Heat seize
Post Reply    Forum -> Not-So-Modern
Author Message
Member
Vespa p125x
Joined: 17 Jul 2020
Posts: 7
Location: Fy51qh
Fri Jul 17, 2020 2:24 am quote
Please forgive me if im in wrong area. Never used a forum before.
Vespa p125x. Premix
150 2nd oversize cylinder
Sip road 2
Heart drilled air filter.
20mm standard carb with a 102 jet.
After a nice 15 mile easy run, i got on a 60mph road, wot got to 50ish,
Engine died, rear locked up. Pulled clutch and stopped.
Kicked it oved started first time and ran smooth, i did not try wot again.
Had a look at plug. A nice pale chocolate colour, guides say its good.
Im not mechanically inclined or and dont know may abbreviations, sorry.

I guess this topic has been chatted about, again sorry if it has.

Screenshot_20200717-112430_Messenger.jpg

Hooked
2003 Vespa ET2
Joined: 05 Apr 2019
Posts: 290
Location: Cambridge, MA
Fri Jul 17, 2020 6:21 am quote
sounds like a massive lean bog.... this has happened to me before and it was very hard to track down..... in my case hte bike ran great unless i went wot for a bit then it would justbog out and die once it hit 8000 rpm.....

i discovered that at those speeds/vibrations, that my airfilter was slipping a crack and letting a massive amount of air in ...but only at that speed...id have to wait a bit before giving more throttle....i thought it was a tuning issue

check all your fittings and see if things might flex at speed...all it takes is a little air
Member
Vespa p125x
Joined: 17 Jul 2020
Posts: 7
Location: Fy51qh
Fri Jul 17, 2020 7:08 am quote
Heat seize
Jixaw

Thanks, i did check to make sure filter and carb were tight, its a funny one as i bought scoot, the cylinder head was a 125, even though piston is 150 2nd oversize.

One person said it needs changing, other said its fine. Not from on here.

Thought best to change just incase. I had done 60ish mph on old 125 head a few times for 3-5 mins all fine.

This time with new head 3 mins 50- 55mph this happened. Doesnt seem like any air leaks or blowing.

I just cant see it being that, but, im not an expert
Hooked
2003 Vespa ET2
Joined: 05 Apr 2019
Posts: 290
Location: Cambridge, MA
Fri Jul 17, 2020 7:43 am quote
im not an expert either...but if you put that 125 head back on does it run ok?...is the spark plug a good color with the 125 head?

when i have done bbks i usually use the oem head..larger heads might affect the air fuel ratio and you may have to tune accordingly

be careful....that cutting out like that sounds like a massive lean bog...you dont want to blow that motor..
Addicted
Bashan 150, CF Moto Fashion 250
Joined: 07 Dec 2008
Posts: 882
Location: Hyde Park, New York
Fri Jul 17, 2020 7:59 am quote
I briefly owned a Kymco Like 50 2 stroke. It had just had a 72cc cylinder put on it and within a mile from the shop it stalled out. I hadn't been paying attention till then so the rest of the way home I stayed off full throttle, opened and closed the throttle and took it easy. It took a few miles after that to break in but ran fine when it finally did.
Molto Verboso
62 VBB1T Round Tail W/ leaner sidecar
Joined: 26 Jan 2019
Posts: 1520
Location: california
Fri Jul 17, 2020 8:24 pm quote
Libby,
the challenge with looking at the plug is that it is showing you a kind of hybrid - of all throttle positions.
Your issue on lock up occurred at or near WOT?
And you recently changed the head?

Start with the basics.
Make sure you dont have an air leak.
If its leaking on intake - you can find that by running the motor and spraying some carb cleaner with the red tube on it at the base of all your connecting points.
For example - between the carb box and cases.
Move it around - spray - look for the motor dying.
If it does - you've found it.

You say you replaced the head?
Perhaps you have a leak there.
That would not show up with this type of test.
Instead - search for how to do a leak test on a vespa.
It's critical the motors don't leak air - and If your head is leaking then it will create problems for you.

Once you have ascertained that there are no leaks - you can move on to other stuff to determine why its happening.
Careful - if you have a leak - you can do some damage pretty quickly.
Member
Vespa p125x
Joined: 17 Jul 2020
Posts: 7
Location: Fy51qh
Sat Jul 18, 2020 1:52 am quote
Thanks all.

