F2 carb flooding

[Read Replica]

Had the carbs off today for a clean. Noticed that brass overflow tube in #1  carb bowl is missing and hole where it should sit is filled with some sort of liquid metal type putty. This has I suppose been done in the past for a split tube or something.
The bike is a good runner but I have never been 100% happy with the carburation.
Does the tube also act as balance line as well as an overflow?
Question is, assuming float height is ok and fuel level is correct will the lack of this tube cause any running issues? Do I need a replacement bowl?

Thanks guys
Andy

[Yoshi823]

I'd leave it as is...then if you happen to come across another set of carbs at some time in the future...or parts of...then replace. You'll soon know if the carb is overflowing anyway...

[Read Replica]

The tube is purely an overflow, is that correct? Not essential to setting up the carburation.

Andy

[SteveD CB500K0]

Yes. Purely an overflow.

They can crack, which leads to a constant leak - obviously your PO used a rather more radical fix!

[Read Replica]

The more I look at this the more I suspect that the tube is not for an overflow at all. I say this because surely fuel will pour out of the airfilter via the slow running or main jets long before the fuel level gets to the top of the brass tube.

I can only assume therefor that it provides more of an equalising / balance function within the carb bowl and I will have to source a replacement.

Does anyone on here have a knackered set of carbs that they would sell or ideally just the #1 float bowl assuming the brass tube is intact.

Cheers guys
Andy

[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

[Read Replica]

New float needles seem to have cured overflow issues and bike now running fine.

Quick question though.
I am still not happy with the lack of brass overflow in carb #1 so am still loooking for a replacement bowl. Are the carbs on the CB550F the same (and subsequently, the bowls) as the 78 CB750F2 carbs?

Chow for now
Andy

[K2-K6]

Hi

The brass tube will normally be above the fuel level with a correctly set float and valve and so have nil affect on any carburation.

BUT........... if the bowl continues to fill the fuel now has (outlet blocked) no route out other than through the carb and depending on arrangement, angle, etc could fill the cylinder!! IF this happens the cylinder will not pass compression when cranked over and will most likely bend the con-rod. I think the tube is important so would install replacement.

Even if it kept getting a small amount of fuel into the motor it is still ultimately drastic if left unchecked, bore wear, oil dilution, leading to bearing / cam failure.

Not trying to scare you, as if all is well then nothing, but it is an important contingency.

Hope this helps.

[AshimotoK0]

Pretty sure I have a spare bowl from a K7 which I am fairly sure  has the same bowl. Will check out the tube on it. If I do have one then you can have it for the cost of posting it.

Still looking for 2 off K0 brass floats if anyone has any to sell.

Cheers

Ash

[Read Replica]

Thanks for the kind offer Ash. I will take you up on it if bowl is compatible.

Even though the bike is running fine at present I would feel easier if things were as they were designed to be.

Andy

[Yoshi823]

The float bowls are compatible between the F2 & K7 carbs in all except jetting.

http://www.cmsnl.com/honda-cb750k7-four-england_model14390/partslist/E19-1.html