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Hey guys -

I've racked my brain over this thing and I can't figure out what's wrong.

I did a full resto on this scooter, having replaced the wiring, CDI, stator rebuilt, and went through the engine. The bike is a 1979 model with a Sito Plus and a 24/24 carburetor with stock jetting. Ever since day 1, it's performed worse and worse. In the beginning, it would just be hard to start, maybe 5-10 kicks. Then it needed starting fluid. Then you'd have to change plugs, kick, then add ether. Now it ONLY runs on ether, dying out after 5 seconds.

-When I pull the plug, it is wet, so it's 100% getting fuel.

-I didn't run a battery for the few days of riding around when it *did* run in the beginning. Would this have fried something?

-Checking spark, it looks yellow/orange instead of white. Perhaps a weak spark?


The only things I can possibly think are that the magnets in the flywheel are weak, or that my timing is horribly off. It's previously run on these settings, which makes me not think it's a timing issue.

Any ideas? I'm totally stumped and don't want to start throwing money at problems I'm not experienced enough to diagnose...
⚠️ Last edited by IllIlIIIllIllIII on UTC; edited 1 time
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Hooked
CUTDOWN PX200.1978 YAMAHA DT 125
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check the float and needle, also replace the spark plug
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also if the sito plus is old burn it clean
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Check the compression. These things will run even if the timing is out quite a bit, but I would check that you got a decent amount of compression first. How are you starting the scoot? Choke on, hands off the throttle?
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Have you tried starting it with the fuel tap in the off position? If you have a weak float/needle situation the pressure of the fuel pushing down from the tank could be pushing past the bad needle/seat relationship and flooding it.
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I'm wondering what you mean by "a full resto" and "went through the engine". Does "replaced wiring" include pulling a new harness? Did you take the carb all the way apart and replace components? What is your timing set at in degrees BTDC? What exactly have you done? The more we know the more we can help.
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ScooterRaton wrote:
I'm wondering what you mean by "a full resto" and "went through the engine". Does "replaced wiring" include pulling a new harness? Did you take the carb all the way apart and replace components? What is your timing set at in degrees BTDC? What exactly have you done? The more we know the more we can help.
Compression was good, so I replaced all bearings and seals minus the rings. Literally a 95% engine rebuild. I pulled a new wiring harness. Fully rebuilt carb. I neglected the paint because I inevitably thrash everything that looks nice.

The timing isn't "set" - I've just got the marks from the stator plate and case lined up. Unlike a car, I've got zero idea on how to set timing on a bike - even after reading the guides online. I'm clueless. The thing that kills me is that it DID run, and well at that - it just took forever to start. With not having messed with it, why would it magically only run on ether and not fuel?

I'll toss in a new plug, but I'm fairly certain that's not the issue. Once I've gotten it running on starting fluid, that usually gives it enough "umph" to burn out the remaining fuel if it was previously flooded. I've tried it multiple times with the fuel on/off/res.
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It's probably something pretty simple...but that doesn't mean it can't drive you nuts tracking it down.


Did you use a "witness mark" on the stator before removing or set it to the case markings. If to the case which mark?

You can always do the "wrench test" on the flywheel for magnet strength and it will give you a chance to check the woodruff key.
⚠️ Last edited by ScooterRaton on UTC; edited 1 time
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ScooterRaton wrote:
Did you use a "witness mark" on the stator before removing or set it to the case markings. If to the case which mark?

You can always do the "wrench test" on the flywheel for magnet strength and it will give you a chance to check the woodruff key.
I actually marked it before disassembly, but moved it back to where the case markings were. My stator plate only has one "notch" for timing unlike others that I've seen.

My flywheel puller is 5+ hours away, but I'll grab it next time I'm home. Has anyone had issues with unreliable running due to weak magnets?
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Grab a couple of photos too. Couldn't hurt
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Yep, that's good advice. Especially if you've had the flywheel off and possibly not torqued the nut up tight enough when reinstalled. Then a sheared woodruff key could cause it to act as you've described. So many keys in two pieces when somebody(me included) discover that 'good & snug' really won't do.
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I don't know anyone personally that had a magnet problem. However some shops will remag by mail. I figure that if they offer this service it must be needed sometimes.
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I've only seen it personally once, on a friend's P150 w/ points. We tried everything else and the bike would occasionally fire, sometimes start, never run well and always die. We finally swapped in a flywheel from a running bike and all the problems vanished. Afterwards we tried the wrench test for kicks and so we could believe our good luck at last. It was pretty weak.
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V oodoo wrote:
Yep, that's good advice. Especially if you've had the flywheel off and possibly not torqued the nut up tight enough when reinstalled. Then a sheared woodruff key could cause it to act as you've described. So many keys in two pieces when somebody(me included) discover that 'good & snug' really won't do.
I'm almost 99% sure I put it on with an impact, as I always take it off with one. When I get my tools next weekend, I'll be sure to update with some pictures. Thanks guys!!
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IllIlIIIllIllIII wrote:
V oodoo wrote:
Yep, that's good advice. Especially if you've had the flywheel off and possibly not torqued the nut up tight enough when reinstalled. Then a sheared woodruff key could cause it to act as you've described. So many keys in two pieces when somebody(me included) discover that 'good & snug' really won't do.
I'm almost 99% sure I put it on with an impact, as I always take it off with one. When I get my tools next weekend, I'll be sure to update with some pictures. Thanks guys!!
Better to use a torque wrench.
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ScooterRaton wrote:
Better to use a torque wrench.
I'm a desperate man. I also don't have a flywheel holder, so an impact will have to suffice. Tighter is gooder, right?
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tightening almost anything with an impact driver is a risky proposition.
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Vespa Motorsport Timing Tutorial
IllIlIIIllIllIII wrote:
ScooterRaton wrote:
I'm wondering what you mean by "a full resto" and "went through the engine". Does "replaced wiring" include pulling a new harness? Did you take the carb all the way apart and replace components? What is your timing set at in degrees BTDC? What exactly have you done? The more we know the more we can help.
Compression was good, so I replaced all bearings and seals minus the rings. Literally a 95% engine rebuild. I pulled a new wiring harness. Fully rebuilt carb. I neglected the paint because I inevitably thrash everything that looks nice.

