by rlpembridge » Wed Jan 05, 2022 7:28 pm
If you're still scratching your head about this issue, rather than proceed on the basis of a problem with jetting, I have one suggestion that may be worthwhile checking.
I haven't been using my Ld much, it stays packed away under a work bench at the back of my garage and only comes out in fine weather. Over the past five years or more I seemed to encounter problem after problem and could not get the machine idling smoothly 'off' choke. Even 'on' choke it would only idle once the engine was fully up to operating temperature.
Having (I think) resolved or checked and dismissed a host of other issues, I became convinced that there was an air leak somewhere in the fuel inlet system. I had timed the ignition with a strobe and was confident that there was no shorting wire. I took the carburettor on and off so many times, replacing floats, needles, gaskets and jets, cleaning everything and looking for any signs or distortion. In the end I gave-up and bought a replacement, modern Del'Orto carb. from Patch Hood at Scooter Surgery.
Of course, everything ran beautifully then. But it was only then that my eye was drawn to the four slits in the manifold of the original carb., where it clamps onto the inlet pipe to the cylinder.
What I saw was that, in the course of very many years of mounting and dismounting the carburettor for one job or another, the tightening clamp had distorted the alignment of those four slits.
With the unit dismounted it was evident that the slits nearest the point where the clamp nut was compressing the manifold sleeve had become dragged / stretched / distorted into an almost fully and permanently closed position. Of course, this meant that the slits on the other side would not become properly squeezed together when the clamp ring was tightened.
Now, I haven't tested this theory or measured the depth or engagement of the manifold over the inlet in comparison to the depth of those slits but I think it is highly likely that the distortion of those slits on the manifold has led to an air leak, sufficient to cause the engine to cut out when it should rest at normal idle speeds.
One of these days I shall do those measurements and then set about re-setting the slits on the manifold - anyone know how much heat that ally manifold can be safely subjected to without risk of cracking?