Topic: Do you need an inline fuel filter or is the petcock filter enough?

[ntm1974]

Do you need an inline fuel filter in addition to the filter inside the petcock?  I can't get the bike to run with the inline filter and don't want to get any potential crap in my carbs.

What filter(s) are you guys using?

[Nortstudio]

Many forum members will tell you that you shouldn't need these in line filters, and they are probably right.  Honda didn't include them as a stock part, and that the filter in the tank should do the job perfectly fine on it's own.  Totally makes sense. 

In my situation, the PO had left me with a tank that was nowhere near perfectly clean, and the bike had online filters on it when I got it.  So I replaced them, and plan on doing a clean on the tank as soon as I can.  At that point, hopefully the in line filters will be unnecessary.

Not sure why your filters would not be working.

Mine look like this one - this is what it looked like after a few weeks trapped in a snow bank in Brooklyn!  Ugh!

[ntm1974]

Many forum members will tell you that you shouldn't need these in line filters, and they are probably right.  Honda didn't include them as a stock part, and that the filter in the tank should do the job perfectly fine on it's own.  Totally makes sense. 

In my situation, the PO had left me with a tank that was nowhere near perfectly clean, and the bike had online filters on it when I got it.  So I replaced them, and plan on doing a clean on the tank as soon as I can.  At that point, hopefully the in line filters will be unnecessary.

Not sure why your filters would not be working.

Mine look like this one - this is what it looked like after a few weeks trapped in a snow bank in Brooklyn!  Ugh!

I had the same filter mounted exactly the same way and couldn't get gas to flow.  Took the filter off and the bike runs.  I was thinking that maybe another type of filter could be better.

[Nortstudio]

Not sure, never had an issue with it.  Did you try to start it up, or just didn't see gas flow, so took it off?

[ntm1974]

Not sure, never had an issue with it.  Did you try to start it up, or just didn't see gas flow, so took it off?

I couldn't keep the bike running with it on.  Took it off and I was good to go (not running great yet but at least getting gas.)  I had it mounted about 1 inch past the petcock.  I hooked a funnel to the filter and it worked, but it was in a vertical position with a high flow of gas.  I'm thinking a different designed filter might be better.

[TwoTired]

Do you need an inline fuel filter in addition to the filter inside the petcock? 
What filter(s) are you guys using?

1 - No.
2- The one Honda supplied.  And, I keep the rust out of the tank or get rid of it if I find it there.

If two filters are better, wouldn't six be even better.

Do you wear multiple layers of underwear?  (Just in case a loud one is really wet?) 

Cheers,

[andy750]

What bike?

A 1969 - 1974 (maybe later as well?) CB750 did not have a petcock "sock" filter and relied on a small screen in the petcock. I use an inline filter on both a 72 and 74 CB750 with no issues.

Honda seemed to learn from previous years including an inline fuel filter in the Goldwing and subsequently later bikes. Just because it wasnt there in the original dosent mean its not useful Plenty of gummed up carbs will testify to that.

Andy

[BobbyR]

I honor opinions on both sides of the arguements. If you peek in between my carb 1 &2 you will find an nice bronze filter with a 90 degree inlet. Cheap insurance and I change it yearly. You do have to make sure you have the gas line smoothly bent and always heading down so there is no place for air to collect in the line.

[Gordon]

Do you wear multiple layers of underwear?  (Just in case a loud one is really wet?) 

Cheers,

That's a fantastic idea!  I think you should patent it.  Sort of like those tear-off visor covers that racers use!

[TwoTired]

Honda seemed to learn from previous years including an inline fuel filter in the Goldwing and subsequently later bikes. Just because it wasnt there in the original dosent mean its not useful Plenty of gummed up carbs will testify to that.

Lots of machines have different filter arrangements than the SOHC4.  If you don't know why it was placed where it was, you cannot use it's existence as proof it is beneficial to the SOHC4.  Would you care to describe the Goldwing fuel system for us to understand why it was needed?  Does the Goldwing use more than one filter in the fuel supply?

