Modern Vespa

I posted earlier about my headlight and not being able to kick start.

Out of curiosity I ran pretty quick and tried to bump the scoot, and it ended up firing up. I ran it around for a couple minutes, turned the key off, and tried to kick it over, and nothing happened.

Does anyone know why I would be able to bump start and not kick start?

I test, when I kick there is no spark, but it obviously will spark because I can get the motor to run.

Thanks all, happy Thanksgiving!

What's the condition of your stator wires and the flywheel magnetism?

Low compression..

Would that have anything to do with a warped cyl head?

Could be a few things- warped head, loose exhaust stub, old rings. If you're curious get a compression gauge and get some numbers. The auto parts shop near me loans them out, so you might be able to find something.

MJRally, I am doing resistance tests now. The stator was replaced twice before I owned it

i've had to bump start Speedy since the '90s
no idea why, but its a good way to wake up before riding.

luckily I have a steep driveway!

Last time I saw you bump start it I almost needed to call an ambulance for you!

things surely got a bit blurry for a while there, but it was looking worse for the 2 assistants later in the day! I think one still has a limp

I have to bump start my scooter every now & again, sometimes removing the key and trying again works but generally when it goes thats me all day, the next day is completely different. I have put it down to the ignition switch, which of course is a after market switch. replacing the switch shortly for an original. squirting wd40 on the switch has helped.

GL You mean essentially into and behind the keyhole itself?

^^^ yes, I have a GS switch where I have to strip the electrical wire, feed it through a small hole then clamp it with a small screw. With this fixing a small piece of copper wire can break and cause an arc between connection points on the switch, thus making it redundant. The other possibility is that water has got between the connections and again making the switch redundant or at least the ignition. This is only my opinion and theory on my set up, but may be something to consider on your set up. WD40, I think means water displacement, so it aint going to do any harm giving all your electrical connection points a good squirt of WD40.

this

Entire agreement with low compression. Get or borrow a compression tester if you are 100 pounds or lower you have some work to do.

BUT. Is your choke working? WHen I had my VNA/P200 bodge working I had to bump it constantly in cold weather. Choke wasn't hooked up.

If its low compression, then surely its a case of replacing the piston rings, worse case scenario replacing the piston, which is not exactly a lot of work. Do you know how many miles the engine has done. I should be able to look at my problem this week, as its getting worse.

Does anyone know the maximum gap of the piston rings in the barrel.

is there a maximum gap?.... the rings are sprung so close the gap

Unless I'm getting mixed up... I think the OP posted somewhere else that his spark plug flew out of the cylinder head while going over a bump. If the threads are knackered and the plugs not sealing properly that could explain the low compression, no?

https://modernvespa.com/forum/post2027269?highlight=#2027269

If this is the fault I suppose it's also possible that a compression test might be misleading...

I'm not sure whether this is relevant, but in the past I had MZs that would only start from a bump. Getting the ignition and fuelling right usually helped, although poor compression probably played a part... a brand new spark plug always helped though.

I switched it out with a brand new plug. I am ordering a new cly head.

Could that really be the reason it isn't starting? (Again, it doesn't even start when it is warmed up)

Like other members has stated:

-Measure your compression (100psi or lower you will need new piston rings).

-Check that your kiil switch is not grounding out somewhere. Is this a points or CDI scoot?

A new cylinder head will not solve your problems. Also check fuel flow, spark, timing. Some people have sheared the woodruff key on the crankshaft and it messes up your timing.

Its not hard to pull the cylinder off. Inspect the bore and piston for wear. Check your piston ring gap.

You may be able to get by with a light hone and new rings to get compression up but if your cylinder and piston are worn its time for an overbore and new piston. It may be cheaper to get a new cylinder kit depending on the machinist's fees.

What ever route you go, check the clearance on the piston/cylinder bore and piston ring gap.

Have the machinist make sure the piston to bore clearance is at a min of 3.5 thousandths of an inch (0.009mm) or you can experience a 4 corner seizure when the piston get up to temperature.

You can measure the ring gap by yourself with feeler gauges. 0.25mm is about right... no smaller that 0.2mm and no larger than 0.5mm. I also measure my ring gap just above the exhaust port.

Good luck.

I'm sure the last is a typo and 0.5mm is what's meant. Good advice by Mr. J.

Reply, ha SDJ. You got me

It's easy to typo - your advice still stands!

do not do that.

It is very stripped. One of my friends said to use some Teflon tape for a tighter seal, but it seemed a little risky to me

Teflon will melt/burn up. You can run a helicoil in and it will be stronger than before.

I'm pretty sure I have like 10 heads from P200. And maybe 4 or 5 EFL transmissions. And a shit ton of other crap I'd like to toss in a dumpster.

Ok, I didn't know about the stripped out spark plug hole in the cylinder head.

Hit up SFvsr on that offer. I'd still do a compression test afterwards...

MR.j

Sorry, I missed you question.

It is CDI and I did OHMs test and everything was okay according to guide I found on here.

Is it odd that when I purchased the scoot, along with all the spare parts and stuff are two or three (look to be used) stators?

Jet200.com has some cheap but good BGM stators. They're like 30 I believe. Alternatively you can go full Ducati from ScooterWest.

Offers on the table if you wanna use mine for testing.

I should be sorry 'cause I didn't read about your scoot model in your sig. Of course its a CDI.

Maybe you received a bonus grab bag of scooter parts or the OP didn't want to go thru the trouble of a stator rewire or coil/pickup replacement. None the less its good to have spares.

Hookup with bigben since he's in the neighborhood.

Meeting with him this weekend. He's helped me out a ton