Two Stroke Motocross

Two Stroke Motocross Forum => General Two Stroke Talk => Topic started by: JoeyG on July 31, 2013, 02:14:10 PM

Title: I finally got a bike!!!
Post by: JoeyG on July 31, 2013, 02:14:10 PM: Well after months of searching and then just giving up on finding a bike, one just falls on your lap! I managed to pick up a 2000 YZ125 for a very good price. The top end is shot but that's no biggie. It has an FMF SST pipe, new rear tire, shifter and a few other little things so I'm very pleased.

I have a few questions, Previous owner installed the pipe and then cooked the top end. What is stock jetting and/or what is a good starting point for jetting? My elevation is around 1300.

Any other things I should look for? I did notice he had the CDI ziptied to the neck of the bike..is that where it goes?

Thanks!!!!
Title: I finally got a bike!!!
Post by: eprovenzano on July 31, 2013, 02:19:58 PM: What is the condition of the cylinder and head. Is there any (up and down) play in the connecting rod?

Start searching for a manual. It will become your best friend through the rebuild process
Title: I finally got a bike!!!
Post by: JoeyG on July 31, 2013, 02:27:44 PM: I don't know yet. I didn't get it till late last night but I'll tear into it after work. I'm going to check for main bearing slop as well as any rod bearing play.
Title: I finally got a bike!!!
Post by: eprovenzano on July 31, 2013, 02:31:07 PM: OK you're on the right track. Inspect, inspect, and inspect before deciding on what needs to be purchased...
Title: I finally got a bike!!!
Post by: Coop on July 31, 2013, 02:33:34 PM: Quote from: eprovenzano on July 31, 2013, 09:31:07 PM
OK you're on the right track. Inspect, inspect, and inspect before deciding on what needs to be purchased...

Yep. Then inspect some more. Never take a sellers word for what a bike needs.

Congrats on the new bike! Post up some pics when you can.
Title: I finally got a bike!!!
Post by: mj4trax on July 31, 2013, 02:40:48 PM: a 2000 yz125 is a wonderful model bike, lots of fun, neutral handling. It should treat you well.
Title: I finally got a bike!!!
Post by: c-slacker on July 31, 2013, 03:33:03 PM: From my research the cause of the meltdown was the SST pipe. The following is a quote from another forum:

"The FMF SST pipe is an amazing pipe.

Why is it amazing? Because in just about every case, it will work WORSE than the stock pipe that came on the bike.

The SST uses a restrictive reverse cone and pressure bleed to intensify the return wave and lower the initial flow out the stinger section of the pipe. What that in turn does is increase piston crown temperatures and make jetting difficult at best.

Now increased piston crown temperatures can be compensated for to some extent with richer jetting. But, by doing that you are defeating the purpose of the pipe, and negating any power gain you may have gotten from the pipe in the first place. Why are increased piston crown temperatures bad? Well, in some cases they are not. You see most bikes are jetted horribly rich from the factory, and raising the piston crown temps in this case will "fool" the engine into thinking it is jetted leaner than it is. Which will in some cases improve power. But in most cases, it will just cause slightly better throttle response and an increase in the spooge out the back of the pipe.

After all that you may be thinking: "well this doesn't sound so bad, why are they saying this pipe is no good?" Good question. Here's the answer. Because of the restrictive nature of the pressure bleed from the pipe, it does not evacuate as efficiently as it needs to. This combined with the piston crown temperature increase yeilds jetting that is too rich. So now you have a pipe that "fools" the engine into thinking it is leaner than it really is, but also makes it much richer than it was previously. Here in lies the second problem. It makes jetting a nightmare. If you jet it by feel, you will be jetting richer, and compounding the too rich condition even more, making the bike run like a slug. If you jet it leaner, you will be increasing piston crown temperatures even more resulting in an engine siezure. Catch-22 anyone?

If you are buying a pipe for your bike, get ANY other pipe. Or better yet, keep the stock pipe."
Title: I finally got a bike!!!
Post by: 2 smokin RM on July 31, 2013, 04:00:13 PM: Congrats on the new bike! Should be a ripper. Just make sure you check everything out a few times before ordering your top end and any other parts you need. Pull the clutch plates out and check them while you're at it. They're cheap to replace and easy if need be.

Check the trans fluid.
Pick a premix that's readily available and fits your price and stick with it. Along with ratio. Should be 32:1

You'll be set for a while with a new top end and some new fluids. Get it running good and youll be addicted to riding it
Title: I finally got a bike!!!
Post by: JoeyG on July 31, 2013, 04:36:20 PM: Thanks everyone I'm really excited about this bike. I haven't been on a bike since 97 so the itch to ride is strong.

Slacker,
That may certainly explain why the top end went poof right after he put the pipe on. I think the SST may be up for sale!!

I have a pic but the file size is too big? Anyone help out with that?

What is a good pipe to replace the SST with? Fatty, PC, Stock??
Title: I finally got a bike!!!
Post by: eprovenzano on July 31, 2013, 04:42:42 PM: Quote from: JoeyG on July 31, 2013, 11:36:20 PM

What is a good pipe to replace the SST with? Fatty, PC, Stock??

Remember you are on a 125... where do you want the power to be bottom, middle, or top... based on that info you can choice a pipe to suit your riding style and terrain.
Title: I finally got a bike!!!
Post by: JoeyG on July 31, 2013, 04:49:05 PM: The bike will be used for MX. When it comes to a 125 I think you want your cake and eat it too type of pipe?? Bottom to mid? Heck a stock pipe just may be the ticket.
Title: I finally got a bike!!!
Post by: mj4trax on July 31, 2013, 06:12:24 PM: I've been pretty happy with the stock head pipe on my '01 yz125.

