Topic: CB350F carb — fuel overflow from odd location?

[jpschroeder]

Hey, this is my first post in this forum. I'm new to working on classic Honda's and recently picked up a CB350F that needed a bit of work and this place has already been invaluable, so thank you.

The carbs on this thing almost for sure need to be rebuilt, but before I went through the hassle I decided to give it a "will it run" attempt (amazingly it fired up on the second kick of the kickstarted). When I let gas run into the carbs for the first time, I got fuel leaks in a number of places, some out the drain tubes coming from the bottom of the bowls — I assume this is just a typical overflow — bad float seal or something like that. However, I also got fuel flowing out of the two brass nipples on the *top* of the carbs.

Checking the manuals I cant figure out what these are for, but their placement makes me suspect it is the vacuum lines. The manual said they need fuel lines on them though? (#4 in fig 3-91, see attached). Either way, nothing is attached to these and fuel comes pouring out as soon as the bowls are full. I expected this from the overflow ports since I assumed the carbs would be kinda gummed up, but I didn’t expect this from this spot.

So yeah, sorry for the noob question, but what are they for, and why would fuel come out of them?

[denward17]

Those brass nipples are for venting purposes of the float bowl.

If you had gas coming out there, you were probably getting raw fuel in the combustion chamber, so needs to be fixed before starting.

Sounds like the float needle seat has some trash in it, how clean is the tank?

BTW, welcome to the forum, good people here....

[jpschroeder]

oh ok, so those are for air as suspected (not specifically linked to the vacuum tubes between the carbs though?).

As for fuel in the combustion chamber.......I did start it up, like 4-5 times actually . What ill effects should I be aware of — is the main concern hydrolock?

And the tank on this thing was an absolute disaster. Super rusty, and the PO had tried to put POR15 in there and it didnt take at all so now there flaking POR15 and rust in there. Thats a problem for another day though, I started this up with fuel from a little test tank, but im sure the PO probably jacked up those carbs pretty good. Im planning to tear them down.

I got the carb kit from 4into1.com, is that any good?

[denward17]

oh ok, so those are for air as suspected (not specifically linked to the vacuum tubes between the carbs though?).

As for fuel in the combustion chamber.......I did start it up, like 4-5 times actually . What ill effects should I be aware of — is the main concern hydrolock?

And the tank on this thing was an absolute disaster. Super rusty, and the PO had tried to put POR15 in there and it didnt take at all so now there flaking POR15 and rust in there. Thats a problem for another day though, I started this up with fuel from a little test tank, but im sure the PO probably jacked up those carbs pretty good. Im planning to tear them down.

I got the carb kit from 4into1.com, is that any good?

Tubes do connect to the brass nipples, routed up above and probably under the seat.
Fuel in the combustion chamber could wash the rings of oil, may even have some in the engine sump, bad for rings.

The tank may have left particles in the fuel lines, won't know until you tear them apart (at least take the bowls off to see).

I've not hear many good things about the kits 4into1 sells, so only use the gaskets/o rings if you can, and clean and reuse your current brass if original.

[carnivorous chicken]

Definitely tear them down and clean them out -- remember to save all of the original brass (if it's still there) as the bike will run better with original jets, etc. Aftermarket jets and float valves are off, and cause issues.

Although it seems pretty clear that you've got blocked or stuck float valves leading to overflowing, you might as well check the brass overflow tubes in the float bowls while you are at it as these can crack and cause leaks too.

Bummer about the tank -- I've used POR15 for years with no issues. If done right, it works pretty well. Not sure of what is best to remove it but maybe you can contact them and ask -- or someone will come along and chime in here.

These are great little bikes. Let's see a photo of the whole bike if you have one.

[carnivorous chicken]

oh ok, so those are for air as suspected (not specifically linked to the vacuum tubes between the carbs though?).

As for fuel in the combustion chamber.......I did start it up, like 4-5 times actually . What ill effects should I be aware of — is the main concern hydrolock?

