Topic: 74 CB350F leaking carbs but runs great.

[KHB]

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!

Before You go crazy pulling things apart I would just take a plastic handle screwdriver out and rap on the fuel bowl a few times with the the handle side.  Those floats can stick up or down after storage and I rap on mine a few times at the beginning of every season.  If it drools the float is stuck down if it backfires the float is stuck up.  I know it sounds real ghetto but you won't ever damage it with some light tapping.  And you will probably have lots of downtime if you take it apart and you arent super experienced with carbs.

Keith

[Dave K]

Unless someone has messed with the carbs, how could there float level be off? It is probably very simple and it caused by several minor things all caused by sitting with gas in them. There is dried up varnish, scrunge,etc. in the carbs that are preventing the needle and seats from sealing off. I would remove the fuel lines from the gas tank, fill these lines and the carbs with a good carb. cleaner and let it sit for a day or two. Then drain the carbs (there is a screw on the float bowl to do this) and flush again. Or, open this screw on the float bowl and blast you carb. cleaner through the over flow vent into the float bowl. It may very well remove the varnish for you and you never touched a wrench. It has worked for me in the past. Don't beat yourself up trying to align and adjust things when there are no reason they are out of spec to begin with. You may only cause more headaches. If it isn't broke, don't fix it!

[wfdudley]

If you've verified that the floats are good, floats are adjusted, float valves are good, and it's still
leaking, then cracked overflow tubes are possible (as has been suggested by others).  This problem
drove me nuts for months.  Water has too much surface tension to pass through the crack, so testing
with water in the bowl proved nothing.  Only when I put gas in the bowl and watched it dribble out
did I realize I had cracked overflow tubes.  Naturally the crack was on the side nearest the bowl
wall, so you can't see the crack.

My solution was to solder the crack shut using a soldering iron and radio solder.

As to swapping engines -- a 400F motor will bolt right in, by why bother?  If you want more power,
buy a bigger (or more modern) bike.

Bill Dudley
SOHC4 #25 (yes, the 25th member of the original mailing list).

[tm53chev]

with ALL due respect, in my experience I have found that the OLD fiber floats will absorbe gas and ride lower in the float bowl causing the carb overflow to puke excess fuel.  You can easily CK the floats by removing them and floating them in a pan of fuel.  They should ride high, if they float low or nearly sink  they have absorbed fuel and are now heaver than originally intended and will need replaced.

[Sprocketwerx]

 Something mentioned over and over again that is just too good to be true. "CARBS HAVEN'T BEEN TOUCHED"
The bike is 35 years old, how does anyone know if they've ever been apart?
Take nothing for granted.
I just had to set floats on a Yammy XS400 that was set @25mm (manual calls for 32). Now I hope and pray the bearings didn't get washed and damaged.

Lots of good advice here so not going to add to it.



PS admin: I have no idea why this came through my personal e-mail. I haven't gotten e-mail from this site in over a year.

[peten]

+1 on the cracked overflow tubes.  have had this on many bikes in the shop and also 2 of my own; my cb550k and my HD Sportster.  quick fix is fuelproof epoxy, but better is a sleeve of either brass tube or a small section of brake line epoxied or soldered in.  soldering is tough, though--gotta be quick with the torch or you melt the aluminum.

[AOD]

Just because it's overflowing out the carbs, doesn't mean it's the carbs fault.

My assumption is the fuel petcock is not turning off completely, even though you're putting the valve in the off position.  This causes fuel to keep flowing...and eventually overflow.

ALL of my vintage bikes with a petcock that has an OFF switch have failed.  They all leak even when off.  I've replaced them, no issues afterwards.

My '71 CB500F did the same as your bike; replaced petcock, issue resolved.

~Adam

[fang]

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

How did this happen?
-fang

[david.haughn]

I know what the problem is. They leak outta the overflow.

That would be the symptom.  The problem is probably, like someone suggested, float height adjustment.  My bike was leaking fuel out of the overflows even after I verified float height.  It turned out that my float needles were installed upside down.  Remember, the pointy end should point skyward.

[Gordon]

Just because it's overflowing out the carbs, doesn't mean it's the carbs fault.

My assumption is the fuel petcock is not turning off completely, even though you're putting the valve in the off position.  This causes fuel to keep flowing...and eventually overflow.

Yes it does.  If the float valves are working properly the carbs can't overflow even with the petcock left in the ON position.  




I guess the O.P. figured out how to get a lot of quick responses to his post!

In the future don't check the "Announce" box in the Additional Options menu unless you actually intend to send an email to all 7000+ forum members.

[nilsey]

Why did i get an email about this run-of-the-mill OSHC forum post??

[SteveMcQ]

Hey, I had this problem too. But it was just one of my 4 carbs. Then, I learned about (slow at times, I know) the drain screws.

