Topic: 74 CB350F leaking carbs but runs great.

[CafeRacin350]

I bought this bike from my uncle and he obviously had worked on it a lot and got it running pretty good. When I got it all I did was change the oil, spark plugs, air filter. This bike runs super great, I've got it up to 90 and probably could have went more but started to get nervous. My only complaint is that it leaks fuel outta the carbs overflow. This is my first bike and I want to work on it myself but am nervous to tear into the carbs cuz they're so touchy. Any suggestions? Is there a way I can just fix the carbs float without rebuilding the carbs?

Here's a picture of her. I repainted it myself, upholstered the seat myself. Still need to do a few more things.
Cheers!

[redschwa]

Don't fear your carbs my friend. Just do a bunch of research. Get the manual and be really familiar with them before you even touch them. I'm a new guy too and pulled my carbs, It wasn't that bad. But try to figure out your problem before you just go pulling the carbs. Good luck and have fun.

[shizzomynizzo]

Had a similar problem with mine, you probably just need to adjust the floats. Pretty easy, search adjusting floats and read all you can. When you have enough confidence, take em off and do it. It's not that hard, and I guess you don't need to rebuild them. if the bowl seals are bad, replace them or you'll leak from there.

[CafeRacin350]

I know what the problem is. They leak outta the overflow. Also, does anyone know if a cb350f engine can be swapped up to a bigger 550?

[uberdoom]

I have been looking to replace my float bowl seals but can't find any commercial products. Any advice? What should I use? Thanks for the advice.

Doug

[Pirate]

I have been looking to replace my float bowl seals but can't find any commercial products. Any advice? What should I use? Thanks for the advice.

Doug

 Look on Ebay for TAS Classic Motorsports.  They have float bowl gasket sets for good prices (I just picked up a set for my 550), and their shipping time is awesome!

[Shooter]

I have the same issue with one of my 4 carbs.  ie one in four is giving me grief!
 
I suspect that I have a bent needle.

Have no fear opening the bottom section of the carb up..its simple...  but take your time ,go slowly and take care so you understand how it fits together and works.

Take  a look at a carb diagram in the parts pdf.

BTW - DO not ride or run it with a petrol leak.  Very dangerous and risk of incineration is extremely probable.

[carnivorous chicken]

You don't have to take your carbs off to do this, especially if it's running well, and especially if you're running the stock airbox. If you use a small screwdriver shaped like a "Z" (can't remember what these are called right now) or a socket with a phillips end you can just drop the float bowls and replace the bottom end stuff, including the valve that's causing your overflow. Might be the float, but check the valve. And what Shooter said: don't catch fire.

[noexit]

you probably just need to adjust the floats.

Before you go messing with the float levels, make sure that: 1. They're floating, 2. The float valves are Sealing. As long as no one else has been in there messing around, your floats shouldn't be off. It's more likely that your float valve is not sealing, causing the bowls to overflow, or the floats have lost their buoyancy. (Probably less likely for plastic floats than metal ones.)

[seaweb11]

Figure out which carb is overflowing by following up the leaking tube and smack the outside of carb bowl with the handle of a good sized screwdriver...............works 50% of the time.

Failing that sorting you out, pull them off and "using a manual" simply adjust the float height. 

[Lars]

Any leaking through the carb overflow tubes, is due to either:

1. Float heights not correct on one or several carbs or they are sticky.
2. Valve needle not closing properly.

It is only one way to do this properly and that is to take the carbs off your bike - don't worry - it is not rocket science. Before you do, try to determine which of the carbs that leak. Here is the procedure how to take the carbs off.
http://www.hondahobby.no/website.aspx?displayid=1361

You do not need to take the carbs off the stayplate, even though that is more convinient as you check the float heights.

1. Check if all the floats swings freely on the bolt. If sticky remove bolt and clean well. When you remove the bolt and float, keep an eye on the valve needle below, it will fall out easily.
2. Check that BOTH floaters in each carbs are aligned and not a bit twisted.
3. Check that all 4 valves are properly seated and that all needles are clean. The valves must be clean, too, with no particles stopping the needle to close properly. If the carbs are rebuild with new valves and needles, they sometimes need to "adjust" to each other to close properly, but that is pretty rare. Assemble the valve/needles and be careful to insert the needle the correct way. (I always try to use all the original parts when I rebuild carbs if possible, only replacing the o-rings).
4. Reassemble the floaters into the carbs.
5. Check the float height on each carb - 21 mm - there is an instrument to buy for this job, often on eBay.
6. Now, put the float bowls back on. Here you might have an anoying problem - if the gasket has popped out of its groove, you will find it to be a bit too long when you put it back. Make a clean cut and remove a few mm. Glue them togehter.
7. Before you replace the carbs on the bike, set your tank on your working bench and hook up the carbs and check for overflow. If they still leak, reopen the ones who leak and adjust the float height. Hook up again until fine.
8. Carbs back on bike
9. Coffe break.
10. Smile and be pleased with your work

