Topic: Fuel Hose Strategy

[Rosinante]

This is not the dumbest question you guys have seen, but it is the most recent:  How do you route the fuel line between the tank at the carbs?  Also, if anyone knows, what numbers do I use to ask for a length of new hose?  Metric, certainly.  What size?

Currently, my hose leaves the tank and heads fairly quickly down toward the fuel nipple on the carbs.  Most of the way down, I have installed a small fuel filter.  The hose slides onto the carb nipple much easier than it slides onto the fuel petcock, so I usually disconnect at the carbs.  It is not perfectly easy to get the hose back onto the carb nipple.

Do you guys use a small inline filter like I installed?  Where do you disconnect, when removing the tank?  How long is the hose?  Is your hose longer than mine?  (Now THERE'S a loaded question)  Will a slightly longer hose work better?  (Loaded question follow-up, for your comical response)

[robvangulik]

Inline filters only hamper fuel flow. There should be a perfectly adequate filter on the petcock.
And a too long hose makes fuel flow uphill, and that doesn't work.

[DaveBarbier]

No inline fuel filter. If your intank filter is in good shape you don’t need another filter. But before any physics majors chime in about fluid dynamics, fuel of course does flow uphill if there’s a column above it. But when you’re really low on fuel and you have an extra inline fuel filter and a relatively long uphill route it might not flow as fast as the carbs need. Especially if there’s an air bubble trapped in the bend.

Doing one little uphill loop is totally fine but I believe with the proper fuel line and routing you don’t need to.

The fuel line you want to use is Honda’s fuel line in 5.5mm. As far as length, I don’t know. Buy a foot and cut it to length. Or if you want clear go with Yellow Tygon in...I think it’s 3/16” diameter which is a little smaller but will still work. I will say that McMaster Carr warns that the fuel rated yellow tygon is NOT compatible with ethanol for extended use.

On my 550 I release the tank from the rear rubber holder and sit it on top of said rubber holder. Then I put a rag under the petcock and reach in and pull the line off the petcock nipple. Then the tank is free.

[evinrude7]

find the most direct route from tank to carbs, going downhill as much as possible.  5.5 mm honda fuel line. 

[Bodi]

Fuel filters are fine. They do not impede fuel flow unless very bad design or clogged... and if one gets clogged, it was doing a good job and there was enough crud in your fuel to warrant its use.
Tube routing is not critical. Fuel flows "uphill" just great if the outlet and all tubing is below the liquid's level. You can loop the fuel line around the engine 10 times... as long as no loop goes above the tank fuel level, fuel will happily flow through the tube and fill the carb bowls.
Air bubbles do not stop flow, they just float in the fuel. There isn't enough flow to a SOHC4 to push them down and through but fuel will gladly flow around them.
These are not 500ci blown top fuel dragster engines using gallons of fuel per second. Although you can restrict flow enough to cause leanout due to the very low fuel "pressure" from gravity feed at a few inches head, it isn't so easy that a clean paper or sintered inline filter will do it.

[Rosinante]

Thanks to all!  By the way, I recently drained old fuel out of this tank and used a timer.  With the fuel filter in place, it took around ten minutes to drain a gallon.  So....flow volume through the inline filter was plenty sufficient for this engine's needs.

[Maraakate]

Fuel filters are fine. They do not impede fuel flow unless very bad design or clogged... and if one gets clogged, it was doing a good job and there was enough crud in your fuel to warrant its use.
Tube routing is not critical. Fuel flows "uphill" just great if the outlet and all tubing is below the liquid's level. You can loop the fuel line around the engine 10 times... as long as no loop goes above the tank fuel level, fuel will happily flow through the tube and fill the carb bowls.
Air bubbles do not stop flow, they just float in the fuel. There isn't enough flow to a SOHC4 to push them down and through but fuel will gladly flow around them.
These are not 500ci blown top fuel dragster engines using gallons of fuel per second. Although you can restrict flow enough to cause leanout due to the very low fuel "pressure" from gravity feed at a few inches head, it isn't so easy that a paper or sintered inline filter will do it.

