Topic: Fuel Level / Fuel Flow - CB500

[Chachi]

I am having fuel flow issues. I am not done analyzing this, but fuel does not seem to flow properly unless the tank is almost completely full. I went for a simple ride around town and had to push home several blocks as a result of this.

Some details...

-Symptoms: bike won't run, sometimes will not start, and will also cut out at stops
-Switching to reserve does not remedy
-Newly added petcock bowl screen and gasket (screen was not previously in place)
-Inline fuel filters (already in place)

If I fill tank close to full, everything runs fine.

To help me out...

What is the visual indicator of how full I can fill the tank? I am filling from a 5 gallon can at home vs. the pump. And what is the visual indicator of how low the tank can be for it to still run or at least run off reserve? My tank holds 3.7 including reserve.

I would like to use my odometer to monitor fuel level, but right now I am trying to determine if the bike is cutting out because it simply does not have enough fuel or is there something else going on affecting the flow.

[Rigid]

Remove any inline filters and route fuel line/lines so they fall continuously to carb. inlet. The in-tank fuel finger screen or bowl under the petcock are designed to be all the filter you will need.

[dave500]

try draining some out so its half full,then with the cap released see what it does,,the cap vent might be blocked?

[fastbroshi]

I think Rigid's got it.  I had the same problem with my 550.  I hadn't introduced any filters, but I'd put a loop in the line to make it easier to remove the line when necessary.  I'd go through about a gallon of gas when she'd start sputtering and I'd have to go to reserve. 

   As far as visual indicators, I don't think Honda ever specified any.  From dry, you should be able to put in 3.7.  You should have to go on reserve with 1 gallon or .9 gallons left, can't remember for sure. 

[dave500]

yeah the fuel line should only go downwards only with no upward kinks or pinches,if you can help it,ill have my tank off tomorrow so ill post a pic.

[Deltarider]

If you look in the Parts List for your model you'll find the stock dimensions for the fuel lines.
For older 500's it is 18 and 30 cm.
For later 500s it is 17 and 28 cm.
The right length more or less guarantees the right flow.
All have 5,5 mm internal diameter, btw.
Extra inline filters are useless and create problems.
 

[Chachi]

I've read the numerous threads here regarding opinions on inline filters. I will eventually address tank issues and remove inline filters. That said, my flow problem seems to start before the filters. With a FULL tank of gas I get good flow out of both taps, however once I'm a bit lower (3/4, 1/2, ?) I only get good flow out of one tap. The one closest to the front of bike flows and the one toward the back of the bike does not. I'm verifying this with fuel lines off. As soon as I fill the tank up, they both flow. Cap open or reserve doesn't remedy when that one line is not flowing when fuel level drops.

[Rigid]

Only one will flow at any given time.  If you wish to test that theory, block the flowing one and watch as the nonflowing one picks up where it left off.  This is normal and is how the needles are fed in operation. 

[Deltarider]

Onl

y one will flow at any given time.  If you wish to test that theory, block the flowing one and watch as the nonflowing one picks up where it left off.  This is normal and is how the needles are fed in operation.

?

[dave500]

the left bank goes to the forward outlet and the right bank to the rearward one.

[Rigid]

Yes?  one petcock outlet flows some, then the other flows some, I have never seen them flow at the same time.  I know it seems odd but that is normal. Had the same problem with fuel flow awhile back on a 450 and it was the line routing.

[Chachi]

Another detail... With tank full fuel flows: from both taps, through both 1st sections of line, through both inline filters (without 2nd sections of line hooked up), but then hangs up on one line after the 2nd sections of line are hooked up. The line that hangs is from the tap that doesn't flow when tank is less than full.

Is this simply an inline filter/routing issue or is there something else to check/test? I will most likely eventually re-route fuel lines without inline filters, but I want to make sure there is not something else happening down the line on the one that is having the flow issue. I would be more annoyed than I am now if I simply took out the inline filters, cut lines to proper length and hooked up without filters only to find out there is something else down the line causing the flow issue.

Note: I have ordered and will be installing a new petcock assembly to rule that out and as a general upgrade.

[Deltarider]

I have ordered and will be installing a new petcock assembly

What type of petcock? There are at least two different types.

[Chachi]

OEM 16950-300-020. I also ordered new replacement mounting screws and gaskets as they are not part of the assembly.

