be checking wrong though

thanks. btw, anything i should replace while in the carb? jets are only about a year old.

160 main, 58 pilot

IMG_4240.jpg

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IMG_4243.jpg

IMG_4244.jpg

IMG_4245.jpg

IMG_4247.jpg

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It's ok that the tit in the inlet needle never leaves contact with the float tab, you just don't want the tab compressing the tit. If you push on the float you will see you can make it compress the tit. Hold the carb at an angle where the weight of the float doesn't compress the tit and take a measurement with it there. The tab that the inlet needle hangs from is the one you bend slightly to get the 14.5mm setting.

In picture #2, see the right side of the silver float arm? It has an extra tab sticking up that the left side doesn't have. That stud that it's contacting is the max drop stop. You bend that tab closer to the stud so the tab contacts it sooner to make the max float drop less. Bend the tab a little and hold the carb so the float hangs down and the tab hits that stop stud and take a measurement. Keep adjusting and measureing until you have 19mm.

See picture #4 where you holding the carb right side up with the float hanging down? See the main jet sticking down? Draw an imaginary line from the center of the main jet straight out to your eye. Set your measuring scale on the bowl mating surface of the carb inline with the main jet as you sight it. Measure up to the flat surfaced edge of the float. That's where you take your measurement.

See the sub frame pivot point just above the rear shock reservoir? About an inch behind that pivot point on the frame, left side, is a black plastic clip/clamp. The 90* end of the vent line goes thru that.

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ok so i bent the tab in (thats the one i was thinking it had to be) measures 19mm. so now I have put a 10mm piece of carb vent hose on the pilot jet...right?

now, that orangish piece in my last pic...what is holding that on? it seems like it would slide right off. no real tabs locking it on...it falls off easy

hey, i heard once that replacing the 3 float bowl screws with allen heads is a good idea...worth doing?

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