Modern Vespa

Out for a jaunt in the sun. Engine siezed coming down long highway at 55. Boo. Kick is stuck. Is this definitely a hard sieze? How will I know? What can I do to get going again? Its hot sunny and a long way from home.

Where are you on 55?

If the kick is stuck, pull the plug and pour some oil in (just a bit)

It may free up as it cools. If it does and the rings are not trapped (still has compression) then you may be able to get it started and limp it home.

If you have a larger main jet, put it in.

Try turning fly wheel by hand just to make sure it was a seize and not something jamming your gears or kickstart. Check it's in neutral of course.

Then what tools do you have? Take off exhaust or head to take a look inside.

Ok folks. I guess it cooled down managed to bump start and get moving. That was fun �� bike locking up in fast traffic .

put a touch more oil in gas for luck.

hey crock. No my speed was 55 �� I was actually on the 133 near Irvine. Now heading south on the PCH.

As soon as it locks up.. CLUTCH IN ! Then let it out when you are out of th traffic, but still rolling and hope is frees up again, easier than pushing later

put a touch more oil in gas for luck [/quote]

Not a good idea, it will run leaner. Hope you got it home and you are ok.

ooops. I was thinking "oil = lube"

I did get home without any more problems. Now to see what damage was done, and to see how to run the engine richer.

To run richer could i go with a bigger main jet? smaller air jet?

I knew that in theory but was too distracted with "oh! i'm skidding out of control". I'll remember next time.

Might want to seriously consider buying a CHT or EGT to assist you in up/re jetting after you have first found and repaired the damage from the hard seize.

Sound advice!

cool. More kit to buy and fiddle with. Any recomendations?

You have to ride at the conditions you have encountered to optimize the jetting. So having a gauge will not help much. Cylinder head temp is useful when racing if one can change the mixture on the run. But first you need to know what "normal' is.

Stick a larger main jet in as a safety cushion and learn how to do and interpret plug chops.

Could it be that something has recently been done to the engine in the form of cylinder work. Also could be a slightly blocked main jet.

Are you sure you put the requisite amount of oil in last time you refuelled.

Seeing that if heat isn't hot on cht its hot on egt or the other way round.

Best to be able to read both.Search cht and egt ..Lots of threads here.

Here's a good one
A case for Temperature Gauges

Thanks for this. My p125x is at stock jetting, but with a larger main jet (103) added a few days ago because i had replaced the old Sito+ exhaust with a Polini Expansion exhaust.
So the Polini exhaust is new. Another recent change is that i replaced the cylinder head last week (damaged plug threads) with a used stock head.
Finally, i was using a Champion L86 plug today, which have seemed to me to have more 'oomph' than the NGK's. Also, it was hot and dry today, and i was going full throttle for 20 minutes into a strong wind.

I just checked the bore and cylinder. There's 2 slight scuff marks, so i will hone and install new rings. At some point i'm planning to install a stock 166cc bore, head and cylinder.

It was the expansion chamber that did it. Well that precipitated it.

One size more jet for piece of mind and do a couple of plug chops at full throttle. You have to use the correct spark plug to do plug chops.
NB recheck the idle mixture/air screw setting as it also has an influence.

In this instance a cylinder head temperature gauge would have alerted you to the rise in engine temperature during the 20 min. run. But won't be of any particular use once you are set up properly.

We've, for the most part, all been there!

new rings = check the ring end gap = don't assume it is correct = .2 to .5mm

chamfer the ports if not done already

check top end nuts for spec after 4 heat cycles

use ultra copper high temp goo = great stuff

*** most people seize there engines after a long fast ride when they are slowing down (off ramp or after a hill climb). The trick is too use you rear brake while keeping the throttle open (at the same opening it was as you were riding). Then clutch in and blip the throttle 5+ times. Don't engine brake ever. If pre mix then blipping the throttle is KEY ***

EGT and CHT are nice
love mine
you want to stay below 400 F CHT and 1300 F EGT
300 / 1250 is safe

wrong

a CHT / EGT can provide warning if a top end leak develops
saved me a few times

leaks happen

Well the Polini pipe is staying because i love that tinny tat-tat-tat sound.

I realise i was running a 102 main jet today (stock is 100), i can now either go up to a 103 or 105. I dont have a 104 Would 105 be too much? what would the effect be?

I'm curious what dropping the Air jet down from the stock 160 would do. Too rich? bad acceleration?

I can see the sense in having heat monitors on the head and exhaust; instead of re-jetting 'blind', i could see in real temp changes, the effects of changing these jets, alongside the 'feel' of performance.

ps - Haynes lists the Champion L86 as stock for the p125x, but i may go back to the NGK's for a bit, just in case, even though i liked the feel of the L86.

thanks for the input

That's interesting. If i remember i seized coming down a rise at top speed, full throttle, after an uphill climb at full throttle. I had probably done 2-3 few rises and hills at full throttle before that. This was on an open, 2 lane highway with cars doing 60-70. So i was going for it Riding like that, into a wind, it's not possible to hear the engine properly. Visual feedback on engine temperatures though, would have definitely made me slow or stop etc.

Any of this stuff only happens at the extreme limit. Not many engines are designed to run WOT all the time.

Racing two-strokes are prone to nip up at the end of the straight just before going into a corner as has been said. Long periods on overrun are not a good idea. Most two-stroke cars have a free wheel to counter this.

But pulling the clutch in and idling down to a slower speed is also not advised as the cooling fan slows down and all the cooling is then gone. Unless it is an emergency situation planning the slowdown is the key.

