sintered bronze (rock) fuel filters - Triumph Forum: Triumph Rat Motorcycle Forums
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post #1 of 13 (permalink) Old 01-14-2016, 10:01 AM Thread Starter
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sintered bronze (rock) fuel filters

I am new to triumphs and this board, but with my recently acquired Legend TT, I am going thru it to get it running up to my standards. I am an old hotrod and racer.

A significant number of the universal inline filters I am seeing referenced on the internet motorcycle sites and on the shelfs at the motorcycle shops are of the sintered bronze (better known as 'rock') filters design.

These are very good filters, but incredibly restrictive and low flow. This means they clog very easily and quickly, as the pores get filled with particulate. They are touted as being cleanable, HOWEVER they never flow as they did when new, and get clogged quicker and quicker. the clogging debris can be miniscule sized, so the filter still looks clean.

In the automotive performance industry, they are steered away from. Yes, they are available at every source known to man in various, sizes, and configurations. But that does not mean they are good. Case in point, in the 70's, GM was using rock filters at the carb inlet fittings. the first thing that most people were told to do was remove the filter and install an inline paper style or screen style filter. I myself have been foiled by the rock filters on many occasions. Low flow, will do whacky things with the float level and needle response, therefore producing inconsistent idle mixture and speed tuning. And also, simply stop flow too.

SO, thats my tip, steer away from pretty anodized filters that have the bronze elements in them. Always use a screen or paper element filter, and replace it regularly. I have seen some anodized filters that utilize a paper element, I will check them out.
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post #2 of 13 (permalink) Old 01-21-2016, 08:38 PM
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Remember, before you add any filter beyond what the factory supplies, that these bikes have no fuel pump. You only have a few tenths of a PSI of head pressure and any added restriction can mean the difference between running and miss-firing.
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post #3 of 13 (permalink) Old 01-23-2016, 03:18 PM
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Remember, before you add any filter beyond what the factory supplies, that these bikes have no fuel pump. You only have a few tenths of a PSI of head pressure and any added restriction can mean the difference between running and miss-firing.
I'm one of those who believes that no additional fuel filter should be used. From the factory, these bikes came with only the duckbill filter. When the fuel level is low in the tank, you only have several inches of head above the duckbill filter, and even less above an additional filter if you install one. Gasoline is lighter than water. And it takes 28" of water for 1 PSI. Long story short, it doesn't take much to block things off and cause problems.
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post #4 of 13 (permalink) Old 02-24-2016, 10:22 PM
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Just thinking out loud...

I went with the Pingel Fuel petcock on my rebuild, PN 6211-CH. This increased the overall inner diameter of the fuel lines to 5/16 (OD is 7/16). The thought was the increased fuel line size would offset the resistance on the fuel flow caused by the inline fuel filter. The new petcock also significantly increased the surface area of the mesh screen from the original one used on the stock petcock. I also added their inline fuel filter, PN SS1C. This has the bronze 'rock' filter, that you speak about, in a cone shape. The cone shape adds to the surface area of the filter. The filter housing is threaded so disassembly is a snap.

I have to admit, so far so good, I have not had any issues, but that is only 4-5 rides on it since I rebuilt the bike. I also stripped the inside of the fuel tank and re-sealed it as well. After rebuilding my carbs, the last thing I wanted to do was to pass trash into them.

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post #5 of 13 (permalink) Old 02-25-2016, 08:13 AM Thread Starter
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when they are new, they are simply restrictive, but typically do not exhibit issues. The instant, you begin to notice some awkwardness in the carb tuning dont follow rabbit trails with carb settings when troubleshooting. look into the filter FIRST THING. you can clean them as best you can, but they will never get close to their new condition. Even though they are billed as cleanable. they really arent; atleast with any method I have seen.

With paper or screens, you know where you stand. With rock (sintered bronze) filters, you only know where you stand when they are new.

I want a nice looking take apart filter, like the currently available ones (in colors of your choice), except that use a paper element or screen assy. In the mean time, I will continue to use a small engine paper element style.

I have been down way way too many rabbit holes of carb tuning with rock filters on cars; only for it to end up being the filter the whole time. I stay away from them now.

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post #6 of 13 (permalink) Old 02-25-2016, 12:28 PM
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Yeah, I had a '58 Pontiac with a 389. It had a sintered filter in the inlet to that big honking 4 bbl carb. Never could keep it clean... And that was a pressure system!

Increasing the diameter of the fuel line will increase the potential flow rate but not the pressure to force fuel through the filter. The only possible benefit there is your bigger filter may have more surface area.

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post #7 of 13 (permalink) Old 02-25-2016, 02:22 PM
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Quote:
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.....The only possible benefit there is your bigger filter may have more surface area.

Ah, yep.

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post #8 of 13 (permalink) Old 02-29-2016, 01:27 PM
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I have one of those sintered bronze filters on my bike for at least 10 years, never had a problem. Then again, it seems to stay clean so that's a good sign. Maybe a clogged filter is an indication of an underlying problem?

One thing I have noticed, is that when the main fuel supply runs out it's very sudden- and switching to reserve takes a relatively long time (a mile or so) to get back to running right. Thinking about it, it could be that the fuel takes a while to percolate thru the filter.

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post #9 of 13 (permalink) Old 03-09-2016, 08:11 PM
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switching to reserve takes a relatively long time (a mile or so) to get back to running right. Thinking about it, it could be that the fuel takes a while to percolate thru the filter.
Could be. When I switch to reserve on the highway, it takes less than 5 seconds to recover at 70 mph.

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post #10 of 13 (permalink) Old 04-29-2017, 09:50 AM
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Quote:
Originally Posted by WSC View Post
Yeah, I had a '58 Pontiac with a 389. It had a sintered filter in the inlet to that big honking 4 bbl carb. Never could keep it clean... And that was a pressure system!

Increasing the diameter of the fuel line will increase the potential flow rate but not the pressure to force fuel through the filter. The only possible benefit there is your bigger filter may have more surface area.
In fact, increasing the diameter without increasing pressure artificially will decrease the natural pressure.

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