The timing isn't "set" - I've just got the marks from the stator plate and case lined up. Unlike a car, I've got zero idea on how to set timing on a bike - even after reading the guides online. I'm clueless. The thing that kills me is that it DID run, and well at that - it just took forever to start. With not having messed with it, why would it magically only run on ether and not fuel?

I'll toss in a new plug, but I'm fairly certain that's not the issue. Once I've gotten it running on starting fluid, that usually gives it enough "umph" to burn out the remaining fuel if it was previously flooded. I've tried it multiple times with the fuel on/off/res.
I watched this yesterday, maybe it will help.

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Try putting one of these in the carburetor.




http://www.scootermercato.com/Scooter-Parts/Carb-Parts/132369
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I like the cover idea. Have you used it?
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I finally got a chance to take some pictures of the stator plate and the location of it. As mentioned, it's got spark, it just looks weak to me. But this vespa has confirmed that I'm an idiot. In the picture of the top view, you can see where I marked it before the teardown, but rotated it clockwise to match the locating notches on the bottom after troubleshooting.


I know it's not much to go off of, but let me know!
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Also, I meant to see what plug I'm running - but I forgot to take a picture. I do know that I have two plugs, both are NGK's, and one is an 8, the other is a 9. Maybe I need a different plug?

The fuel is non-ethanol fuel that's roughly 6 months old. I've run my bikes on fuel that's easily 1-2 years old, so I don't see it being "bad", but it's always a possibility...
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Even a bad spark plug can create a spark that might look good. Replace the plug with a B7es or a B8es. I use a B9es just because i'm mainly on the highway most of the time.
Double check that your exhaust isn't plugged. I've had mice and chipmunks make nests in my Sito.
Replace fuel with new gas.
Just keep ruling out the simple stuff. Those 3 things are simple and cheap to do.
If you still can't start it after that, tie a rope around the back bumper of a car or other bike and hold on to the other end to get a pull start....oh, and get it on video too.
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Oh, and what brand CDI did you replace your old one with?
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whodatschrome wrote:
Oh, and what brand CDI did you replace your old one with?
It's just one of the basic blue ducati CDI Units that scootermercado offers. I wasn't thrilled with the quality of the stuff I received from them, so it could be a possibility - but most CDI units I've seen either work or don't.

I'll go by the auto parts store tonight and grab a handful of plugs, does any heat range work the best?

I'll have to work up some sort of gravity feed for the fuel system, filling it with fresh fuel.

I got the SITO used, and burned it out when I repainted it - flowed well 5 months ago - hasn't run more than 20 minutes since being on.
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What's the condition of the outermost green wire that plugs into the CDI? How's the insulation integrity?
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MJRally wrote:
What's the condition of the outermost green wire that plugs into the CDI? How's the insulation integrity?
I replaced the whole wiring harness, but I'll check. What does this wire go to?
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Could it possibly be a bad spark plug wire? I've never had one go out, but perhaps?
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IllIlIIIllIllIII wrote:
Could it possibly be a bad spark plug wire? I've never had one go out, but perhaps?
Absolutely.... I'd check both the HT wire AND the plug cap... both of those items can go bad, and they're easy to change... and pretty inexpensive..

1st I'd nip both ends of the Plug wire and get a nice new fit at both ends... if that doesn't help, I'd fit a new plug cap... and if that doesn't do the trick, I'd replace the plug wire..

Could be something simple like either of those..

Good luck.
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Since you replaced the harness don't worry about what I was asking. The outermost green wire goes to the kill. Older P200's have ignition problems because that green wire starts to corrode and ground inside the frame. When the wire grounds the ignition dies and it'll cause headaches.

Try Mr. V's check on the spark plug wire and cap. Make sure those are solid. If they are, get a multimeter and check out resistance values of the stator wires that go to the CDI. Use this thread I started to find p200 values. Stator Values Wiki

If that doesn't reveal any problems, see if you can borrow/buy a replacement flywheel so that you can check and see if the magnets are the source of all your headaches.
⚠️ Last edited by MJRally on UTC; edited 1 time
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The flywheel de-magnetizing is a rare occurrence, even when the flywheel is stocked apart from the stator for several years. If the engine has been sitting around with the ignition in place, you can pretty much cross that off your list.
Hint: stock flywheels with stators inside, just to be on the safe side.

In any case, the wet plug seems to indicate an ignition issue rather than carburetion or fuel starvation. I've only personally experienced pickup failure as working well when cold, and progressively dying as the engine heats up, but an old pickup can act out in different ways apparently. If you own a multimeter, check that your figures @ the CDI are around the following:

white + red = 110 (pickup coil, sends the signal for correct ignition)
white + green = 500 (sends the power)

If one of these is way off, you've likely found your culprit. If the pickup fails, the spark is sent at the wrong time or not at all, if the yellow coil (green wire) is out of whack, the spark will be too weak to run properly. Pickup coils fail much more regularly than the other, so it's always a component to pay attention to (and have a spare of in advance) when ignition trouble arises.
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