Roadholder 370 - October 2018

22 established that the choke slide and cable were operating correctly, we removed the right-hand carburettor. The needle and clip were observed to have moved up within the throttle slide spring. Flushed with success, we attempted to fit the improved design clip to correct the problem. The fit is not easy as the clip must be placed over the throttle cable end before inserting the cable in the slide, and then fitted to the needle, whilst keeping the slide spring compressed with the throttle cable still fitted into the slide. All four hands available were required! A spring compressor tool would help. The improved and standard clips are shown in situ below. The idea of the improved design is presumably to provide less opportunity for the spring to 'catch' on the clip by it being round and flat over nearly all of its surface, as compared with the standard clip. Patrick took the bike for a spin. The engine running had changed but not necessarily for the better with the engine still running rich and stalling occasionally. Which brought us on to the needle jet. "It's the needle jet stupid" In John Healy's document, he mentions a noted Triumph expert who has the above statement printed on a T-shirt along with a picture of the needle jet. And it's entirely true that it's always worth checking, as the needle jet operates over such a wide part of the throttle range (needle jet ⅛ to ⅓ throttle, needle and needle jet ¼ to ¾ throttle). We checked the needle jet from Patrick's carb using a 2.7mm drill bit (a close match to the standard jet fitted of 0.106"). This had a lot of play and the jet (shown on the left below) is clearly well worn when compared to a new jet (shown on the right). A new needle jet was fitted, and Patrick took the bike for a run which indicated all was much improved. According to Healy and others, needle jet wear occurs before needle wear and is a relatively common occurrence. I'd also suggest that a needle loose in the throttle slide spring could potentially contribute to increased wear of the needle jet. I measured the worn jet at 3mm, i.e. 0.118", that's more than eight sizes above 0.106". The largest jet AMAL supply for any four-stroke Concentric is 0.115". To say the jet was badly worn would be an understatement. As Healy's document states, 'any defects in the needle jet are amplified because the size of the area formed by the i.d. of the jet's orifice and the diameter of the needle are so small. The typical orifice of the needle jet is 0.106" and the o.d. of the most AMAL needles The improved clip The standard clip