87 125m won't run right

[3>4]

I don't have a manual

[Dave8338]

Here is a link to your Honda Service manual. Print out the parts you need.
http://campaigns.hondampe.com.au/Mot...n85atc125m.pdf

Start at page 41 in the manual.

Here is an exploded diagram of your carb and below the picture, is a complete list of the internal parts.
http://www.bikebandit.com/oem-parts/.../m1877#sch6727

[3>4]

So if it needs the top end done that would cause it to do that?

[Dave8338]

It "could". There are several factors at work, here. The first thing you need to do is establish a check list of potential problems.

I've seen some pretty loose engines that still run amazingly well BUT, everything else was in check.

You have Three sections that you need to cover, thoroughly:
1) fuel / air
2) spark
3) compression

If all of those check out correctly, it will run.

The 185 engine in my little trike is SHOT, SHOT, SHOT. As soon as it warms just the slightest, I can leave a trail of blue smoke for 1/2 mile. Louder than a bag of s in a paint shaker, and leaks from EVERY seal. Just add oil. Carb is spot on and ignition components are new. Still runs strong...

[3>4]

I think it needs rebuilt. When it warms up it starts smoking.

[3>4]

I tore the top end down. The piston and rings look fine. When I cranked it over I could hear air getting out. I think it might be a bad gasket or something.

[Dave8338]

Are there any signs of carbon build up or "burnt" spot on the head gasket? It is nearly impossible to visually inspect a piston and rings, unless it hatched in the jug. You need to measure your piston to wall clearance, ring end gap, and the ring groove, for wear.