Topic: '80 DOHC CB750F - carb rebuild but won't stop flooding

[tdskip]

Hi guys - hope everyone is having a good week. Some good news / bad news here.

Good news - got her running and she feels strong.  I pulled the carbs apart, cleaned everything well, and then installed it all back together. Started on the button once I got the pilot screw right. A bit rattly at low idle but smooth once underway and good power.

Bad news - when I test fired her I noticed that I had a bad (as-in near constant) fuel overflow problem on one of the carbs that lead me to rebuild the carbs in the first place. Post-rebuild I have just as bad of a leak - ugh.

Floats moved freely before buttoning everything back up, float height looked correct (non-adjustable floats on this year) and I used new float valve. I did not replace the float valve seat. EDIT - I didn't specifically clean the seats either, this may well be the issue as the bike sat for 12+ years before I got it.

It's not like there is just a minor leak, it's full on flow like the float isn't doing anything at all. Anything jump out as the likely cause here?

Thanks!

[BenelliSEI]

Full flow usually means something is jammed, stuck, or upside down? One carb only?

[tdskip]

Full flow usually means something is jammed, stuck, or upside down? One carb only?

Hi! Thanks for the response.

Definitely not upside down, did that first go around. 

I checked to make sure everything (floats and needles) moved freely before reassembly.

One carb is the problem child, I had a second one briefly overflow but then it stopped.

[HondaMan]

It is often caused by tiny bits of crud in the fuel lines, some coming from the tank (crusty inside) and/or from old fuel lines that just got moved, and maybe cracked a little, inside. What I try to do in these cases is: open the float bowl drains all the way, then open the fuel petcock and try to 'flood' out the bits thru the valves and into into the float bowls. There, they can't cause harm. If you start by first draining all 4 bowls and then open the petcock, this increases the flow a little and helps some.

In the case where the tank is the culprit, you may be stuck with trying to use an inline fuel filter to trap it until you can fix the tank inside (hint: use POR15, don't even THINK of trying anything else...).

[Bodain]

It's not like there is just a minor leak, it's full on flow like the float isn't doing anything at all. Anything jump out as the likely cause here?

Why don't you assume what you just stated is the problem. Take carbs off bike. Reproduce flow of gas to the carb when the carbs are sitting on the bench. If fuel is flowing into bowl and continues overflow. The valve seat is not cutting flow of gas... It ain't magic.