Topic: 1973 CB350 Four Fuel Delivery System Questions

[zerokreativity]

First of all, I ask that my ignorance be forgiven.  This is my first real engine-related project so I'm not doubt a bit green...

My father recently gave me his 1973 Honda CB350 Four which he bought brand new.  It's got 40k+ miles on it and has been sitting for about 7 years at this point.  I got everything cleaned up, new oil, new filters, and filled the fuel tank with gas (my father had completely drained it when he stored the bike so no worries about old gas.

Upon filling the gas tank it began to leak out of the petcock.  Shifting the petcock into the ON position resulted in a slower leak and fuel began to dump down the line (there's a clear section that I could clearly see fuel/bubbles flowing through).  Within seconds gasoline began to leak out of what I now know to be called overflow lines under the bike.

I got the situation under control but am wondering what went wrong here.  I understand that a seal on the petcock may be bad (I can replace that easily enough) but why did the fuel just dump into the carbs and into the overflow lines?  Is this really how the bike works or is some stopper not functioning?

[svenD]

congrats with the 350,try letting it sit for a day with fuel petcock on,this will help dried gaskets & seals to recover,if it leaks from the overflows try tapping the floatbowls with spanner to help floatvalves to seal.At end of day shut the petcock now open the drain plug on the first carb ,allow fuel to drain into a small tray that will fit under the bowls.now open petcock and flush any crap from the bowl,shut petcock,replace drainplug,repeat with the other 3 carbs remember to clean the strainer in the petcock.NO SMOKING! your fuel system should now be good to go Good Luck!

[zerokreativity]

So aside from a bad seal in the petcock it sounds like the float valve in the carb(s) is stuck wide open, correct?

[svenD]

yes,find out which carb or carbs is dumping then try gently tapping the floatbowl
 thats the aluminum underside of carb containing the level control(float mecanisem).

your bike is ment for dayley riding,the 7 years in the garage or what,will not have been good for the carb internals,there will almost certaintley be some gonk/residue in them if you are luckey you will be able to flush most af it out the drain plugs,then hopfully get it running with some kind of carb cleaning fuel additve in the tank,then hopefully a little patience and DAYLEY use will dissolve the last of the gunk.repeat the bowl flushing weekly until the overflow is cured.

if the problems persist you are looking at a probable strip and rebuild+reajustment of the carbs,which requires considerable experiance/good workmanship IMO

[zerokreativity]

I decided to take apart the carbs entirely.  For the record they were nasty on the inside - covered in a good thick layer of varnish/dried gasoline/whatever.

Everything went back together just fine after a good cleaning but all is not well.  When I twist the throttle the carbs don't return to their closed position - they basically just stay wherever I twist the throttle to.  Good for cruise control, bad in general.

Does something need to be lubricated?  Did I just put it back together slightly wrong off and things aren't sliding quite right?

Any input is appreciated.

[fletcha221]

disconnect the cables from the carbs, and re-route them, they are twisted. Mine did the same thing. I built my 350 from the ground up, if you have any questions, please let me know!

[zerokreativity]

When I tore the carb out to rebuild it I only disconnected the cables from the carb itself and never had to really move the cables anywhere.  The carb fell back into place just fine before I went and took them apart so I'm thinking it's got to be something specific to the carb that I either screwed up or need to lubricate a bit.

[fletcha221]

Try this:

Disconnect the throttle cables. Use a screwdriver to open the throttles, if they snap right back, it's the cables. They might be pinched under the tank, etc.

[zerokreativity]

Tried it.  They stayed stuck open.

[fletcha221]

obviously, the spring is attached, right?

The actual carb essembly isn't rubbing the frame/ wiring harness stay?

Are the lifters (attached to the throttle essembly rod), centered between carbs 1&2 and centered between 3&4?

Other than that....I'm really trying to think of what could be binding.

[flybox1]

fletcha beat me to it...
is the return spring not springy? attached?
mine pulls so hard it'd pinch your finger off....

