So I have an old tired 1986 1.3.  When I first got it it would cruise at 70mph and it has slowly gotten weaker ane weaker over the last 10 years.  I found a complete 1.3 for $80 and could not pass it up.  I am a want-to-be mechanic and would like to end up with a motor that is at least as strong as the original stock motors.  I also found a Weber carb and have installed it on the intake.  Will the stock fuel pump work? 

When I go to rebuild it should I use the old pistons?  I see on ebay where people are selling "high compression 1.3 engines".  How is the high compression achieved? 

Any advice would be much appreciated

When you tear down the block you will know better if you need pistions in your rebuld.  If they are pitted or baddly scored on the sides it would be better to just replace them with new, they are not that expensive and come with most rebuild kits anyway.

Tear down the block, check the pistions, then take the bare block to a machine shop and have them check the cylinders for roundness (they can oval over time) and the deck for flatness.  They can then let you know if it will need to be bored and decked and if you will need to order pistions/rings in an oversize.  They will also check the bearing faces for you and let you know if any machine work will be needed there and if stock or oversize bearings are needed.  They can also dip the block so you are working on a nice fresh piece of metal instead of the old oily mess its probably in.

You can drop off your head at the same time and get a good valve job, which will do wonders on an old motor.

I just went through this and lucked out as everything checked out ok on my 1.6 swap.  I was able to order all stock sizes and the cylinders only needed to be honed.

Just ordering a rebuild kit and hoping no machine work is needed is not a good idea.  

By the way, I have a bunch of 1.3 stuff for sale if you end up needing anything...

Thanks for the advice.  So are the flat-top pistons a good idea if I have to replace them?  Where are you with the parts?  I am in Eastern WA.

I'm in Tulsa OK. the parts for sale are listed here, I might have some other stuff around but this is what is cleaned up and ready to go now... you probably have all of this if you have two complete 1.3's to start with.

http://www.zukiworld.com/forum/classified-ads/88-samurai-parts-in-tulsa-may-ship/

I bought my rebuild kit on ebay from Mishimoto I think.  Very complete kit with water pump, oil pump, pistons, gaskets, bearings, rings, yada yada...

I can only post what LowRange has to say...
"If you are looking at adding a few more ponies to your powerplant, high compression pistons help in a big way. These are high quaility, long lasting pistons without the standard bevel in the top of the piston. This adds a little more compression to the mix for a little more power and when your only starting with 60 horse power, a little bit goes along way!

Adds about 1 pound of compression. Still retains valve reliefs.

Available in Standard, .020, .030, or .040 sizes and kit comes with wrist pins and new high quality pistion rings."