[TwoTired]

The two outlet taps are fed from the same horizontal source into a log type manifold.  Therefore, the first outlet will get most off the drainage, unless the head pressure is high (full tank), or there is back pressure on the near line (normally from float valve closure, bowl full).

If the buildings are close enough, and are rolling with enough speed, you can jump the space between.  Not enough initial speed, you then fall between the first and second building.   But, if you make the first jump. As, you lose speed you fall off the second building.

The fuel system is a gravity feed system. It makes miniscule physical difference which fuel outlet is attached to which carb pair.

An line filter becomes restrictive as it does its job of trapping particles.  When they trap enough particles, they hinder fuel flow.  So, they must be tested at some frequency for flow capability or replaced on a routine/scheduled maintenance interval.

Cheers,

[Rigid]

"I would be more annoyed than I am now if I simply took out the inline filters, cut lines to proper length and hooked up without filters only to find out there is something else down the line causing the flow issue" 

It escapes me why someone would not take simple, practical, and correct advice, accomplish a simple test of removing the filters and routing the line properly, and then just buy a petcock to replace one that has proven to be functioning properly.  Ideas anyone? 

[TwoTired]

It escapes me why someone would not take simple, practical, and correct advice, accomplish a simple test of removing the filters and routing the line properly, and then just buy a petcock to replace one that has proven to be functioning properly.  Ideas anyone?

Mostly because it is hard for inexperienced or un-knowledgeable people to differentiate between good and bad advise. Certainly this forum has both.

Some just tally the popularity of responses and pick the most popular.  This, of course, is no guarantee for correct action.  But, at least you're in the popular crowd if it's a mistake.  And, if you can win a vote, that's all that matters.

Even lynch mobs got it right sometimes.  But, no one punishes the mob, right or wrong.  We have several "cliques" in this forum.  Speak outside their common doctrines and they persecute mercilessly.  It's more important to be within a popular crowd even in an internet society.

Isn't base human behavior great?      

(not)

[CoachDoc]

"I would be more annoyed than I am now if I simply took out the inline filters, cut lines to proper length and hooked up without filters only to find out there is something else down the line causing the flow issue" 

It escapes me why someone would not take simple, practical, and correct advice, accomplish a simple test of removing the filters and routing the line properly, and then just buy a petcock to replace one that has proven to be functioning properly.  Ideas anyone?

This topic (inline filters/loops in the fuel lines) has been bandied about on this forum before. From my personal experience I can tell you that I have in-line filters and an associated down/up loop in the fuel lines on my 550, and I've done it this way for 35 years with absolutely no problems. Others have posted the same. I agree that in an absolute sense this setup may deliver less fuel per second to the bowls, but in practicality this has never been an issue for me. Back in the 70's I road the 550 across rural Nevada and once spent almost 1/2 hour at 100 mph. Even that extreme situaton did not exceed the fuel demands of my system. The reason I like the inline filters is simply this- I think they do a lot better job of filtration than the petcock screens. No small rust particles clumping up in the bowls, etc.

[Rigid]

"I would be more annoyed than I am now if I simply took out the inline filters, cut lines to proper length and hooked up without filters only to find out there is something else down the line causing the flow issue" 

It escapes me why someone would not take simple, practical, and correct advice, accomplish a simple test of removing the filters and routing the line properly, and then just buy a petcock to replace one that has proven to be functioning properly.  Ideas anyone?

This topic (inline filters/loops in the fuel lines) has been bandied about on this forum before. From my personal experience I can tell you that I have in-line filters and an associated down/up loop in the fuel lines on my 550, and I've done it this way for 35 years with absolutely no problems. Others have posted the same. I agree that in an absolute sense this setup may deliver less fuel per second to the bowls, but in practicality this has never been an issue for me. Back in the 70's I road the 550 across rural Nevada and once spent almost 1/2 hour at 100 mph. Even that extreme situaton did not exceed the fuel demands of my system. The reason I like the inline filters is simply this- I think they do a lot better job of filtration than the petcock screens. No small rust particles clumping up in the bowls, etc.

I certainly agree.  I have bikes that have no problems with filters or line routing.  Others seem to be very sensitive to any restrictions or line routing issues.   I just couldn't understand why someone would not just reroute the lines and remove the filters, if just for experimentations sake. 