I have a fuel filter and running 1/4" fuel line on my bike and things have been just fine.

[Don R]

 I've  mentioned before I had a fuel filter that would not flow, I could blow air through it into the tank but fuel would not come back out. I believe there was a gel caused by moisture and alcohol.
 On the other hand, my brother bought a new 750 k4 and always ran his fuel line down to the starter cover, through a filter and back up to the downturned fuel tee. The bend was at the bottom and air could go up either way. He rode it for over 30 years like that.  Same with his 1100 yamaha. Stock also works awesome, probably best.

[70CB750]

All you need for filtering is the petcock sediment bowl.

Fuel line should not go up the hill, route it accordingly.

[Bodi]

"All you need for filtering is the petcock sediment bowl."

Change that to "all I need" and it gets a bit closer to truth. Explain why so many float valve leak issues go away with an inline filter. I do not care whether or not you like them. Stop preaching nonsense. BTW: the bowl is not the primary stock filter, and is there to separate water not catch dirt.

"Fuel line should not go up the hill, route it accordingly."

Pure bullsh!t. As well as being near impossible. Get real.

[70CB750]

"All you need for filtering is the petcock sediment bowl."

Change that to "all I need" and it gets a bit closer to truth. Explain why so many float valve leak issues go away with an inline filter. I do not care whether or not you like them. Stop preaching nonsense. BTW: the bowl is not the primary stock filter, and is there to separate water not catch dirt.

"Fuel line should not go up the hill, route it accordingly."

Pure bullsh!t. As well as being near impossible. Get real.

Whatever 

Inline filter was never supposed to fix float valve leaks, but it it works for you, my congratulations, Mr. MacGyver.  If I were you, I would fix float valves to get rid of leaks instead of depending on inline filter but I do things my way.

Fuel tank is above carburetors and that means that you can indeed lead a fuel line down the hill to deliver the fuel.

I am not sure what your problem is but what I posted works for me and for many others.  Maybe spend more time wrenching and less time attacking people? 

[Bodi]

Maybe spend more time on facts.
Tiny bits of dirt will stick in perfect float valves and let them drip - not a problem for those of us who close the petcock but still undesirable. The tank screen has a fairly large mesh that does not stop small particles: a paper or sintered filter will.
Obviously the tank is above the carbs. But every fuel line I've seen goes down then up to the carb stack fuel inlet(s).

I stick to facts and experience, not rumours and made up stories. I'm not perfect and I've learned from more mistakes than I can remember.

Stuff your "MacGyver" BS where the sun doesn't shine.

Honda has made plenty of engineering and design mistakes - maybe you recall the battery vent that dissolved chains? The rocker shafts that wear out? Car engines that destroyed themselves every 50k miles due to bad head design? There are lots of others.
There is no intelligence in believing that Honda somehow made perfect motorcycles and any modification is sacrilegious.
Improving machinery is a hallmark of invention.

I will not be bothering to continue this pointless conversation. Enjoy your ignorance.

[Scott S]

 Bodi, is the attitude really necessary? You could have relayed everything you said without the attitude.

 The mesh in the stock filter(s) is XXX microns (can't remember the exact size) and is smaller than any orifice in the jets and carbs. A clean fuel system and properly set up stock fuel line, filter and hoses has never been an issue for me.

[70CB750]

 

[Rosinante]

FWIW, I once had a carb leaking fuel down the overflow hose and onto the street.  The bike was a CB750K5.  I saw the fuel on the road one morning while visiting a friend in Portland.  Upon further examination, I discovered a hard black thing, like a small rock or something, inside the fuel rail, resting against the top of the float valve pin, holding it open.  Upon further examination, I noticed the petcock screen was intact and FAR, FAR too small to pass an object of this size.  I do not think that little black rock thingie got through the screen.  My best guess, then and now, is that the inside of the rubber fuel hose petrified and sluffed off, and got into the fuel rail.  I replaced that section of hose and never had that problem again.  Periodic replacement of that hose might make some sense.