Its running with the new head on. But, changing the head and putting on the heart drilled air filter are the only changes. I used that red rtv stuff to make sure the head is sealed to barrel.
I did not have this issue with the other head on. And i did thrash it a few times.

I will have to try the carb cleaner route.
When weather dries up. Im in uk. Raining today lol.
I
Molto Verboso
62 VBB1T Round Tail W/ leaner sidecar
Joined: 26 Jan 2019
Posts: 1520
Location: california
Sat Jul 18, 2020 5:29 am quote
The heart drill also has a significant effect.
Didn't realize that was just executed before seize.
Heart drill requires some up jetting.
RTV is not really recommended as it doesn't hold up well to fuel over time.
It's possible tho you have more than one thing happening as well.

Even if you are leak free - assuming you were properly jetted before - you should go with a larger main jet now.

Suggest:
- Check for leaks - its gotta be leak free or all bets are off.
- Get some larger main jet sizes - start about 10 points larger than you are.
- Follow the method here: 62 Allstate Cruisaire - getting it back on the road (Page 10)

The game is to walk the jet size down from too rich to just right.
If no leaks and proper main jet - you should have both power and your seize sorted.
Member
Vespa p125x
Joined: 17 Jul 2020
Posts: 7
Location: Fy51qh
Sat Jul 18, 2020 4:25 pm quote
Thanks again.

I have gone from 102 pre seize
To
105 but i havent had chance to run it. Just kicked over and blipped it. Seems to rise and fall well. But. It seemed liked that with a 102 in it.
Addicted
GL, PK, PE200 with hack, Sears Rust Badge
Joined: 24 Apr 2012
Posts: 865
Location: Deep in the heart of Texas
Sat Jul 18, 2020 5:22 pm quote
If your rear wheel locked up I would definitely pull the cylinder and check the piston and cylinder walls before running again. While you're in there wiggle the crank around to see if its looser then expected. See if the crank or main bearing is moving. Also, the clutch takes a beating when it locks up like that. That brass bushing on the clutch can scar and the basket main plate can sometimes bend.
Addicted
BV 350
Joined: 22 Nov 2016
Posts: 637
Location: Nebraska
Sun Jul 19, 2020 2:05 am quote
Maybe
I'd go richer on your main jet. Depending on what type of fuel you are using (ethanol?) I'd guess slightly lean, from the plug color. Unless fuel mileage is a major concern, 2-strokes seem to be happiest running a bit on the rich side.

Blipping the throttle won't tell you much about jet size. The engine needs way more fuel when under load. Your float level is correct, and your float needle isn't obstructed? Under full load, if there is an obstruction in the fuel system it can draw down the float bowl, causing a lean condition.

If the engine actually seized, I'd take a close look at the cylinder and rings. If the rings or cylinder were damaged, there will be increased blowby, almost certainly causing overheating, and perhaps another seize.

You shouldn't need RTV, and it may interfere with heat transfer. Check for flatness of mating surfaces with a piece of glass, and use the recommended gasket. You are torquing the fasteners, right? If the head 'rocks' on a piece of glass, it will need to be flattened. Unless badly warped, some sandpaper with WD-40 on the glass should get the job done.
Addicted
2007 Stella 150
Joined: 02 Nov 2019
Posts: 761
Location: Rochester, Minnesota
Sun Jul 19, 2020 4:22 am quote
Put a temperature gauge on the spark plug and monitor the temperature. You know what can happen when the rear locks up. Meters are cheap and easy to install.
Member
Vespa p125x
Joined: 17 Jul 2020
Posts: 7
Location: Fy51qh
Sat Aug 01, 2020 8:00 am quote
Thanks
Thanks to all the replies. Cant find any air leaks, decided to put the old head back on, at same time checked barrel. All feels good.
Upped the jet, seems fine, but not taken it above 40mph since.

Decided to buy a new modern scooter, for longer runs, and keep the old vespa for local use.
Hopefully putting the old head back on and upping jet will be fine

Thanks again to all who offered advice, appriciated
Rallies Europe 2016   Vespa Wasp Pin Badges   AF1 Racing Vespa Austin
Post Reply    Forum -> Not-So-Modern
[ Time: 0.2405s ][ Queries: 27 (0.0265s) ][ Debug on ]