[turboguzzi]

with all due respect to your bike and problem, I am rather interested to know why your posting arrived to my private email as a "forum announcements and important notification"

Would like to leave the option to recieve them checked, but only if forum memebers will respect each other's privacy and use this option for REALLY important stuff that is relevant for us all,

Thanks

TG

[seaweb11]

Any leaking through the carb overflow tubes, is due to either:

1. Float heights not correct on one or several carbs or they are sticky.
2. Valve needle not closing properly.

It is only one way to do this properly and that is to take the carbs off your bike - don't worry - it is not rocket science. Before you do, try to determine which of the carbs that leak. Here is the procedure how to take the carbs off.
http://www.hondahobby.no/website.aspx?displayid=1361

You do not need to take the carbs off the stayplate, even though that is more convinient as you check the float heights.

1. Check if all the floats swings freely on the bolt. If sticky remove bolt and clean well. When you remove the bolt and float, keep an eye on the valve needle below, it will fall out easily.
2. Check that BOTH floaters in each carbs are aligned and not a bit twisted.
3. Check that all 4 valves are properly seated and that all needles are clean. The valves must be clean, too, with no particles stopping the needle to close properly. If the carbs are rebuild with new valves and needles, they sometimes need to "adjust" to each other to close properly, but that is pretty rare. Assemble the valve/needles and be careful to insert the needle the correct way. (I always try to use all the original parts when I rebuild carbs if possible, only replacing the o-rings).
4. Reassemble the floaters into the carbs.
5. Check the float height on each carb - 21 mm - there is an instrument to buy for this job, often on eBay.
6. Now, put the float bowls back on. Here you might have an anoying problem - if the gasket has popped out of its groove, you will find it to be a bit too long when you put it back. Make a clean cut and remove a few mm. Glue them togehter.
7. Before you replace the carbs on the bike, set your tank on your working bench and hook up the carbs and check for overflow. If they still leak, reopen the ones who leak and adjust the float height. Hook up again until fine.
8. Carbs back on bike
9. Coffe break.
10. Smile and be pleased with your work

Yeah, that's what I said..... except if you hit it and it knocks it free, well there you are then

[Reverend66]

If it's only pissing itself parked on the side stand no worries, the little fellas just do that. If it upsets you just make sure to turn of the fuel at the petcock when you park her. Sticky floats more than likely like everone has said, will more than likely cure itself. Just sold my '73 350F to buy a '76 750 F1 and I'm already missing the little fella, Best running bike I ever had.

[highsideuk]

Had this on several bikes that have not been run for a long time.

It is unlikely that anything has worn out or got bent or anything like that just because bike has not been used for a while.

The only thing it has ever been on anything that I have owned is dirt (most likely rust from inside the tank) stopping the needle valve(s) from seating properly. This means they do not stop fuel flow and so the carbs overflow when the engine is not using much petrol.

The "proper" way to fix this is to drop the float bowls off and take the floats off and then you can take the needle valves apart and clean.

BUT a quick fix which has usually worked for me is to flush the dirt out of the needle valves without taking anything apart. To do this you...

1) Turn the petrol tap OFF
2) open the float bow drain screws to completely empty the float bowls. Once empty, CLOSE THEM(that way you are less likely to forget!)

The floats are now sitting on the bottom of the empty bowls and the needle valves are wide open.

3) make sure you have plenty if petrol in the tank and turn the petrol tap ON.

The idea is that with the petrol flowing through the wide open needle valves you have a good chance of flushing any dirt into the bottom of the float bwols where it will do no harm.

If it does not work, repeat a couple of times, then give up and do it properly!!!!

Cheers

[Jim H]

with all due respect to your bike and problem, I am rather interested to know why your posting arrived to my private email as a "forum announcements and important notification"

Would like to leave the option to recieve them checked, but only if forum memebers will respect each other's privacy and use this option for REALLY important stuff that is relevant for us all,

Thanks

TG

I was wondering the same thing, I only ever posted on the 750-A topic

[Zonda]

with all due respect to your bike and problem, I am rather interested to know why your posting arrived to my private email as a "forum announcements and important notification"

Would like to leave the option to recieve them checked, but only if forum memebers will respect each other's privacy and use this option for REALLY important stuff that is relevant for us all,

Thanks

TG

I was wondering the same thing, I only ever posted on the 750-A topic

+1 lurker

[crazypj]

+2, whats so important?

