Hi everyone!

I've completely stripped the carb on my SY250 to give it a good clean. However, since coming in from the garage to eat tea, put small dude to bed etc. I can't remember how the needle/ throttle slide assembly goes back together. There's a small washer with a tab/tang on it, does this go underneath the needle clip (between circlip and throttle slide) or on top of the needle clip (between circlip and retaining plate assembly)?

Hope this makes sense and that someone can help!

Hi straycollie2,

The tanged plate you describe sits on top of the needle/clip and is fitted after the throttle cable is positioned, it is there to prevent the needle coming out of position and to prevent the t'cable nipple from springing out, the tang usually sits down into the t'cable groove inside the slide.

Bye, PeterB.

Hi, thanks for your response, but I obviously didn't explain myself very well. It's not the large tanged bit that retains the cable nipple, but the small washer about 6mm dia that is part of the needle/ slide assembly. However, I also emailed Birkett's the same question and the official answer is that it sits on top of the needle circlip when the needle is inserted into the throttle slide.

Regards

Straycollie2

I revived this old topic on account of its releavance.

First off, the info from peterb is incorrect since the SY250R stock TK carb is not the style cable retainer he described.

The info straycollie got from Birketts is accurate and correct.  There should be a small washer with both a tang and dimple.  The tang is inserted into the applicable hole in the slide.  The dimple serves to engage the opening in the needle clip, preventing the needle from rotating during engine operation, provided the clip is snug in the needle groove.

Here is my main reason to bring this forward.  My 2005 SY250R was purchased several months ago.  I removed the engine and suspension, rebuilding the bike as I assembled it.

I did disassemble the carb, cleaned, and reassembled it.  Upon riding the bike, the jetting was always a bit rich.  Obtaining pilot jets and a nozzle is diffiucult in the USA, though I tried to order them, planning to rejet the carb to get smoother running.

Without all the jets I desired, my choice became to adjust the needle clip position.  I had not removed the needle during the major teardown.

Upon removing the carb slide needle retainer, I noticed someone previously installed the tanged clip under the needles clip, thereby raising the needle, causing the rich jetting.

In an effort to see a change to less rich engine running, I installed the clip in needle slot 2, and correctly assembled the tang washer position.

With just some test riding around the yard, the engine runs very clean, and no longer rich.  Next I plan to raise the needle one clip groove to the middle, as it was when assembled incorrectly, to verify that setting.

In simple terms, if the tang washer is installed incorrectly, and positioned under the needle clip, vs correctly which is on top of the needle clip, the needle is raised the thickness of the tang washer (and dimple), or raised about slightly more than a clip position.

Assembly sequence, needle with clip into slide, tang washer on top of needle, needle retainer / cable holder with spring holder for needle next, secured with screws.  Then slowly rotate needle and clip until you feel the gap in the clip engage the dimple.

https://www.dropbox.com/sh/v5ajoxauk61dg1p/7l-WHt7QpL?preview=PartslList_SY250R_05.pdf

No doubt downloading manuals and parts catalogs is worthwhile.  Besides the one you linked, I also downloaded pretty much all the years they offered the SY250R.

As for the carb being assembled wrong, the illustration may have helped the previous person that assembled it, then again, maybe not.

Proper orientation of carb slide and needle assembly details.

 

 

Sorry to butt in the small o ring on the main jet any 1 know what size it is? 

On 3/2/2018 at 12:01 PM, bondy said:

Sorry to butt in the small o ring on the main jet any 1 know what size it is? 

I could be wrong, but thought the main jet was seated against a washer.

hello PMK there is a washer but there is also a groove on the main jet with a o ring on it I got 1 from a local motor factors he gave it me for nothing so not bad I do have a brand New scorpa carb original still in the box.

After some tinkering around with engine tuning, and I won’t post my actual jetting since it can be varied for other parts of the world, I want to mention that the needle clip groove position is quite sensitive to jetting on the SY250r.

I found that running in the middle groove, while not bad, was rich.  The exhaust showed signs of spooge and a wet tailpipe.  Also, the engine could be felt to be rich when riding.  Not blubbering rich, just slightly rich and it showed in the transition from pilot jet to needle.

I tested the next clip groove leaner.  The engine ran clean, accelerated ok, but had a slightly soft exhaust note and soft accelleration.  Also, you could faintly here the engine wanting to ping and ever so hinted at surging.

To work within the two settings, I fabricated a 1/4 mm thick shim to provide a mid point between grooves.  These are also easily purchased, but I opted to punch one from shim material rather than wait.

The shim was installed under the clip, raising the needle 1/2 a groove.  Essentially place the needle position at clip groove 2.5.  In this setting, the engine runs absolutely clean, but is now crisp with a good exhaust note.  No pinging or surging is there currently.  The engine accellerates strong with no hesitations.

Possibly the TK carb, the 26mm carb size, and the engine exhaust combo have made it this fine to adjust.  I do not have any optional needle jet sizes, so possibly the next leaner brass needle jet is sized to be 1/2 steps of the clip groove.  But I am not sure for a TK, plus the needle jet would need to have a trip from a Japan warehouse, to a UK Yamaha dealer, then sent to me in tne USA.

Simply sharing.

Edited March 21, 20188 yr by pmk