Filters do NOT block gum formation in the carbs.  They only block particulates.  They only need to block particulates that are larger in size than any fuel orifice inside the carbs.  The small bits just pass right through the fuel system without any harm caused.

But, I like like this testimonial the best. 

I use an inline filter on both a 72 and 74 CB750 with no issues.

Here is an equivalent testimonial.
I've been wearing a hat all my life and I still haven't gone bald.
(And my mother's brothers were ALL bald!)   

Or how about this one?
I've been using synthetic oil in my engine and it still hasn't needed a rebuild.

I still can't understand why two filters are better than 6 or 7 in popularity. Isn't more always better? 

Cheers,

[nomad]

A couple of things...

When I took my petcock out ('74 750), the particulate filter had slipped off of the tube and was floating around in the tank.  Here are my questions...

If it slips off, what good is it?  How do you go about getting it back on without taking everything apart?
If/ when it gets clogged, how do you get to it without (again) taking everything apart?
If you have to run on reserve, how does that filter in the tank help?  It didn't appear by it's design that it filters at all in the "reserve" position.

It seems to me that by using a clear inline filter/ screen and getting rid of the internal screen, you make maintenance easier and it'll be easier to see when it needs to be cleaned or changed.  Any down side other than it not being period correct?  All you'd be doing is moving the filter from inside the tank to outside... plus you'd be able to filter the "reserve" in the process.

[TwoTired]

When I took my petcock out ('74 750), the particulate filter had slipped off of the tube and was floating around in the tank.  Here are my questions...

If it slips off, what good is it?

None, for your oddball case.
However, the stock one does not "slip off".  Your example clearly had some meddling occur to it, and/or you have never seen how a new one has a shoulder in the molding to prevent the assembly from going into the tank.
You may as well ask, "what good is a tire removed from the wheel?"

How do you go about getting it back on without taking everything apart?

It inserts from the petcock side of the tank bung.  One nut gains access and then the same nut goes back on.
I admit surprise that you think this difficult/mysterious.
http://www.cmsnl.com/honda-cb750-four-k4-usa_model482/partslist/F++11.html

If/ when it gets clogged, how do you get to it without (again) taking everything apart?

It rarely gets clogged, as normal fuel sloshing washes it.  If the tank is so bad that sediment builds to two inches in the tank,you've got more than a filter issue.
It is quite easy to get to for your model.  Note: the SOHC4s have at least three different styles of fuel tap filter.

If you have to run on reserve, how does that filter in the tank help?  It didn't appear by it's design that it filters at all in the "reserve" position.

The correct filter for your valve, has a sock over a standpipe  The base of the filter has two exits.  The non tube one is the reserve feed, both filtered.
I'm going to take a wild guess and say someone put a filter from a 77-78 model fuel tap in your tank.   If so, that would explain your floating filter and lack of reserve operation.

It seems to me that by using a clear inline filter/ screen and getting rid of the internal screen, you make maintenance easier and it'll be easier to see when it needs to be cleaned or changed.  Any down side other than it not being period correct?  All you'd be doing is moving the filter from inside the tank to outside... plus you'd be able to filter the "reserve" in the process.

The stock in tank filter needs no maintenance.  It pretty much self cleans until the tank needs an internal cleaning.
An external filter needs regular inspection and replacement as it gets more restrictive with the particles it traps. When it gets restrictive it starves the engine of fuel and can lead to overheating, burned valves, etc. unless you change it on a regular replacement schedule or flow test it regularly.

The proper stock filter for your model, filters all fuel feeding the carbs.  Use the wrong parts and SURPRISE, it doesn't work well.

I do agree if you refuse to use the well working fuel valve filter, you should have a filter somewhere in the fuel supply before feeding the carbs.

Cheers,

[Tretnine]

I run an inline filter. The Honda one should be enough, but oddly, since I started my inline filter I haven't had any stuck float issues. I can see the reasons why right through the nice, clear body.

[benjamin550]

I think an big point here is that if your tank has rust, fix it. Don't mask the problem by adding another filter. Fix the original problem first.

I de-rusted my tank and had a little bit of rust left from flash rusting so I'm going to use an in-line filter for the first few tanks before I open the tank back up and insert to 30 dollar stock honda filter. Its a short term solution to get all the rust OUT of my tank first. We'll see how it works.

