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Discussion Starter · #1 ·
I was riding around today picking up a few things and on the way back I just jumped on the freeway and was cruising back at about 70-75 and all the sudden it started loosing power and died on me, I got it over to the side of the road and checked the gas plenty of gas, only 40 miles since last fillup and was able to get it to start again. Got back on the highway and about 2 miles down it died again, pulled it over flipped it to reserve and got it back running again. Needless to say I got off on the next exit. Riding down the city streets it was fine so I got back on the freeway and went another 2 miles to the next exit and it was fine. Looped back and came home, stopping off and topped the tank off with more premium.



When I got home I pulled the plugs just out of curiosity and the left plug was not even tight, pulled it out and it was dark brown on the electrodes and black around the threads, the right plug was about the same but a little tighter but not much.



Does it sound like a fuel problem or was a loosing compression on the cylinders, it felt like fuel, should I pull the fuel valve and check the inlet screen?
 

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I was riding around today picking up a few things and on the way back I just jumped on the freeway and was cruising back at about 70-75 and all the sudden it started loosing power and died on me, I got it over to the side of the road and checked the gas plenty of gas, only 40 miles since last fillup and was able to get it to start again. Got back on the highway and about 2 miles down it died again, pulled it over flipped it to reserve and got it back running again. Needless to say I got off on the next exit. Riding down the city streets it was fine so I got back on the freeway and went another 2 miles to the next exit and it was fine. Looped back and came home, stopping off and topped the tank off with more premium.



When I got home I pulled the plugs just out of curiosity and the left plug was not even tight, pulled it out and it was dark brown on the electrodes and black around the threads, the right plug was about the same but a little tighter but not much.



Does it sound like a fuel problem or was a loosing compression on the cylinders, it felt like fuel, should I pull the fuel valve and check the inlet screen?
yes,from what you say,id say fuel related.have you an inline filter
 

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It could be a few things and these kind of problems can be a PITA to track down.



Things that have caused similar to me,



1:Blocked vent holes in fuel filler cap.Drilled slightly bigger and high pressure air blown through.



2:Reversed in-line fuel filter/blocked fuel filter/Dirty or Faulty Petcock/Tank crud.





3:Carb float heights gone out.



4:Not me but vacuum Petcocks going faulty.



5:Faulty bad contacts at the main fuse and holder.



6:Faulty kill switch



7:Bad ignition wire somewhere in the circuit.



8:Coils over-heating.



There's some to start with.
 

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Shep has given you a large checklist to work through.

your comment ......started to loose power[means to me,gradually]this indicates fuel.not electrical...normally an electric fault is instant,,,fuel problem is much slower.



so,on that thought.

have you an uninterupted flow of fuel to the carbs.then are they clean,ie.no debris leaving your tank and ending up blocking a jet within the carb.
 

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First thing I would check is the vacuum petcock. It is possible something is amiss there. Less vacuum at high speed. Same thing happened to me, and the spring in the petcock had somehow turned sideways. The lower vacuum at high speed was not enough to allow gas flow, but at lower speeds and higher vacuum it was. See DaveF's thread HERE



I wound up altering my petcock to eliminate the need for vacuum.
 

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First guess is always gas if it's acting like that. You have a few more things to think of with the vacuum petcock. Rust in the tank caused a similar feeling a few years back for me. And it really sucked.
 

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Discussion Starter · #8 ·
Yeah I drained the tank and there was a bunch of crud in there again, not lined
I got a gallon of denatured alcohol and did the old nuts and bolts trick. I got all kinds of brown crap out so hopefully that did the trick. My vacuum petcock is pretty shady too, Mr.Softy how did you modify the petcock to make it non vacuum. I ordered a rebuild kit for it from George Fix on Ebay but it wasn't the correct one.



Boulder CX500, I though about that after posting, I should have titled it "Fizzling out on the Freeway"
Anyway I will put the tank back on in the morning and take for a test.
 

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You probably want to do a real clean and line on the tank or soon you will have the same problem again.







to change a vacuum-operated fuel tap to manual operation only - is to undo the four screws that hold the vacuum diaphragm cell together, and remove the spring. Then put it back together. A safer job will result if you fill the two small spiggots on the vacuum cell with a fuel-safe plug in each - just in case the fuel diaphragm leaks.
 

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Yeah, I took the spring out. I had to drill the rivets out and replace them with small screws If I remember correctly. I left the vacuum line attached.
 

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Discussion Starter · #11 ·
I put the tank back on and fired it up, fired right up too even though I ran the float bowls dry, I usually have to crank it a couple seconds to get gas down there so I think it is much better now, I will probably take the tank off again in the near future when I have time and clean it again just to be safe. If the weather is okay I will take it out tomorrow morning and run it down the freeway and see what it does.
 

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I put the tank back on and fired it up, fired right up too even though I ran the float bowls dry, I usually have to crank it a couple seconds to get gas down there so I think it is much better now, I will probably take the tank off again in the near future when I have time and clean it again just to be safe. If the weather is okay I will take it out tomorrow morning and run it down the freeway and see what it does.
I just went through the same thing. Bike was fine under 55mph or so, but at higher speeds it would suck all the gas from the bowls faster than they were refilling. Mine was a small crack in the vacuum operated diaphram in the petcock.
 

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Ya, I done the "Mariachi-Fix" on my gas tank 2 years ago. Still holding up well. And, yes, the brown chit I got outta there. OH MY!
 

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You should check the vacuum hose from the right manifold to the vac fuel valve for split ends. Vac leaks here can cause decreased vac petcock opening, manifested most at higher speeds due to lower vac "pressure" and also higher fuel needs. This is common on original hoses as this particular hose is of a lower specification (as are many vac hoses).
 

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Discussion Starter · #15 ·
Took a quick 40 mile shake down ride this morning, its much better, a lot smoother which I think was from the loose plugs and it goes like a bat out of hell again, peg the speedo in 4th hammer it into 5th and away we go
Doing 70 in 4th for about 5min and it was fine there too. So I think I need to order a kit to line the tank sometime in the near future. I know it was talked about on the old forum but what is a good product for cleaning and lining the tank, cleaning it with the nuts and bolts is crud and tiresome.
 
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