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Discussion Starter #1
Having trouble w/ ? Runs like a bat outta hell for 20 miles, then dies...like fuel restriction.... carbs rebuilt 90 miles ago & adjusted for this issue but still exists... affects ALL carbs so gotta be fuel? Throttle cable? Gas tank venting? HELP please馃檮
 

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20 Miles is a fair distance to attribute a fuel issue but never say never.
Wonder if the Fuel tank is not venting and the build up in the tank is preventing flow.
Need some more specifics of the issue me thinks.
 

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Discussion Starter #3
20 Miles is a fair distance to attribute a fuel issue but never say never.
Wonder if the Fuel tank is not venting and the build up in the tank is preventing flow.
Need some more specifics of the issue me thinks.
Yep.....I鈥檝e tried popping the gas cap to equalize....didn鈥檛 work.... it certainly acts like fuel restriction that 鈥渃lears up鈥 after sitting 20-30 min.....overnight & it runs great馃槉

next step is checking filter screen above petcock? Imyw/ you... why 20-25 miles before restriction? Crap in filter screen floats up to do it exactly again? doubtful....
Again....carbs rebuilt this spring after 40 years of sitting in garage....all were amazed at condition.... but I realize it鈥檚 gonna take some tweaking馃槉

I鈥檓 sitting in the shade right now cooling it鈥檚 heels again.... made it 1 mile this time馃お
 

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Discussion Starter #5
But sgain....bat outta hell for 20 miles?
Yep.....I鈥檝e tried popping the gas cap to equalize....didn鈥檛 work.... it certainly acts like fuel restriction that 鈥渃lears up鈥 after sitting 20-30 min.....overnight & it runs great馃槉

next step is checking filter screen above petcock? Imyw/ you... why 20-25 miles before restriction? Crap in filter screen floats up to do it exactly again? doubtful....
Again....carbs rebuilt this spring after 40 years of sitting in garage....all were amazed at condition.... but I realize it鈥檚 gonna take some tweaking馃槉

I鈥檓 sitting in the shade right now cooling it鈥檚 heels again.... made it 1 mile this time馃お
clutch?
 

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Discussion Starter #8
Clutch doubtful, I am leaning towards Fuel now you've given some more details.
I'd have the filter screen out for sure.
馃憤馃槉.....so there could be a 鈥渇loater鈥....light enough to float out of petcock tube/filter, then float around 鈥榯il it gets sucked back into the filter.... really may have nothing to do w/ temperature..... I鈥檒l try the filter.... 馃憤馃槉
When did you pop the gas cap, before or after it quits?
before....a couple of times.....preventative....when i thought i felt it faltering....

finally limped it home...took 3, 25 minute 鈥渃ool downs?....not convinced it has anything to do w/ hot engine, though. But would fire up no problem after 鈥渞est鈥

did pull the petcock...sludge in reservoir....& some in one of tubes to 1 carb....filter was clean though...looked like a sludge mixture of rust flakes from 46-year old gas tank.... have not taken it out since, but the mechanics of the petcock/ filter/reservoir are a bit confusing? Reservoir is below filter & distribution tubes to carbs.... what good is that?
When did you pop the gas cap, before or after it quits?
 

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Discussion Starter #9
Will refill tank w/ fresh fuel & try again tomorrow.....is the such a thing as 鈥渧aprlock鈥 on these animals? W/ slide diaphragms & no fuel pump? ..... basically problem MUST occur BEFORE carbs as it affects ALL 3馃お
 

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Motorcycles can suffer from Vapor Lock but the Fuel has to get very very hot to turn to a Vapor and once the heat source is removed (Engine off) will return to a liquid state very quickly.
 

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Motorcycles can suffer from Vapor Lock but the Fuel has to get very very hot to turn to a Vapor and once the heat source is removed (Engine off) will return to a liquid state very quickly.
[/QUOTE]
 

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Above was my mistake, did not mean to quote. More information please. The S3 uses three individual fuel lines. From left to right each line is longer in length. If you have a fuel starvation problem it is extremely unlikely that you would consistently loose all three cylinders at the same time as fuel lines contain unequal amounts of fuel. So that is my first question, when it quits do you in fairly rapid sequence loose one cylinder after another or do you loose all three simultaneously? If you consistently loose all three simultaneously you probably have an electrical problem related to heat. Rather easy to make a preliminary diagnosis. With all the appropriate warnings necessary concerning hot engines and gasoline. Have you switched to reserve which uses a separate stand pipe and screen, have you pulled a fuel line when it quits to see if it is empty? You could install a clear line or a clear inline filter to monitor fuel flow. When it quits you could pull a plug introduce a few drops of fuel, reinstall plug and see if that cylinder fires for a few revelations, at this point some will recommend ether, up to you but that can lead to damage. Hard to imagine an ignition problem as the S uses three sets of points, condensers and coils. Try the above tests to determine if it is actually fuel starvation.
 

