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I just picked up a 79' cm400a from a co-worker and it had an in line fuel filter installed between the carb and petcock. A different co-worker said that an in line fuel filter is a bad idea on this bike. Cant seem to find any reason why this would be the case.
 

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I use inline fuel filters on all my bikes and they have never been a problem.
If the filter in the tank that is on the petcock is good an inline filter may not be needed.
 

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I don't know about your bike but I run inline filters on my 450K6 and 500T with no problems.
 

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Welcome to the forum,good to see another 400a,fun bikes great around town, as for the inline filter it wont hurt a thing but if your bike has the proper in tank filter you don't need it.
 

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Some have reported issues using the filters with very fine elements. The typical pleated paper elements seem to work ok but, as stated earlier, if you have the petcock screen in place and a clean tank, it isn't really necessary.
 

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To each their own. My belief is that two redundant in-line filters mean four unnecessary joints, each of which is a potential leak point.
 

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I don't know about your bike but I run inline filters on my 450K6 and 500T with no problems.
Would like to see a pic of the filter And line route,, the petcock outlets and carb inlet are in such proximity(right side) on my cb450k5... every filter I have tried, even the tiny 45 degree comes into contact with the throttle linkage. Also, can anyone suggest a good fuel line wall thickness to eliminate "easy" kinks with semi sharp turns.. thin wall stuff tends to flatten.
 

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Auto part Engine Vehicle Car Family car
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One here shows no throttle linkage to get hung up if a filter is installed.. the other does (like mine).. anyone had luck locating and installing one in this location?..
 

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Would like to see a pic of the filter And line route,, the petcock outlets and carb inlet are in such proximity(right side) on my cb450k5... every filter I have tried, even the tiny 45 degree comes into contact with the throttle linkage. Also, can anyone suggest a good fuel line wall thickness to eliminate "easy" kinks with semi sharp turns.. thin wall stuff tends to flatten.
Auto part Fuel line Engine Automotive exhaust Pipe


And this is the correct routing

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If the oe tank tap filter is so good, why does "rust mud" end up in the carb float bowls ?

Yes a well flushed tank is good, as is a clean filler cap and proper storage, with on condensation issues, but what about the small hole in the tank oe filter ?

The oe filter with a different tap with a second "brass filter screen" and sediment trap, like to one on the 450 dohc picture.

The 400 with an in line filter, small vw type, that fits real well behind the side panel tank "grommet" just needs a well placed 180 degree bend and some side panel trimming to accommodate the new fuel pipe route works real well. Yes some more joints and "weak links", possibilities of fuel leaks etc., but they can be "acceptable" if executed properly.

A magnetic rust mud "attractor" as well as a well cleaned and flushed tank may be the route, or un hydroscopic fuel.
 

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You can see the "kink" issue I am having with thin walled tubing..
here is the smallest 90 degree filter I could find.. you can see the "placement" is great, and eliminates the kink.. HOWEVER, the linkage gets caught up with the large part of the filter. As I looked at these pics .. I may try re-mounting the filter again..BUT instead of it going 90 degrees directly to the carb, twist it a bit so it points away from the bike then route the line curved back.. The only part that may contact the linkage would be the pointed part of the filter..
Gonna have to get back to you guys and see what is what..
 

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Maybe get the factory hose, that is what I am running.

If you want more (better) pictures of mine, I can take them this afternoon just let me know.
 

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Thanks.. no need.. I was more curious if anyone found a filter or "set up" that was "short and sweet" for a DOHC. The filter route /setup would be perfect for a SOHC since no linkage is on the side of the carb. As for fuel line, I try to run non-ethonhol fuel.. but here in Ga. I swear it still contains SOME alcohol (fuel lines get hard)... gonna "test" the fuel soon to check...
 

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Thanks.. no need.. I was more curious if anyone found a filter or "set up" that was "short and sweet" for a DOHC. The filter route /setup would be perfect for a SOHC since no linkage is on the side of the carb. As for fuel line, I try to run non-ethonhol fuel.. but here in Ga. I swear it still contains SOME alcohol (fuel lines get hard)... gonna "test" the fuel soon to check...
Just to make sure, we have the same bikes, your is a K5 and mine a K6. I have no problem with lines interfering with the throttle linkage.
 

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I can see that in your pics, the fuel lines also are longer...
I was looking for like routing in the shortest route, but come to think of it.. your setup may lend to being able to lift the tank "UP" off the frame for access without removing it...
WOW.. thanks, look for one solution and find two..
 
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