I've flown a few big S.T.s over the years and have never been happy with the carbs on them. Having heard so often that switching to the pricey O.S. 7D carb is a surefire fix, I've always been tempted to give that a try. Recently, I was looking at my Irvine 1.20 (nice engine!) and thought to check if its carb would fit my 2300 - it does - exact same diameter mounting flange (17mm). IMO, having run a few Irvines, I think that their carbs are every bit as good as O.S. I e-mailed Paul at Just Engines in the UK about availability and price. Paul responded offering a great price for the Irvine carb and even better price on Moki carbs, which in his opinion are an even better carb. Having a 2300, 3000 and another 3250, I ordered an Irvine and 2 Moki carbs to try. Reading a few reviews, apparently the Moki carb is a very, very good carb. I'm looking forward to trying this out this next summer. For those of you looking for a cheaper alternative to the O.S. 7D carb, give Paul a call. You might be able to turn your big tigger from an attractive paperweight into a powerful and reliable runner. I've run my ST2300 about 5 times on the test bench with my Irvine 1.20 carb. I like what I'm seeing. I can hardly wait to try the Moki carb!