Starting/running issues with kx 125

[Xtremesports445]

Well, to start off i'll give u a bit of my bike's history. My bike has always ran a bit rich, but i can still run it with 42:1 yamalube without fouling plugs. The beginning of my issue is when i first noticed that if i left my gas on for around a half hour or more the bike would seem flooded and therefore be hard to start. After the first few times this happened, i discovered that if a turned the gas off, then tipped the bike over and drained some of it, the bike would start up. Since my dad is lazy and I don't know much about carbs and didn't want to take it apart, and didn't know what was wrong, i just decided to always turn off my gas when i stop.
Anyways, i went riding friday and the bike seemed to be riding like it always did for probably an hour. I was riding in deep sand and I started to notice that it seemed to be losing power. After a little while longer (ten minutes) i could definently tell that it was. That is when i stopped and pulled in the clutch to see what it was, and of course my engine instantly died. After that i couldn't get it started. My first thought was that i had fouled a plug, but that wouldn't make sense because i was running 42:1 yamalube and it had never fouled a plug w/ it before. I decided to check it out though anyways. I pulled the plug and it was a perfect tan color, as it should be.. so it wasn't that. I checked spark, the air filter, and tried doing my little flooding technique, but nothing worked. after having to get towed back to my car, me and my dad looked at it for a bit. My dad was able to finally get it started by holding the throttle wide open (which we had already tried before but this time it worked). So i took it for a test spin. it again seemed to be slightly weaker in power, if i had to guess it seemed weaker up top and similar still in low. throttle response still seemed decent. I brought it back to the car and killed it. and couldn't get it started again. after that we decided to pack it up and just head home.
when we got home we took my carb off and we opened her up. everything seemed fine. my theory was that the float height was too high, causing constant flooding, therefore causing lost power and hard starting. But we checked the jets and the float and they seemed fine, no dirt. i also checked the slide and the needle. they seemed fine. so now i think the problem lies in the reeds. Am i correct?
thanks for reading my overly detailed story and helping me out here! :)

 

[adam728]

Sounds to me like it's time for an engine rebuild. Loss of power and hard starting is a sign of low compression.

Also, gas fouls plugs, not oil. You would be LEANER and less likely to foul a plug running a 32:1 oil mix, plus you'd have better lubrication for longer engine life.

 

[Xtremesports445]

bike has always started fine before this and the compression still feels strong. Are you saying that if i got a bigger pilot jet or main jet instead of smaller that it could solve my fouling problems?

 

[adam728]

No, I am saying mixing more oil in your gas causes the air/fuel ratio to be leaner and reduce fouling. You seemed to be under the assumption that the smaller amount of oil in the mix the less likely to foul a plug. The opposite is actually true.

You said you had been riding hard in deep sand, take really taxes a bike. When was the last rebuild? How many hours on the current topend? You may have simply gotten to the point that it is worn out! Buy/borrow/steal a compression gauge and see what the bike really has for compression. The "feel" method is a really poor one, since most bikes will gradually lose compression over time and you won't really notice it.

 

[Xtremesports445]

i will look into buying a compression tester. i assume you can just buy them at sears or lowes? And my bike fouls plugs at 32:1 and not at 42:1 so what u said doesn't make sense to me. I know u think it's probably the top end, and i can see that, but lets assume that it's not for right now, then what would u say it would be?

 

[adam728]

Auto parts places would be your best bet for a compression tester. Cost/quality varies a lot, you could pay $25 or you could pay $150, so look around. Some places like Auto Zone will let you borrow them for a returnable deposit.

Could also be reeds. Are they frayed or chipped? Sprung so they aren't sealing shut all the way?



It is very hard to oil-foul a plug. I know a group of guys that break their stuff in running 15:1. Lots of smoke, but no fouling.

99% of the time (completly made up number) a plug fouls because of too much fuel in the mix. If you mix more oil (like 32:1 instead of 42:1) you are getting less gasoline into the engine because of the extra oil (jets will pass the same amount of fluid for either ratio, so if there is more oil there has to be less gas).

If you are having troubles fouling plugs and everything checks out good (float level, reeds, compression) then you need to spend some time and jet your bike correctly. It's one of the best mods you can do.

 

[MX86]

i'm going to have to agree with adam on this one.. time for a new top-end. there is a theory i learned while riding in sand. always go one jet bigger then you would normally run just for the fact of the added stress. a plug is cheap compared to a topend