Topic: Active Overflow

[Vintageguy]

Have a 1978 CB750F. Great bike. Love it. Lately however, I get gas out the carbs overflow when I turn on the petcock. I believe it's a stuck float at times, because it stops when I begin to ride. Or is it a plugged jet? What can I do short of a carb dismantle/rebuild?
Thanks for any/all responses.

[Cevan]

I just had this issue and it turned out to be cracked overflow tubes.  I soldered them and it appears to have resolved the issue.

[willbird]

Taking the float bowls off with the fuel turned off is a good place to start, look to see if there is any "stuff" in the bottoms of them. Any foreign matter coming through the needle and seat from the fuel lines and or tank can hold the float valve open and cause issues like you are seeing.

Plugged main or pilot jets should not cause the float bowls to overflow.


Bill

[Don R]

 You might have luck by draining the bowls and then turning the fuel on. A tiny bit of grit or goo may flush out.

[HondaMan]

Like DonR said ^^^: or, if you remove the bowls (painful on the later bikes) you can see the bits in the bowls that are causing the stuck floats.

It is possible that the strainer inside the gas tank is crumbling now, and has open spots that let tiny crud make it into the carbs, not good. You can replace that filter, but you must do it by draining the tank, then removing the old screen and plugging in the new one: it is available from Honda. I have one of those kits around here somewhere.

[willbird]

Like DonR said ^^^: or, if you remove the bowls (painful on the later bikes) you can see the bits in the bowls that are causing the stuck floats.

It is possible that the strainer inside the gas tank is crumbling now, and has open spots that let tiny crud make it into the carbs, not good. You can replace that filter, but you must do it by draining the tank, then removing the old screen and plugging in the new one: it is available from Honda. I have one of those kits around here somewhere.

My CB750K2 was stolen when it was my fathers and they stole gas tank and side covers. He found a replacement tank locally back in the 70's. I never had petcock off until recently, I found that the petcock had no standpipe at all. it was sucking right out of the bottom of the tank all the time. Never gave me a lick of trouble and being used to early 70's gas I avoided ever coming close to reserve so I never knew.

Taking the fuel line off with petcock off, putting it into a container and flipping to reserve will give you an idea if you have "stuff" in the bottom of the tank if your petcock has a reserve setting.

Bill