And the tank on this thing was an absolute disaster. Super rusty, and the PO had tried to put POR15 in there and it didnt take at all so now there flaking POR15 and rust in there. Thats a problem for another day though, I started this up with fuel from a little test tank, but im sure the PO probably jacked up those carbs pretty good. Im planning to tear them down.

I got the carb kit from 4into1.com, is that any good?

Tubes do connect to the brass nipples, routed up above and probably under the seat.
Fuel in the combustion chamber could wash the rings of oil, may even have some in the engine sump, bad for rings.

The tank may have left particles in the fuel lines, won't know until you tear them apart (at least take the bowls off to see).

I've not hear many good things about the kits 4into1 sells, so only use the gaskets/o rings if you can, and clean and reuse your current brass if original.

Julie Seal sells viton o-rings for the 350F. I bought a set, they look good, but I haven't installed them yet.

[jpschroeder]

Bummer about the tank -- I've used POR15 for years with no issues. If done right, it works pretty well. Not sure of what is best to remove it but maybe you can contact them and ask -- or someone will come along and chime in here.

These are great little bikes. Let's see a photo of the whole bike if you have one.

I have searched high and low for answers to this question. I tested a chip of it in acetone, and it didnt even soften it. The only thing ive seen online that seems to have success is methylene chloride — which is tough to get. Some forum somewhere was talking about B15/B17 from Benco (https://www.bencosales.com/products/p/benco-b14-6hemb-twyxy) but as far as I can tell you need to be a "shop" to buy it.

Picture of the bike attached! Fairly complete overall. Its missing the fork covers and the airbox, I got an original Airbox for it i plan to install after the carb work — but the fork covers Ive found are so expensive....

Anything else you see in the pics that jump out as "wrong"?

[Nurse Julie]

Vent tubes attach to those brass nipples, they hang down the back of the carbs and dangle below the bottom of the frame well below the swing arm. You will have 6 tubes dangling in total, 4 float bowl overflow tubes and the 2 vent tubes.

[carnivorous chicken]

Looks great. Some stuff that's not factory of course -- the exhaust most obvious. But it's also missing the fork ears and gaiters. The seat has been recovered at some point, and it looks like someone had bar-end mirrors on it, or weights.

[bryanj]

ANY aftermarket carb kits are dubious, you are better off cleaning the original brass

[seanbarney41]

Try Yamiya for parts.  Don't be afraid of the fact that they are in Japan, impeccable quality and service, with shipping to the U.S. that is faster than most sellers located here.

4 into 1 sells useless garbage.

[jpschroeder]

Looks great. Some stuff that's not factory of course -- the exhaust most obvious. But it's also missing the fork ears and gaiters. The seat has been recovered at some point, and it looks like someone had bar-end mirrors on it, or weights.

How can you tell the the seat has been recovered? Educate me. Another question ive struggled to find an answer for online: are the fork ears/gaiters/covers compatible with any other hondas of the era? Finding CB350F specific stuff is tough.

Try Yamiya for parts.  Don't be afraid of the fact that they are in Japan, impeccable quality and service, with shipping to the U.S. that is faster than most sellers located here.

4 into 1 sells useless garbage.

Ok, noted about 4into1 and ill check out Yamiya.

[carnivorous chicken]

How can you tell the the seat has been recovered? Educate me. Another question ive struggled to find an answer for online: are the fork ears/gaiters/covers compatible with any other hondas of the era? Finding CB350F specific stuff is tough.

The strap should have a buckle, that mounts on the lower part of the seat, and there should be chrome trim around the bottom.

[HondaMan]

Finding CB350F specific stuff is tough.

That might be the understatement of the year!

Be sure to stay tuned here if you go into the engine: there are currently NO manuals available besides the skimpy Honda shop manuals, and it is extremely easy to screw up a top-end job on this particular (and CB400F) bike.

