Modern Vespa

I recently rebuilt a 1962 VVB motor and I am having a starting problem that is really baffling me. Here are my observations/facts:

- When I got the bike running one time yesterday, I had to kick more than 50 times.
- I can't get the motor restarted after the first fire up.
- I have strong sparks.
- Choke is on when kick.
- Mixture screw is set at 1 1/2 turned out from close.
- Idle screw turned out 2 1/2 turns from close.
- Brand new carb.
- I get occasional loud backfires from the exhuast when I try to restart. The motor still would not start.
- I see a mist of fuel coming out of the carb intake when I crank
- I see the same mist when I did get the motor running.
- Compression is good.

Lastly, when I did the compression check by placing my finger in the spark plug hole then cranking, I seem to get just plain air. Shouldn't I get aersolized petroil instead?

I'd appreciate your feedback. Thanks!

Make sure you don't have any gas leaks into/from the carb that'd stop fuel flow.

Take a straw and put a bit of gas directly into the carb above the air mix screw (I recently did this with my Del'Orto, never worked with anything else, so I apologize if that moots the procedure entirely) and kick it a few times.

I had to do this with my air filter off, which scared the bajesus out of me while working outside, but it worked out. By doing this you also get a clear view of your choke pulling, ect. If your air filter is all mucked up after all that kicking, you may have a flooding problem, or just an issue with the fuel not getting pushed where it should.

Pull the flywheel and see if the woodruff key sheared. Double check your timing.

Also double check the jets to see if they are really clean.
Even if you have a new carb, you could have some crap in
the tank that plugged a jet.


Rob

Thanks for the sugestions.

Mirror-Fx, I have been cranking with the air filter off. I will try the straw trick.

Early rejecter, I check the flywheel operation and there doesn't seem to be anyhting that would indicate a broken woodruff key. However, I don't know how the timing is set on my motor since I don't know how. Would incorrect timing severaly affect starting issues. I mean, when I crank there is no sign of combustion.

I am also wondering about the lack of petroil mist in the combustion chamber. Is is possible that I installed the piston wrong or have blockage in the transfer ports, etc?

is the plug wet? Plug wet = getting fuel. then you have an ignition or timing problem. Plug dry = jet plugged or other fuel related issue. Isn't there an arrow or something that points to the exhaust port?

It certainly can. You'll need to check it. There're instructions here:

http://www.scooterhelp.com/tips/timing/points.timing.html If you're getting backfiring, something must be getting in. It is possible to install the piston incorrectly -- there will likely be an arrow at the top of the piston; it should be pointing towards the exhaust port on the cylinder. I'd set the timing first; if you still have starting or poor running issues after that check the piston if you think you may've installed incorrectly.

+1 on spun flywheel/points/timing problem.

Also, suggesting that one put gas directly into a a backfiring motor is a very very dangerous proposition.

Sounds good, I will try setting the timing first.

So, if I somehow got the motor to run before, I can safely assume that I am getting something to combustion chamber?

It's hard to tell from looking at the spark plug. When I got it up and running before, the tip looked dark. The tip stayed clear since yesterday when I could not get the motor to strat at all.

I vaguely remember paying attention to the arrow and orienting it towards the exhaust side.

There isn't really a "setting" for the throttle stop screw.

Here is an update. As many of you suspected, it was a timing issue. Specifically, it was a sheared woodruff key that grossly offset the timing. Good job, Early Rejecter! The motor now starts on 1-2 kicks and idles great.

Now on the next problem. I don't know if this indeed is a problem. I just don't know. How does shifting of gears work in a Vespa motor? Am I suppose to be able to shift through all gears at any given time when the scooter is stationary? Or do I need to be moving in order to shift to some gears? I can't seem to shfit through all gears with the bike not moving.

Thanks,

Min

that is normal. the only shift at a stand still is from neutral to 1st.

Good to know!