[ntm1974]

A couple of things...

When I took my petcock out ('74 750), the particulate filter had slipped off of the tube and was floating around in the tank.  Here are my questions...

\

This blows my mind.  Maybe I am misunderstanding what the petcock fuel filter is.  Is it #9 in this schematic?

http://www.bikebandit.com/houseofmotorcycles/1974-honda-cb750k4/o/m9235#sch398555

The petcock looks the same as my 74 cb350F.  Am I missing something or is there suppose to be another tank filter in addition to the "screen" in the petcock?

[phil71]

I think what is confusing people is the direction of flow. the "on" tube and the reserve pickup (the mounting flange of the fuel cock) reach the diverter holes, and a third hole sends that down through a tube in the center. that tube fills the little bowl which eventually fills up to pass through the screen and to the outlet, which is then split into two. so the little screw on bowl is raw from the tank, and it then passes thru the screen. Which is really pretty fine.. sediment settles to the bottom of the bowl, and when you remove that, you can just dump the debris out, and yes it's true, that screen is pretty much self cleaning because of that design.


*one little "i learned the hard way" tip: if you unscrew your petcock from the tank and mess up the fiber washers, you can't use other washers or o-rings... you wont be able to shut the fuel tap off.

[cookindaddy]

ntm - I have a 78 but my fuel filter is the same neat little screened tower thingy.

Installed correctly it will protect your carbs very well. I initially installed an external filter until I checked out the in tank filter, bought a new one and have had not problems since. And my tank is not perfect (some rust) but the Honda in tank filter stops all that residue from reaching the carbs.

[nomad]

Ok, so here's what I found.  The old petcock I took off looked exactly like the new replacement (still in the box) you see in the picture.  Now, along with the old petcock, I found the tube shaped screen you see in the upper right of the picture.  I thought that was the one and only filter  supplied by Honda.



At that point, I took the bowl off of the new petcock and found part number 9 (as mentioned by ntm1974)... a disk shaped screen.  This disc is obviously the screen that is meant to be used with this petcock (obviously... because it came with it).  At some point in this tank's life, it had the sleeve type of filter to find it's way into it.  This must be why I found it floating around in there.  Maybe the PO lost his original disc or maybe he thought doubling up on the filters would be a good idea.  Regardless, THAT is what confused me.



On a side note, the tube on the new petcock is longer than the original that came out of it... leaving more for reserve.

[cookindaddy]

Completely different on the 77/78.
I don't have a picture, sorry.
There is one filter and it is much bigger.
Perhaps tomorrow I can make a picture of that filter.

[Gaither]

While I agree Two-Tired and others are correct - one "factory" filter is enough, I run a clear, inline filter.
The tank is clean and the "factory" filter is clean and I have 2 new "factory" filters on the shelf.

I realize it isn't necessary. However, it just makes me feel better about fuel filtration. Also, I can quickly look at this clear filter and see what is coming out of the tank. That pleases me and affords me peace of mind.

***The trick is, don't allow this to cause you to install a sag in your fuel line - remember this is gravity flow. A sag in the line WILL cause problems. Without the sag problem, I think this one is just a matter of personal preference - even IF it isn't necessary.

Incidently, without a sag in the line, an inline filter will work in any position. Mine is horizontal.

To each his own?

[Gordon]

While I agree Two-Tired and others are correct - one "factory" filter is enough, I run a clear, inline filter.
The tank is clean and the "factory" filter is clean and I have 2 new "factory" filters on the shelf.

I realize it isn't necessary. However, it just makes me feel better about fuel filtration. Also, I can quickly look at this clear filter and see what is coming out of the tank. That pleases me and affords me peace of mind.

***The trick is, don't allow this to cause you to install a sag in your fuel line - remember this is gravity flow. A sag in the line WILL cause problems. Without the sag problem, I think this one is just a matter of personal preference - even IF it isn't necessary.

Incidently, without a sag in the line, an inline filter will work in any position. Mine is horizontal.

To each his own?

