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GS650G high RPM on freeway

  • Thread starter Thread starter jeffsbig12
  • Start date Start date
J

jeffsbig12

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Hi everyone!! This is the best form ever..I picked up a 1982 GS650G with 8,500 miles on it,pretty clean don't know history but i think it was stored outside and covered. Went thru bike complety ,carb o/haul,value adjust (values were tight),and all parts of bike serviced. Compression was wthin 15% each other but low around 140lb. It now has around 22,000 miles on it and has been running rough. Have adjust values every 5,000 miles,I have 2 low cyls 1 is 25lbs the other is 60lbs, add oil for wet test and they came up allitle 30lbs.value problems,and the low comp.of 140lbs rings ? My quess from sitting and moisture cause rust to form. Then back on road and ring cyl.wear? RPM's at high speed freeway driveing at 80 mph taching 7000 rpms, can it handle that with out doing engine damage? Thanks for your imput and thoughts. Jeff
 
Double check your procedure on adjusting the valves, as I've seen bikes where the experienced owners made math error, or sequence error and had the valves 2-1/2 times too wide. A properly running 650g can do 80mph all day long and mine has. I can't remember if the rmp's are right for 80mph.
 
^^^that tach looks "lazy" to me. sticks just past 5000 but I think I can hear more change....and I'm really sure my tach would above that at 70mph (120 kmh here)

RPM's at high speed freeway driveing at 80 mph taching 7000
Click to expand...
that makes sense to me (I have a 650G) but again, these ol' tachs do not seem to age well. The magnet wheel that drives the needle is steel and magnetised steel is not a forever thing....but neither is the lubrication inside. Goes to gum after 30+ years.

But checking the gear ratio would be a best-test for accuracy. I could easily be wrong. They can over-read too if the cable is jumpy if the"counter-spring) on the needle is tired....
 
IIRC, my 650G turns about 5400rpm at 60 mph. I think it must be at least another 1000rpm at 70mph, and can do it all day, so 7000rpm at 80mph could be right.


Did I read the OP correctly? Did you say 25 and 60 lbs?Nobody has mentioned it yet, but I think you know that's not good. It shouldn't even run at those numbers, but if it's only running on two cylinders, it might not be firing on those two. You could be dumping raw fuel out the exhaust, and/or risking hydrolocking.

It could be rings, or as CharlieG says maladjusted valves, or you might have a blown gasket.
 
BigD_83 said:
IIRC, my 650G turns about 5400rpm at 60 mph. I think it must be at least another 1000rpm at 70mph, and can do it all day, so 7000rpm at 80mph could be right.
Click to expand...

It's simple math and linear:

If 60mph = 5400rpm then 80mph = (80/60) x 5400 = 7200rpm

That seems high to me, but I don't have a 650 to try it with.


Mark
 
Maybe I'll get a chance to run it a little faster this evening...will let you know what comes up.
 
From this thread


According to the June 1981 Motorcyclist test, at 60 mph in top gear, the engine was spinning at 4,634rpm.



EDIT- Given the math, that should work out to be around 6200rpm at 80mph.


EDIT 2- After a brief run in rain coming down hard and fresh enough to make the roads challenging, my 650G was indicating just a tick over 4500rpm at 60mph in 5th gear. Conditions were too poor, and the chance of radar up ahead made me keep my speed in check. So, by the Mark's math, I'd be a little over 6,000rpm at 80 mph.
 
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