petcock/fuel issue

got the '83 xj550 back on the road running great and now with an in-line fuel filter. rode around town a little and then about 10 hard miles on the highway when she started coughing like she was out of fuel.. while rolling I switched to reserve and then right back to prime (IDK why, as I always switched to reserve when I ran low on gas) and she came back to life. I parked for a while then took off with the petcock switched to on and she started coughing again in less than a mile so I finished my fide home on prime figuring the vacuum petcock died. well today I put -7PSI vacuum on the petcock and she flowed fine on ON. and I measured the vacuum on the manifold line that goes to the petcock (engine idles around 7psi and fluctuates a lot without restricting the 1/4" line.). at speed, she does about 10PSI vacuum. So I ran her for a while at idle and fast idle pulling 7psi vacuum on the petcock and she ran fine. And then I think I switched back to the manifold vacuum line on the petcock without incident.. The manifold vacuum line looks fine (no leaks) and so the only thing that's different here is adding the in line fuel filter// (but switching to prime should be no different).. There's not much else this could be but now I'm wondering if that Orange IDK what kind of 1/4" rubber hose is softening up at temperatures and leaking.. (but then it should run like shit).

 

it needs to be vacuum line not fuel line, with the higher vac at highway speed the line is likly to be collapsing. or kinking at a bend.
buy a length put it on cheap fix if it works after that. next would be a petcock problem.
prime does not use the vacuum to flow.
are you using a paper element filter? you should be using a metal element.

 

I thought vacuum line was always lighter than fuel line.. It's not kinked and I did have it on for one long ride but maybe it softened up.. good point/.. Yes, I'll grab a piece of vacuum line and try that. and yes, it's a paper element filter. what's the problem there?

 

Vacuum line is (generally) smaller in diameter, but has a greater wall thickness.

 

it has been stated here that paper is not a good choice for mc filters . i use one i get at napa have to order then $2.95 come in the next day with clamps 740-1158 rated for 4 cylinder motorcycles in online specs
you may have to push the filter element into place with a small screw driver inside the filter body.

 

this link has three suppliers of the filter.
http://www.xjbikes.com/forums/threads/how-to-install-a-fuel-filter.6352/

 

oh, you guys are great. the orange rubber line I have is really thick walled and I think it's silicone. but I'll try something else and look at that line today if I'm riding later.. and I recognize those sintered metal element cone filters. Used to install them on small engines.. fit in tight spots and think I have on on my cb750.. will grab one of them for good measure..). I'll google paper element filters for motorcycles, but what's the issue? and what about moving the element with a screwdriver (the paper filter or metal?)>

 

The paper element filters generally do not allow enough fuel flow to keep up with your engine's needs. They are typically engineered for small engine use.

 

when my filters came in with the sintered metal cone had fallen out of the cup inside of the filter. I used the back side of a drill bit to push it back into place. (the one I have in the package still is out as well) went in snuggly and I could not get it to fall out again.
they tried to get me to buy an off the rack one they had in stock but they were not rated for 4 cylinder motor cycle as the one I ordered and it came with clamps, they wanted to sell me lawn mower filters.
I think you should still replace your vacuum line , once you do that if you still have a fuel flow problem you will have to look at the petcock it has a filter on it in the tank.