Wednesday, May 02, 2012

Mixture screw weirdness 

I've been struggling with the carb balance. Not in the usual way of it being a bit fiddly but that the mixture screw for the rear cylinder didn't have an optimum point. The more it was screwed out, the faster the engine went, until the screw fell out! This is just wrong, as opening the screw should gradually make the mixture too rich for a warm engine and the revs should fall and maybe even cease.

I'd checked this and that and enquired on a morini email list and the general consensus was that something was probably blocked. This evening I replaced the cold-start enricher plunger on the front (good) carb and having removed the jet gave the channels there a good blast of cleaner. The lever had broken off the old one and it didn't work well anyway. On the rear, I squirted through the idle circuit from various points and saw jets of cleaner emerging beneath the slide. The inlet manifold didn't look perished so it was cleaned, replaced and the clips replaced firmly.  Finally, I also fitted the washer and O-ring on the idle mixture screws and set them to 1½ turns out.

The engine started fine and after a quick run I have done a preliminary rebalance. Hooray, the rear mixture screw does now have a maximum open position; it's further out than the front, but such is variation. I need to let it cool and check cold starting and general idle again. 

As a little job, that turned tedious, I lengthened the gear change linkage adjustable part to see if that would reduce the number and frequency of false neutrals. Now I've  reasons to go out for a quick spin tomorrow.

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