Inline fuel filter purpose

[carpe_diem]

When I got my bike serviced, the mechanic added an online fuel filter between the petcock and the carb. Now I get the idea behind them - if there's any crap in my tank or the petrol, the filter will catch it before it fouls up my carb - but is it really worth having? It doesn't look like any rust or gunk has appeared in my tank and given it costs me about 8 ponds to fill my tank I use the premium petrol, so I can't see where the need to filter would come from.

This isn't me moaning, by the way. It cost me £3.24, which I don't begrudge paying at all. I just wondered if anyone had an opinion on whether they're worthwhile, as a quick Google has turned up very little and I have m4d r35p3c y0 for the BCF hive mind.
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Currently riding: Suzuki EN125 | Previous rides: Vespa 125PX, Yamaha SR125

[-]

Yes. Tank filters are crap and I've seen a few almost melt recently on 80's bikes, could be ethanol, who knows?
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TZR250 2MA road, TZR250 1KT road, TZR250 2MA race, TDR250, YZF-750R Boost colours.
Jaguar S Type 3.0 V6 Sport R, VW Transporter T5 GP LWB Shuttle 140ps DSG.

[Banana_B1]

Apparently' they slow the rate of fuel feed to the carb, although it's nice to have a transparent filter for knowing when it's dirty + easier to clean w/o draining fuel off and removing petcock from the tank. If i used an in-line filter id be tempted to remove the petcock's filter in order to counteract fuel starvation but i'm no expert.


Teflon-Mike may enlighten us here with a wall of scientific text
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The entire Butthurt BCF wrote: Spam Flame Abusive Redundant Off Topic Boring Disagree Confusing

[Kickstart]

Hi

If under specced they will slow down the fuel flow, and possibly enough to become critical.

I wouldn't expect any difference in the amount of rubbish in the fuel between cheap fuel and premium fuel; indeed a busy supermarket will probably go through enough fuel to minimise how long it stands in the tank.

A cheap filter is cheap insurance for rubbish in the petrol.

All the best

Katy
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[MCN]

Shit gathers under and around the filler cap. Every time you open the cap you introduce some (tiny amount) crap into the tank. It will be this stuff a filter will catch if it's big enough or if the filter media is absorbent and attracts that sort of stuff.
When you service you can replace or wash out the filter.

If it doesn't affect fueling when new but it does later then it may be blocked.
'Some' paper element types can swell if water is present too.
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Disclaimer: The comments above may be predicted text and not necessarily the opinion of MCN.

[carpe_diem]

Thanks everyone, very helpful stuff and given to all.

Lets hope my bike doesn't go on fire. While it would no doubt help with visibility (as an L-plater on a 125 I am obviously invisible) I don't really relish the idea of doing a full-on Ghost Rider down Lara Croft Way.
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Currently riding: Suzuki EN125 | Previous rides: Vespa 125PX, Yamaha SR125

[WD Forte]

I reckon the flow restriction is a bit of a red herring unless it's a really bad quality filter, become clogged and/or you have a gas guzzling monster bike.
On a frugal 125 you could probably strain it through an old sock and not know the difference.
Your mechanic did the right thing IMO
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bikers smell of wee

[-]

On my 250 twins, I fit one for each carb, after the t section splitter on the fuel hose. Some who fitted just one before the T section of fuel pipe could suffer starvation at times.

They were ridden throttle to the stop almost everywhere though on race bikes.
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TZR250 2MA road, TZR250 1KT road, TZR250 2MA race, TDR250, YZF-750R Boost colours.
Jaguar S Type 3.0 V6 Sport R, VW Transporter T5 GP LWB Shuttle 140ps DSG.

[Jewlio Rides Again LLB]

Amal do good quality filters
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[Alpineandy]

I'd like to say that they don't make filters that are crap enough to effect a 125 but they probably do now in china...
Really any decent filter won't affect the flow and can only be a benefit. The grade of fuel is irrelevant to how much crap is in it.
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[Triton Thrasher]

[nitrosurf]

Unless it's a high pressure fuel injection system shouldn't the fuel that fills up the filter housing maintain enough pressure in the lines so as to not cause starvation? There's a constant flow of fuel out of the filter as it's constantly being filled up, so the carb is getting the same amount of gravity fed fuel as before? Unless as stated by others the filter becomes blocked and stops allowing fuel past...

🏍
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"Multiple exclamation marks," he went on, shaking his head, "are a sure sign of a diseased mind."

[Rogerborg]

[carpe_diem]

[Alpineandy]

[Alpineandy]

[RhynoCZ]

[MCN]

Even though they were designed to not have filters doesn't make that right.

They were possibly made to cost constraint.
The designer forgot to add a filter.

Etc.

I would suggest some sort of filter would be better than no filter.

Mostly, a filter is fitted to match the design of the device it is protecting.
So if the part can handle 20 micron particles without detriment then nothing better/closer than a 20 micron filter would be required.

Even with a matched filter in place you may still have to consider restriction to flow and 'settlement of detritus' after the filter.

Some designs use a deflectors/centrifugal intervention to slow the rate of flow and cause/allow 'stuff' to fall out of the stream into a collection space. (maintenance area).

Filtration can be complex and a bit like trying to understanding a women.
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Disclaimer: The comments above may be predicted text and not necessarily the opinion of MCN.

