Modern Vespa

I've mentioned this problem before, but not looking at it this way, and I have minimal 2-stroke experience, so please forgive any redundancy Also, going back to the US in 10 days so may not have time to sort this out definitively.

My '00 Typhoon 125 2t sat for at least six years. I got it running this summer (including cleaning the carb internals which were in surprisingly good shape). The compression felt low to my thumb test, so a new cylinder/piston/ring set is on order but has not arrived yet.

The problem persists of severe blue/white exhaust smoke only when hot.
It starts immediately when cold, and idles normally. But after driving for a few minutes, when the throttle is opened wide, the clouds of smoke are impressive. It also seems to have a vibration at lower speeds/engine RPM which is not there at higher RPM. IIRC this can be a sign of excessive richness?

I did check the automatic choke for 35 ohms resistance, and getting 12 volts with the engine running. Could the choke still not be functioning and closing the enrichment passage? Or the worn rings causing smoking only when hot? Or both...

I am aware that I can take the choke off and apply 12V to see if the pin extends. But I anticipate that the rusty-looking screws may be hard to remove even if I take the carb off... just looking for experienced diagnostic tips

A two stroke bike that has stood for six years could have a number of smoke related issues. Firstly the simple stuff, your exhaust and crankcases may have an accumulation of old two stroke oil. When the bike is hot this gets burned off. This smoke should be blue and should reduce over time

If you are getting white smoke its likely to be gearbox oil being pulled in through hard crankcase seals. This is easy to check as your gearbox oil level will drop.

If its crank case seals its unlikely to go away and unless you have the skills and sometimes a pressure press to install new seals then its off to a bike shop for a strip and rebuild.

Interesting, thanks. That very heavy muffler could have a lot of oil sludge in it... how much time though... a few hours of operation?
Come to think of it, when I stopped today after about 10 min of operation, the muffler outlet ID looked wet. Smells like motor oil. It is bluish (hard to keep a close eye on it when riding though).. smells like normal burning engine oil. Does burning gear oil have the same sulfur smell as the oil does? I have the skills but not the tools in this small village That won't be an inexpensive job if I have to pay for it. Thanks for the input!

Does the brand or composition (mineral, semi-synth, full synth) of the two-stroke oil make a difference? Right now I have semi-synth 2T oil in it...

The reason I ask is, I used to have a '73 Mercedes 220D, a 60 hp diesel that I rebuilt myself, and it ran beautifully with liquid dinosaurs in the crankcase. At one oil change I used synthetic - and it rattled (noisy combustion, not bearing knock!) like a coffee can of ball bearings every time I stepped on the "gas". Oil pressure was normal, and it didn't blow blue smoke out the tailpipe, but somehow the smooth and orderly flame front during injection was affected. I promptly changed back to mineral and the noise immediately disappeared... put 50K miles on it before the body finished rotting out and I sold the drivetrain.

The typhoon 125 ran fully synthetic two stroke oil .

Can't burn the gear oil as it's on end of transmission and no where near the crank seals .

Have you checked the oil pump setting / adjustment ?

2 strokes started using synthetics in the 80's and has continued since because of tighter tolerances in engineering of designs. also they emit less pollution than conventional oils.

I still love the old 2 stroke bean oil smells though and have some I add to my chain saws just for that smell, just a 1/2 ounce replace of bean oil in my regular mix ratio of synthetic oil.

Thanks.

I don't know how to do that adjustment... Haynes manual on order but won't be here in time. Could you elaborate? If the oil mix was too rich, wouldn't it smoke as soon as started, not just when warm/hot?

If it's doing this every time you start it after it sits for a while, there's a high probability that the check valve in the carburetor, where the oil injector line is, is bad. So oil is seeping in when it's not running, getting down into the crankcase and burning off when you start it. This usually lasts a few minutes, just long enough for anyone driving behind you to develop a very strong dislike for you and your scooter. But then it goes away.

Thanks, something else to check! I have run it only for about five minutes max but the cloud behind me when I open the throttle is impressive. Guess I need to take it for a longer run (when there is little traffic)

Oil pump left side front of transmission case , Behind rubber cover . With closed throttle adjust pump so line on body & cable holder line up . It's easy once you know .

Thanks, 'fly. Would that adjustment have changed a lot with the bike just sitting, though? Also I was hoping for an easier-to-reach check/adjustment Doesn't look like much fun even if can be done with the engine in the bike...

This morning I took it out for a longer run. Immediate startup, no smoke putting through the village at low speed, but on long uphill grades, the more throttle, the more smoke. At WOT it's quite impressive and I made sure no one was in sight behind me before I fogged the road! The quantity of smoke never did lessen so I think it's unlikely to be accumulated oil in the crankcase or muffler.

Then I started back down through small farm roads in the valley. Minimal to no smoke even when occasionally opening the throttle. Reached the highway again and hit the gas - minimal smoke for 5-10 seconds , but then it rapidly thickened again to the original smelly bluish clouds

Seems like it's related to the temperature of the engine - still thinking rings at this point. Won't know until I tear it down.

My new top end set has taken 10 days so far for DHL to move it from Germany to "Parcel Center Greece" (possibly Athens). Still has to get to Crete and then to my village... I am not impressed with their molasses-slow service unless this is some cheap economy category. Anyway I only have a week left here and not sure I want to work that much more on it this year... there's always next summer!

From what I remember the pump was easy to check & adjust .
Have you looked at the oil pump setting lines , Does the cable and pump move freely when you open throttle ?