Topic: No fuel to 3 and 4?

[CenTex750]

Totally frustrated at this point.

Has anyone else had this problem?  Just soaked and cleaned the carbs, yet it seems no fuel is getting to #3 and #4 cylinders beyond idle. After stopping the motor, there is barely any fuel in the float bowls for 3 and 4, while 1 and 2 are full.

Thoughts, PLEASE?

[Gordon]

Floats may just be stuck, although they typically stick in the down (open) position, but they can also get stuck, for whatever reason, at the top of their travel.  Try tapping on the float bowls with a screwdriver handle.  If that doesn't do it, then pull the bowls off to see if fuel will come out at all when the valves are open. 

What bike is this?  On my 750 it's possible to install the bowl gaskets incorrectly so that they interfere with the movement of the floats.

[TwoTired]

The fuel feed is a little different among the many models available.
On some, 3&4 are the farthest from the fuel tap and even "uphill" while on the side stand.  So, you may just be on the brink of the fuel level getting bellow the stand pipe in the tank.
Have you tried the "reserve" setting?

[Duanob]

If it's a 550 74 - 76 model it may be a the fuel tap. One hose flows to carbs 1 & 2 and the other flows to 3 & 4.

[splitt]

If it has the single feed "T" between carb #2 & #3, either the "T", or the fuel rail feeding #3 & #4 carbs may be plugged.

[jonzen1977]

I have 78 supersport carbs on my bike, and this happened, only on reserve, because the reserve petcock hole was partially plugged.  Worked fine on "ON", just starved 3&4 on reserve.

[CenTex750]

Thanks guys!

Gordon - When I did a full carb cleaning, I reset the floats to Clymer-spec and cycled the float needles ad nauseum to see if they'd stick, and they moved freely the whole time.  I really think I've ruled out the float valves at this point.  I am eager to get the leaky bowl gaskets replaced however.

TwoTired - Yep it's on reserve, but the fuel level's a little low - gonna fill her up and see if it helps

Duanob and Splitt - gonna recheck the flow through the fuel lines, again.

Jonzen - thanks - I'll re-overhaul the petcock when my replacement petcock o-ring comes in.

[KingCustomCycles.com]

I had a 450 with the dual petcock outlet that would run the left bowl dry on acceleration.  Turns out it was the fuel line routing with a slight rise as it went across the carbs to the other inlet.  I set it up to descend all the way to the inlet and it was fine.  Drove me crazy.  I have heard fuel filters will air lock and block fuel, although I have never experienced this.

[TwoTired]

When I did a full carb cleaning, I reset the floats to Clymer-spec ...

What carbs do you have, and what was the actual measurement spec you used?

[CenTex750]

KingCustomCyles - Thanks man, I will shorten the hose going to 3/4 so it's downhill all the way.  PLEASE let that be the fix!!

TwoTired - Stock Keihins, measured 26 mm from bottom of carb base to bottom of float in the float needle open position...

[TwoTired]

Well, we STILL don't know what bike you have.  And, some of the Keihins needs a float measurement of 14.5mm.
I'm not sure why we should share information with you if you won't even tell us what you are working on.

I'm done.  You've successfully shared your frustration!

Good luck with your problems!

[CenTex750]

TwoTired - sorry.  Been trying to figure out how you guys put the one liners below your nickname.  That way I wouldn't need to post it with every thread.

1976 CB750K.