Topic: Inline fuel filter versus cleaning/replacing petcock filter?

[AndyEmmDee]

Hi All

I have a (new to me) 1972 CB500 that I'm currently working on - I bought it last week and immediately got to work on cleaning the carbs since the bike didn't idle, but would run if you got it started and kept the throttle revving (indicated dirty pilot jets to me).

So while I'm waiting on parts and I have the carbs off the bike, I'm trying to think ahead and do what I can now to prevent having to rip the carbs apart every 6 months/year after they get gunked up.  I've found some sand-like substance in the carbs so far that seems to clean off relatively easily, but I think I could prevent having to do that if I were to install some type of filter (I've ordered new 5.5mm fuel lines to replace the old ones on there).

I've read a bit on this forum and elsewhere that inline fuel filters can be a problem for some, in that unless the tank is full, you won't have enough gravity/pressure on the fuel lines to push through the filter and feed enough gas to the carbs.  In some cases, I've read of bikes cutting off after 1-ish gallon of fuel is burned.  I don't want to be left stranded somewhere like that, but I don't want to have to clean my carbs very often either.

If I decide not to install the inline fuel filter, how do I go about replacing or cleaning the petcock filter (aka petcock screen, aka tank filter? or are those different things)?  I haven't found any good resources or guides on disassembling the petcock and cleaning that filter, and I'm a bit new to wrenching, at least enough that I wouldn't want to go in blind.

Can anyone provide advice one way or the other - either make a case for or against inline fuel filter - or otherwise provide a guide on how to remove/replace/clean the stock petcock filter?

[markreimer]

I originally used in line filters on my 74 750. I had the fuel starvation issue at times but it was more so related to fuel line routing I think. That said, I've since stopped using the filters for the last couple years and have had no issues. It helps that my tank is pristine.


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[540nova]

I run inline filters. They're cheap insurance, and have not given me any starvation problems.


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[carnivorous chicken]

I run inline filters. They're cheap insurance, and have not given me any starvation problems.


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Second that. It's one of those hot button things though, someone may just come along and rant against them...

[drumstyx]

I'd run an in line filter even if my tank was pristine...It's just cheap insurance. If you're having flow issues (never have, and I run them on plenty of bikes) either reroute or use a higher flow (more expensive) mesh filter.

[jonda500]

The stock 500 petcock screen is easy peasy to clean (it doesn't have the sock filter in the tank that later models have).
Actually when you unscrew the sediment bowl you'll probably find the screen doesn't need cleaning, just clean the sediment out of the bottom of the bowl and screw it back on, not too tight! The holes in the screen are smaller than any of the holes in the carbs, but if you're really worried you can also drain the 4 carb float bowls to flush out any fine sediment that's collected in there. -yes I am one of those ppl who have had problems with inline filters, such as very hard re-starting after switching to reserve when I've let it run dry...
John

[Stev-o]

If you're getting crap in your carbs you should clean your tank.

Best way to keep your carbs from gumming up is to ride your bike at least monthly.
Might not be possible in NC?

[flybox1]

My 750s intank filter was gone long ago.
No issues keeping the flow downhill with this type.

[Deltarider]

I've had nothing but bad experiences with inline filters. This was decades ago. The worst was that sometimes for weeks there was no problem and then out of the blue problems occurred. That drove me insane because by that time I had completely forgotten about the filters. Here's my solution. Make sure you have the filter the bike came with. Anything thas passes that filter can't be a problem and an extra filter adds nothing. A mechanic that owned a CB500 himself learned me to every three months drain the floatchambers and pour the fuel back in the tank. And - most important - have the fuellines at standard length: 18 and 30 cm for the CB500 models with the old type petcock and 17 and 28 cm for the newer type petcock. This with a standard ⌀ of 5,5 mm and you'll have no chance of any kinks.
I wonder how people that run inlinefilters and say they've no problem can be sure about the fuellevel in their floatchambers. Goodness knows how long back then I had been riding too lean before the problem became manifest. Why risk it?

[markreimer]

My 750s intank filter was gone long ago.
No issues keeping the flow downhill with this type.

Hey now those are cool and would be perfect when using the stock hose routing on my 74 750 where the lines go through the carb mounting plate. There's really no room for the regular inline filters without causing a kink.


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[flybox1]

 "Visu-Filter 90deg"  Yeah...they fit in there nicely w minimal fuel line.  I've maybe got 7" of fuel line total.

@Delta....I should perform a test next time i have my tank off.
Fuel flow through out the tank vs flow out the tank and through the filter...over 1 min.
(pour the gas back into the tank to keep things as equal as possible)
If the difference is negligible....

[Deltarider]

@Delta....I should perform a test next time i have my tank off.
Fuel flow through out the tank vs flow out the tank and through the filter...over 1 min.
(pour the gas back into the tank to keep things as equal as possible)

Good initiative. Should be measured by collecting fuel over the drain openings in the floatbowl.
The problem I had (during a vacation) was that everything worked fine for maybe a fortnight and then - maybe beacause fuellines and filters had moved a bit unnoticed - I had problems. It doesn't take much to disturb fuelflow on a CB500/550.

[flybox1]

Fuel flow through the carb passages is restricted before it gets to the bowls, regardless of where the source gas comes from.
Test should be done at the petcock outlet and again at the filter outlet......just my thought 
If wide open filtered tank flow is at equal to wide open tank flow, then the issue with bowl level only arises when sustained demand is greater than the flow rate of a less than clean filter.

