1992 SA50P Sudden no start

[den052]

Was driving the moped yesterday and performed flawlessly to 40mph. Parked in garage overnight. Next morning no start. Spins over but no firing. Checked spark, jumps 1/2 inch no problem. Tried new plug with no response. Then checked for compression and feel alternate sucking and slight compression with finger covering sparkplug hole. Pulled reed assembly to check, everything seems ok and no damage to reeds. I am a mechanic that is familiar with the 2 cycle operation. Anything else short of pulling the jug and checking rings that I can look at?

I mean it ran flawlessly last night before I turned the key off in the garage. Now it spins over like it normally does but will not fire up. I know it won't fire without proper compression, but why the sudden compression loss? Could I have blown a crank seal suddenly?

Stumped!!!!
Thanks, Dennis

[patthesoundguy]

Try a new plug, they can fail and will fire outside the cylinder but not inside. If it drove you to where you shut it off suspect something simple

Sent from my Nexus 7 using Tapatalk 2

[bfowler]

Perhaps you had an air leak somewhere and something happened to the piston or rings. Mightve been that it was running fine at WOT but experienced high off throttle temperatures leading to some overheating issues. If a new plug doesnt work might want to check compression.

[kingearwig]

If it isn't blasting air past your finger over the plug hole it definitely doesn't have enough compression. I wouldn't bother with a compression tester. You can take the exhaust off and look in the exhaust port and look at the piston and rings. But I would just tear into it. Take the shock bolt off and the motor mount bolt out and disconnect the wiring and throttle and brake and fuel line and oil line and drop the motor right out of the bike. I think bfowler is right... probably melted the rings to the piston.

[den052]

Ya, thats what I figure. It should be blasting air past my finger. I do have a compression tester but no need to use it. That was my next step was to tear it down and inspect. Based upon the age of it, I will probably replace the crank seals also along with anything that is worn. A lot of people don't know how important the crank seals are on 2 cycle engine engine operation.

Thanks for the replies.
Dennis

[den052]

Well, probably should have done this first as I suspected something mechanical. But thanks for answering my post as I thought something happened unique to SA50 specific.

Removed jug and found 1 ring completely gone with 2nd ring stuck. I am going to disassemble the engine and completely clean all parts to flush out broken ring pieces if any. Replace crank seals, gaskets, piston and rings, and reassemble. Surprisingly the cylinder wall looks good with no scores. A light hone job and reassemble should be fine.

Used to get 80mpg (USA). After overhaul, might get 120mpg. LOL. Cannot believe it ran so good before as the upper ring had to be gone for a while. I could hit 45mph and maybe a little more on a good day.

Thanks again, Dennis

[den052]

Hey, whats up with searching for a gasket kit for a 1994 SA50P? No blow up diagram exists to order the gaskets by piece-meal or complete kit? I did find the crank seal part numbers though.
Thanks, Dennis

[dun rite]

I use these guy's but several other's exist Bidebandit.com cheapcycle.com to name a few.

view this http://www.collegebikeshop.com/fiche_se ... veh=131284

[kingearwig]

12191-GAH-A00 is the part number for the base gasket
12251-GW0-000 head gasket
you'll probably want these too intake manifold gaskets.
17111-GAH-A00
17112-GAH-000

[kingearwig]

oh... if you are going 45, someone de-restricted your sa50p. You may want to research some more but I believe that most people who run de-restricted sa50p's either get the sa50 higher flow oil pump or add a small amount of 2t oil in the tank when they fill up. Also I would recommend a plug chop when you get it running to see if you have proper jetting to help with the life of your motor in the future.