Having had problems with my Series 2A/Zenith 361v I read with interest the exchanges in this forum and think I may have something to contribute. Firstly, I must stress that I'm a rank amateur as far as vehicle engineering is concerned so I'll apologise in advance to those of you who are specialists, and issue a word of caution to the others.
My problem began with the engine stopping when it should have been idling. This strange behaviour persisted for 20 odd miles but then developed into something more disabling. The engine, when under power, would begin spluttering and after a minute or two of this it would stop completely. After a rest it would start again but very quickly spluttered and expired. The RAC confirmed fuel starvation; their engineer saying that he could see the main jet in the carburetter functioning but couldn't see the idling jet working at all. He managed to get things going enough to see me home with a "crafty trick" that he "hadn't used for years", he said. Having got the engine running, he then revved it and whilst it was revving sealed the mouth of the carburetter with his hand until the engine almost stalled, at which point he released his hand. Clouds of black smoke were expelled from the exhaust and the engine recovered. He claimed that this technique creates high vacuum levels in the carburetter which can often remove blockages from jets and air/fuel passageways. It seemed to have worked as I was then able to drive the 2 miles back to base but sadly, by the time I got back the problem was returning.
OK. So having read all this stuff about distorting joint surfaces in 361v, I followed the advice, dismantled the carburetter and lapped all three surfaces; the float chamber, the carburetter top and the emulsion block. I should mention that when I started, I could see no evidence of distortion, however after a few rubs on the wet and dry it was evident that were quite significant high spots (low spots depending on your perspective). It took a good half an hour of continuous rubbing to get all three components perfectly flat and smooth. A carburetter overhaul kit was obtained from Brookwells at Newton Abbott (great firm) and all of the jets and gaskets were replaced with new from this kit, except the slow running jet which was strangely absent from the kit. I checked that I had the complete set and this was confirmed. I checked with other suppliers and their kits didn't include this item either. How peculiar! I soldiered on and re-installed the rejuvinated carburetter (except that it had the original slow-running jet).
The engine started at first try after priming the fuel system with the priming lever on the fuel pump but very quickly it would stop if I tried to let it idle. No amount of cajoling and adjustment of the volume control screw would persuade it to idle. I then thought of the slow-running jet, so I dismantled the carb and removed it. Imagine my surprise when, on close examination I found that it was also a non-return valve with a tiny spring and steel ball inside. Maybe it was this that was sticking? It was certainly impossible to move the ball against the spring by blowing into it. I obtained another slow-running jet from a redundant 361v, this also was a non return valve, however I could move the ball against the spring by blowing on this one. So this was installed in the rejuvinated carb. After re-uniting the carb with the engine, hey presto, problem solved!
What has this got to do with neat fuel dribbling from the emulsion block? Well. it seems to me, that whilst my problem was mainly the result of this non return valve sticking shut, what might happen if it stuck open or the spring failed to hold the ball against its seat?
Finally, a quote from the Zenith documentation pointed to in this forum (wish I had had it in the beginning)"...In certain applications of the 'IV' carburetter the slow-running jet 22 has incorporated a ball valve. The purpose of this valve is to eliminate back bleeding of air into the main carburetter jet circuit." Could it be that if the pneumatics and hydraulics of the carb have been compromised by the distorted gasket surface problem then back bleeding of air might suddenly become bleeding of fuel?
