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SOHC.co.uk Forums => CB350/400 => Topic started by: AndyD on April 28, 2020, 05:25:52 PM

Title: Leaky carbs
Post by: AndyD on April 28, 2020, 05:25:52 PM

Hi all,
I know it's a common issue the carbs leaking through the overflow and sure enough the poor old gal suffers this indignity as well after refurbing the carbs.
Everything cleaned and reassembled fine with new O rings etc.
Spent a few happy hours setting the float levels having read many topics on here - ended up using the method with carbs on side and very slightest pressure on the float pin.
First time on test she dribbled happily so took apart again and re-cleaned the float pins etc. and checked float levels again.
Put back on test and again 2 carbs started dripping straight away - 1 quite a constant flow, the other a slower drip.
I'm guessing this means the float pins / valve may need replacing so i wondered what opinions were on different replacements available (trying to keep spend down so cheaper the better!).
Any views welcome
Cheers,
Andy

Title: Re: Leaky carbs
Post by: Johnwebley on April 28, 2020, 05:42:19 PM

Could be as simple as sticking float

Give each of the leaky carbs at solid tap with a plastic screwdriver handle.
and when we get chance to ride them for longer.
Put some Redex cleaner in the tank.

Help to keep the carbs free

Sent from my SM-A750FN using Tapatalk

Title: Re: Leaky carbs
Post by: TrickyMicky on April 28, 2020, 07:13:52 PM

Before spending any dosh on parts, one problem which bugged me a couple of times is the spindle pins which the floats pivot on. They can get gunged up with infrequent use, so remove pins and very gently give them a polish with some VERY fine wet & dry, and see if that helps. Stay healthy, Mick.

Title: Re: Leaky carbs
Post by: florence on April 28, 2020, 07:39:07 PM

might sound crazy but carefully inspect the brass pipe in the float chamber.  I have had different Hondas develop a hairline crack in this tube.  No matter what your float height, petrol will leak out.  It's very easily missed and makes one suspect the float or the valve.  Also make sure the floats float and are not filling up with petrol.

Title: Re: Leaky carbs
Post by: AndyD on April 28, 2020, 08:17:41 PM

Thanks all
I tried tapping bowls but no effect
Took pins and floats off and checked all move freely
Checked the brass tubes and all seem fine
Suspect the float valve so will try swapping the fast leaking one to a different carb so hopefully will show if that’s the problem.
Cheers
Andy

Title: Re: Leaky carbs
Post by: andut on April 28, 2020, 08:55:12 PM

Andy,. Give the valve and seat a good clean and polish.  I use a cotton bud and a bit of Solvol to get the seat clean.


Andy

Title: Re: Leaky carbs
Post by: taysidedragon on April 28, 2020, 11:45:19 PM

You can check the brass overflow tubes before fitting bowls onto carbs.
Half fill the bowl over a catchtray or bowl. If the tube leaks it will  drip. Sometimes it can creep between the tube and the alloy bowl.

Title: Re: Leaky carbs
Post by: Oggers on April 29, 2020, 10:07:38 AM

Another vote for floats not floating for me. I had a GS550 whose floats did not rise to the occassion and it spewed forth from the drains  every time it came to a standstill. Personally I would check them out and fix/replace if required.

Title: Re: Leaky carbs
Post by: Nurse Julie on April 29, 2020, 10:21:45 AM

I would start with float needle and seat and then put all floats in a bowl of water and make sure firstly they all float and secondly they all float at the same level.

Title: Re: Leaky carbs
Post by: billywingnut on April 29, 2020, 10:25:20 AM

When I did my restoration I decided to buy new service kits, I also checked each float bowl before re assembly for leaks as mentioned  earlier. It has leaked on only one occasion after being stored for a while, a gentle tap stopped it and it hasn't happened since in over a year.

Title: Re: Leaky carbs
Post by: florence on April 29, 2020, 12:07:59 PM

I think modern petrol is causing problems.  My CB350 has brass floats, one of them developed a hole, it was tiny but when I pressed the area the whole thing fell to bits on one side.  Also, I had a float bowl holed and float bowl tube split.  All on the same bike, which is why I have put on some AMALs I had lying around.  Back when I rode the bike, the original carbs were always temperamental, sticking diaphragm/sliders, so will be interesting to see what it is like with slide carbs.  Sorry, I'm digressing.
 

Title: Re: Leaky carbs
Post by: SeanFD on April 29, 2020, 01:25:46 PM

Quote from: Nurse Julie on April 29, 2020, 10:21:45 AM

I would start with float needle and seat and then put all floats in a bowl of water and make sure firstly they all float and secondly they all float at the same level.

Also try holding them under the water - like looking for a puncture - in case the hole/crack is at the top. When you take them out give them a shake and listen for fluid inside.

Title: Re: Leaky carbs
Post by: AndyD on April 29, 2020, 02:32:55 PM

Again thanks everyone
Plenty of things to check when I get away from work today.
I didn't know that the floats were hollow on these so will check them in water.
Also will clean the float valves again just to be sure and the brass pipe for leaks

If all else fails are there any good / bad recommendations on repair parts - eBay has quite a few offering from around the world varying enormously in cost and contents.
On the GS1000s the strong recommendation was never use anything except original due to quality issues - is that the same fro these bikes?