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Discussion Starter #13
Above was my mistake, did not mean to quote. More information please. The S3 uses three individual fuel lines. From left to right each line is longer in length. If you have a fuel starvation problem it is extremely unlikely that you would consistently loose all three cylinders at the same time as fuel lines contain unequal amounts of fuel. So that is my first question, when it quits do you in fairly rapid sequence loose one cylinder after another or do you loose all three simultaneously? If you consistently loose all three simultaneously you probably have an electrical problem related to heat. Rather easy to make a preliminary diagnosis. With all the appropriate warnings necessary concerning hot engines and gasoline. Have you switched to reserve which uses a separate stand pipe and screen, have you pulled a fuel line when it quits to see if it is empty? You could install a clear line or a clear inline filter to monitor fuel flow. When it quits you could pull a plug introduce a few drops of fuel, reinstall plug and see if that cylinder fires for a few revelations, at this point some will recommend ether, up to you but that can lead to damage. Hard to imagine an ignition problem as the S uses three sets of points, condensers and coils. Try the above tests to determine if it is actually fuel starvation.
Thanks to ALL馃榾..... working suggestions/input thru....as you can tell, imysemi-new at this again, after 40 years馃槉. I knew a lot about my S3 when i rode in 70鈥檚...as the 2-stroke takes work to have fun馃槉....
1). Reexamined the petcock... now the gas flow makes sense... main stem DOES deliver fuel below filter, so lightweight sludge, aka small rust flakes, COULD eventually float up & clog filter, the 鈥渟ettle鈥 when turned off....overheating NOT the issue, just mistakingly 鈥渁ssumed 鈥?

2). Seems the carbs go out in rapid succession... doesn鈥檛 just 鈥渜uit鈥....loses power, then quits.... unequal fuel amounts in unequal lines makes sense馃槉. HOPE it is not electrical馃お

vacuum in gas tank MAY still be an issue....

during my 鈥渢est drives鈥 today I鈥檒l pay more attention to all as i now have better ideas as to what to look for...silver lining.... I鈥檓 getting reacquainted w/ my super S3馃榾馃槑馃憤

i will keep you all posted and again...THANK YOU to all馃槉馃憤
 

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From your description it sure sounds like fuel starvation. Is there a way you can safely vent the tank while riding it? Maybe with low fuel level in the tank you can ride without the cap gasket and not have it leak.

1981GPZ550 had a good idea re: pulling a fuel line off the carb right after it dies, although that will allow a path for air to get up to the tank so if the line is empty it might not stay empty for long. Installing clear lines as he suggested is probably the best (and safest) idea.
 

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Discussion Starter #16
Ok.....was REALLY hoping it was petcock/fuel stem/filter, but alas.....pulled it again after latest episode....clean filter & sludge reservoir....

popped the fuel line at carb immediately after it quit.....free-flowing fuel to carb(s).....so.... leading to electrical?
 

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Sure looks like electrical and since it takes 20 miles it seems like it is heat related.

What you could try on the next fail is to quickly remove one plug and test for spark. If you have no spark then you have confirmed it to be an ignition problem. Wait the usual 20 minutes and test for spark again just to be sure. If the spark returns after the cool off period we are closer to solving the problem, but I fail to see how all three sets of points, all three condensors or all three coils could somehow fail at the same time. This points to something like your kill switch or ignition wiring with a bad connection but that does not explain the 20 mile failure or the cool-down fixing it.

We have a real mystery here. But it would be great to first prove that when it quits, you have no spark.
 

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Discussion Starter #19
If it is electrical, then whatever connection it is would seem to expand? w/ heat? and GRADUALLY break connection.... it starts to 鈥渂og鈥 before finally 鈥渂ogging 鈥 & dying.... as in more throttle required w/ less response... until finally reaching point of 鈥渂og & die鈥

Q: could a 鈥渃entralized lack of spark鈥 lead to too much unburned fuel in all carbs, leading to what SEEMS to be bogging/flooding caused by unburned fuel?

COULD account for an electrical issue being disguised as a fuel problem?
 

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Discussion Starter #20
Electrical goes from battery to ignition switch to 3 different coils, w/ a side wire to a kill switch .... leading to a 46-yr old solder job at battery, ignition switch (entering as 1, leaving as 3) or kill switch ....?
 
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