Chinese Scooter Club

stirlinggaz · Sun Jul 13, 2008 1:17 pm COMPRESSION

hi all,
decided to have another go at getting the scoot to start.
its a jinlun jl-50 "fighter" 4 stroke.
theres petrol in it, & its getting to carb.
also getting a healthy spark.
tried some petrol in the plug hole & it started & ran for about 2 seconds, then cut out, lol.
tested compression & its 120psi.
is this normal?
anyone know what it should be?
or any other ideas?
cheers,
GAZ

Yellow Scooter · Sun Jul 13, 2008 2:22 pm

When a motor starts without the carburetor and/or gas is sprayed straight into the intake, 99% of the time the carb is either plugged up or totally shot.
Have you tried cleaning the carb? I don't mean a small shot of STP in the gas, I mean remove some screws and really get in there and clean it. Take off the float bowl, remove the 2 jets, spray carb cleaner thu them, and again with the bottom blocked with your finger, to clean out the tiny side passages. A small sewing needle is great for poking out any micro-debris that could be clogging those passages too.
Take the choke off and spray into the enrichment chamber, Pop the top off and check the diaphragm for tears, Careful taking that part off, it's spring loaded. ;) Since you got the top off, ya might as well spray that out too before putting it back together. Put it back on the bike after its reassembled and try it. ;)
If it don't start after all that, the carb's a gonner. :|

stirlinggaz · Sun Jul 13, 2008 5:23 pm UPDATE - now running!

hi,
carbs been off, dismantled, cleaned thoroughly with carb cleaner.
& all blown through with compressor.
& it all looks in reasonable shape.
besides, I never give up on a carb, seeing as its so easy to replace parts! lol
anyway found what I think was the problem.
inlet manifold was split. wrapped some gaffer tape round it. & it now starts!
its been lying in my shed for over a month since a mate dropped it off as a non runner.
only faults found : split manifold,
loose wire at starter (now soldered)
needs replacement front panel.
battery's fucked. (got a spare one though)
so I just need to put it all back together! lol seeing as I completely dismantled it! (didnt know where to start, so I ripped it apart, lol)
anyone know where to get replacement plastics?
cheers,
GAZ

Fox · Sun Jul 13, 2008 5:33 pm

Buy a new one:

http://www.baotian-scooters.com/carburetor-inlet-manifold-assmbly-p-2559.html?cPath=513_368_377&osCsid=91f94fc721f7bf84ccf3ee69ef550520

jpmacd733 · Sun Jul 13, 2008 6:27 pm

120 psi for compression is very good - almost like new.

Joe

Billy Madison · Wed Aug 06, 2008 11:17 pm

what is the compression for a 2 stroke engine

jpmacd733 · Thu Aug 07, 2008 1:37 am

Billy Madison wrote: what is the compression for a 2 stroke engine

Billy, you need 90 psi compression for an engine to start 2 or 4 stroke, just as a reference. The 120 psi for a 4 stroke is normal. Don't have any specific for a china 2 stroke but 120 psi would still be a good runner for a 2 stroke. On Honda 2 strokes I've replaced rings and got 150 psi. So, there is at least a range for you 120 to 150 psi for a like new 2 stroke. For your scoot, 80 cc, you are maybe pushing the 150 psi.

Joe

Billy Madison · Sat Aug 09, 2008 12:59 pm

Even thou I been reading about compression on a 2 stroke engine and saying 100 is good the vento zip manual says 148 max 139 min. I though that was high but I stand corrected. What I think happen is when I hit that bump in the road it broke the oil cam gear or something with the oil injection and starveed the motor for oil. since it still cranks over I'm going to replace the rings and hone out the cylnder and fix the injection pump but should run premix instead