Topic: CB550 - Fuel not reaching the carbs

[Joshevelle]

Hello All,

Lately I have had some problems with my carbs going empty on gas. Setup: no tank filter, new line filter (paper type), full gas tank, restored petcock, restored carbs and properly leveled.

The problem is that sometimes, while riding, the carbs goes empty, therefore the engine dies, then I close the petcock and open it again but the gas does not flow, shacking the carbs doesn't help either. I've disconnected the filter to see if the problem is in the tank/filter but the gas flows perfectly out of the filter (while disconnected).  I've tried to blow air thru the gas to the carbs and it is like totally blocked.

Most of the time when this happens, I could stay on the side of the road for no more than 10min and then the gas starts flowing again (I haven't find the reason).

Yesterday, it happened again while riding home but I couldn't get the gas to flow again, so after 30min I called a friend and he helped out. He bought me a new 1/4" hose and a brass T connector (I had a plastic one) and after install them the gas flowed perfectly. I thought I was set and I was riding home (with my friend tailing me) and after ~300m the engine died again. I unplugged the filter and tried to blow air to the carbs, they where blocked again. We couldn't make it run again and we had to load my bike onto his truck.

While restoring the carbs, I didn't see any damage on the float needles, however, as far as I know, when the float needles are damaged, the gas overflows, they don't stick to the needle seat.

What do you guys think? I'm I missing something? Other than the needle seats and float levels, what would you guys check?

Thanks for your help.
Josh

[flybox1]

start by cleaning your tank and petcock.
Install a new in-tank sock filter.
if you cant, and HAVE to run an inline filter, make certain there are no uphill sections of fuel line.
the gas needs to be flowing downhill.
to test OFF the bike, take the tank off, and install your fuel line and filter just as you would run it on your bike.
turn on the fuel tap and see how gas flows.  it should flow unimpeded.
if it seems to slow, take your filler cap off, and see if it improves. if it does, you're getting vapor lock and need to service your filler cap vent hole.

[Joshevelle]

Thanks for the reply flybox1.

I've tried the same with the filler cap off but it doesn't help. However I do have uphill sections in the fuel line (because of the inline filter). I thought it would not affect since the gas pressure would perfectly reach the carbs, anything lower than the gas tank level would try to reach the tank level, so thought that a small uphill section in the fuel line would not be a problem, I'm wrong?

Unfortunately the previous owner cut the tubing of the petcock, so I can't install a in-tank sock filter. I could probably adapt something inside.

[flybox1]

Use a 90deg filter and get rid of the uphills.  Keeping your tank more than half full helps, too.

[Joshevelle]

That's a great idea! I will try that.

Thanks a lot!

[Duanob]

If all that checks out, you might have problems with the floats/float valves sticking closed.

[Joshevelle]

If all that checks out, you might have problems with the floats/float valves sticking closed.

Do you know the reason of valves sticking closed?

I would think that gravity and fuel pressure would unstuck them but as I mentioned, is impossible to blow air into the carbs, so I also thought the float valves are stick closed.

[flybox1]

blowing into the carbs thru the fuel line wont tell you much.
taking your bowls off, letting the floats hang down, turning on the fuel, then checking each float and valve for fuel shutoff, will.

[Duanob]

If all that checks out, you might have problems with the floats/float valves sticking closed.

Do you know the reason of valves sticking closed?

I would think that gravity and fuel pressure would unstuck them but as I mentioned, is impossible to blow air into the carbs, so I also thought the float valves are stick closed.

I would say from mostly sitting and varnish build up. Possibly a float is hanging up on something that wasn't installed right? They mostly stick open but stranger things have happened. Flybox1 mentioned a way to find out above. Process of elimination my friend. Start at the tank and work your way down into the carbs for fuel flow. If fuel flows good into the carbs then you will be remnoving and cleaning and checking them.

[Joshevelle]

blowing into the carbs thru the fuel line wont tell you much.
taking your bowls off, letting the floats hang down, turning on the fuel, then checking each float and valve for fuel shutoff, will.

The problem is that I haven't been able to reproduce the problem while the bike is not running, it only happens when I'm riding. The first time this happened I disassembled the carbs and double checked the gas flow in each one of them. I couldn't find any problem, so I cleaned the valves and the valve seats and assembled them again.