PJ

[DickG]

I had the same problem with my 1977 Honda 400/4 F2. I rebuilt it about three years ago after it had not run for twenty years. All four carbs overflowed badly. I checked everything - float height, flotation, etc. Nothing wrong there. I replaced the needle valve assemblies with new ones. Still the same. The next step was a set of new Viton tipped needle valves. Still the same.
I then examined the chambers into which the needle valve bodies are plugged with a magnifying glass. At the point where the O-rings seat the Mazac was badly pitted. Was this why petrol was pouring out of the overflows? Although the valves were shutting off petrol was leaking past the O-rings.
I tried fitting the needle valve bodies back into the carbs with a smear of Loctite Instant Gasket (the orange coloured one) around the O-rings. Bingo! I now have non-leaking carbs! The Instant Gasket has to be completely petrol proof, so that rules out a lot of the available ones.
The carbs have been leak free for over two years now, proving that the problem wasn't float height or worn needle valves but a 'worn' carb body!

Dick Ganderton

[martin.g.g]

There are several reason that floats bowls leak fuel most easy some more difficult

•   Float height wrong so would need to reset the float height
•   Dirt in the needle valve not allowing the fuel to be shut off so would need the needle valve cleaned and the carb gallery’s cleaned out best with the carbs off the bike were you can clean the carbs fully
•   Worn needle vales. Replace the needle valves
•   The seals on the main jets and needle valves are prone to perishing and letting fuel pass if old. So a new set of jet seals may be needed. If replacing the jets they come with new seals, but if not the seals are available from NRP up north
•   Float bowl overflow tube leaking at base. This is a problem that I had on a CB550, the over flow tubes were leaking at the base were they pressed into the carb bowl body. To check this remove bowl and place finger over the top of the brass over flow tube and blow into the part that comes out of the bottom of the carb bowl(or other way round). No air should escape if it does a new carb bowl need to be sourced unless it can be sealed on the outside & inside joint with something that is petrol proof (possibly tank sealant applied carefully)

Some advice is that if the bike has been standing removing the carbs and giving them a good clean outside first then strip and clean one carb at a time do not mix the carb bits around as this may cause other problems. Just do one carb at a time in a clean space keeping the bits in a container so you don’t lose any bit (ice cream is good one for each carb, mark the outside what carb goes were),and follow the book, and don’t rush the job, an air line and a tin of carb cleaner is very useful and don’t for get to wear eye protection when using carb cleaner stings like a b---h.

[Ironman]

It looks like you've had some pretty good advice thus far.  I had the same problem with my 74 CB550K. I solved the problem by removing the float bowls, cleaning the float needles, and adjusting the float levels.  I removed the float bowls without removing the carbs and was able to adjust and clean everything just fine. One tip is to get yourself a can of air used to clean dust on computers, and after you've cleaned the needle jets, blow air through the holes to make sure nothing is clogged.   Also blow air through the hole where the needle jets are seated.  Once all is done reassemble, use new gaskets if you've got'em, and last I recommend you install inline fuel filters on both gas lines to  keep the tank rust out of your carbs.  Also sometimes the floats stick to the bowls after assembly.  It's good to have a rubber hammer for those cases to give a light tap on the bowl sides.  I had this problem after I reassembled mine and a couple of light taps broke it free and I've never had a gas leak since...Cheers

[offrdk5]

I had similar problems. I put some Sea Foam in the tank and took it out and opened it up. It stopped leaking.

[gregory1975]

Everyone has made a pretty comprehensive list of why a carb overflows.... I  know one more I didn't see yet (sorry if I missed someone stating it)... the overflow tube can actually be cracked on the inside of the bowl.  I am in Florida but I hear it freezes in other places  and that can crack these tubes.  There are posts on this site you can search for to see pics and solutions.

[Alan F.]

I know what the problem is. They leak outta the overflow. Also, does anyone know if a cb350f engine can be swapped up to a bigger 550?

It won't bolt in, but if you fancy a long expensive custom build... it can probably be done with enough work.
Maybe a 400 will bolt in, I'm not sure.

[pelermon]

Very cool mod on your 350f.
I have four of them and you gave me a good idea for one.
I love these with 8" handlebars.
What is the front fender from?

Get use to removing the carb rack.
It only takes about 5 min. not painful at all.
With them laying on a bench its much easier to trouble shoot.
Just getting past "what a pain" wall and just slipping them off is key.
My bet is obstruction in the needle and seat.

I like the idea of Loctite Instant Gasket (the orange coloured one) around the O-rings.