SOHC.co.uk Forums > CB750

F2 carb flooding

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Stewartgh:
Andy,

Maybe you are talking about a different tube if what you say is true, but I also had concerns about this on a previous 750F1 I owned and one of the brass tubes on that was missing and the hole blocked, the tube I am refering to is the one in the centre of the bowl and around 1 inch or so in length which come up between the float, if it is this one then for sure it is the overflow and mine being missing made no difference to performance, in fact if you look in the parts list the rubber tube that fits directly onto the bottom of the flaot chamber is even refered to as an overflow tube, but from what you are saying maybe you are talking about a different tube, or maybe your rubber over flow pipes are not going in the right direction? Just a thought, mine always ran fine without one of these tubes and as the float levels were good I never had any kind of leak.

Read Replica:
Thanks for your response Stewart.
Yes, we are talking about the same tube. The reason I thought it may not be purely for overflow purposes is that when trying to set float heights I have had problems with the float valve not sealing (or so it looks like) and thus allowing flow to continue to the bowls. The first sign that the bowl is getting too full is petrol coming back through the pilot jet drilling in the inlet side of the venturi. This occurs with no flow coming out of the drain point from the brass tube on the base of the carb bowl.

Cheers
Andy

Yoshi823:
From what I remember about the float valves they have a small rubber tip to them...so there should be negligible wear on the valve seat. So it must be another reason why that particular carb is flooding. I would swap one of the other float bowls across temporarily until such time as you've cured the flooding problem. #2 won't be useable as it has the accelarator pump mechanism attached to it, but #3 & 4 are useable.

Bryanj:
If fuel comes out of somewhere else first then either the carb orientation has been alterered OR all the tubes have been blocked off

Read Replica:
Still struggling to stop the carbs flooding. I think I have tried most routes open to me. I am setting the float heights at 14.5mm using a template made from info on this site, so I am happy that floats are set correctly. I have even gone to the extremes and set the levels really low but still getting overflow. I have purchased new float valves and fitted these.

If I hold the carbs upside down so that the float valves are seated and then blow through the fuel hose I get no air passing until I rock the carbs forward and the float valves come off their seat and then good flow is obtained. This would lead me to think that the floats are seating and stopping flow as designed.
I have also satisfied myself that the floats are not holed.

Looking down through the brass bodies to where the float valve tips sit there does seem to be some wear around the edges of the seats and not a sharp 90 degree edge. This is indicated by a slightly shinier ring at the sealing edge of the seat. It is difficult to tell exactly though with my eyes. This area would appear to be chief suspect now though, so are new seat bodies available and are the originals easy to extract.

Thanks for any further ideas
Frustrated but having fun
Andy

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