50cc bogging down and stalling  By  grieve (Read 2,777 times)

Sounds like you've got a good plan.
I'm assuming in those 2 years you've never adjusted the valves or cleaned the carb?
Prob want to do both either way, but I'm thinking there's a good chance it's the valves since it seems like your problems arise once the scoot is nice and hot. Esp of its stalling the valves expand and are probably close to, if not, closed.
And either way cleaning and adjusting the carb should improve your performance

How many miles until u change your oil. ? It should be done at least every 1000 miles. I change mine on average about every 500 miles.

Wow , I put around 6,000 miles on my scoot every season. Last year I rode in the winter so I probably put close to 8,000 miles on her.

Ok so my feeler gauge arrived this morning and I got work started. Things did not go according to plan...

The valve adjustment was fairly straight forward. They were was too tight. Loosened them out to 0.05mm, tightened the nuts and rechecked. Still all good so started reassembly. This is where things started going downhill.
Got the valve cover back on ok, but while tightening the nuts on the U-shaped tube thing that sits over the valve cover, the outside one just sheared the bolt clean off flush with the engine. Not good... I don't know what this thing is or does but it can't be good.
After that I reattached the battery, started it up and let it run for 10 minutes. Pretty much as soon as I got on and tried to ride, the old problem resurfaced. Bogging down, need full throttle to keep from stalling, no power to wheel.

So in I go to the carby, follow alleyoop's tuning instructions. Some changes to idle speed while adjusting A/F mix screw but seemingly minimal so I decide to pull the carby and clean it. Pretty much every screw I removed fell down and got magnetically stuck to the most inaccessible spot on the starter motor.
The smaller brass jet (?) in the middle of the carb was very slightly blocked. I cleaned it with a single strand of wire out of some electrical cable an put it all back together. Tried readjusting, no change from previous results.

Also the hose that runs from the valve cover back to some little box near the back wheel is cracked at both ends. I taped it up. What does this hose do? And could it be causing my problems?

Basically everything is exactly the same as before except I sheared the bolt off something and I am sorely tempted to set fire to the scooter.
It still runs reasonably well when cold but after 5 or 10 minutes its all over. It blows a bit of black smoke when it's misbehaving, none when running well.

Any thoughts? Could it be the rings or something? And what is the mystery part I broke?

I'll go and look up how to post pictures...

Looks like my picture posting attempt wasnt successful. I used [IMG tags and linked to my dropbox account...?
I'm posting this from my phone so the other options like Quick reply and the picture button dont show up on the mobile version of the site.

You broke off a bolt to the pair system. Not a huge problem but not something you should let go. Try to get the bolt out. And the hose from the valve cover is just a vent line. It just lets the cover vent. Neither one of these could be your problem. Are you 100% sure you have the valves adjusted right? I thought i did on my first try but i was way off. Might want to check them again, and make sure the scoot is completely cooled off before you adjust them.

Ok so long story short - I checked my work on the valves, they were fine.

I then rechecked that the carb, jets and everythings else in there was clean and put back together properly - it all appeared to be.
Then when everything was reassembled I couldnt start the bike at all.

Fuel to the carby was good, fuel was IN the carb too.
Checked for spark - consistent but seemed weaker than it should be so I ordered in a new CDI and coil. A few days and $15 later that arrived and I put it in. Strong spark but still not start.

Even with a spray of starter fluid I was still only getting a coupke of revs out of the engine before it died so I decided to order a new carb.

That arrived today and Ive just put it in and started the scooter and had it running nicely.
When setting the carb up I turned the mixture screw all the way in and then 2 1/2 360 degree turns back out.

Took it for a quick ride and top speed seems to be about 2/3 of what it used to be and when I wind back the throttle the revs are slow to drop. Otherwise it seems responsive and has good initial acceleration.

Do you guys think I just need to adjust the mixture more? From memory does revs being slow to drop mean its running lean?