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Not RUNNING right

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I have a 2001 Yamaha YZ125 that is not running right. It sputters taking off and in certain spots in gears. It likes to gallop in all gears. If its in 5th gear and you let off it will gallop until you give it full throttle. And last it does not like to stay running even if the choke is on.

What we have done so far is take the carb apart and cleaned it. We messed around with the idle, air screw and even the throttle setting. We can get it to idle kind of fast at the beginning but then if you go ride it, it will die.

What we have been told is that the carb might need to be boiled, and check the compression and if it is less then 100 it needs to be rebuilt by a mechanic at a off-road vehicle business. 

Whats wrong with it? Are they right about the carb and the compression 

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gallop isn't exactly a term you find mechanics or mechanical sorts using.   maybe try a vet?   or you could tell me/us exactly what your plug looks like and things like is it smoking a lot,  does it miss when you try to reach the upper rpms etc.   A picture of the plug would be nice.  I bet you havent' checked the float level yet,  either,  so you may want to google that. 

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idling fast but then having no power under load is a sign of an air leak (at the head, the intake, or the crank seals)

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On 5/2/2017 at 11:52 AM, ossagp said:

gallop isn't exactly a term you find mechanics or mechanical sorts using.   maybe try a vet?   or you could tell me/us exactly what your plug looks like and things like is it smoking a lot,  does it miss when you try to reach the upper rpms etc.   A picture of the plug would be nice.  I bet you havent' checked the float level yet,  either,  so you may want to google that. 

The plug is a little black but not bad. We took the head off and ran the piston up and down and wiggled it in the cylinder and it was loose so we are thinking that the rings are gone. We talked to two mechanics and they said it probably is the top end needs rebuilt or the rings are bad.

 

On 5/3/2017 at 9:54 PM, jaguar57 said:

idling fast but then having no power under load is a sign of an air leak (at the head, the intake, or the crank seals)

How do you tell if there is a leak or not?

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yeah,  all a 2001 would need is rings.   Usually when you have a bike that old there are lots of things it needs catching up on.  rings, piston, cylinder etc will make yours run better,  but what I am guessing you are trying to describe is a misfire would get better with the hard part change, but wont go away without some tuning and other things like lower end seals and the leaks that you may be having issues with.  In most cases black, means too rich, or more fuel in the air fuel mixture than is necessary.  pressurizing the cylinder and crankcase will show you where your leaks are.  I use an adapter made from a sparkplug,  a compressor of any kind including the ones that come on jump starters, and a plug to plug off the exhaust.  from there it is expose at least the ignition side seal and use some soapy water.   no more than 8-10 lbs of air pressure.  

Edited by ossagp

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signs of leaks:

HEAD- grunge on the outside of the cylinder starting at the head gasket

CRANK- take the plug out and the side cases off and spray soapy water onto the seals while cranking the engine over. bubbles indicate a leak. If the right seal is bad then you will have more smoke in the exhaust from burning the transmission oil that leaked into the crancase.

INTAKE- with the engine idling just spray water all around the intake area. if that lowers the idle speed then there's a leak.

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Sometimes just taking the mag cover off when you have the bike idling will make it pick up rpm.  Sometimes nearly to a crazy pace.  That indicates a bad seal.  But just like the water on the base gasket or spraying something like wd40 etc around the possible leaks,  failure to make an rpm change doesn't always mean you don't have a leak.  

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1 hour ago, ossagp said:

Sometimes just taking the mag cover off when you have the bike idling will make it pick up rpm.  Sometimes nearly to a crazy pace.  That indicates a bad seal.  But just like the water on the base gasket or spraying something like wd40 etc around the possible leaks,  failure to make an rpm change doesn't always mean you don't have a leak.  

Whats seals do i look at? Do you have a diagram of what seals?

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the crankshaft seals are the ones I was talking about.   just go to something like bikebandit.com and pull up the crankcase and engine diagrams and look for the seals and you can get a good idea of the layout.  there are places online that you can download manuals,  though I have never used ones (preferring paper ones).   you have a 125 that was excellent in it's day and it isnt too hard to make them that way again.   

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First thing I'd do is pull the carb and tear is completely down so it can be properly cleaned along with all the jets etc.

Second thing I'd do is pull the reed block and then clean and completely reseal it to ensure no air leaks.

These are the most common source of issues with 2-strokes.  They are also the quickest and cheapest things to do.

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We replaced the piston ring and with all new seals. It seems like there is more compression then the first time but not enough i think. When i went and drove it, it does the same thing. When you are in high gear and let off and when you go and get back on it it just acts like it just want to be full throttle. At this point i dont know what to do besides taking it to the shop. Any suggestions?

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