[Chachi]

I appreciate everyone's advice. I'm working through and testing various things and my specific question of the moment is: if fuel flows in and out of the inline filter, but essentially stops flowing when the fuel line is connected to the output end of the filter what are some potential culprits? Line routing? Petcock issue? Other things to test/check? This is only happening on one of my lines.

I am working with the filters in place as fuel flow was not an issue when I first got the bike, but now is and they were installed when I got it. I am trying to determine what changed or what is the real cause of the lack of flow in one of my lines. Once I feel confident I have resolved it I will consider a change in my fuel line set up.

Also, when I install my new petcock I will also have a better idea of how dirty my tank actually is. And lastly, how difficult is it to mount new fuel lines to their respective carb connection? I've read it wasn't exactly easy.

[Rigid]

Full float bowl? Stuck needle?  You are going to have to tear into it a bit more to get anything resolved.  If you want to know how bad your tank is inside, a flashlight is your friend.  Maybe drain the tank through a filter and rinse to be sure?  Have you verified the gas cap vent is open and flowing air?  Have you dropped the petcock bowl if you have one?  Maybe inspected the finger screen in the tank?  How about draining the float bowls with the screw at the bottom for that purpose and inspecting the fuel that comes out?  Keep us posted.

[Chachi]

Float bowl drain is on my list. Flow issue doesn't resolve with vent cap open. My next step is check out tank and install new petcock and work down from there. Petcock won't be here until Friday though.

I've read previous threads, but... is the petcock bowl screen sufficient filtration for a mildly rusty tank or are inline filters a worthy idea until tank is properly dealt with?

[TwoTired]

This topic (inline filters/loops in the fuel lines) has been bandied about on this forum before. From my personal experience I can tell you that I have in-line filters and an associated down/up loop in the fuel lines on my 550, and I've done it this way for 35 years with absolutely no problems. Others have posted the same. I agree that in an absolute sense this setup may deliver less fuel per second to the bowls, but in practicality this has never been an issue for me. Back in the 70's I road the 550 across rural Nevada and once spent almost 1/2 hour at 100 mph. Even that extreme situaton did not exceed the fuel demands of my system. The reason I like the inline filters is simply this- I think they do a lot better job of filtration than the petcock screens. No small rust particles clumping up in the bowls, etc.

There IS a science to this.

The down and up loop traps air at the high points in the fuel route.  When there is plenty of gas in the tank, the head pressure is sufficient to move past these trapped bubbles.  It is when the fuel level in the tank gets low and creates low head pressure, that it becomes problematic to fight the reverse pressure created by the air bubbles in the lines with such a low head pressure.  The effect is that you have less usable fuel in the tank, or you run the engine with lower float levels, leaning the engine mixtures.  The significance of the latter depends on how the engine is tuned.  It does matter if it is in stock tune.

You cannot keep bubbles out of the line with these carbs, as each time the float valve opens, air at the top of the float chamber rises into the fuel inlet/lines.  When the fuel line routing does allow the air to rise to the fuel value, it becomes trapped.

In line filters can do "a better job" of filtration.  For a while, anyway.  But, such a level is unnecessary.  You don't need to trap particles smaller than will fit through fuel metering orifices.  Such particles simply travel through the engine and out the exhaust.  Anyway, it is better to keep rust from the tank, than cover it with a band aid.  ALL the stock SOHC4 screens and filters stop particles that can block fuel orifices.

I have yet to find anyone state they replace the filter(s) at some regular intervals or provide a rationale for its replacement/maintenance schedule.

For the non-scientific, I suppose I should add that I haven't used an inline filter on my SOHC4s since 1975 and have never had a carb block from particulates sourced from the fuel tank.  (Gum and varnish formations inside the carb won't be blocked by ANY filter.)
Further, I have been able to keep the engine running with the fuel in the tank running down to only 0.1 gallons left. (Finally found a filling s station.)

As a parallel, I do know people that have successfully jumped off roofs.  I also know some (not all) that got hurt in the process.  Such is life.

Cheers,

[Rigid]

 A dirty tank can plug a very large filter in less than 1 mile.  I have proven that.

[TwoTired]

A dirty tank can plug a very large filter in less than 1 mile.  I have proven that.

Yes, for sure.  And, I forgot to add, that a good stock filter will make added in line filters last much longer. 

I still wonder why only one inline filter is suggested.  Wouldn't three or four more make the fuel even cleaner?   

{jk}