Engine Problem with RM125

Well, this is my first post on this forum too bad it is with a problem. lol

I have a 1983 RM125 that will start up fine on the first or second kick and idle all day. It has no power and anything more than about 10mph it will bog really bad and backfire occasionally. Here is what I have done so far.

1- Replaced spark plug
2- Replaced head gasket
3- Cleaned carb(already clean but I cleaned it anyway)
4- Messed with richer and leaner jetting
5- Tried without fuel filter
6- Checked reed valve(perfect condition)
7- Checked the spark by taking out the plug, grouding it to the case and kicking it over. I'm not positive but I think it was fine. It made a small blue spark.
8- I knew the compression was a bit low so I got it bored and put a new piston and set of rings in and replaced the head and base gasket.

This year did not use an exhuast valve just a hole with a support going from top to bottom.

The only thing I can think is that the spark is too weak. Or maybe even a late? If this is the case should I just replace the coil? I also heard somewhere that this year had a low and high speed coil. Is this true?

Thanks

If it were a magneto stator problemwould it need to be replaced completely or are they usually repairable.

Anyone?

Yeah, the pipe is clean. The only problem with it is a small dent in the header maybe 3mm. deep. I don't think something that small would cause any problem so I left it. I tore the carb apart and looked checked everything. I put new jets in it too. The air filter is bran new and oiled.

Though I think I finally got it figured out. Of all the things I did trying to get this to work this is probably the easiest, lol. I took the magneto cover off and started checking the resistances between all the connections and all. I found one of them had a fair amount of corrosion between the bolt and connector. I cleaned it all off and then started it up. It fired right up and ran 10 times better.

So it works fine now except I have two more problems.
1- Till about 1/3rd throttle it doesn't have much power and kind of bogs. I'm thinking I should open up the pilot air screw?

2- An employee at a motorcycle shop told me I should run 85wt. 2 stroke tranny oil. So that's what I did. When breaking it in though it was very hard to shift. From neutral to first was fine but it was very hard to get it out of neutral. Sometimes I would but when upshifting higher it would always drop back to neutral. I started looking in the service manual and found a table that said to use 20-40w motor oil. I couldn't find any 20-40 so I ended up buying 20-50. After about the first two shifts it worked fine and shifted right everytime. So it works but I wanted to make sure that the motor oil is the right thing to do. I don't want to end up blowing the tranny. I've heard old clutches that slip but would I know if this was slipping?

Thanks