Guess what? No need to take bowls off, adjust valve needle, etc, etc.  Just discovered that one drain screw WASN'T CLOSED ALL THE WAY.

Whoever had the bike before had left it open just enough to piss over itself.

Just as well, sort of, 'cause the bike had been sitting a while and had tons of water in it - and in the float bowls.

Last time I put it up for the winter (last November), I drained the bowls good, and closed the screws I'd opened good.

No problem this year.

Allbest,
SMcQ

[Kev Nemo]

Why did i get an email about this run-of-the-mill OSHC forum post??

I think we all did-that's why there's three pages worth of answers to someone who hasn't cleaned his carbs.

Top right corner under the header-white bar with a magnifying glass in it labeled "search"- type "carbs leaking". There are 17 pages worth of posts on this,man.

I find it ironic that you can figure out how to email everyone in the forum about this problem but you can't use the search function.

[sohc4Lat]

Wish I had stock in Sea Foam! Great stuff. Smells really good coming out the tail pipes! Good preventative maintenance.

Got her all healed up yet? Keep us posted on the progress! ~Jeff

[sparker]

Just want to thank you guys for all the advice!  Everytime I go onto this site I get back amazing amounts of information - very useful!  And thanks for the TAS Classic Motorsports link!  It's good to have ressources!

[brinplourde]

This may be a day late and a dollar short but motorcycle classics magazine is rebuilding a 500 right now.  each issue, july/august 2009 is #3 of the series, they do a different part.  they have already done the carbs and explain it quite well.  you can find them on the web.  good luck!

[Kawasoski]

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.

I agree completely with  this sentence.

[rm56]

Hello, It is not that hard to remove the carbs on any Honda four. I highly recommend you buy a service manual. If your carbs are leaking out the overflows you most likely will need to adjust the float level. Z-1 Enterprises sells a slick carb gage for $5-10 bucks. Since your bike has been sitting you should also buy 4 new float gaskets and replace the old ones. A bit of caution, I own a 74 CB 750 and in between my carbs are two "T" pipes that connect all four carbs to fuel from the hose. The pipes on my bike has four o-rings on each one, they were very old when I bought the bike and one day when I went to start it they leaked so bad I shut it down until I could replace the o-rings. Parts are still available. Call a local Honda shop first, some times if you walk in they will go the extra mile and I recommend talking to an older guy like me who is familar with these bikes. No offense but the younger guys don't know much about "old school" bikes and usually blow you off on the phone. David Silver Spares in England is super fast for Honda parts, also try Classic Motorcycle Supply in the Netherlands CMSNL. I bought tons of stuff from both and they are Honda OEM parts. Avoid aftermarket parts like the plague, they don't fit and they don't last. Lastly take a good close look at all your fuel hoses, if they are cracked, old or just look like crap spend $5 and put new hoses on. Why risk it?

[loudfastugly]

get carb kits with new float valve / needle seat assemblies.  that will cure your leaky carbs.  I do this all the time.  You can clean/adjust/rebuild all you want, but if you don't replace those  35-yr old float valves they will just keep on leaking.

uh, I happen to sell them, at a price better than the "other guys" please visit http://www.loudfastugly.com

[spate51]

If the leak is not the overflow, it may be from the small O rings on the fuel tubes between the carbs.  If those dry out, as long as the petcock is on, there will be a leak.  O rings can be purchased from NAPA (get metric) but you have to take the carbs off the common plate adapter to get the tubes out.  Had to do this on my 550K.

[kghost]

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

How did this happen?
-fang

First.....welcome to the board.

Second....Quit emailing everyone on it.

Its Really Really Annoying

[Dave-and-his-550]

lol, ya I just saw this in my inbox. I thought a forum moderator sent it to everybody considering it said "Announcement" but apparently the OP can send this topic to everybody? How? Please tell me, I'm gonna have fun with that little gem  jk

[Ryan 550k]

lol, ya I just saw this in my inbox. I thought a forum moderator sent it to everybody considering it said "Announcement" but apparently the OP can send this topic to everybody? How? Please tell me, I'm gonna have fun with that little gem  jk

Oh great
Lets just quit while we're ahead shall we?

[Dave-and-his-550]

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.

I agree completely with  this sentence.

I agree with your sentence also. Wait, which one?

[schmors]

I had the same issue of leaking from the overflow on my cb350 twin.  It ended up being a crack in the brass tube/post that comes up in the middle of the float bowl, the one with the little hole in the top for the fuel overflow.  There was a crack up the side so it would leak even though there wasn't too much fuel.  Check that out by filling the bowl with water and plugging the top hole and blowing into the bottom of the float bowl where the fuel drips out and look for bubbles. I JB welded mine, it works, but after a little while the gas eats through it.