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some carb help on a xr250


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picked up a xr250 a week or so ago and have been doing some work on it. since this only pertains to fuel, what I did with the fuel/engine/exhaust was:

1. overflow was leaking. took carb apart cleaned out jets and needle valve. leak seems to have stopped.

2. ceramic spray painted the exhaust (shouldn't have made a difference)

3. temp clear fuel line with filter

4. adjusted valves.

5. the snorkel has been removed (i did not do it)

6. OEM exhaust with I believe an aftermarket insert.

7. unsure which jets, but was running 'ok' when i picked it up.

8. new plug and air filter.

bike seems to be running ok except for idle. It was surging (which i believe is a lean condition), and generally unstable at idle. i read thru the manual and it said to turn the pilot screw out until the rpms start to die off. well mine never did and the screw has about 4-5 threads visible when looking at the side of it. Is this too far out? I kept unscrewing and the rpms kept rising. the idle improved quite a bit but i don't want to be out on the trail and loose the screw.

the high RPMs are a little lacking too but i'll figure that out once I get this down.

thanks!­čśĆ

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found some info looks like i'll want to go with a 135/48 combo with what has been done. probably makes sense since i kept raising the fuel level and the bike kept liking it.. i'm going to check which jets i'm running then order probably.

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i think i'm gonna order a 48/135/138 and go from there. might as well get another jet while i'm placing an order (138) incase I need it. i'm gonna check if I need anything else (might be missing oring from pilot screw) and make an order tonight.

might get a new float too, see if that helps the overflow problem.

one other thought i had was i replaced the air filter. it may have been running ok/richer if that was all clogged up, now with a new one its pulling as much air as it should with the snorkle removed.

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I don't know if this is helpful or not. On my xr the needle and needle seat were worn enough that fuel would get by at closed throttle. This caused all sorts of havoc with the idle and idle mixture. With new needle and seat the mixture screw actually works and the bike is much crisper off idle. YMMV

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yes it is listed as #3 in the parts diagram ( I dunno what year you are dealing with). I just bought the carb kit off of ebay. Came with pretty much everything except a float and the diaphragm thingy for only a few bucks more than the factory needle jet set.

I does make sense that turning the mixture screw out a few turns would somewhat compensate for a undersized pilot jet.

This is how mine is setup. For riding at altitude in Montana. Which I know has no bearing for you at basically sea level. Plus your bike is probably a heck of a lot newer (all most everybody's bike is).

87' xr250r no snorkel, uni filter, super-trap exhaust (8 plates) with the welds ground off inside of header

42 idle jet

132 main

clip in middle position (3rd groove from bottom)

air mixture screw 2.75 turns out

Sometimes the bike shop will just trade you out jets.

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yes it is listed as #3 in the parts diagram ( I dunno what year you are dealing with). I just bought the carb kit off of ebay. Came with pretty much everything except a float and the diaphragm thingy for only a few bucks more than the factory needle jet set.

I does make sense that turning the mixture screw out a few turns would somewhat compensate for a undersized pilot jet.

This is how mine is setup. For riding at altitude in Montana. Which I know has no bearing for you at basically sea level. Plus your bike is probably a heck of a lot newer (all most everybody's bike is).

87' xr250r no snorkel, uni filter, super-trap exhaust (8 plates) with the welds ground off inside of header

42 idle jet

132 main

clip in middle position (3rd groove from bottom)

air mixture screw 2.75 turns out

Sometimes the bike shop will just trade you out jets.

hmm thanks for the heads up. why is your slow jet smaller than stock? i know on mine at least (99) the 45 is the stock jet?

mine seems to like 5ish screws out and the RPMs kept climbing so i'm thinking it needs more fuel. I have an OEM exhaust with some aftermarket insert and no snorkel with a new air filter.

any idea if the 91-96 keyster kit would fit my carb? i've heard mixed things from keyster except for their gaskets, could be a worthwhile investment for $40 either way tho. i'm also used to tuning Vmax carbs which get a bit ridiculous.

thanks for the response either way tho! i ordered jets from TT here along with a few other OEM bits and pieces.

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  • 2 weeks later...

got the new jets in (finally!) swapped them out. idle is much better at 1-3/4 turns with the 48 jet. high jet still breaks up a bit with the 135, may try the 138, needle may need to be adjusted too. couldnt' get a good run in tho as it was getting late.

another problem tho. my carb sticks off idle with the engine on. did some reading and it seems after time the vacuum from the engine pulls the slide against the bore. got a used carb very cheap locally and going to try that slide along with new throttle cables. hopefully that helps. anyone have any other advice?

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Ugh okay. i'm really on my last sane thought here. tried all day to get her jetted and i got the issues to kind of move around but still didn't like it.

swapped my slide from another carb over and it got rid of the throttle sticking, but still having issues. please help!

1/2 - 3/4 throttle, mid/high RPMs it will kind of pop pop pop. not a lean pop but will loose power from what it should be and nto take off

3/4 - WOT, mid/high RPMs, it will pop pop pop but eventually take off.

are these lean or rich conditions? I tried a 128/135/138 main and none seemed ot make a difference really. the 128 i think was too lean

also tried the middle and richest needle settings. the richest setting on the needle helped a bit but not too much.

low RPMs everything is great, small throttle openings, WOT, front end pulls right up, but once i get into mid-rpms it pop pop pop. (once again not a lean pop though really).

small throttle openings up until mid rpms or so work well too.

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tried a bunch of different settings today too. no luck. similar symptoms all around. sounds lean to me but the plugs are still black as hell. tried a higher temp one too. about ready to rip my hair out

gonna try a compression test for shits n grins but my adapter wouldn't screw in for some reason.

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figured out my stumbling/popping. it was a dirty ground. cleaned it up and no more issues. was not jetting.

with gordon mods, what do most people run for needle? I put it back to stock and have the slow at a 48 and the main at a 135.

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  • 2 weeks later...

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