What I did noticed is that the valve is not the "metal cone" type, it is the black plastic one. Would that affect at all?

 

[Joshevelle]

If fuel flows good into the carbs then you will be remnoving and cleaning and checking them.

I hate to say it, but yes, I will do it this weekend.

[harisuluv]

blowing into the carbs thru the fuel line wont tell you much.
taking your bowls off, letting the floats hang down, turning on the fuel, then checking each float and valve for fuel shutoff, will.

The problem is that I haven't been able to reproduce the problem while the bike is not running, it only happens when I'm riding. The first time this happened I disassembled the carbs and double checked the gas flow in each one of them. I couldn't find any problem, so I cleaned the valves and the valve seats and assembled them again.

What I did noticed is that the valve is not the "metal cone" type, it is the black plastic one. Would that affect at all?

 

Yup that is the wrong valve for a 74 and corresponding carbs.  The real part has a matching valve and seat.  The one you have is for PD style carbs, and it is just the float valve, the stock seat is pressed in and not replaceable (practically).

[Joshevelle]

The real part has a matching valve and seat.  The one you have is for PD style carbs, and it is just the float valve, the stock seat is pressed in and not replaceable (practically).

Thanks for stepping in.

I lost you there, so I have the wrong valve but I have to buy both valves and seats? I do have the pressed in seats.

[harisuluv]

ok so you have a 74 bike with later style carbs (PD).  If you have pressed in seats you have PD carbs.  The rubber tipped valve is then correct.

[flybox1]

Firts, eliminate the obvious cause....uphill fuel lines.

[seanbarney41]

Have you checked your float bowl vents for blockage?  How about the fuel cap vent?  Next time the fuel won't flow try opening the tank.

[Patrick]

Your problem is probably the inline filter. I have to run inlines on my Yamaha XS11. If you don't set them up straight vertical you tend to get a gas bubble in the filter. Happens all the time just like you describe. Used to happen to me until I set the filters right.

Patrick

[Joshevelle]

Your problem is probably the inline filter. I have to run inlines on my Yamaha XS11. If you don't set them up straight vertical you tend to get a gas bubble in the filter. Happens all the time just like you describe. Used to happen to me until I set the filters right.

Patrick

I do have a bubble in the inline filter! I will buy the petckok screen and remove the inline. That would also remove the uphills.

I tried removing the tank cap but didnt help.

[Joshevelle]

Have you checked your float bowl vents for blockage?  How about the fuel cap vent?  Next time the fuel won't flow try opening the tank.

Hello, thanks for your suggestions.

Yes, I already checked the bowl vents and installed new hoses. Opening the tank did not help.

I will remove the inline filter but unfortunately the petcock screen is not available in Mexico, so I have to wait to go to the states, hopefully in around three weeks.

No more riding until I solve this problem 

[flybox1]

http://www.ebay.com/itm/Compact-Clear-Inline-Fuel-Filter-90-Degree-1-5-8-x-1-1-4-Motorcycle-/191626943418?hash=item2c9ddb1bba&vxp=mtr

[Scott S]

 What about the vent hoses on the carbs? They also have to be open to allow the bowls to fill. I've seen people connect them together when they should be open to the atmosphere.

[Joshevelle]

http://www.ebay.com/itm/Compact-Clear-Inline-Fuel-Filter-90-Degree-1-5-8-x-1-1-4-Motorcycle-/191626943418?hash=item2c9ddb1bba&vxp=mtr

Thanks for the link.

I would wait to go to the states and ship it to an address there rather than ship it to Mexico, it would take ~2 months to arrive here. Mexican postal service sucks. Thank you though.

[Joshevelle]

What about the vent hoses on the carbs? They also have to be open to allow the bowls to fill. I've seen people connect them together when they should be open to the atmosphere.

Both hoses are new and open to the atmosphere.

[scottly]

Have you verified that the float bowls are empty by opening the drain screws?

[Joshevelle]

Have you verified that the float bowls are empty by opening the drain screws?

Actually no, I haven't done that.

Do you know an proximate quantity of fuel that should be inside the bowl? I could go and ride around carrying a measuring cup and when this happens I could empty the bowls in it.