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Aug 3rd 2018, 08:39 AM   #1
 
  Aug 2018
  Oregon

high rpms

ok, here's a quick question, i'll post details in my reply. any help on why my rpms are so high?
Aug 3rd 2018, 08:46 AM   #2
 
  Aug 2018
  Oregon

ok, at idle, cracking the throttle quickly, and letting go quickly, the rpm's will go to 4500 and stay there for 10-15 seconds or longer. i have had the carb apart, pulled the jets, cleaned the carb, the plunger is smooth and pops back down when i move it (who knows for sure while it is running). i did not disassemble the choke (accel pump?) so perhaps there is a vacuum leak coming through that port??? i installed a new boot between the carb and the head. i have sprayed around the carb to see a change in the RPMs and i get nothing. there also is valve clatter (separate posting due to not getting my post approved). i don't know if they are related. What is my next step?

i inherited this motorcycle, so i do not know its history. I have posted this 4 times now, so i hope this works. i may have forgotten to add something, because of trying this many times over 2 days. so I may add more later if people ask questions or have suggestions. Thanks for understanding.
i appreciate any help especially if you have experienced and fixed this type of problem.
Aug 3rd 2018, 09:26 AM   #3
 Pavement Tested's Avatar
 
  Jan 2016
  Bremerton

  '08 GSX1300R, '06 GSX-R 750, '17 KTM 690 Duke
Does the throttle snap shut from full open? (i.e. open the throttle all the way and let it go) Is there a nice crisp, audible snap when the throttle shuts? Does it respond the same thru the full range of steering from handle bars all the way left to all the way right?

Note: the bike should not be running for this test.
Aug 3rd 2018, 09:45 AM   #4
 
  Aug 2018
  Oregon

yes. and when i watch, the throttle on the carb fully responds; it fully turns back down quickly and stops on the idle screw, and yet it is still revving at 4500 RPMs
Aug 3rd 2018, 09:48 AM   #5
 
  Aug 2018
  Oregon

i am considering putting in a second spring on the throttle plunger. how stiff is that spring supposed to be?
Aug 3rd 2018, 03:06 PM   #6
 Rusty Nail's Avatar
 
  Jan 2016
  Sandy

  2013 Spyder
If it snaps shut the spring should be strong enough. For the rpms to remain high I think you need extra fuel and air. I dont think a vacuum leak alone would do this. Maybe one of the floats is sticking open. Or there could be a problem with the choke circuit leaking by under high vacuum. But all I know about this bike is that it has carburetors.
Aug 3rd 2018, 04:04 PM   #7
 SXVINWA's Avatar
 
  Feb 2016
  Tri-Cities

Did you try dropping the idle a little bit to see if you are hanging at the edge of a transition port?
Aug 3rd 2018, 07:12 PM   #8
 
  Aug 2018
  Oregon

if i set the idle low, it doesn't matter. if it is idling fine at 1500 and i crack the throttle, it goes to 4-5k and stays there.

yes it has 1 carburetor . the spring i was talking about is on the throttle plunger, not the throttle plate.
Aug 3rd 2018, 08:23 PM   #9
 SXVINWA's Avatar
 
  Feb 2016
  Tri-Cities

According to the internet, the idle is supposed to be set at 1200-1300.
Aug 3rd 2018, 09:29 PM   #10
 
  Aug 2018
  Oregon

ok, mabye it was 1200 ,or maybe it was 1500, but either way, if it was 800, it still will act the same way when the throttle is revved slightly, ,or when driving and changing gears, the rpm's will be 4-5000 i do not understand the problem here. if you don't have a possible solution, have a good day elsewhere.

the thing sits there and idles at 4500 all on its own. heck, even 6,000. and the throttle is closed. the idle set screw is not the issue.
Aug 3rd 2018, 09:32 PM   #11
 DocB's Avatar
 
  Feb 2016
  Poulsbo, WA

  Aprilia RSV Mille, CB77 (AMA Nat'l landspeed record holder), CB750K, CB750F
Here's what google turned up about someone having the same problem with a GN125 -

"Found a little fuel jet hidden in the casting of the float bowl which was gunked up."
Aug 4th 2018, 03:54 PM   #12
 
  Aug 2018
  Oregon

thanks Doc, I'll give that a try next. i did pull two jets, and yes one was small, but it's worth a second try.
Aug 6th 2018, 08:10 AM   #13
 DocB's Avatar
 
  Feb 2016
  Poulsbo, WA

  Aprilia RSV Mille, CB77 (AMA Nat'l landspeed record holder), CB750K, CB750F
Sounds like you pulled the main and slow jets, which makes perfect sense. I wonder if maybe the guy was talking about some other passageway in the fuel bowl casting being clogged rather than an actual jet. It seems unusual for anything other than an overflow vent to be in the bowl, but I don't know anything about the GN125. Or he may have been referring to something in the carb body in the bowl area rather than in the bowl itself?

I have had carbs that had hidden "power jets". You might want to look up an exploded diagram of the carb to see if there is some other jet you missed.
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