noob 2 stroke questions

[mr db]

Hello,

This is my first post on these forums and I have a few questions about 2 stroke bikes. I have a buddy who is willing to sell me his 04 yz125 for a $1000. That seems like a pretty good deal to me. He just had the engine rebuilt also. This will be my first bike. Currently I borrow a Honda crf150 when I ride with my friends. I am 5'11'', 165 lbs and will be doing trail-riding.

I hear that the yz125 is a great bike but is it the right bike for me? I am very good with 2 stroke engines. I have built many liquid pocketbike engines in the past. But I want something reliable that i dont have to worry about seizing up when i am miles away from civilization. A few questions I have are...

1.- Is this bike suited for trail riding?
2.- How often does the top end/rebuilding need to be done?
3.- Is this the kind of engine that constantly needs to be tuned?
4.- Are parts expensive?

thank you,
Robert

 

[sharky243]

Only you can tell if it's the right bike for you. I see alot of riders using the 125cc 2 strokes for harescrambles, because they are light. A good rule of thumb that I always use is 20 hours on a piston max. More often depending on how hard you ride and how high of an RPM you run it at. If you are planing long distance trail rides, I sugest a good 4-stroke like a yamaha WR250F, or a Honda XR model. 4 strokes are better suited for long run times and are better on fuel. They also tend to be a bit more reliable. As far as parts, they're about the same as any other bike. One thing to keep in mind as far as what brand to get, find out what the closest dealer sells, and what the turn around time is for parts. As far as tuning goes, unless you are racing it, pretty much just set the bike up and leave it alone. You may have to re-jet for colder temperatures though on either 2 or 4 strokes. Check the burn on the plug periodicaly to monitor the jetting.

 

[inotocracy]

2 strokes generally require more maintenance, buts its cheap and easy to do. 20 hours on a piston seems kind of overkill IMO, unless you're running the bike really hard (racing conditions).

 

[mr db]

do you guys normally wait to change the rings along with the piston or is that changed more frequently? Also are these engines pretty easy to open up and do the work myself? lastly do you guys normally use yami parts or other manufactures like wiseco?

Around year there are not many trails so my rides wont be too long. And there is a yamaha dealer right down the street from me.

thank you for all the help

 

[Patman]

2 strokes generally require more maintenance, buts its cheap and easy to do. 20 hours on a piston seems kind of overkill IMO, unless you're running the bike really hard (racing conditions).

:laugh: Really? Ever actually LOOKED at the service requirements on a current 4 stroke? Pretty much the same top end life as a 2 stroke. Oh sure you can push the limits but that's the same for either one and crank pieces through the case cost pretty much the same.

A YZ125 might be a good fun trail bike if it suits your style and you are really the only one that can decide that since we know virtually nothing about you. My son rides a CR125 and loves it but he's not a putt-putt rider.

If you want a good reliable solid bike then the best advice I can give you is make sure the bike you are riding is in tip to condition with all maintenance performed to the letter of the factory service manual. Then make some smart add ons like a pipe guard and skid plate and take some basic spares & tools as well as a few wraps of duct tape and some cable ties. I ride one of the ultimate run forever bikes (XR250) but I've never had issue with any bike I've owned as it was kept in a good state of repair. The flip side being I've spent more time helping people that didn't maintain their bike get thier bike running at the trial or on the trial than I can even remember.

 

[inotocracy]

:laugh: Really? Ever actually LOOKED at the service requirements on a current 4 stroke? Pretty much the same top end life as a 2 stroke. Oh sure you can push the limits but that's the same for either one and crank pieces through the case cost pretty much the same.

Well sure they recommend that but every 20 hours or so seems so damn... frequent. Anyone here honestly redo their top-end every 20 hours (not on a race bike)?

I've always been told and read that 4-strokes are a bit more complicated and expensive to work on, and I do own an XR100 but other than regular oil changes there isn't much else I've done to em. It doesn't get much use at all.

 

[flyingfuzzball]

I do own an XR100 but other than regular oil changes there isn't much else I've done to em. It doesn't get much use at all.

:laugh:

wrong type of 4 stroke. that thing compared to the modern race 4T's is like a minivan next to a corvette

 

[inotocracy]

Sure it isn't a high performance machine, but its still a 4 stroke :p

 

[flyingfuzzball]

yea and the minivan is still a car.

