Zenith problems

[JDNSW]

A few weeks ago, my 2a decided it woould not idle without the choke half out. This obviously meant a blocked idling jet. Yesterday I managed to find the time to pull it apart to clean it. Sure enough, a bright light and a hand lens showed it was completely blocked. The main jet was partly blocked as well. Blew them out and also cleaned the float bowl which had a few flakes of "something" in it. Where this came from was a bit of a mystery.

Last time I had this experience it was the paper filter just before the carbie coming to bits. I replaced this with a gauze filter, that should not have let through anything large enough to block the jets. However, I found something interesting when closely examining the emulsion block. I should mention that this is a new "Chinese copy" Zenith, about a year old, but hasn't done much mileage. The emulsion block has a number of passages used in the manufacture, but blocked off with small brass plugs. These (or at least one of them) appear to have been additionally sealed with a dab of some sort of glue or loktite. I found one of these dabs flaking off. Almost transparent, it would be perfect for blocking a jet. I peeled it right off with a blade.

Upon reassembly the performance is back to normal - on level ground you can gently engage the clutch in first with the engine idling at about 450-500rpm, and then accelerate smoothly without any hesitation.

[whitehillbilly64]

Good work John.
Was your "Chinese" copy fitted straight on Or did you pull apart and check things, before fitting.
I have one to fit later. Plus an original one I have in the process of restoration. Have sorted out the warping. Just need to reassemble.

whitehillbilly

[JDNSW]

It just fitted straight on and worked very well - but not for long. It started running rich, and I eventually diagnosed this to a leaky float, which was replaced by the supplier. I have also had issues with the O-ring not seating properly, possibly due to dirt or manufacturing shavings that got on the seat while I was diagnosing the float.

I would not touch it unless it misbehaves. If you need to pull it apart, be aware of the fact that this O-ring sealing is the weakest point on these carburettors. When reassembling always ensure that everything is scrupulously clean, and start the four scres holding the top on, and then tighten the two each side of the O-ring evenly, a little at a time before tightening the other two. This will minimise the chance of distorting the top cover or damaging the O-ring. Thhis advice, of course, applies to any of them, not just a new one!