[Don R]

 I'm on both sides of this story, my brother ran his fuel lines below the carbs then through a big filter and back up to the bottom of the carb inlet. He has done it this way since getting his K4 new and never had a problem.
 I ran filters on my F1 and had starvation problems on the Honda sohc world tour, Once in the winter I pulled the fuel line to drain gas into my snow blower and nothing would pass the filter. I could blow air into the gas tank through the hose but fuel would not drain out. Figure that one out.  My sandcast 750 died in the country last fall and I blew into the gas tank, after doing so I could see fuel moving through the clear filters. It took doing that twice to get home, so I removed them and have had no trouble since.
 The K1 I'm doing now had the tank flushed but it got some grit inside, maybe at the paint shop. The grit goes past the screen and petcock and settles in the float bowls. I flushed the tank through coffee filters in a funnel until it ran clean.
 The moral of the story is, if you run filters consider carrying a spare. I think the filter problems have something to do with fuel additives like ethanol and condensing moisture forming a gel.

[Don R]

 I did a poll last fall, lets see if I can find it.

[BobbyR]

I have used the exact setup on my K8 no issues. If you have straight downhill runs as shown you have no problems. When you get creative, things go wrong

[Don R]

 I have run the lines with filters down and back up like my brothers bike and downhill all the way. Didn't matter still had problems both ways. I used the big and small filters, paper and bronze.
 A strong ring magnet glued or tied to the bottom of the petcock bowl may catch more grit if it's rust related.

[carnivorous chicken]

A mechanic that owned a CB500 himself learned me to every three months drain the floatchambers and pour the fuel back in the tank.
I wonder how people that run inlinefilters and say they've no problem can be sure about the fuellevel in their floatchambers.

Delta, I know we're on different sides on this one -- I have been running inline fuel filters for 20+ years and had a fuel flow issue once -- when the filter did its job and prevented sediment getting to the carbs. Changed the filter -- easier than dropping a 2 or 3 bowl -- and I was back on the road.

But I'm curious -- why would you drain the float bowls and pour it back into the tank, presumably with any and all sediment that may have found it's way there? Why not just dump the 60oz of sediment-enhanced gas? That I just don't get.

I'm sure about the fuel level in my bowls because my bike runs great through the power band, doesn't run hot, and my plugs look how they're supposed to.

Again for the OP -- personal choice, some people run em, some don't, but as others have said a perfectly clean tank, lined if need be, is the first step. 

[Lostboy Steve]

My 750s intank filter was gone long ago.
No issues keeping the flow downhill with this type.

Hey now those are cool and would be perfect when using the stock hose routing on my 74 750 where the lines go through the carb mounting plate. There's really no room for the regular inline filters without causing a kink.


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I use the same style filter and after a few years and many miles my bowls looked great even with a questionable tank.


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[jonda500]

A mechanic that owned a CB500 himself learned me to every three months drain the floatchambers and pour the fuel back in the tank.
I wonder how people that run inlinefilters and say they've no problem can be sure about the fuellevel in their floatchambers.

But I'm curious -- why would you drain the float bowls and pour it back into the tank, presumably with any and all sediment that may have found it's way there? Why not just dump the 60oz of sediment-enhanced gas? That I just don't get.

If it's just sediment or water it's easy to carefully pour most of the fuel off the top and back in the tank, then discard the last little bit with the debris in it. If there's floating debris simply skim it off the top first. If I found crap suspended in the fuel I would absolutely dump it all, but it just hasn't ever happened...
John

[Deltarider]

If it's just sediment or water it's easy to carefully pour most of the fuel off the top and back in the tank, then discard the last little bit with the debris in it. If there's floating debris simply skim it off the top first. If I found crap suspended in the fuel I would absolutely dump it all, but it just hasn't ever happened...

Same here. If you do it say every three months, it's not likely you'll find much anyway. Most times I find nothing  at all and that's with the standard petcock fuelfilter only.

[Lostboy Steve]

A mechanic that owned a CB500 himself learned me to every three months drain the floatchambers and pour the fuel back in the tank.
I wonder how people that run inlinefilters and say they've no problem can be sure about the fuellevel in their floatchambers.

But I'm curious -- why would you drain the float bowls and pour it back into the tank, presumably with any and all sediment that may have found it's way there? Why not just dump the 60oz of sediment-enhanced gas? That I just don't get.

If it's just sediment or water it's easy to carefully pour most of the fuel off the top and back in the tank, then discard the last little bit with the debris in it. If there's floating debris simply skim it off the top first. If I found crap suspended in the fuel I would absolutely dump it all, but it just hasn't ever happened...
John

To each their own, I must say that is very frugal of you though.


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[Dunk]

The tank on my K5 is full of crap, like it was glass beaded inside and not cleaned out before paint. I did what I could with some diesel and a long scrub brush but don't want to screw up the decent paint on it. After maybe the 4th time cleaning crap out of the carbs I put an inline filter on and haven't had an issue since then with the slow jets plugging and very minimal stuff in the bowls when I pulled them last.

My K1 has a new repop tank and I only use the factory screen mesh filter in the petcock, never had a problem.

On previous bikes I've only run inline filters when I've had issues with chronic junk in the carbs, never had issues with fuel flow but I try to keep the line as short as possible and generally headed downhill or level.

[janne_83]

I’ve been reading about issues with fuel filters; that the the flow doesn’t work properly. I bought my first filter and would like to know opinions; should I except a normal flow with this type of filter? The strainer material itself is, I think, nylon.

[jonda500]

except a normal flow with this type of filter 100% of the time is not 100% guaranteed - after running dry a mysterious err vapourlock? or something can prevent fuel flowing - it happened to the yamaha I used to own more than just once or twice!
John