AIRCOOLEDRDCLUB FORUM

My 250B takes a few kicks to get started, it also seems less than gutless until the needle hits 3500 then it goes manic.
I whipped the heads and barrels off and checked the rings. I measured the end gaps on the left cylinder, bottom ring 2.4mm and top ring 3.2mm. The bores are perfect so I have ordered new rings
As an aside I noticed the reed blocks are a brownish plastic/resin material I was expecting alloy

3.2 mm? 

My god, groundhog day, it took me months to sort this out, as c50 says its an eye, 1000% certain. 

Thanks Ken, I really appreciate you taking the time to do this for me, and other forum members.

I am happy that I have a pair of genuine 5I4 needles.

What I was also trying to understand is why a genuine service manual and a genuine parts list would have (different!) errors:-

1) As per my very first post, the service manual for the 1973 pre A showed a needle of 5J6.
2) The First Edition parts manual from December 1972 definitely shows the needle as 514. I have attached a scanned copy of the original page from my manual (ie not an online one), but it might need enlarging to view properly.

I guess it's just human error.

At least having this discussion highlights that care must be taken, even when viewing original documents.

From Genuine Yamaha original RD250B (European) Spec sheet. Notice officially the European 522/1 B's kept the US jetting. I am still not 100% convinced UK 521/2 B jetting (No 2 slides 5L3 needles) was officially anywhere else but the UK) According to Yamaha docs they weren't. Also note the official clip position for the needle on euro 522 models with 361 carbs, I have a had an Italian euro B with this set up.!

Second and third are from Genuine US Service manuals. Also note slight pilot (#30) in some US specs (never seen one though always been #30) and some US 250B's with a 90 main jet in the 250!  usually slight main jet size adjustments, float height spec change. Probably to suite altitudes and average temperatures, all given different part numbers. Wonder if that carb list has all this info correct?

That is more like it.  Definitely an I, CAP LETTER i, on that Needle.
However, Gen Yam paperwork does show 1, figure 1, on my lists.
I like the pic of that Needle, can't see the Mikuni logo but that looks correct.

5port