[flybox1]

when you worked on your carbs, did you remove and clean the slides?
varnish can get lodged in there and slow their return.

got your push-pull cables reversed?

[fletcha221]

Long time Flybox!~ hope the 350 is still kickin!

[zerokreativity]

Getting the spring reattached was probably the hardest part of the carb re-assembly process.  It is most definitely in there correctly though.

The carb assembly isn't rubbing on the frame or anything - it feels like there's just a huge amount of resistance to it internally.

Here is is immediately after I took it off the bike:


Close up shot:


During:


After:


See anything put back together distinctly wrong?

[flybox1]

you bet!  
i get her nice and hot a few times a week  

yours?  

[zerokreativity]

when you worked on your carbs, did you remove and clean the slides?
varnish can get lodged in there and slow their return.

I'm very willing to bet this is what's going on.  Any way to clean this up without taking the entire carb off and apart again?

[flybox1]

fk, cant see the pics.
with the cables detached..
do you get smoothe push-pull at the throttle?
if you lift the cable attachment lever on the carbs, is there no return spring action, or does it just stay up/open?

[flybox1]

when you worked on your carbs, did you remove and clean the slides?
varnish can get lodged in there and slow their return.

I'm very willing to bet this is what's going on.  Any way to clean this up without taking the entire carb off and apart again?

yes, you can do it w/o removing the bank of carbs, but i would suggest you take them off any way, and go thru everything again to be sure its not something else working against you...

[zerokreativity]

fk, cant see the pics.
with the cables detached..
do you get smoothe push-pull at the throttle?
if you lift the cable attachment lever on the carbs, is there no return spring action, or does it just stay up/open?

Direct link to the "after" shot:  http://i572.photobucket.com/albums/ss164/TurboPig/CB350Four/DSC_0839.jpg

The throttle itself turns very smoothly forward and back when the cables aren't attached to the carbs.

If I manually lift the cable attachment lever (not easy) it gets stuck in place.  I can push it back down fairly easily but the spring just isn't quite strong enough to do it solo.

[zerokreativity]

when you worked on your carbs, did you remove and clean the slides?
varnish can get lodged in there and slow their return.

I'm very willing to bet this is what's going on.  Any way to clean this up without taking the entire carb off and apart again?

yes, you can do it w/o removing the bank of carbs, but i would suggest you take them off any way, and go thru everything again to be sure its not something else working against you...

I figured as much.  Any special advice on cleaning the slides?

[fletcha221]

My 350 is SOLD! But the guy loves it... It won an award at a local bike night!

[flybox1]

w/o the spring attached, is there still resistance?
if yes, then pull the carbs and the slides.
probably goo in there too  

[flybox1]

My 350 is SOLD! But the guy loves it... It won an award at a local bike night!

NOICE!
hope you got the right $ for it!  

[flybox1]

when you worked on your carbs, did you remove and clean the slides?
varnish can get lodged in there and slow their return.

I'm very willing to bet this is what's going on.  Any way to clean this up without taking the entire carb off and apart again?

yes, you can do it w/o removing the bank of carbs, but i would suggest you take them off any way, and go thru everything again to be sure its not something else working against you...

I figured as much.  Any special advice on cleaning the slides?

CARB CLEANER, SIMPLE GREEN and the toothbrush of your worst enemy! 

[fletcha221]

meh.....I got $3300. hahaha only bad part is that I spent 4

[flybox1]

meh.....I got $3300. hahaha only bad part is that I spent 4

4  
oh well....i've had $700 worth of fun before  

put me down for a Cendse Bikeworks tee when they become available  

[fletcha221]

We are working on getting a website going! The t's will be along shortly!

[CB750_KBC]

Thanks guys. I'll check fuel delivery next. I used to have a bunch of 60s/70s Suzuki bikes, so a lot of the parts and engineering is somewhat familiar to me. I remember the "sock" or filters were always faulty on those bikes - so thanks for jogging my memory.

Thanks!
KBC