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Old 08-22-2012, 11:08 PM
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kenhiraihnl's Avatar
Pearl City, HI
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Walbro felt filter for clunk

Hereís some info on Walbro felt filters used for clunks in the fuel tank (in case you didnít already know.) My engine began running crappy, i.e., wanting to flame-out after rolling inverted, on long down lines, etc. I overhauled the Walbro carb, changed the CM-6 (which looked perfect), and played with the needles. I finally decided to re-plumb the tank. It only took a few minutes, since Iím using a Fiji water bottle and PSP fittings. When I disassembled the Walbro felt filter I discovered that it has a micro-screen, just like the one in the carb. It was apparently clogged with that jelly-like substance that seems to grow in pre-mix fuel. I changed the clunk, and the engine is running like new again. The new filter that Iím using is an Oregon 07-206 which is smaller than the Walbro, and doesnít have the micro-mesh screen. FWIW. Ken
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Old 08-22-2012, 11:49 PM
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Had you by chance changed 2T oils recently?
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Old 08-23-2012, 12:56 AM
If it flys, it's good.
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Pearl City, HI
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Quote:
Originally Posted by Jedijody View Post
Had you by chance changed 2T oils recently?
No...I've been very satisfied with Stihl HP Ultra at 50:1 (buy it by the gallon)...That Walbro clunk has been in the tank over a year...Herve was at the field today, and he says he has less filter clogging since he switched to Redline...FWIW...Ken

EDIT: A few flights ago, I forgot my fuel jug and "borrowed" some fuel from a buddy who was breaking-in his engine with Penz Air-Cooled at 32:1...hmmmmm?
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Old 08-23-2012, 01:14 AM
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You should be changing filters at minimum annually. The Stihl won't cause any issues if used up within a reasonable period of time. Say within a two or three months.

I've seen the Walbro filters go a couple hundred running hours without needing changed, but that was when using a constant formula fuel that was highly controlled in containerization. What we obtain from gas stations is not really controlled at all. There is no filtering between the delivery truck and the gas station, and there is rarely any cleaning of tanks at the gas station. Station pump filters are changed when the flow rates fall off.

Gas delivery trucks don't just haul gas, they also haul diesel, methanol, and some other fuels. Those tanks are not cleaned or flushed between loads. Only the more knoledgable drivers purge the loading headers when they haul different fuels. So most don't do that. A load of gas can easily have 4 or 5 gallons of diesel left over from the last load go into the underground tanks with the gas.

The message in all that was not to expect to see your fuel filters last for years and years. Check them once in awhile. if they look dark in color, change them. Annually at minimum.
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Old 08-23-2012, 01:28 AM
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Quote:
Originally Posted by kenhiraihnl View Post

EDIT: A few flights ago, I forgot my fuel jug and "borrowed" some fuel from a buddy who was breaking-in his engine with Penz Air-Cooled at 32:1...hmmmmm?
There's you're problem. Can't mix two different brands/types of oil unless you want to make some slippery jello. Even if you emptied the tank first, there was enough fuel and oil in the filter to cause it.

I have Walbro filters that have been installed for 3-4 years running Stihl HP Ultra, the oil doesn't clog filters, friends clog filters.
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Old 08-23-2012, 01:30 AM
If it flys, it's good.
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Pearl City, HI
Joined Apr 2007
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Quote:
Originally Posted by Unmanned View Post
You should be changing filters at minimum annually. The Stihl won't cause any issues if used up within a reasonable period of time. Say within a two or three months.

I've seen the Walbro filters go a couple hundred running hours without needing changed, but that was when using a constant formula fuel that was highly controlled in containerization. What we obtain from gas stations is not really controlled at all. There is no filtering between the delivery truck and the gas station, and there is rarely any cleaning of tanks at the gas station. Station pump filters are changed when the flow rates fall off.

Gas delivery trucks don't just haul gas, they also haul diesel, methanol, and some other fuels. Those tanks are not cleaned or flushed between loads. Only the more knoledgable drivers purge the loading headers when they haul different fuels. So most don't do that. A load of gas can easily have 4 or 5 gallons of diesel left over from the last load go into the underground tanks with the gas.

The message in all that was not to expect to see your fuel filters last for years and years. Check them once in awhile. if they look dark in color, change them. Annually at minimum.
OK...another lesson learned...thanks to you and Jody...
-Ken
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Old 08-23-2012, 06:13 PM
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Now I'm wondering if I should change my felt clunk. A few weeks back I took a vacation where there was no sthil ultra and I used some briggs 2 stroke oil. And Last year I was using cheap wal mart 2 stroke oil before I seen the errors of my ways.
So far my engine has been running good But my durbo rubber stopper has now shot the craps and is in need of changing
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Old 08-23-2012, 06:40 PM
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If you're going to be changing stoppers it's a great time to be changing filters. Just makes too much sense to do that while it's opened up. Only a surgeon would close and reopen to fix something they saw while in there the first time for something else
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Old 08-23-2012, 08:10 PM
RTK
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I've had one walbro felt clunk in use for over ten years with no adverse affects yet
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Old 09-07-2012, 01:31 AM
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Tuusula, Finland
Joined Oct 2007
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Have you guys tried a chainsaw tank clunk? That is the best clunk we have found here in extreme north. It is a bit bigger in diameter than felt clunks, but works OK with soda bottle tank. it's made of some porous ceramic like material and it really suck all fuel out of the tank if set properly. Plus it retains a fairly good dose of gas. At least local Stihl chainsaw dealer has those.
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Old 09-07-2012, 05:06 PM
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Denver, CO
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I personally like that the Walbro clunk has the micro screen under the felt.

It keeps any stray felt fibers out of the carb.

It also keeps any crap like you discovered in there from ultimately going to the carb filter.

I would rather do a precautionary annual change of the felt at just a couple bucks than rebuild the carb.

Still, good to be aware that the screen is under there and could be plugged if you are having issues.
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Old 05-05-2014, 10:51 PM
Gettin' Lower!
Joined May 2009
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Just a quick question.
Did you guys have to richen up your engines when using a felt clunk?
Cheers
Grossy
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Old 05-05-2014, 10:57 PM
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No.
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Old 05-05-2014, 11:15 PM
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Overly detailed and long winded answers aren't really necessary
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Old 05-06-2014, 01:27 AM
Gettin' Lower!
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Ok then. I may have other issues, as my H needel is around 2.5 turns out on my TMM106.
The reason I asked was, when I sucked through it, it felt restricted.

Cheers
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