[Piercee100]

I fitted an inline filter after breaking down in the Blackwall tunnel one day. 30+yrs worth of crap in the tank of an H100 was a nighmare to try and remove.
Be warned though, first filter was a clear plastic one (cd case type plastic) and melted one day for no reason. As someone suggested it may have been modern chemically fuel. Replacement is the softer dvd type plastic and has been fine for 3 years now.

Does have the advantage that seeing the fuel flow, helps diagnose problems too
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Rides: Honda H100a (Retired), VT500e (Sold), Kawasaki ZX400 (sold), Kawasaki GT550 (Sold), Suzuki Inazuma (Daily), Honda CD185t (Broken), LML Star 2t (Last run edition).

[Kickstart]

[MCN]

I replaced the fuel filter under my car last year.
2.0 BMW (Devil's fuel)

I usually cut filters open because it allows you to see wot's wot (and I'm anal)

The black colour is the up-stream side the light colour is the down-stream side.

This car has used Supermarket/Branded fuel at all times.

The black is most probably microscopic 'dirt' particles not refined out by the fuel refiner. Or maybe bacterial life which lives in water and eats the carbohydrate. There are Biocides available to deal with that.

For a Diesel (and petrol) this can be a problem if it has very close fitting parts as some of this stuff is abrasive (from deep in the Earth) and can wear out pumps and injectors over time.

Even Natural/Landfill Gas powered engines need sophisticated filtration to remove silica which can bake onto surfaces in the combustion space.
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Disclaimer: The comments above may be predicted text and not necessarily the opinion of MCN.

[Teflon-Mike]

Principle is good... Practice tends to be less wonderful.

When I started out in trials; adding an inline filter was a top tip I was offered; filling in the field from gerry-cans, it did make sense.

In practice; in-line filters have, over the years, given me far more grief than they have ever 'saved'; there's usually a nylon strainer on the tank petcock anyway; and often another either in the union on the carb or above the float needle.

On the old clunkers; if the tank is in such state it's regularly dragging crap down the lines to clog jets; it'll clog an inline filter quick enough too; solution is to get the crap out the tank before you start; hence I'm such a fan of POR15 treatments done 'properly'.

On the dirt-bikes? Advent of the internet has revealed some issues with 'rotten' tanks as they have got older; but then Montesa were quite quick to fit GRP tanks to thier bikes, so many accounts seem to be due to natural age delamination, or running mentholated fuel; either modern 'pump' E5 or US E10, or straight ethanol, or home blended....

Poss. Interesting asside; cota's user manual, actually offers suggested recipes for making 'Petroil' pre-mix! Basically 3% two-stroke to pump petrol, but gives alternative suggestions for using 'straight' vegetable oil and using washing up liquid to make it emulsify! and that's in the factory user book! Badger may offer more insights on the topic as resident Meth-sniffer; but the old Castrol-R, was actually a vegetable based castor oil, and didn't mix well with oil-based petrols, I'm told; hence many folk in the classics would use various recipes of mineral petrol and ethanol or meths, with vegetable oil and deturgent, to make it mix and get the octane rating to suit thier motor; and not just for two-strokes!

However; alchohol kills glass resin; and Montesa used GRP tanks... except in the UK whee C&U regs begged they cut the bottoms out and used the GRP seat/tank unit as no more than a cover for an alloy tank... so my bike is saved the issue of GRP de-lam or Longbridge tinworm!

Do benefit from using a strainer-funnel when jerry filling though; but from the pumps? Volume they pump every day? Filters the regs demand they have between tanks and pump? Liklihood you will get any significant crud in the tank from the forecoart aught be pretty slim... but of worried about it, a strainer funnel to catch it at source is still probably more use than an inline filter, that wont stop the motor conking if it clogs, just save having to strip the carbs to clean it out!

So best case, in-line filters are of dubiouse benefit to my mind, these days, even 'dirty filling' off-roaders.

On road bikes, they have frequently given me hassle; more so on multi's where they may have the flow capacity, but they dont have the 'peak' flow capacity when four carbs all want thier float bowls topped up. Small gravity feed 'head'; and short route to carbs, often makes placement to avoid air-lock or back-siphoning awkward.

So on the whole, generally made more problems than they have ever solved or prevented.

Occasionally useful to see fuel flow when fault-finding; but a clear piece of winscreen washer pipe is better.

Only inline filter I have NOT had any hassle with is, as Jewlio mentions, is a small, genuine Amal, glass-bowl, inline filter, on the Cota, that does seem to 'work'.

Plastic ones, I have never had much joy with, and the larger-ones that suggest greater flow capacity, often been the ones that have given most grief; for unobviouse reasons, but problems went away when removed, so 'something' didn't work.

IF the bikes running and running OK, and you aren't getting starvation hesitation when you open the throttle and drain the float bowl or anything; its probably doing no harm... but it's probably not doing much good either.

But if anything 'prompts' the notion of fitting an inline filter, an inline filter is probably not the answer, tackling the symptom, not the cause. Tackle the problem upstream; make sure the tank's clean, the petcock good, petcock strainer if it has one good; and the fuel going in the tank clean... AND it's most likely the 'problem' will persist and be revealed when you grasp the nettle and strip the carb(s).
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[talkToTheHat]

My suzukis and my virago all had in-line filters as standard. I replaced the virago one when I bought the bike and two tanks later it was massing and the filter was full of crap. Replaced and the next filter lasted until the annual service. Very grateful I didn't have all that crap in my carbs.

Replace filter before using an aggressive fuel system cleaner and again once the cleaner has flushed crap into the filter. They're piss cheap.
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