Sun May 23, 2021 7:07 am

Hooked
'75 VBC Super
Joined: 05 Oct 2013
Posts: 124
Location: Santa Cruz, CA
 
Hooked
'75 VBC Super
Joined: 05 Oct 2013
Posts: 124
Location: Santa Cruz, CA
Sun May 23, 2021 7:07 am linkquote
I have been following 108's thread (https://modernvespa.com/forum/topic174104?highlight=wheel+locked+while+driving) to try and make sense of what causes a rear wheel lock up. Something in the gears, yes... or caught between gears, yes. Other???

Mine happened to me on my ride yesterday, going about 35-40mph and I was in 4th gear. Was on a straight away with a mild incline so I could hear the engine starting to strain in the gear and I was thinking, I need to downshift to 3rd. That is when it happened, the rear locked up and I went into a skid. Luckily, I was on a straight and stayed upright but hell if it doesn't make you pee a little. What I was more concerned about was getting rear-ended by a close following car. No one was behind me so lucked out there.

My reaction was to pull in the clutch which I did, remember then the engine stalled when doing that, and while seated peddled the scoot off to the side of the road. Not more than a min after all this, I kickstarted the engine, purred nicely hopped on and slowly made it back home without incident. I do recall on that drive back the engine one time started to abnormally slow while in gear, like it was constrained from power. Fearing it would lock up again I pulled the clutch and rev'ed the throttle and all was good.

I played the situation over in my head a hundred times... the only thing I can think of was that I let the engine rpm drop too low in 4th which made it stall and lock up?

i had cracked the case a couple months ago, to clean out a mangled woodruff key, inspected and cleaned everything. So I no there isn't anything foreign causing the lockup.
Sun May 23, 2021 7:36 am

Addicted
'79 P200, '74 VBC Super, '80 100 Sport (sold to new home!)
Joined: 23 Jan 2012
Posts: 758
Location: 32 37' 40" N, 117 2' 53" W
 
Addicted
'79 P200, '74 VBC Super, '80 100 Sport (sold to new home!)
Joined: 23 Jan 2012
Posts: 758
Location: 32 37' 40" N, 117 2' 53" W
Sun May 23, 2021 7:36 am linkquote
Re: Rear wheel locked up - NOT while changing into gear
chilidog wrote:
I have been following 108's thread (https://modernvespa.com/forum/topic174104?highlight=wheel+locked+while+driving) to try and make sense of what causes a rear wheel lock up. Something in the gears, yes... or caught between gears, yes. Other???

Mine happened to me on my ride yesterday, going about 35-40mph and I was in 4th gear. Was on a straight away with a mild incline so I could hear the engine starting to strain in the gear and I was thinking, I need to downshift to 3rd. That is when it happened, the rear locked up and I went into a skid. Luckily, I was on a straight and stayed upright but hell if it doesn't make you pee a little. What I was more concerned about was getting rear-ended by a close following car. No one was behind me so lucked out there.

My reaction was to pull in the clutch which I did, remember then the engine stalled when doing that, and while seated peddled the scoot off to the side of the road. Not more than a min after all this, I kickstarted the engine, purred nicely hopped on and slowly made it back home without incident. I do recall on that drive back the engine one time started to abnormally slow while in gear, like it was constrained from power. Fearing it would lock up again I pulled the clutch and rev'ed the throttle and all was good.

I played the situation over in my head a hundred times... the only thing I can think of was that I let the engine rpm drop too low in 4th which made it stall and lock up?

i had cracked the case a couple months ago, to clean out a mangled woodruff key, inspected and cleaned everything. So I no there isn't anything foreign causing the lockup.
Hard Seize? Pull the head and take a look at the piston and cylinder for scoring. Take a look at the plug, and if you dont have a temp gauge, get one...they are inexpensive and vey helpful. Do you premix or do you have autolube? Is the engine stock...(prob is if you were in 4th at 40... )

Last edited by modkuo on Sun May 23, 2021 7:41 am; edited 1 time in total
Sun May 23, 2021 7:40 am

