Planet Minis

blurry · 07-15-2008, 09:29 AM

I was heading home on my YSR50 last night from work - she was running like a top! all of a sudden the tone of the motor changed and there is no power. She doesn't want to rev up to where the power is and has lost that high pitch whine.

it's a 91 - all stock - that had been sitting for 10 years

last month we:
- replaced all the seals that don't involve removing the top or splitting the cases
- rebuilt the carb
- new plug (gapped)
- new clutch
- fiberglass reeds
- replaced the injection oil and primed the system
- lined the gas tank.

Put about 50-80 miles on since this work was done.

I did put the slide for the carb in 180 degrees rotated - fixed that and she was running great!

The plug has a cardboard color - HOWEVER - the part of the electrode that is bent to create the gap - right on the curve it is black with oil.

engine turns fine, nothing seems wrong. bike as horrendous to start now. starting with the chock on is impossible - I need to kick it over about twenty times while fiddling with the gas to get it running and then rev it up by hand - even with a brand new plug.

HELP! She's only down since last night and I'm already missing her!

thanks for any advice!

BlackBeard · 07-15-2008, 11:09 AM

sounds like the top end blew, most likely need to replace the piston/hone or re-bore the cylinder

blurry · 07-15-2008, 11:16 AM

what the heck would cause that to happen?

BlackBeard · 07-15-2008, 11:21 AM

i dont know, i had the same thing happen on an old 2-stroke 80 i rode. ran perfect then all of the sudden sounded different in pitch and wouldnt rev. in my case my engine seized and the crank bearings blew but lets hope thats not the same for you as you said it still ran correct? mine completely shutdown very slowly though.

BlackBeard · 07-15-2008, 11:21 AM

id put money on it that either the injector got plugged or your ring caught the port.

arlindsay1992 · 07-15-2008, 11:26 AM

I had something similar happen on a Z50R. I was riding around and it was running great. Then it would only rev to 3/4 rpm, then 1/2, then 1/4. Then it would only idle. Started and idled fine but wouldn't rev at all. Turned out there was a spec of dirt in the main jet allowing the motor to idle but when it started pulling fuel it couldn't. So check the carb and make sure it's all clean.

07-15-2008, 09:29 AM	#1 (permalink)
blurry PM Newbie Join Date: Dec 2006 Location: liverpool, NY Posts: 15	YSR50 sudden loss of power :( I was heading home on my YSR50 last night from work - she was running like a top! all of a sudden the tone of the motor changed and there is no power. She doesn't want to rev up to where the power is and has lost that high pitch whine. it's a 91 - all stock - that had been sitting for 10 years last month we: - replaced all the seals that don't involve removing the top or splitting the cases - rebuilt the carb - new plug (gapped) - new clutch - fiberglass reeds - replaced the injection oil and primed the system - lined the gas tank. Put about 50-80 miles on since this work was done. I did put the slide for the carb in 180 degrees rotated - fixed that and she was running great! The plug has a cardboard color - HOWEVER - the part of the electrode that is bent to create the gap - right on the curve it is black with oil. engine turns fine, nothing seems wrong. bike as horrendous to start now. starting with the chock on is impossible - I need to kick it over about twenty times while fiddling with the gas to get it running and then rev it up by hand - even with a brand new plug. HELP! She's only down since last night and I'm already missing her! thanks for any advice! Last edited by blurry; 07-15-2008 at 09:32 AM.

07-15-2008, 11:09 AM	#2 (permalink)
BlackBeard "ZBBT" Join Date: Oct 2007 Location: 50 riders Posts: 1,770	Re: YSR50 sudden loss of power :( sounds like the top end blew, most likely need to replace the piston/hone or re-bore the cylinder

07-15-2008, 11:16 AM	#3 (permalink)
blurry PM Newbie Join Date: Dec 2006 Location: liverpool, NY Posts: 15	Re: YSR50 sudden loss of power :( what the heck would cause that to happen?

07-15-2008, 11:21 AM	#4 (permalink)
BlackBeard "ZBBT" Join Date: Oct 2007 Location: 50 riders Posts: 1,770	Re: YSR50 sudden loss of power :( i dont know, i had the same thing happen on an old 2-stroke 80 i rode. ran perfect then all of the sudden sounded different in pitch and wouldnt rev. in my case my engine seized and the crank bearings blew but lets hope thats not the same for you as you said it still ran correct? mine completely shutdown very slowly though.

07-15-2008, 11:21 AM	#5 (permalink)
BlackBeard "ZBBT" Join Date: Oct 2007 Location: 50 riders Posts: 1,770	Re: YSR50 sudden loss of power :( id put money on it that either the injector got plugged or your ring caught the port.

07-15-2008, 11:26 AM	#6 (permalink)
arlindsay1992 "High Speed Record Guy" Join Date: Mar 2006 Location: Virginia Posts: 3,534	Re: YSR50 sudden loss of power :( I had something similar happen on a Z50R. I was riding around and it was running great. Then it would only rev to 3/4 rpm, then 1/2, then 1/4. Then it would only idle. Started and idled fine but wouldn't rev at all. Turned out there was a spec of dirt in the main jet allowing the motor to idle but when it started pulling fuel it couldn't. So check the carb and make sure it's all clean.

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