CrabsAndCylinders said:You could check to make sure the floats float. If they do then recheck the float heights. Is it only one carb or all that leak fuel?
CrabsAndCylinders said:Dumb question but are they leaking from the overflow or could it be very bad gaskets, cracked bowls or if they have drains, from leaking drains?
jpmobius said:So, do you have a stock airbox? If so then your simplest plan will be to keep it. If not, getting it to run well with pods may not be too dreadful (some bikes are evidently). Replacing the carbs altogether will be dreadfully expensive unless you get used, and whether stock replacements or from an alternative bike, you either are where you are now (you already have stock used carbs) or will likely see plenty of jetting work to get it to run properly - of course you could get very lucky - but it's not usually how it goes. The vacuum valve itself is not a bad thing. If it works, it's fine. If it has issues (this is not your carb leaking problem) then fix it. Just because others say it has problems does not mean it is terminal. Of course you can simply eliminate it as long as the petcock works properly manually so you can turn off the fuel when you are parked. If you bought aftermarket rebuild kits it is very possible that this is an issue. If you kept your old parts put them back in. The assembled height of the needle/seat assembly is CRITICAL, and aftermarket assemblies often are not correct. You can "fix" that problem by adjusting the tang that sets the float height, but you trade one problem with another, which is screwing up the kinematics of the float mechanism by having the tang not meet the needle's tensioning pin at 90o when the fuel level is correct. While you're thinking about this, make sure you have the correct washers under the seats as this will hugely affect the resulting assembled height of the parts. Another reason to have the OEM factory gasket, seat and needle. For the record, these parts almost NEVER need to be replaced unless mechanically damaged by corrosion or stupidity. I've seen some wear on 2-stroke race motors, but otherwise consider them to be lifetime reliable only needing cleaning and polishing to be good as new. As previously mentioned, it would be good to know EXACTLY where the leaks are. I reckon everyone is presuming it is from the bowl overflows. Assuming that to be the case, you should take off the bowls and fill them up with gas on the bench almost to the top of the overflow tube. If no leaks, you can go back to troubleshooting the floats, mechanism and need/seat assembly.
The Jimbonaut said:Dude I'm totally enjoying reading through your build - anyone working on '81 CB750K is cool as f*** as far as I'm concerned. Might be a bit biased, but hey.
If you're still having issues with your carbs, there's a dude called Mike Nixon (he has his own website, you can google the guy) - he knows a ton about Honda carbs. I got a ton of help here on the forum with mine, and spoke to Mike a load as well. Got mine running like champions, yours will too mate.
Keep on keepin' on, high fives from Montreal