:nener:

 

[inotocracy]

Its a van, actually. Mini-van. :)

 

[sharky243]

It's not so much a wear thing you have to worry about. Your piston takes the most abuse out of all the parts on the bike. Yes it may still run good and make lots of power well after 20 hours of run time, but the metal fatigue is something you can't see. The piston skirt gets weak from "fatigue". If it is left in too long, it can shatter and cause major internal damage. For the price of a piston and rings, I would change it before it blows up. That will keep the bike reliable. So let me see....Hmmmm! $200 for a piston, or $1000+ for a full engine job, piston, cylinder, crank, and possibly crankcases too ? HMMMM !!!! Hard discission !!! Just my 2 cents !!!!

 

[Patman]

What most people do is ignore things and buy a new bike and pass the potential problems on to the next guy. Then somewhere along the line a piston shatters, a crank or rod fails and there are expensive busted metal pieces all over. At this point people blame the bike or engineer or company that built it and not the real reason. There is a real and valid reason that the specifications in the factory manual should be met and it's to keep the really expensive pieces from needing to be replaced. Sort of like people that never change the oil in say and XR100. Sure it will run with road tar in the cases.... for a while and a lot longer than most bikes but even it will die long before it should.

Most race bikes have similar requirements no matter 2 or 4 stroke it's just the 4T has more moving parts and thus needs even more love than a typical 2T but the common parts typically have a similar life span.

That being said there is no reason to not take a bike that is in unknown condition and recondition it to a level that will make one comfortable taking it on an extended ride with some level of comfort that they will return to where they started.

 

[FruDaddy]

I shattered a piston once, good compression feel, good power, I was even enjoying the ride (until the 10 second of funny noises before the shutdown). I hear rumor that they run best right before they blow. Proper maintenance is not a bad idea.

 

[sharky243]

You see, thats the whole point I'm trying to make. You can spend alittle now and do the maintainance, or take a chance and hope you don't have a catastrophic failure before you finally do change out the top end.

 

[inotocracy]

Yikes! Never experienced a piston shattering first hand, but I suppose if you've been through it you're probably a bit more strict about that 20 hours. Think I may need to start marking my calendars ;)

ps: I do change the oil on the XR100 :p

 

[UserFriendly169]

Hello,

This is my first post on these forums and I have a few questions about 2 stroke bikes. I have a buddy who is willing to sell me his 04 yz125 for a $1000. That seems like a pretty good deal to me. He just had the engine rebuilt also. This will be my first bike. Currently I borrow a Honda crf150 when I ride with my friends. I am 5'11'', 165 lbs and will be doing trail-riding.

I hear that the yz125 is a great bike but is it the right bike for me? I am very good with 2 stroke engines. I have built many liquid pocketbike engines in the past. But I want something reliable that i dont have to worry about seizing up when i am miles away from civilization. A few questions I have are...

1.- Is this bike suited for trail riding?
2.- How often does the top end/rebuilding need to be done?
3.- Is this the kind of engine that constantly needs to be tuned?
4.- Are parts expensive?

thank you,
Robert

1. From what I hear the yz 125 has more power than the crf150. The yz is a full size frame but is still relatively light... You're a little bit heavier, but I don't believe that should be an issue sine it's not by much. I would imagine the bike would fulfil your expectations.
2. Don't know.
3. It's a 2stroke... Think of it like a Ferrari, so ya it needs tuning up relatively often.
4. I can't imagine they would be anymore expensive than parts for another bike in its class.

$1000 is a great deal on a used yz 125, but be cautious: either your friend is really awesome or there's something up with the bike... My two cents

 

[mr db]

alright guys thanks alot for all the help. Yea ill def change the piston and rings every 20 hrs. And yea i was thinking the same about the fact that something might be wrong with it. Im going to take it up to the local dealer and have them check everything b4 i buy it.

I'd like to put a tach/speedo/hour computer on it. Any suggestions?

He says he never changed out the clutch so I am wondering if that will need to be changed. Do you normally use the OEM or a HP clutch?

Lastly I've heard alot about "powervalves" on 2 stokes. What are they and do they require special maintenance or anything?

 

[sharky243]

Barnett makes a good aftermarket clutch, but in your case just trail riding, OEM works fine as well. The power valve controlls the exhaust flow. It opens at lower RPM's and redirects some of the exhaust gases through "surge ports" which gives the effect of a long header pipe. This boosts the low-mid range torque. 125cc's don't have much there anyway. At higher RPM's, the valve closes off the "surge ports" and opens the exhaust port fully which boosts top end power. The power valve has a great effect on the power band, when and how hard it hits. There's not much for maintainance other then cleaning it, making sure it moves freely, and inspecting it for wear whenever the top end is apart. Oven cleaner works good to clean the carbon and sludge from the power valve components.

 

[mr db]

I think i will wait until I bought the machine to see if it needs a new clutch. Thanks for all the help.