My float car float bowls have a drain hose at the very bottom, and a screw which opens that valve.  The hose then drains to the ground in front of the swing arm.  Emptying a float bowl is as simple as opening the valve with a screwdriver.  If a clear hose is installed there, and if the other end of that hose is lifted above the float bowl, and then the valve is opened, the clear hose will show the float level!  This is an example of fuel flowing uphill.  If the clear hose were allowed to go downward six feet, then back up to above the level of the float bowl, the hose would still show the float level (after the float valve had time to pass enough fuel to fill that long length of hose.  I think fuel, flowing through a hose of virtually any length, would get from the tank to the carbs as long as the hose remained completely below the tank.  I think the stories we heard in this thread support that.

I also think insults and personal attacks do little to change physics.  They change peoples' degree of credibility and apparent maturity or lack thereof.  But they do not add to the technical discussion.  Take deep breaths.  Go for a walk.  Focus on the technical discussion. 

[70CB750]

Rosinante:

I am not sure if you know that the search on SOHC4 does not work.  I usually use Google and look for results from here.  Anyway, here is a discussion on fuel routing by people who know more than myself:

http://forums.sohc4.net/index.php?topic=178369.0

I buy Tygon line either on ebay or at the local hardware store, I have always several feet of different sizes in my shop, it comes handy.  With Tygon, there is no need for clamps.  Dorothy (K0) and Red before swapping carbs for PD was easy - two lines from the petcock, one went down and through the hole to the T and the other on top of air insulators to the T between 1 and 2 carb. 

After I went with PDs I combined petcock lines via some soldered copper tubing and from it it goes to between 1 and 2 - Red has K3 tank, but 78F engine and carb - petcock on the right and carb input between 1 and 2.

The 900 had vacuum operated valve - aka the spawn of satan  - and I ditched it after she left me stranded on the road.  The line is just short Tygon S, no science to it.   I used fuel filters long time ago but it was nothing but trouble so I stopped using them and never looked back, also never had any troubles from using only the petcock sediment bowl for filtering.  Most of the time I fill with ethanol free gas - see my signature - and I am pretty sure that helps too.

As always, this is nothing more than my $0.02

[Rosinante]

Thank you.  Some of the best advice I get is "Jim, you are over-thinking this.  Again."

The '78 has the petcock on the left side, quite close to the input nipple between 1 and 2.  Routing on this bike is already pretty simple.  There are no T-fittings.  Just one hose from petcock to a single nipple.  About six inches.  The petcock on my bike has no sediment bowl.

The brain trust here suggested 5.5mm Honda hose, so I got some.  I assume this is ID.  Have not installed yet.  You and others suggest Tygon.  The clear yellow stuff, I think.  But does this come in metric sizes?  If so, am I looking for 5.5mm still?  If not, then what size?  5.5mm comes out to about 7/32, which I do not expect to find.  And finally, is there a retailer which would have it?  Or is Internet my best bet?

[Scott S]

 I, personally, am not a fan of the Tygon. It looks cool and you can see thought it to check fuel flow, debris, etc., but it's ALWAYS hardened and discolored over time on my bikes.

 I use 5.5mm line from 4into1.com or eBay. By it by the foot. It's cheap and when you add it to a larger order, you can get enough to do 4 or 5 bikes. I've used it on other makes and models as well. The 5.5mm I.D. works like a Chinese finger trap and actually tightens up when you slip it on and when you pull on it. I rarely even use the little wire "hose clips".

[Stev-o]

I use 3/16 from the local auto store, cheap and always available.  No clamps needed.

Dont overthink it.

[Rosinante]