Will update after the next round

Cheers,
Andy

Title: Re: Leaky carbs
Post by: H2Eric on April 29, 2020, 04:11:49 PM

This problem sounds very familiar. If you have to replace the float needles and seats use genuine parts, others are pretty dire from my experience. As Julie says check that the floats float and they are all at the same level, mine didn't. I replaced the float needles and floats on my 350F and all is now tickety-boo and leak free. I had a similar problem with brass floats on an H2 which sank i.e. full of holes and full of petrol. Allens Performance came to the rescue with 3 new floats, problem solved and that was long before ethanol problems.

Cheers all

Eric

Title: Re: Leaky carbs
Post by: taysidedragon on April 29, 2020, 07:33:27 PM

I bought rebuild kits from David Silver for mine and they work just fine. They are Keyster kits that sometimes get bad reports. Maybe there are fakes on the market so buy from a reputable dealer.  :)

Title: Re: Leaky carbs
Post by: AndyD on April 30, 2020, 07:14:21 PM

Thanks again,
Had another go at the carbs this afternoon
Floats all float and evenly so I think they are OK
Bowls don't leak so guess the brass pipe is OK
Cleaned float valves again (shiniest part of the bike now!)
Checked float heights again
Put back on test and after a few seconds two carbs have a happy trickle from the overflows.
Turning the fuel supply off and then back on again the trickle doesn't reappear, only a drop forming on the overflow pipe.
I'm pretty sure it's worn float valves so I'll order up some replacements and see if that sorts it.
While waiting I might start on a CB900FD I finally hauled out of the shed on a sunny day last week - mind you it's a lot heavier than the 400, especially with seized brakes!!

Cheers,
Andy

Title: Re: Leaky carbs
Post by: SteveD CB500K0 on May 01, 2020, 07:21:13 AM

FZ.

(https://uploads.tapatalk-cdn.com/20200501/3e401a5b59bd8ef26476b6793e39968d.jpg)


Sent from my iPhone using Tapatalk

Title: Re: Leaky carbs
Post by: Laverda Dave on May 01, 2020, 09:11:09 AM

Andy, have you run the engine since rebuilding the carbs? I (and others) have suffered similar problems after rebuilding the carbs with new valves etc. Try running the engine for a while and the dribbles may stop, they did on mine. Nothing more frustrating than continuing to remove and strip the carbs!

Title: Re: Leaky carbs
Post by: AndyD on May 01, 2020, 11:12:36 AM

Oddjob,
I agree the FD is a lovely looking bike and can't wait to get stuck into restoring this one.
Bought it almost 10 years ago from the original owner who'd started replacing the fork seals in the late 80's, given up and left it in the garage ever since.
Pic attached shows her on arrival with just some front end bits missing (all in boxes), second pic shows her now having been pulled from her slumber in a slightly damp shed in my garden so more surface rust than when I bought her.
Paintwork is really good and I've got a new 4-2 exhaust (chrome not black sadly) to go on so hopefully can get her back to pretty original state.
[attach=1][attach=2]

Cheers,
Andy

Title: Re: Leaky carbs
Post by: AndyD on May 01, 2020, 11:17:03 AM

Thanks Dave,
You may well be right - I haven't put the carbs on at all yet, hoping to make sure they didn't leak before trying to.
Not sure how hard the 400 ones are to get on and off but with other bikes it's been one of the most awkward, annoying and sweary jobs so I hoped (probably hugely optimistically) to get away with doing it once.
I ordered the carb repair kits from DSS last night so will give new float valves a go for starters.
One thing I noticed was that the 4 float pins varied hugely in how springy they were so maybe have had a hard life and are a bit tired.
Cheers,
Andy

Title: Re: Leaky carbs
Post by: Laverda Dave on May 01, 2020, 06:35:35 PM

Is that YOUR shed  :'( :'( :'( :'(

Title: Re: Leaky carbs
Post by: AndyD on May 01, 2020, 07:30:13 PM

Dave,
'Had' to build the garage a few years ago mainly because the sheds were too full of 'projects' and there was nowhere to keep the shiny finished ones.
Of course as soon as I got more space temptation took over so now the garage is also filling up - and the sheds are still packed!
Luckily have an understanding wife!
Cheers,
Andy

Title: Re: Leaky carbs
Post by: AndyD on May 01, 2020, 08:33:04 PM

Good spotting
The XT is a 250, the smaller GS is a 550, the grey one is a GSX1100EZ ( katanas ugly sister) and the red one is a CB1100f
The turbo was a real impulse buy - couldn’t resist it but no idea where to start with it!
Cheers
Andy

Title: Re: Leaky carbs
Post by: Golfcarmad on May 02, 2020, 01:01:31 PM

I have just had same problem after complete rebuild.
So I took carbs out-and cleaned everything again meticulously.
In my opinion when springs inside move a little sideways-this causes the issue.
Mine are fine now-just clean them and be gentle putting bowls back on.