[carnivorous chicken]

Looks great. Some stuff that's not factory of course -- the exhaust most obvious. But it's also missing the fork ears and gaiters. The seat has been recovered at some point, and it looks like someone had bar-end mirrors on it, or weights.

How can you tell the the seat has been recovered? Educate me. Another question ive struggled to find an answer for online: are the fork ears/gaiters/covers compatible with any other hondas of the era? Finding CB350F specific stuff is tough.
.

Forgot to add —- most of the 350F stuff is specific to the bike. I also misspoke — this bike doesn’t have gaiters but rather metal lower parts that go with the fork ears; both are painted the same color as the tank and side covers. Best place to find them is here — or eBay.

[jpschroeder]

Update: I disassembled the carbs, and they are filthy inside. My ultrasonic cleaner should be here soon so ill get those back in shape soon. However I have 2 more problems.

1. The fuel coupling between the inner and outer carbs — those are supposed to be brass right? On mine they were plastic and one was all cracked up. Of course, I cannot find this part in the part manual, not even sure what its called, but I definitely need a replacement. Any ideas?

2. On the carb adjuster arm there are little boot gasket like things. Mine were pretty worse for wear. Are these to keep water from getting on the springs? I also cannot find replacements for those it seems. Thoughts? Also the little springs in the adjuster are pretty rusty. i can probably clean them up, but replacements would be nice too if anyone knows of where to get em.

[bryanj]

The parts you want you will have to get from another set of carbs

[jpschroeder]

Well thats not what I wanted to hear...If it comes to that, I wonder if I could 3d print those parts

[HondaMan]

I know one set in the Denver area has 3D printed ones. The owner made them in 2012. I haven't seen him since 2015, but he was still riding it then.
He also made new rubber seals out of a cut up inner tube. I'm thinking I might practice at that myself: my 350F carbs don't look so good, either.

[bryanj]

I might have the fuel tubes from a 400 on a junk set but not the rubber mechanism covers, there are a lot of bikes out there without them as 350, 400 ,500 and 550 all use them.
Postage from UK to US is not cheap but i will look if you wish

[jpschroeder]

Super kind offer @bryanj, let me bark up this 3d printing tree a bit and see if it goes anywhere. Ill probably come groveling back to you shortly.

Also — those interconnects are supposed to be brass are they not? Mine being plastic must have been some previous repair job? I’m thinking if I can model the part accurately I could get them machined on a CNC mill out of brass or aluminum.

As for the rubber gastket/cover/boot thing on the actuator, ill try to model that too I think. I’ve heard/read/seen that TPU works pretty good as a gasket material in low/moderate heat environments, so that could be something I get printed too. It would be cool to have a parts repository somewhere of pieces/parts to these old bikes that have been modeled so folks can reproduce them when needed.

[MauiK3]

Wouldn't the bowl vents need to be routed up under the seat for some relatively calm air?
The connector tubes would work in brass, pretty easy to machine.

[bryanj]

I have seen both alloy and plastic fuel tee pieces but not brass, though it should work fine.
Not guaranteeinh i have the parts you want, i just have a big box of old carb bits from totaly fubared carbs!!

[jpschroeder]

I’ve modeled the fittings. If anyone is interested, the STL and STEP files are attached. Now I need to find someone who can actually manufacture this. I have a simple 3d printer but I dont trust the prints to be fuel tight (perhaps I should test that)

[HondaMan]

I’ve modeled the fittings. If anyone is interested, the STL and STEP files are attached. Now I need to find someone who can actually manufacture this. I have a simple 3d printer but I dont trust the prints to be fuel tight (perhaps I should test that)

The Orings provide the sealing action you need. The hard part is: the Orings must squish 3%-8% of their rubber diameter to seal correctly without making it impossible to slide the TEE or Union into the carb bodies. If the compression is too much (like over 10%) then in about 6-8 months the carb holes will split from the slow, constant pressure, ruining the carbs.

I won't go into HOW I know this little factoid, other than to say it was an expensive lesson.