Honda-SOHC

SOHC.co.uk Forums => CB500/550 => Topic started by: petermigreen on June 13, 2017, 09:57:41 PM

Title: No.1 Carb keeps leaking!!
Post by: petermigreen on June 13, 2017, 09:57:41 PM

Bit perplexed by this one. I've managed to set my carbs up ok with the exception on No1 which no matter what I do just keeps leaking.

I did a bit of research and found some M6 x 0.75 grease nipples which I drilled out to create a means of seeing the fuel level in the float bowl. I thought this would give me an insight into what's going on in the bowls but now I'm more confused than ever.

[attach=1]

Even with the level below the seam I'm still seeing a drip out of the overflow. Obviously the image only shows one drip but it is continuous and about 2 a second so not inconsequential.

I can only surmise that the fuel level I'm seeing in the tube is not correct (don't know how this can be) as fuel is obviously getting into the top of the overflow tube.

Also, presumably the float valve isn't sealing if the fuel in the bowl remains high?

Any thoughts?

Thanks in advance, Peter

Title: Re: No.1 Carb keeps leaking!!
Post by: mike the bike on June 13, 2017, 10:21:40 PM

I seem to remember a post about this before.  IIRC it was down to the brass overflow tube having a split in it.  To test this theory,  try swapping two of the float bowls to see if the problem migrates.

Title: Re: No.1 Carb keeps leaking!!
Post by: petermigreen on June 13, 2017, 10:29:03 PM

Yes Mike that would explain it, however, I thought I've swapped bowls before but will definitely try that.

Thing is, as I was trying different float heights, I left out the gasket for ease and even had fuel coming out of the gap between the bowl and carb body as you'd expect with no gasket, which seems to point to very high fuel level even though the level in the sight tube remained below the line? Scratching my head.

Thanks, Peter.

Title: Re: No.1 Carb keeps leaking!!
Post by: mike the bike on June 14, 2017, 07:11:35 AM

My theory is the petrol climbs up the side by capillary action.

Title: Re: No.1 Carb keeps leaking!!
Post by: petermigreen on June 14, 2017, 07:14:06 PM

MIKE! You nailed it!
Dropped no1 bowl off and held in hand filled with petrol and lo and behold drip drip. With a magnifying glass could just see a microscopic crack in the overflow tube. Didn't think it would work but ran a bit of solder up it and its stopped the leak.
Pat on the back for Mike.
Cheers buddy.
Peter

Title: Re: No.1 Carb keeps leaking!!
Post by: mike the bike on June 14, 2017, 07:45:22 PM

Proper job.   Another success for the forum.

Title: Re: No.1 Carb keeps leaking!!
Post by: paulbaker1954 on June 16, 2017, 12:27:23 AM

Glad you solved it I had exactly same problem and it had me similarly perplexed for some time

Seems this is a common problem with thin wall brass tube

Funnily enough I bought a set of carb balancers off a guy on fleabay that weren't that old and two tubes also had hairline cracks in

Any clever metallurgists amongst our flock?

Title: Re: No.1 Carb keeps leaking!!
Post by: Bryanj on June 16, 2017, 06:12:16 AM

Water in the fuel gets into the tubes and freezes causing cracks

Title: Re: No.1 Carb keeps leaking!!
Post by: mike the bike on June 16, 2017, 07:14:31 AM

Very unlikely,  given those tubes are empty and surrounded by petrol.

Title: Re: No.1 Carb keeps leaking!!
Post by: Bryanj on June 16, 2017, 11:09:18 PM

Usually happens when left over the winter and bowls empty