Re: Question: 1980 CB750F has carbs from a 900 - yes or no?

Posted by gonebiking-2 on Sep 07, 2008; 4:41am
URL: http://vintage-and-classic-hondas.81.s1.nabble.com/Question-1980-CB750F-has-carbs-from-a-900-yes-or-no-tp458280p458283.html

Thanks for keeping me updated. I`m always interested to see how people are going with their Hondas. But nothing surprises me when it comes to carb problems. You get folks who are little bit mechanicly minded and they think they know everything. The problem with the floats being back to front is nothing new ! What happens is owners take the carbs off , turn them upside down to work on, remove the floats , and because they have forgotten that the floats are upside down they put them in back to front , and then wonder why the hell the bike wont run properly. Make sure you follow the instructions word for word in the manual, check that the butterflies are all opening at the same time, connect four vacuum gauages to the carbs, also make sure that the idle mixture screws are turned all the way in and then back them off one and half turns.  Start the bike and get it up to normal operating temp. Then start to adjust the throttle settings making sure that all four readings on the vacuum gauge are exactly the same. ( Clymers should tell you what the vacuum readings should be) Once thats done, some very minor fine tuning  of the slow idle mixture screw will be required to finish off the tuning.  The idle speed should be around 1000 RPM +/- 50 RPM.  While I think about it, check the number of teeth on the front and rear sprocket. For reasons best known to Honda, the CB750s had a 15 / 44 tooth set up. They went like hell and revved al the way to the red line on the open road. But I changed my rear sprocket chain and front sprocket when they wore out to a 15/40 set up. Big improvement all round. Any thing smaller then a 38 tooth rear sprocket, and she problably wont get off the the start line. But then Honda in their infinite wisdom may have altered the gearbox ratios for the USA market where as in Australia and South Africa  they all had the 15/44 set up. Weird !!!