Topic: Fuel Level / Fuel Flow - CB500

[CoachDoc]

TT, I'm about to meet you halfway on this question. Last weekend I found some small 90 degree filters which will eliminate the loop in my fuel lines. Trapped air will not be eliminated entirely, but somewhat reduced I'm sure.

[TwoTired]

TT, I'm about to meet you halfway on this question. Last weekend I found some small 90 degree filters which will eliminate the loop in my fuel lines. Trapped air will not be eliminated entirely, but somewhat reduced I'm sure.

In addition to the filter screens and sediment bowl? (74, right?)

Cheers,

[CoachDoc]

TT, I'm about to meet you halfway on this question. Last weekend I found some small 90 degree filters which will eliminate the loop in my fuel lines. Trapped air will not be eliminated entirely, but somewhat reduced I'm sure.

In addition to the filter screens and sediment bowl? (74, right?)

Cheers,

Do I detect a wee bit of sarcasm there? Yes, a '74, and yes it will be with the screen and sediment bowl. Just like you can't be too rich or too thin, my fuel can't be too clean...... lol

[TwoTired]

Not so much sarcasm, but wonderment.   
I have a 74 Cb550 as well.  It's never had an inline filter, and it does have rust speckles in the tank.  I just rinsed the sediment bowl once a year.
This bike has been sitting the last couple years, though. (Swing arm bushings worn out.)  We'll see what a chore the carbs will be next year, I guess.  (I need to finish the 78 550 for spring sales.)

Cheers,

[Chachi]

Update... I noticed a small puddle of fuel under the overflow tubes this morning. The fuel valve has been off and bike has not been started in 24-36 hours. I've started and tested in the driveway and fuel flow appears to be back to normal - this is a visual check that both inline filters (clear, conical, visu) are full of fuel whereas previously only one filter was constantly full.

I am still going forward with the petcock replacement and potential rerouting of fuel lines without inline filters, but does this mean my immediate issue was a stuck float or something similar? Coincidence or not, the temperature dropped about 20-30 degrees last night.

In pic, overflow tubes were routed that way as I was going to attempt to drain float bowls.

[Rigid]

Maybe I missed something.........what did you change to correct the fuel flow and why is fuel draining out of the carbs a good thing?

[Deltarider]

Check if there are any cracks in the fuel lines, in particular where the lines are attached to the petcock. I had this. Thougt it was my turn to replace the O-rings on the T-joints. Turned out one of the fuel lines had split just a bit at the petcock. Fuel followed the outside of that line (obeying the law of gravity). Easy to fix. O-rings at the T-joints after 35 years are still OK. 

[Chachi]

No fuel line cracks. This fuel definitely came out of the end of the carb overflow tubes.

I haven't changed or done anything. I have been waiting to for my petcock to come in before I did anything else. I came out this morning to the fuel 'puddle' and now fuel flow appears to be normal. I think carb overflow tube #4 (outside one on right/kick side) is the one that dripped. That same carb tube will drip some (a small negligible amount) after running, where no other overflow tubes seem to really drip at all.

1 - What would make the overflow drip that amount while bike has been sitting with fuel valve off for two days?

2 - How is this related to the prior fuel flow issue?

It is interesting (relevant?) that carb #4 did the dripping and it was the fuel line to carbs 3/4 that was not flowing.

I'm attempting to understand of all of these symptoms to figure out what needs to be addressed.

[Rigid]

It sounds like your petcock is leaking internally and allowing fuel to pass in the closed position, that will be cured with the new one. #4 has a leaking float needle, float level set too high, or a cracked copper overflow tube inside.  The latter is a bit hard to spot sometimes, they crack along the length beginning at the bottom where it enters the bowl housing.

[Chachi]

Thanks. I'll have the new petcock on this weekend. Looks like that carb overflow tube is continually dripping with bike off/fuel off. Maybe it has been slow-dripping for two days in the garage and that was the cause of the puddle.

[dave500]

special request,fuel lines from the other side.

[Chachi]

Thanks Dave.

[dave500]

if the lines lay against the head once its hot you might get vapour lock as the fuel heats up in the line,make sure they are retained away from the manifolds and head.

[Chachi]

Update... I pet the new petcock assembly on and inspected the tank. The original petcock was pretty rough. The standpipe had about a 1/2" or so broken off the top. The tank looked fairly clean to me. There is definitely some rust, but it visually looked alright and nothing of concern came out at the end of the tank drain.

However, I still seem to have a fuel flow issue and a continually leaking overflow tube on carb #4. I took the float bowl cover off of #4 and it was full of (clean) fuel. Having no experience with this, I put the cover back on and have decided to take to it my mechanic. I have someone relatively close by that is great with these bikes. I wanted to take to him anyway to give the bike a good inspection so this is my excuse to do it. Plus there are a few other things I want him to deal with too. I'll update with the official diagnosis/fix when he's done. I know if I attempt to do anything else it will do more harm than good. For now I turn the fuel valve off a few minutes before I'm home to try and run out any excess fuel in bowl #4 to prevent it from dripping so much.

[grcamna2]

The carbs need looked at.

[Rigid]

Be sure your mechanic is familiar with the unique needs, and failure modes, of the SOHC4.  He may well do more harm than good also.  Most just charge too much, in my opinion.  Maybe he will know a bit about these bikes and actually help.  Keep us posted on what he finds.

[Chachi]

Update...

It's been a month and the bike has received the attention it needed. I picked it up yesterday and I am happy to report that I am back on the road with a great running bike. Quick back-story... I picked up the bike a few months ago and it is my first. It ran pretty good, but then started having some issues that I could not resolve. I took it to my mechanic who did a great job getting it where it needed to be.

Here's a run down of what he did:
-Complete carb rebuild and overhaul (see attached pic of carb parts on work bench)
-Set floats, sync, adjust, etc.
-Repaired fuel leak on #4 overflow tube*
-Fixed oil leak/non-functioning oil pressure light w/new sender unit/oil pressure switch
-Replaced front brake master cylinder
-Replaced drive chain
-Checked/adjusted valves
-New o-ring seals on valve covers
-New plugs
-A few other misc things

*The fuel leak on #4 was interesting. It kept leaking after he replaced the carbs. He went through that process a few more times only for it to keep leaking. He finally found a hairline crack on the tube in the bowl. The fuel level was correct in the bowl and not overflowing through the top of the tube, but it was leaking through the crack. He repaired it with a custom-made tubing cover until I can find a salvage part to replace it with.

There are a few additional things I need to take care of in a few months and I know these bikes are full of constant surprises, but at least I have confidence in what I am currently riding.

[Chachi]

Start/idle/rev after warming it up today.

72 CB500

[grcamna2]

It's always nice to have a fine running engine;that sounds good.