Topic: 1977 CB400f Carb woes

[JPS888]

Hi, new to this forum, Please HELP , have running issues , terrible flat spot under slight load & will not rev out, leaks fuel after running through overflows even with petcock switched off .
Have now changed float needle valves & cleaned fuel bowls & refitted with service kits from David silver.
Still slight hesitation & flat spot under slight load but not all of the time ! although running 80% better than before.
Any ideas ? Float level height ?
Thanks .

[JPS888]

Getting desperate, anyone out there with any ideas ? please.......

[MoMo]

Have the carbs been completely apart to clean the midrange/emulsifier tubes? That item can be problematic on the 400 four, especially if the bike had been sitting for any period of time...Larry

[JPS888]

Thanks Larry will try that one next then !!!!!

[flybox1]

Have the carbs been completely apart to clean the midrange/emulsifier tubes? That item can be problematic on the 400 four, especially if the bike had been sitting for any period of time...Larry

^^^this!

[Cundalini]

If fuel leaks out the overflow pipes when running or not ,the float bowls are the wrong height OR a valve isn`t seating properly.In that there is something trapped like a bit of grit stopping the valve closing.

[fmctm1sw]

Make sure your standpipes in the float bowls aren't cracked....

[JPS888]

Thanks guys, will check both these , bike wouldn't start for a minute or two last night ! seemed to have a fuel starvation problem , so does this lean towards float height being wrong....~? will have to have carbs out again at some point...A :Dlthough they have stopped leaking through the overflows since replacing the needle valves.

[camelman]

It leans towards your carbs being dirty.  Check the FAQ for a description of how to clean your carbs.  You'll have to go through them in detail to make sure everything is good.  Carbs and a bad battery at the typical culprits on these bikes.

Camelman