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Emulsion Tube 2005 250x

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#25 is in fact the emulsion tube. You should be able to get it out without removing the carb, my question is why do you need a replacement? Lost the old one? 

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#25 is in fact the emulsion tube. You should be able to get it out without removing the carb, my question is why do you need a replacement? Lost the old one? 


I wanted to replace it because it has quite a lot of hours on it, and I seem to have an issue with idling and low rpm. From reading other threads it may be worn causing it to leak more fuel during idle. Last year I replaced the mid gasket and put in a remote fuel screw. It's running a lot better now, but I have a sickness called perfection. I'm seeking professional help but until then I'm going to try the emulsion tube lol.
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the emulsion tube will have zero effect on idle and does not "go bad" with high hours. the only circuit that would impact idle quality is the pilot. 

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I had read somewhere on this forum that the emulsion tube was a wear item and should be serviced when overhauling an FCR carb.

 

When I purchased my used '08 CRF250X with unknown hours or past maintenance history I went thru it from A to Z,

 (original owner likely had raced it, 2nd owner wasn't too mechanically inclined) 

upon closer inspection with a magnifying glass and flashlight, the emulsion tube and needle showed absolutely no wear at all.

Edited by mlatour

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Difficult to inspect but if the needle jet wears it is usually an oblong wear pattern. I've had wear that was not visable to the eye that was fixed with a new needle jet.
The needle jet will wear from needle vibration,  but not the emulsion tube. And then the problem is usually a bit of richness transitioning from the slow circuit up to about 1/4 throttle. Honda sells needles and needle jets as a kit. JetRUs sells individual parts,  but their needles are Keihin and not the multi taper style sold by Honda.  JD Jetting has the multi taper OEM type of needles.

On edit: Some confusion on emulsion tubes and needle jet that are common on other Keihin carbs, the FCR  uses a combination emulsion tube and needle jet, but calls it a needle jet holder, Keihin calls it a Main Nozzle. 

Edited by Chuck.
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Thanks for the details Chuck,

mine runs very well but it's certainly something I'll inspect during the end of season/winter storage teardown.

With only three 1" holes in the airbox, pilot (#42) and needle (NLAT) are stock, only the main jet has been conservatively increased 2 sizes (#135)

 

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Wow I went up to a 149M before going bigger with a JD Jetting Kit.  But rejetting does increase throttle response which can be good/bad depending on where you ride and experience/expectations. Since I'm an old XR rider I'm more comfortable with slower throttle response.

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Most of my riding is done below 1/2 throttle.

I think I've only gone wide-open throttle once since getting the bike last year,

just make sure there was no bogging anywhere in the rev range.

Despite the smallish main jet, IMO it accelerates very well and has a decent upper midrange pull (stock exhaust).

 

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Where I usually ride I doubt if I get past half throttle unless on a logging road. I tried the R header and Yoshimura TEC muffler but prefer the bottom end of stock for the trails that I ride.

A quick check for the main is WOT until past the torque peak and then roll back the throttle to  3/4, the power should drop off as you roll back, if it picks up the main is too small.

Edited by Chuck.
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 The needle jet holder can wear into an oval, which can let more fuel by even at idle.  

Jim.

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