Yep -- I know it's not that hard -- but -- the '72 250 CZ I have had for a while runs well with a 230 main -- and the recomendations I got from the experienced fellow who sold me the new carb was to run a 430 main -- huge difference, I rang TD Hatrick and asked them -- they said 430 main "in the ball park", put in a 430 and it fuels up and drowns itself in about 30 seconds -- put in a 330 main and it runs but fourstrokes on WOT and when I do a plug chop it's black. Put in a 270 and it runs lovely and the plug colour is tan but is getting hot and has nipped up twice now.
So yes -- it should be easy -- but it ain't -- it may be my inexperience -- eg -- was told this morning that I'm wastin' my time (or at least making my work a lot harder) by using 98 pump fuel -- told it's a lot easier to get plug readings with avgas. I accept that and will start again with avgas (when I get a rebore because the bore's stuffed now). Also was told this morning that the carby I have is a 38 not a 36 -- but it measures 37 and TD Hatrick told me that a carby that measures 37 "should be" a 36. So there are a few variables -- like when I get the new piston I will run it for a while on 30:1 pre-mix -- and when I go back to 40:1 after say 1/2 hour of running the fuel will be a bit thinner and will flow a bit more through the same jet.
So -- will get a rebore -- have ordered a full set of jets from 420 down to 300 -- will get avgas and will run the new piston richer rather than lean (because I learned the first time it nipped up that it can happen in 20 seconds -- and that took me a few hours to get the piston ring free in the grove 'cause it was welded in) and I will start at 430 main and work down -- but I'm a bit nervous at this stage -- it's been a lot of work and a bit on money and combined with my inexperience and zip people around here who have years of experience who can come out to the "bush test track" and advise me -- I get to the point where I'd like to hear from someone who has a
Mikuni (38 not 36!) on a non reed 73 motor who can say -- this is what I use and I can go a bit richer than that as a starting point.
