Thx Blumbly + Gadge for the above advise and I now think I've worked it but just for the record, the engine I'm working on is a 160 cc full crank engine having points ignition. The carburetta has the knurlled idle speed adjuster knob but I am missing the large spring .... Its gone and I'm bugge#ed if I can find it hence the request for assistance in finding the correct one.
The conclusions that I've drawn from your advice is as follows but please correct me if you think I've speared off in the wrong direction:
1. If the carburetta has the knurnelled idle speed adjuster then one should use the 150 gm red spring (CRO3417A). The spring working tension can be altered by turning the knob in and out to obtain the optimal idle speed and top end speed...... seems to make sense!
2. If the carburetta is the later model one without the idle speed adjustment knob then its a bit of trial and error using the different available springs. If this conclusion is correct then one would have to purchase all 5-springs (and probably 5-cans of VB to assist in keeping the patience) and do the trial error experiment by sequentially replacing the springs on the operating engine and seeing how it goes)..... Again, seems to make sense but why would the highly skilled Victa engineers replace a simple knurlled knob speed adjuster with some thing as laborious as a trial and error spring replacement procedure???
I am however a little unsure as to what affect the installation of brass washer(s) under the throttle valve assembly would have on top end speed and whether in fact the trial and error spring substitution negates the installation of the brass washer that was offered as a means to reduce idle speed?
One last query, prior to pulling down the engine, it was really smoky. I ran the engine with new fuel and 25:1 2-stroke oil. I'd fitted new needle in the carburetta so I'm sure it wasn't flooding and I'd fitted a new air cleaner to ensure that there wasn't an air flow restriction. - Gentlemen, in your highly learned opinion, can the different available large spring tension or faulty small spring (the one that fits under the diaphragm) alter the air/fuel ratio to cause a rich mixture to the engine and hence the smoke?
Thx - Bumps