Sagging in the fuel line isn't the problem, it's an upside-down "U" that causes problems by trapping air in the line.  The fuel lines on both of my bikes, with in-line fuel filters, run down below the carbs and then back up to the fuel inlets.  This does not cause any issues because there is no up-down arc to trap air.

[TwoTired]

Now, along with the old petcock, I found the tube shaped screen you see in the upper right of the picture.  I thought that was the one and only filter  supplied by Honda.

I've never seen that type tube filter on any 74 Honda.  The 75-76 and the 77-78 both have a different size filters.

Sagging in the fuel line isn't the problem, it's an upside-down "U" that causes problems by trapping air in the line.  The fuel lines on both of my bikes, with in-line fuel filters, run down below the carbs and then back up to the fuel inlets.  This does not cause any issues because there is no up-down arc to trap air.

I'm not sure why your long loop isn't giving a problem.  Perhaps it's because you don't run the tank very low on fuel?  The higher the fuel level in the tank, the more "head pressure" is developed.  Bubbles in the line, counters the head pressure, which is the weight of the column of fuel above the exit orifice on top of the fuel valve.

There is no way to prevent air from entering the fuel line.   The top pf the carb bowl is where the float valve lives.  There is fuel on one side and air on the other.   Open the valve and they exchange material, putting fuel in the bowls and air into the lines where they will collect at any high points in the connection between fuel tap and carbs.

I'm glad you have noticed a problem, but, if you ever want to use all of the fuel in the tank, I suspect you will.

Cheers,

[Gordon]

I'm not sure why your long loop isn't giving a problem.  Perhaps it's because you don't run the tank very low on fuel?  The higher the fuel level in the tank, the more "head pressure" is developed.  Bubbles in the line, counters the head pressure, which is the weight of the column of fuel above the exit orifice on top of the fuel valve.

There is no way to prevent air from entering the fuel line.   The top pf the carb bowl is where the float valve lives.  There is fuel on one side and air on the other.   Open the valve and they exchange material, putting fuel in the bowls and air into the lines where they will collect at any high points in the connection between fuel tap and carbs.

I'm glad you have noticed a problem, but, if you ever want to use all of the fuel in the tank, I suspect you will.

Cheers,

I routinely run my tanks to reserve, and then another 20+ miles on reserve.  Occasionally sputtering into the gas station with only a tiny amount of gas left to slosh around in the bottom of the tank.  The way my lines are run, and the fact that these are gravity-fed systems which are open at both ends means the only fuel left that I can't easily access is the amount trapped in the few inches of line that runs below the level of the inlets.

[TwoTired]

I routinely run my tanks to reserve, and then another 20+ miles on reserve.  Occasionally sputtering into the gas station with only a tiny amount of gas left to slosh around in the bottom of the tank.  The way my lines are run, and the fact that these are gravity-fed systems which are open at both ends means the only fuel left that I can't easily access is the amount trapped in the few inches of line that runs below the level of the inlets.

If you don't mind, could you tell us your tank capacity and the most fuel you ever put in the tank?

I once drove my Cb550 F on reserve a really long way 45 minutes on a very slow winding road, sloshing the fuel over the saddle to keep the carbs filled.  Still running when I pulled in, the tank holds 4.2 gallons and I put in 4.1 to the brim.  Thought I was going to have to walk that day.  I'd never run the level down that low, before or since.
This bike:

[Gordon]

I routinely run my tanks to reserve, and then another 20+ miles on reserve.  Occasionally sputtering into the gas station with only a tiny amount of gas left to slosh around in the bottom of the tank.  The way my lines are run, and the fact that these are gravity-fed systems which are open at both ends means the only fuel left that I can't easily access is the amount trapped in the few inches of line that runs below the level of the inlets.

If you don't mind, could you tell us your tank capacity and the most fuel you ever put in the tank?

Sorry, I only take note of the amount long enough to do a quick mental calculation of the fuel mileage, and then it's promptly forgotten.  On the 750, which has a 4.5 gallon tank, I normally put in less than 4 gallons, but I know it's gone over 4 several times.  The times I've rolled in on fumes, there's not even enough left to slosh around in the bottom.