My brother put a PC platinum on his 2000 yz125, and we noticed very little difference. If anything it seemed to rob a bit of the bottom power to add to the top end. .... but it's barely noticeable.
Title: I finally got a bike!!!
Post by: eprovenzano on July 31, 2013, 07:45:36 PM: I think (someone please correct me is I'm wrong) (again) The fatty will rob some off the top, but will boost the bottom end, the PC will rob some of the bottom and will boost the mid to top. I'd go with a stocker at 1st (cheapest option) and then decide where you need more or less.
Title: I finally got a bike!!!
Post by: citabjockey on July 31, 2013, 10:23:52 PM: Open an account on phtotbucket.com.
Upload your photo(s) there.
Hover over a photo in your album view and you will have a menu popup, click on the "IMG" item.
Then go to you posting window over here. In the text area right click on you mouse and select "paste". Some gibberish looking kinda like
Code: [Select]
(http://blahblah/some stupid things/bikephoto.jpg) will show up. submit the post and there it is!

Quote from: JoeyG on July 31, 2013, 11:36:20 PM

I have a pic but the file size is too big? Anyone help out with that?
Title: I finally got a bike!!!
Post by: JoeyG on August 01, 2013, 02:23:48 AM: Ok, I found out its a 1999....No biggie. I did pull the cylinder head and found the leading edge of the piston cooked. Is that from running cheap gas? Isn't lean just burn a hole about center of the piston? Also noticed the cylinder is 55mm, does that sound about right? These are plated cylinders and can't be bored like a steel sleeve?
Title: I finally got a bike!!!
Post by: Stusmoke on August 01, 2013, 05:54:26 AM: 55mm x 54.5 mm bore and stroke sounds right. Congrats on the new bike, leave it pinned.
Title: I finally got a bike!!!
Post by: eprovenzano on August 01, 2013, 01:48:10 PM: My son had a 99... strong engine, pretty much bullet proof with basic maint. As far as the piston goes, no it does not had to burn a hole the the top to be lean. How does the cylinder walls look, and scarring or scratches? How about the head? While its down, clean the power valve. One tip if you disassemble the power valve for cleaning, take pic's and notes as to its settings... (don't make the same mistake as me and take it apart and forget how it goes back together)

If all is well, get a new piston, ring(s) and top end gasket kit. While your waiting for parts, takes the time to pull the wheels, re-grease the wheel bearings, swing arm bearings, etc. Go over the bike looking for loose or missing bolts / nuts. Be prepared to replace some nuts and bolts with the correct hardware. Its all part of resurrecting a bike... Now is the perfect time to go over the bike to make sure all is correct, and when ready she will reward you by putting a huge smile on your face.
Title: I finally got a bike!!!
Post by: JoeyG on August 01, 2013, 05:10:14 PM: Thanks again for all the great info. The head looked fine but it certainly was lean. Walls are iffy but it may just be aluminium buildup from the piston. The previous owner did not take care of it as it has missing bolts and broken hardware. I will certainly take pics of the power valve. Any idea where or how the cdi mounts? Also do think I can het away wit& the sst pipe or just scratch it for a stock pipe? I found one from an 01 and I think it should work.
Title: I finally got a bike!!!
Post by: mj4trax on August 01, 2013, 10:28:52 PM: That bike is 54 mm stock. If your piston is 55mm and the cylinder is plated, that means somone had the cylinder stripped, bored and replated at +1mm.

If your cylinder looks good, I suppose I'd just buy a 55mm piston and be done... otherwise, you could send it out to a plating shop and they may be able to get you back down to 54mm... not sure on that one.
Title: I finally got a bike!!!
Post by: JoeyG on August 10, 2013, 09:27:22 PM: Well I got the cylinder off and it has a sleeve in it. Also the powervalve rod was broke and noticed that a piece of the exhaust bridge broke off. I don't think it will hurt anything but never know. The cylinder ended up being a 99 but the chassis is a 2000 or 2001 as I purchased a 99 exhaust and it doesn't fit. Found the intake boot that bolts to the reeds ripped and the carb is a keihin and not a mikuni. So I'm starting with stuff I have no idea if it works or not. This is turning I to quite the project. Piston and gasket kit will be in Tuesday so I hope to Have it up and running for Wed. Practice day at the track.
Title: I finally got a bike!!!
Post by: mj4trax on August 11, 2013, 10:52:41 PM: good luck.

It's criminal what some owners do to their bikes. I've had to learn from experience that condition is king when looking at bikes as repair costs from an irresponsible PO can add up REALLY quickly.

If you do end up putting more $$ into the bike than you wanted to, make yourself feel better by thinking about the fact that you are resurrecting the bike and saving it from the scrapyard.
Title: I finally got a bike!!!
Post by: JoeyG on August 13, 2013, 01:57:54 PM: It amazes me as the more I dig into this bike the more things I find. Maybe it's just being anal but so many simple things that never got addressed. Worn throttle cables, Loose spokes, install all the proper hardware! In the end I will still have less in it than if I purchased a running bike and I'll know what's done just as I get older I can't see throwing money away by not doing simple maint.

As soon as I get a chance I'll post some pics. It a super tight budget build, just get it running so i can ride.