Hi Everyone,
So it's been quite a while since I've had a scooter. Used to run myvento.net back in the day, but haven't owned a scooter since 2006. I ran across a deal on Craigslist this week and couldn't pass it up -- a 2008 JCL 50cc (139qmb) with a busted tail light, one plastic panel that needed to be replaced, and a very obvious fuel delivery problem. It has 600 miles on it, and I grabbed it for $240. It looks like the TaoTaos and other chinese scoots that I seem to see everywhere these days. The only downside is that I think my Harley may be jealous
I got it home and started working on the mechanical issue first (not running). I removed and cleaned the carb (it was spotless inside, but I blew it out thoroughly with carb cleaner for good measure and verified jets were clear). Still wasn't running - didn't appear to be getting gas. Fuel filter was fine. I bypassed all of the emissions crap that was connected to the intake manifold (and vaccum line for fuel valve) with no changes, then I bypassed the fuel valve completely. Started right up. Fuel valve appeared to work, but you would have to put pretty heavy suction on it to get it to work.
Picked up a new fuel valve for $9.50 locally and grabbed a replacement tail light for $25 (local eBay distributor sells locally out of his warehouse). Have plastics and a battery on order (kickstart works).
Installed fuel valve, tail light, and then went on to maintenance related items... Replaced fuel filter, installed quality fuel lines, changed gear oil, and motor oil (synthetics all around), cleaned air filter element.
Re-installed the seat this evening and took it for a little ride around my neighborhood. It drove fine, less power than the two strokes I had back in the day (but I expected as much). The only problem I encountered was that when I came to a stopsign, it would just about stall out unless I hit the throttle a bit.
So I figured idle fuel/air mix or idle screw issue.. Adjusted idle fuel/air mix first, then turned up idle to where the wheel was barely spinning, and then backed it down a half turn or so. I let it warm up on the stand then hit the throttle and let it rev up pretty good, then hit the rear brake and held it. Same symptoms -- would immediately bog down and die unless I hit the throttle.
Searched around and determined the next step was to check valve clearances. Intake was set at .005, exhaust was at .005. I adjusted the intake to .004 and left the exhaust alone. Didn't make a lot of difference running wise, still sounds a little like a sewing machine
Re-tested, same deal.
Disconnected all emissions stuff on the intake side (maybe a vacuum leak?), re-tested, same deal.
So I pulled apart the airbox, pulled out the filter element, and started it up. Left one screw in so I could split the box apart while running. Did this (no filter element, half of airbox off), revved it up, issue gone. Re-attached the half of the airbox with the crankcase vent going into it, died immediately.
Restarted it, revved it up with the airbox split, and it looks like the crankcase vent is dumping off some gasses after revving (going out of the intake holes on that side of the airbox). I left the airbox split and put the intake end (where crankcase gasses were coming out) inside of the other half that was attached to the carb -- instant bog down. Take it away, idles normally.
Symptoms:
After high revving, gasses that are coming off of the crankcase breather hose and into the intake seem to be creating a rich condition which causes the scooter to stall. The scooter idles normally during and after warm up, and seems to drive normally.
Any idea what could be causing this? I know I could just run the crankcase breather hose elsewhere (catch can routed to dipstick with a pcv, or route a hose from the valve cover to the back of the scoot), but I would rather leave the emissions stuff intact. I also don't want to hide the symptoms if there is a real issue that is causing this that I could address...
I'm kind of missing my two strokes, lol.. no emmissions stuff and no valves or cam - simpler times
Thanks,
Rob