CARBS / drain lines

[Luis Etchenique]

question --

Do the carbs' drain lines have to be in place during the motorcycle's normal operation ? or ... can I just connect them when/if I need to drain the carbs ?

I ask this because I just rebuilt my CB750F SS DOHC ( as a race replica ) with pod filters, and I want to keep the engine as clean and uncluttered as possible, and I'm not sure if they function also as an overflow safety feature for a malfunctioning float bowl.

As always, thanks for any info you can provide me with.

-- Luis

 

[SenseAmidMadness]

They do function as overflow protection -- there are overflow tubes installed from the factory in the carb bowls which go straight to the drain passage and bypass the drain screw.

I personally bought some transparent yellow Tygon fuel line, 1/8 inch I think, for my 1980K and routed all four of them with T-fittings to drain behind the right footpeg for safety. If a carb decides to overflow while I'm riding I definitely don't want it on top of a hot engine.

It's up to you how safe you want to be, but if you don't want to run the overflow lines there are a couple ways you can lower the risk of stuck float. One is to run an inline fuel filter, ideally the paper element type so that it will filter out any junk coming from your tank. You can hide those pretty well underneath the tank most of the time. The other is to make sure you always keep the tank nearly full with fresh non-ethanol gas.

If I were doing a custom build and wanted a perfectly clean look with a good fuel filter, I'd see if I could modify the original petcock inside the tank to take a removable paper filter instead of the original fine mesh screen.