Hello all!

I'm still working on this 1987 LT80! Mr. LT80 helped me out with my drive train problems some months ago but now i have bigger problems! My son was riding the thing, ran out of gas and could not restart it. I checked for fuel flow, spark and compression, in this case 2 out of 3 is bad!!! the compression was about 25psi, i ordered a weisco .20 over piston set, carefully dissassembled the engine had the cylinder bored reassembled the same way i took it apart (i have no manual) it started just fine, ran 10 minutes made some really terrible noises then no compression again! I dissembled it and found the piston and cylinder destroyed! looks like a ring came out of its groove and made a mess of things! So i ordered a new .40 over weisco piston set went to the machine shop to have it bored and the machinest told me i installed the piston backwards! that the arrow should point to the exaust side of the cylinder. OK the first one was my mistake so i made sure to properly assemble it this time, i got it all together (made sure it was correct)! Tried to start it, it started and ran for a minute but badly! I checked the compression buy placing my finger over the hole and it seemed good, so i pulled the carb and reed plate only to find a chunk of metal holding the reed open! Being i had already purchased a power intake kit w/ new reeds new jet and uni filter i figured now was the time to install it, Now it wont run at all! I again checked the spark which was good, its getting plenty of fuel but the compression is holding at 65 psi, i poured a little transmission fluid into the cylinder and checked the compression again and it holds at about 90psi, I guess my question is: is it possible the rings are not seated? My son is really discourged and i really cant blame him, he just wants to get rid of this thing and start out fresh with something else! Sorry for the long post but i wanted to get enough info. as to get a good response! Any help would be greatly appreciated!

 

I'd like to know:
What clearance did the shop give the piston?
Did you check the rod bearings?
Are the new reeds sitting down on the reed cage?
What jet did you install?

 

Mr. LT80 to the rescue again i see!!!

as for your questions, I brought the cylinder and the entire weisco kit w/instructions to the machine shop, This is a reputable shop known for their work on small 2 strokes so i don't know exactly what size they bored it too. As for the jet, i purchased a power-up intake performance kit from midwest mini's off of e-bay i just e-mailed them for the jet size, the reeds are boyesen power reeds and i made sure they were sitting nice and flat on the reed cage, the rod bearings had no noticable play so i reused them, I will get back to u with the jet size when i get it! Now that i think about it, the thing started before i put the reeds and jet in it and seems to be getting alot of gas so maybe i will try putting the stock jet back in! But that still wouldn't explain the low compression.

Thanks again your past help was greatly appreciated!!

 

Ok i'm back, I just recieved the information from midwest mini's on the jet size, its a #90 I hope this helps!

Thanks!

 

I figured that I'd take a few days to think about this one.
It surely puzzles me also. I agree that there shouldn't be a compression problem.
nothing you have added or done should be a problem.
I'd really like to know how much clearance they gave the piston when bored.
[img]i/expressions/face-icon-small-confused.gif[/img] [img]i/expressions/face-icon-small-blush.gif[/img] [img]i/expressions/face-icon-small-confused.gif[/img]

 

sometimes the case bolts will losen and suck air into the cases causeing the bike to run lean which will ruin a piston in no time but just a thought you might want to check them. its not good for our kids to sit inside when they could be riding.[img]i/expressions/face-icon-small-smile.gif[/img]

 

did you ever get this fixed? I wonder if end gap on rings were properly lined up with the piston nub when you put cylinder on, or if it might have shifted? This could cause it to work okay and get worse quckly,and might explain the chunk of metal holding reed open, and loss of compression.