Any Dirtbike guys?

Sorry this isn't XS650 related. But it is Yamaha IT :-(

Any dirt bike guys that can help me out? I'm new to the two stroke world but can't seem to find a forum for my Yamaha 79 175 IT & 81 250 IT.

- How can you test that the forks and shocks are good?

- Compression – I tried to start the 175 I and even though it was getting spark and fuel I was getting nothing. I threw the compression tester on it and first kick was 30, second 60ish until finally it maxed out at 142. Is that a valid test???

- When the bike came to me the whole front end was apart. I threw the brake line and tried to bleedd it but after 100+ pulls I'm still getting little air bubbles and no compression. Does this take a long, long time?

Two strokes are pretty simple but there are a few things that can really be hard to diagnosis. Are you sure you have a spark and is it timed right? Check your coil, stator, and timing. Your compression seems pretty good. You can also check the reeds. If there bad it will make it hard to start and run badly when it does. The carbs also get gummed up pretty bad on a two strokes. The front brake, you need to rebuild the master and maybe the caliper.

Thanks for the advice. Not sure why I didn't even think of timing. I'm going to need to find a manual for these, does anyone have a scanned one? What the heck are reeds

Would the reed valves affect the compression?

Yes. Reeds act like valves for a two stroke. They are right after the carb, before the piston, on the intake side. Take them off and see if you can see any gap in them, if you can they need to be replaced.

great site for dirt bikes www.allthingsmoto.com lots of people can help you out there

mmmmm, 2-strokes. Someday, I'll have an RZ350... :drool:

hotrdd said:

Sorry this isn't XS650 related. But it is Yamaha IT :-(

Any dirt bike guys that can help me out? I’m new to the two stroke world but can’t seem to find a forum for my Yamaha 79 175 IT & 81 250 IT.

- How can you test that the forks and shocks are good?

Click to expand...

When the back keeps trying to pass the front (swap)
Those old monos were kickers, thats for sure. Rebuilds are specialized, so expect $$$.
Those bikes are bulletproof, but broken pistons kill em. Go out and pull the top end if you are planning on some seat time, measure it up and repair as needed. Pretty easy, and you will be glad you did.
Back in the day, those two bikes were perfect for the terrain where I learned to ride.
P.S.
Ask around for a good machinist for your cylinder that is 2stroke freindly.

You might give this forum a try:

http://www.yamahaenduro.com/

Basics of a reed valve:


Air cooled ringdings are chimp simple and easy to work on. They will clank like a paint mixer when cold (piston slap) but run great when warm. The average air cooled two smoker will need reringing every riding season, otherwise if you use good quality oil (I like Bel Ray and Yamalube myself) the cylinder and piston itself can go probably 4 or 5 seasons.

I don't know of anyone who still rebuilds those old DeCarbon monoshocks. Maybe that forum will put you onto someone who does.

My cr480 was on the same set of rings that I installed and ran, hard, for 5 years.

Never use klotz or a soil, its terrible. Motul or Castrol

My first dirt bike was an it175. It was a blast for a 13yr old just starting out. Sorry I'm not much help its been years. Post up some pics.

Yah I got both bikes for $150 so I don't have anything into them. Except for the plastics The 175 is in good shape. The 250 needs a lot more TLC but with my boys getting older I thought they would be fun to play with for a few seasons. Otherwise I'll sell them.

Thanks for all the help. I've got some reading to do.

Well here comes the same old story. I got busy with things and these bikes sat for a while. In the meantime I've been playing on the XS650 and picked up a 05 KTM Adventure S.

I tore into both bikes and the 250 will get sold as it's more work and CC than I want for the boys. The 175 is in really good shape with really only cosmetic issues. So I tore the carb off and gave it a good clean.

Bike wasn't running when I got it but after cleaning the carbs I can get the thing to idle on the second or third kick. The problem is that if I roll on the throttle the engine just bogs down and almost dies or almost dies and then screams through the RPM's. I assumed it was running way to rich so I dropped the main to #190 but that hasn't helped. I also confirmed that the pilot jet was clean but am not sure where to go from here.

There are two screw knobs on the side of the carb. What are the default adjustments on them and what does each one do?