Hooked
'75 VBC Super
Joined: 05 Oct 2013
Posts: 124
Location: Santa Cruz, CA
 
Hooked
'75 VBC Super
Joined: 05 Oct 2013
Posts: 124
Location: Santa Cruz, CA
Sun May 23, 2021 7:40 am linkquote
I pre-mix. Wouldn't a hard seize not allow me to start up and run again?
Sun May 23, 2021 7:44 am

Addicted
'79 P200, '74 VBC Super, '80 100 Sport (sold to new home!)
Joined: 23 Jan 2012
Posts: 758
Location: 32 37' 40" N, 117 2' 53" W
 
Addicted
'79 P200, '74 VBC Super, '80 100 Sport (sold to new home!)
Joined: 23 Jan 2012
Posts: 758
Location: 32 37' 40" N, 117 2' 53" W
Sun May 23, 2021 7:44 am linkquote
chilidog wrote:
I pre-mix. Wouldn't a hard seize not allow me to start up and run again?
when the piston cools down, it will start again. you describe it straining a bit again....the piston may have been heating up again, expanding and getting ready to seize one more time. take a look and you can rule it out then look elsewhere if needed.
Mon May 24, 2021 2:42 am

Hooked
PX 200
Joined: 25 May 2016
Posts: 285

 
Hooked
PX 200
Joined: 25 May 2016
Posts: 285

Mon May 24, 2021 2:42 am linkquote
Glad you didnt eat tarmac... but 4th is probably way more scary than my spill...

Yeah, the PX is back together, and test riding with semi rich (completely wrong...) jetting to see if it holds up.

I can put my lockup on the worn gears, worn output/drive shaft and loose gear selector. Didnt spot anything else which seemed obvious to be causing the problem

But I'm wanting to change the clutch spacer to one produced by Scooter and Service as a precaution though, not sure if it added anything to the cause of the lockup.
Mon May 24, 2021 4:30 am

Ossessionato
62 VBB1T Round Tail W/ leaner sidecar
Joined: 26 Jan 2019
Posts: 2315
Location: california
 
Ossessionato
62 VBB1T Round Tail W/ leaner sidecar
Joined: 26 Jan 2019
Posts: 2315
Location: california
Mon May 24, 2021 4:30 am linkquote
Chil dog,
What you experienced was a seize caused by the piston expanding and locking in the cylinder.
They are scary.
"Weird - what is that screeching sound?"
"Oh! its my back tire!!!"

It's not related to premix per say.
It is instead related to how your scooter is jetted, and how hot it got.
The other time that it slowed down - was the piston swelling again - but not quite enough to fully seize.
The rev you did dumped fuel in to the cylinder - and helped cool it.
This avoided a full second seize.

You likely need to upjet your scoot's carb.
It has a jetting system made of three jets if you are on a stock large frame.
An Air Corector, a main jet, and an emulsion tube that connect them - making up the "main stack"
And then an idle jet which handles the first 1/4 throttle.

Tell us more about your scoot.
Someone can help yo with improving your jetting.
What model of scoot
What motor - stock?
What exhaust?
What carb?
What air filter?
What cylinder if different than stock?
...
What jetting main stack?
What idle jet?

Question: have you recently upgraded the exhaust or changed/added anything to the motor?
Mon May 24, 2021 5:19 am

Ossessionato
2 matching N.Z. '69 VBC Super, 177cc Racer, VespaCross Bodge, Puch SRA150, Piaggio Zip 100! & others
Joined: 26 May 2013
Posts: 4045
Location: That bushfire place
 
Ossessionato
2 matching N.Z. '69 VBC Super, 177cc Racer, VespaCross Bodge, Puch SRA150, Piaggio Zip 100! & others
Joined: 26 May 2013
Posts: 4045
Location: That bushfire place
Mon May 24, 2021 5:19 am linkquote
Soft seize... well done on pulling the clutch.
Now you know why most experienced Vespa riders have 2 fingers hovering over the clutch lever when knobbin it
Mon May 24, 2021 7:54 am

Ossessionato
1963 VBB2T
Joined: 07 Nov 2012
Posts: 2511

 
Ossessionato
1963 VBB2T
Joined: 07 Nov 2012
Posts: 2511

Mon May 24, 2021 7:54 am linkquote
charlieman22 wrote:
Chil dog,
What you experienced was a seize caused by the piston expanding and locking in the cylinder.
They are scary.
"Weird - what is that screeching sound?"
"Oh! its my back tire!!!"

