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Okay so just got done rebuilding 2002 XR 250 and need help. Got it started up and it seems to have exhaust coming out of carb. A little exhaust is coming out of exhaust but when I throttle it up it doesn't increase and it just dies. Than I see smoke coming from engine intake boot going from carb to engine. It runs and idles fine. I put everything in time and all specs on valves completed. Is there anyway I did timing on wrong stroke? I'm boggled!

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So, , you did a complete engine rebuild? Just top end? What?
It runs and idles fine?
Hmmm, , grab your Manuel and double check everything related to the timing. Cam, valve,and ignition(advance) . And don't freak🤤. Probably something simple. Good luck and keep us advise. G.

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Idles good but when revved it falls flat on face and dies and whites pressurized smokes coming out of carb boot. Would it even start or idle if I timed it on wrong stroke?

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How long was the bike down during rebuild? Was fuel left in the carb during that time?

Everything else being put back together right, a dirty/plugged up fuel screw passage will cause it to bog and die when giving throttle.

Be sure you don't have water in your fuel.

Make sure you didn't overfill the engine with oil.

You're saying exhaust and smoke are coming out of the carb. Are you using both words to describe the same thing?

If anything is making it past the carb boot at either end, you don't have a good seal.

Be sure you don't just have some oily residue on the head and it's burning off as the engine gets hot.

Set the engine up like you were going to do a valve clearance check. Make sure your at TDC on the compression stroke and that you can feel wiggle in all 4 sub-rocker arms.

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It was only down a few days, no fuel left in the carb. I just got done completely cleaning it again this morning. I went through all passages and jets with guitar string and sprayed out. Fuel was fresh. Well When I poured oil in beck the first time it overflowed and ran down engine. I saw it burning off of headers and maybe it's coming from head idk. I put in 1000cc and it was overflowing. Thought it took 1300?well idk if it's exhaust coming from carb boot but it was coming from between the triangle boot that bolts to head. And I know it's sealed really good cause I tightened it down today.

Big thing is would it start so easily and idle if it was that far out of time? The only problem it bogs and dies under acceleration. Or if i slowly let back off of throttle it will idle way down almost to the point it stalls but will pick back up. Also runs better since adjusting the throttle stop screw and mixture screw. I know mixture is 1 1/4 out and how are you suppose to set throttle stop screw? I just set it barely open with diameter of paper clip? Thanks

Force10... nothing blocking it

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5 minutes ago, Westhall55 said:

Force10... nothing blocking it

It was a longshot..when you have stuff apart strange things can happen though. "Where did that little piece of rag go I had"...lol

 

Hope you get it sorted out.

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17mm as shown in the pic is a good initial setting. Measured from where the idle screw exits the screw boss, to the contact face on the throttle drum pulley.

Then set it later to the idle speed you want. It should not be so low that it barely lopes along like a Harley. I think suggested RPM is 1200-1300.

How much oil was in the engine when you added that 1000cc? Was it and the frame completely drained, oil filter change or not? 1300cc is with a drained engine and frame. If you don't know how much is in it, you should drain everything and put in the proper known amount.

1 1/4 turns out on the fuel screw may be good enough to get it running, but you should fine tune it for best off idle throttle response "on the rich side".

No, it wouldn't run very well, if at all, if it was way out of time.

 

throttle2.jpg

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Well I drained the engine from drain plug, I didn't drain anything else. Think we have found problem with smoking! To much oil! Also thanks for the advice on the 17mm. This is awesome man!!! You just have me everything and I'm going to try it tomorrow! So you have to drain frame and motor?

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3 hours ago, Force10 said:

It was a longshot..when you have stuff apart strange things can happen though. "Where did that little piece of rag go I had"...lol

 

Hope you get it sorted out.

Yeah used to work in a small engine workshop - countless times the muffler was blocked up with wasp nests

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3 hours ago, Westhall55 said:

Well I drained the engine from drain plug, I didn't drain anything else. Think we have found problem with smoking! To much oil! Also thanks for the advice on the 17mm. This is awesome man!!! You just have me everything and I'm going to try it tomorrow! So you have to drain frame and motor?

Yes, both engine and frame. Here's frame drain point. You probably don't need to drain the frame just to do a top end, but adding oil to top off the engine, as you've found, isn't going to take as much. You need to pay attention to the height on the oil dipstick in front of the gas tank. Warm the engine to operating temp and let it set idling, level on a stand, for 5 minutes, without touching the throttle. Then shut it off and immediately remove the dipstick, wipe it off and reinsert it without screwing it in. Then pull and check the level. Add or subtract oil til it's right.

When doing an oil change, drain both points, plus the oil filter if replacing it.

XR250 Oil Drain.JPG

Edited by Trailryder42
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So on those bike does the oil drain out of the frame when you drain it from the sump ?

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Ding ding ding! Well after all was said and done it was a combo of things! Way to much oil! Drained and fixed! Throttle stop adjusted to 18mm and 1 1/4 turn out of mixture screw! But backpressure problem was a dirt dinner nest in baffle! Pulled it and sprayed out with carb clean and blew it out and BAM it fires right up and is perfect!!!!!!! Thanks to y'all it is fixed and ready for this weekend!!!

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If you over filled the oil check the breather hose if it has a bung in the bottom pull the bung and drain the out from that too. glad you found the problem!

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If you overfilled the oil.  Check the seals around the kick starter and shift lever to make sure they are not leaking.

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