Like many problems the more we dig the more we discover.

When you get past th first handfuls of lockups it is easy to remember, no more scares or flat spots on tyres.
Th worst is a blowout, ohh so wobbly... Or a 2 wheel drift coz you (ie I) used wheelbarrow tyres!

Spread insecticide on the tires first?

Bung in a bigger jet! 102... Off you softie!

I've got 140, and want bigger!

Others will offer better advice on this, but 115-120 sounds good... It's fun to try.

115+ with a 20/20 SI carb on a 125cc??

i'll try anything once. What can i expect?

Agree with Spiderwebb. First put a gauge on and then up-jet per recommendations people are giving you and then run it to see what your temp is. You can then adjust again and use the gauge and plug checks to see what's happening. Your current jetting probably contributed to your seize so don't be too minimal in your first adjustment. A leak at the exhaust slip-on can also cause your temps to rise dramatically so keep an eye on the gauge - the new exhaust joint often develops a leak and needs re-tightening after a few hundred miles.

Seriously, 2 stroke scooters should come with a gauge installed from the factory. Hell, I even put one on my '70 Triumph M/C so I can keep an eye on the ethanol and additive impacts. Without one, a rider is flying blind.

i just really wanted to drop this graphic somewhere. tongue firmly planted in cheek.

Your L86 plug is like a 6 NGK plug = too hot. Go to a 7 ngk or 8 for extended runs. Try the 105 and work down, I think the 103 should be just about right.

this kit is cheap
it is nice to have every jet

http://jet200.com/catalog/product_info.php?products_id=2134

Thanks, i didn't know the L86 was equal to a NGK 6. Ironically the other plug that i have had good experience with is the NGK 8, and i have now switched back to that.

Switched up to a 105 for now. Also the i tightened up the exhuast to cylinder connection. It was not 'loose' but the bolt was definitely not as tight as when i installed the new exhuast 4 days ago. I'm hoping all these details will keep me away from another sieze.

Really appreciate all the input form this forum. Very cool.

Really appreciate all the input form this forum. Very cool.

So long as you know and accept some is of no seriousness at all, other is taking th piss, and a bit is useful. But there is a lot of experience and many seizes here

You must have let off the gas after cresting the hill, your shit was already super hot and needed FUEL to cool off. When you let off the gas instead of riding it out, KA-POW! Just a guess. Yeah you need to jet your bike properly and stop guessing.

I've done done stupid shit like that. Sounds like you are after it again though. Do yourself a favor and set up your bike the right way.

You are lucky you did not eat it.

hmm not sure i've been guessing that much. The bike was set up with stock jetting, manufacturer recommended for the model but with the addition of a larger main jet recommended for running a specific expansion exhaust. The plugs (stock recommended plugs) has been in peak condition from tip to base. My mistake was running too hot stock plug, at full throttle, in 90+ degree heat, for too long, and not making sure that in those conditions i was running richer and taking better care of the engine operation. I've learnt a lesson for sure.

I know the feeling... It happened to me like 4 or 5 times on a new POS Pinasco 215.. Ironically, every single stock barrel or aftermarket malossi o polini kits that I have had on my scooters never ever failed.

Mine not only soft seized a few times but it also hard seized and the piston just came out like blue cheese (imagine grabbing a cookie and destroy the cookie with your hands) that how the Pinasco was.....

So you went with the "recommended" jetting for the expansion chamber, that "someone recommended". I get it. Good luck with that. You should also try also try wearing Tivas next time you are out marauding on a 90 degree day.

Seriously, read up on how to properly jet a two-stroke. Every bike is different. Get yourself a full jet range and don't take recommendations on how your scoot should be jetted.

My set up was pretty much out of the jetting 'text books'. Realizing the jetting on the bike i brought was wrong (e.g. it was often dying at idle), I re-booted with stock jetting plus some extra main jetting for the non-stock pipe, stock plugs and then plug chopped, the plug-chop results were solidly in the 'good - very good' range with full throttle giving me around 55+mph. Where i think i came unstuck was that running the bike for 20-30 minutes in the Low 80's at a peak jet setting, was going to give me problems when i took the bike on a decent 2 hour ride at 90+ degrees. I hear what you are saying though, you really have to know jetting beyond the basics to not keep coming unstuck like i did. Appreciate your input.

cheers

ps- i 'll definitely not be sporting those tivas or anything similar.

High ambient temperature is not the reason you seized. Nor is the length of time you were riding. And for the record 90f (32c) is not that hot. It was the jetting, but I think you got that message already.

High ambient temps should make it richer, if anything (I think). Cool dry air tends to lean things out a bit.

Good luck.

Yeah seems to me that on a dry frosty morning scoots run better. Real crisp

Receiving message, loud and clear!

Yes, i can wrap my head around ambient temps and riding for longer times do not directly cause seizing, but wouldn't it be fair to say that if a scooter is set up 'too lean' etc, then it will most likely seize on an extended run, at full throttle, in 'high' temps, rather than on a short run to the corner store on a mild day? Generalisation, i know, but some truth in it, no?

Not necessarily. It would more likely seize on a dense air day when the dense air would make the mixture the leanest. That would be in dry (not humid) cool (not hot) conditions. A lower altitude also results in denser air than higher altitudes. Additionally, many people up-jet their main, but fail to fatten the SI/Pilot which effects a lot of midrange. I've had a scoot run hotter (seen via CHT readings) at midrange than at WOT until I resolved that.

Might want to read this;
http://www.dtec.net.au/Air%20Density%20&%20Tuning.htm