1983 yz80 need help

Hi, I have a 1983 yamaha yz80. It runs and idles well, new piston and rings, porting, gaskets and oils but it bogs as soon as I give it thorottle, and won't go into the powerband. It is set to the stock jetting. I also made sure my crank bearings are good, no play at all. Can anyone tell me what might be wrong?

Jetted to lean? Jet to rich? Let it warm up real good. Like 5 min of slow riding. Then run it. Try turning the choke on. Does choke make it better/ worse?

It won't let me take off it stalls. Even after 10 minutes of idle and revving in neutral, but I can't turn the thorottle any more than one eighth or it will bog and stall. It is at stock jetting

And I mix at 30:1

Choke makes it better but it floods waaaay too easily

Try two steps larger on the main jet. If worse try two steps smaller ( than original) on main jet. If there is no perceived difference. It probably not a jetting issue. Might try 40:1 on oil and make sure you use new fuel/oil. If the carb hasnt been cleaned that would do it too. I. Fact if the carb was not cleaned during latest tear down do that before anything else. Soinds lime a POS is stuck in your main jet. Idles, runs on choke, but not on throttle...

Unlike previous poster has mentionned, do not change the premix ratio to 'fix' a problem...


Have your reeds been replaced lately?

They might look okay (no physical damage) but they are a wear item and become too 'flexy' with time.


If it revs freely while in neutral but bogs when put in gear, I'd have a look if your clutch was dragging.

Edited by mlatour

The clutch is good, the reeds seem pretty bad but I have been told they are ok for now. I will try cleaning the carb, I set the little pin in the carb to the 3rd position from the top. There are 4 positions on it.

Cleaning / adjusting the carburator is a good start.


Worn reeds make the engine run richer than normal, so does worn rings,

fix / replace what is worn instead of trying to compensate for it.


Changing the premix ratio or re-adjusting the jetting is 'fixing things backwards' if components are worn out.

I didnt mean to permanently change the oil. Just one of many things to try to figure out the real cause. Probably not the best method nor necessary but 30:1 is a lot of oil even for n old bike. I doubt a 83 yz85 is being raced. Still sounds like shit in the float bowl not passing through main jet. Ill bet my nickel on it.

A fresh spark plug and a visual inspection ofnplug might not hurt either

When I get home today I will try everything you all said

I think I have this all wrapped up, the carb is now clean, everything is set to stock and it runs and drives, but still won't let me turn the thorottle any more than 8/10 or it will bog but I don't need to turn it all the way because it still needs to be broken in, after that I'll get new reeds. Thank you all for your help.

Sounds like jetting now for sure. Plug check should tell you which way to go. Hard to know without riding it so check the plug. Black and wet is too rich. Light light color and dry as a bone is lean

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