Topic: 350f carb problems

[twincityrider]

Hi All,

1972, cb350f

Having some serious issues with my carbs.  I've taken them off and cleaned them three or four times now, and put in all new carb rebuild parts.  I have not fully disassembled the four carbs from the throttle body.  Carbs are adjusted properly and floats are adjusted correctly as far as I can tell.  No leaks when mounted on bike.  My issue is it doesn't seem as though when I open the petcock from the tank, gas is actively moving into the gas line to the carbs.  A quarter of the bottom of the line between the tank and the carbs has gas in it (the rest is air).  Is this normal?  Gas flows freely through the line when not hooked up to the carbs.

When I try and start the bike I'm getting good suction from the intake side, good spark, but can't get it to start up.  Spark plugs seem slightly damp.

Thoughts?  I'd really appreciate it.  Bike is rebuilt and looking good if only it would run!

[ohiolarsen]

You can find out if you're getting any fuel into the carbs by opening the drain screws on the bottoms of the bowls - does fuel flow out the tube?  If not, then the needle might be stuck in the seat.  Will the bike start on starter fluid?  Does it sputter at all and try to start?

[twincityrider]

I'm getting fuel out of the bowls.  I've tried ether with no success.  Got a couple back fires out of it without ether but no real success.

Any chance there are some mysterious air passages that I missed when I cleaned the carbs?

[ohiolarsen]

I don't know if you missed any air passages, but if it won't run on either, I wonder if something else is wrong.  Was this a complete engine rebuild?  Is the ignition timing correct?

[twincityrider]

Yeah, complete rebuild.  I double checked my valves.  They should be airtight (went through them all I have good compression).  Like I said, I have spark but I'll double check to make sure my timing is right.  How could it be off though?  I'm drawing a blank on that one.  I haven't touched the ignition timing.  Thanks Ohiolarsen.  Much appreciated.

[flybox1]

yeah, some bubbles are normal...the fuel will start to flow as its sucked up by your jets..
dont worry. the bubble will eventuallyclear.

if your carbs are operating correctly, and its just a bubble issue, and it REALLY bugs you...you need to burp the baby!

cut your fuel line as short as you can.  secure it tightly to the carbs and then stretch it to the petcock. secure it with a clamp.
the shorter the better as it creates less space for bubbles to stick.
once hooked up, turn your PC on, and while sitting onthe bike, lean it as far to the right as you can to get gravity to aide in moving the bubbles up into your tank...and if needed, get someone to wiggle / flick / tap on the line to free the bubble. you may have some fuel out the overflow tubes tho.

[twincityrider]

brilliant stuff flybox1.  yeah it's a big bubble.  could that in and of itself be the problem?  i'll see if that does it in an hour

[flybox1]

fuel will always pass the bubble if your PC is opened. its a gravity thing.  but it may take some time, and coaxing, to get the bubble to pass up into your tank. 
if you ride, and run out of gas then its not the bubble, its your tank thats vapor locked, PC clogged, or your fuel valves in your carbs closed/clogged. 

[twincityrider]

There's no reason it shouldn't run without the air filter attached right?  i've been trying to get it running without being connected to that garbage.  just straight carbs until I know it runs.

[flybox1]

it'll run lean above idle....but it will run.
set all the AF screws to 3/4-ish turns out

[twincityrider]

Just pulled spark plugs.  Cylinder 1 isn't getting fuel/air mixture.  It's dry and clean.  Crud in the fuel rail somewhere?  Should've started on three cylinder I would think.  Ideas?  Thanks everyone.

[mattcb350f]

She backfires but won't start and the plugs are wet? It may be that the coils are hooked up wrong or something like that.

Have a look at the wiring under the tank where the coils connect and make sure the colour coding matches. Timing is also important, as well as point adjustment. If the point plate was ever removed during the rebuild then it will need to be re-timed.

I use the static method with a simple battery/light bulb/wire set up with good results. A search on the subject should give you lots of info.

 Matt.

[ohiolarsen]

If you're getting fuel out of the #1 bowl, then I wouldn't think the fuel rail is the issue.  Like Matt said, if the timing or points are out of adjustment, she may just backfire.
Chris

[twincityrider]

Fully disassembled the carbs yesterday.  Turns out the fuel connector between carbs 1 and 2 was split (see picture of unbroken black connectors).  That would make sense because I wasn't pulling gas from the carb inlet between 2 and 3 to cylinder 1.  So the carb bodies are soaking in some yamaha carb cleaner (this time I'll go through them with some old guitar strings to make sure I get all the gunk out).

My problem is this: where can I find a replacement fuel connector between carbs 1 and 2?  Not listed as a part on any site I know of.  I can find new o-rings here http://www.harpritsan.com/Carb_17Orings.html.  

Thanks everyone for the help.  Almost got this beast on the road in time for a Minnesota winter.

[twincityrider]

found this.

http://forums.sohc4.net/index.php?topic=65224.0