Hi Guys, I have a question for the CB750 serial number gurus out there. I just bought a 1972?, well that's what the title says. When I got there I see the original pipes are HM300 not HM341, but they are super nice so who cares. The side covers are almost perfect. The green color is like one I had back in the 70's. Turns out the guys the original owner, moved here (Chicago) about 9 months ago and has no garage to put it in. I buy it, check out the build date and it is 9/71. The serial numbers are frame: 111520, Engine: 1114865. What? I thought that 1972's serial numbers began with 2, like 2005201. Anyway that would explain the pipes. Any help would be greatly appreciated. Thanks 
WOW! 
Thanks to all for the help. It has painted headlight ears, a seat latch not a lock, no idiot lights on the handlebars. With the serial numbers being what they are, I'd say its a 1971. Pictures soon.
Don't forget that back in those days the japanese manufacturers did not follow US traditions of model years. They changed the models when they wanted, hence the "K" numbers. The serial numbers track with "K" numbers, not years. We titled them in the year we sold them, and some sat in warehouses over the calendar year before being sold. Hence there are 1969 and 1970 titles for K0s, 1970,71, and 72 titles for K1s, 71 and 72 titles for K2s and so on. The CB750 followed more closely to calendar years than just about any other model but that was simply coincidence.
Honda was sued by an American consumer for their 350s as there were years when there were as many as 3 different "K" models in one calendar year. The consumer had asked the dealer to guarantee him that he had the most currrent year model, The dealer did so. But the confusion was over the "K" number, the consumer bought the most current year, but not the most current "K" number, which is what the consumer had really meant. Honda lost the suit and shortly thereafter adopted calendar year models as did all jap manufacturers. The CB175 wqas particularly bad about having multiple K numbers in the same calendar year, and crossing over the new year.
The problem was not quite as bad as my explanation makes it out, in totla number of units affected. but Honda was sued and lost. According to "OriginalHonda 750, a Restorers Guide to SOHC 750" by J Wyatt, (and my fading memory having worked as a teenager in Honda dealers back then) there were original (KO) titled in 69 and 70, the K1 was available in Sept 70, so those were titled 70, 71, and 72 (warehouse holdovers). The K2 was available March 72, the K3 was available Feb 73. So you can see the mess the titling could be. And misleading to an unsuspecting public who put the K numbers together with the years. Starting with the K4, Honda standardized the K numbers with the model years.
Based on your frame numbers you have a K1 which could have been legitimately titled 70 (well not with your build date),71, or 72.
