DOHC CB750K Ltd

Greetings gentlemen!

So I picked up my first bike, a '79 CB750K 10th Anniversary Ltd. a few weeks ago and purchased some supplies today (filter, oil, spark plugs, battery, charger/tender).

After some repeated attempts with very little success, I'm unable to get the bike to start. She cranks over, but it's as though she's not getting proper fueling.

I noticed that when I turn the fuel tank petcock from the OFF position to either the ON or RES positions, the bottom of the carb starts to leak like a tap. I really don't think it's supposed to leak that much.

I'm pretty new when it comes to carbs, but I have been working on autos with EFI for the past 3-1/2 years, so I'm definitely up for tackling this challenge. I'd just like some insight before I start to take everything apart.

I was told by the previous owner that it would benefit from a rebuild, as it's been sitting and only been ran once a month since 1998. I plan on putting velocity stacks w/ a screen mesh filter on it and an exhaust in the future, so I've been told that I'd have to get larger primary jets.

Can anyone point me in the right direction regarding the carb rebuild/jet upgrade?

First thing's first though, I'd like to get that leak dealt with. I've included a photo and encircled the areas where fuel begins to run the moment I move the petcock out of the OFF position. Why would it be leaking this much, and would this be a reason why my bike doesn't want to start?

Thanks

Floats and needles are probably stuck.

You'll probably want to pull the rack and clean the years of crap out of them and un-stick the float needles.



-Tom

Tomorrow I plan on ripping the airbox and carbs off the bike. Would I just be removing the bottom covers of the carbs and cleaning the components up, or is there more to it than that?

You'll want to pull the bowls (covers) off the bottoms so uou can get an idea of what you're looking at. Odds are after a few years of stale gas the bowls will be full of tar and/or corrosion (hope for a low humidity environment) Best bet is to pull the bowls, the jets (idle and main) the diffuser (usually attached to the main jet) and dunk them in Chemtool Carb Dip (available at pep boys) ....*Warning* it will eat rubber so it's best not to put the rubber bowl gasket in with the bowl... Removing it may tear it, however....so be careful.
Keep in mind the slides should mobe up and down freely in the carb, and the butterfly valves should als move smoothly when activated by the throttle cable.

I'll dig up (if someone doesn't beat me to it) a more "How to clean a CV Carb" guide tomorrow.

**Also** if you remove the airbox and do not re-jet and change the slide spring your bike will run like sh*t.

-Tom

Don't rule out having pinholes in the overflow tube or a leaky screw either. Easiest way to check is to just pull the bowls off and fill them with gas and see if they leak. But yeah, they could definitely benefit from a rebuild. If you need any spare parts, let me know. I've got two complete sets of carbs for this bike, and a box full of assorted carb parts.