It's not related to premix per say.
It is instead related to how your scooter is jetted, and how hot it got.
The other time that it slowed down - was the piston swelling again - but not quite enough to fully seize.
The rev you did dumped fuel in to the cylinder - and helped cool it.
This avoided a full second seize.

You likely need to upjet your scoot's carb.
It has a jetting system made of three jets if you are on a stock large frame.
An Air Corector, a main jet, and an emulsion tube that connect them - making up the "main stack"
And then an idle jet which handles the first 1/4 throttle.

Tell us more about your scoot.
Someone can help yo with improving your jetting.
What model of scoot
What motor - stock?
What exhaust?
What carb?
What air filter?
What cylinder if different than stock?
...
What jetting main stack?
What idle jet?

Question: have you recently upgraded the exhaust or changed/added anything to the motor?
Well explained , made perfect sense even to me.
Mon May 24, 2021 4:43 pm

Hooked
'75 VBC Super
Joined: 05 Oct 2013
Posts: 124
Location: Santa Cruz, CA
 
Hooked
'75 VBC Super
Joined: 05 Oct 2013
Posts: 124
Location: Santa Cruz, CA
Mon May 24, 2021 4:43 pm linkquote
Thanks for the great explanation - very helpful.
charlieman22 wrote:
You likely need to upjet your scoot's carb.
It has a jetting system made of three jets if you are on a stock large frame.
An Air Corector, a main jet, and an emulsion tube that connect them - making up the "main stack"
And then an idle jet which handles the first 1/4 throttle.
Happy to hear that we can start with the jetting and not pulling the head or cracking the case. I did that already about 2 months ago cleaning out the mangled clutch side wooddruff. At the time when everything was apart, the clutch, gears, crank, all look great. It should be as the engine was rebuilt 6 months ago with hardly any riding. Piston did show some carbon on the top and in the head but that should be typical... running a bit rich possibly. Cleaned and reassembled.

Interestingly, I have been thinking that there was something not right about my carb. As I have been slowly making adjustments to throttle and mixture screws, I have noticed that there wasn't any change to idle and speed.. At one time I had the mixture and idle screw closed and the engine was still humming away at idle. I thought it was due to a long break-in period.

I have always avoided messing with jets because to me it seems like some strange voodoo that i didn't rightly understand. I guess it is always a good time to learn...
charlieman22 wrote:
Tell us more about your scoot.
Someone can help yo with improving your jetting.
What model of scoot - '75 VBC 150 Super - American Market (built in Genoa, Italy, Sears sold them in the US in the 70's)
What motor - stock? - Stock - no mods
What exhaust? - Stock
What carb? - Dellorto 20/20 - new
What air filter? - Stock filter in the box
What cylinder if different than stock? - Stock
...
What jetting main stack? - I would think stock what came with the new 20/20 carb. Never messed with it... some voodoo that I didn't want to disturb.
What idle jet? - - Never looked or checked it.

Question: have you recently upgraded the exhaust or changed/added anything to the motor? - Nope- running complete stock until I it running, broken in and then will consider upgrades. I have a 20/15 Dellorto carb to try and was thinking of updating the exhaust.
Mon May 24, 2021 6:58 pm

Ossessionato
62 VBB1T Round Tail W/ leaner sidecar
Joined: 26 Jan 2019
Posts: 2315
Location: california
 
Ossessionato
62 VBB1T Round Tail W/ leaner sidecar
Joined: 26 Jan 2019
Posts: 2315
Location: california
Mon May 24, 2021 6:58 pm linkquote
Ok - well - its hard to know what damage was done from the seize.
What often happens is - the aluminum from the piston melts over the top of the ring - pinching it - so it can't expand and seal properly.

Know that's not what you want to read...
But in any event - job one right now is to get the jetting sorted.
If you have to pull the cylinder and put new rings in/clean up the ring slot on the piston, in the end, it wont be nearly as bad as splitting cases.
In fact - plenty of YouTube videos on doing it right on the bike - so engine stays on.

But first - how about the jetting?
If you take off your air filter - you will see two brass thingy's with slots for a screw driver.
Big one is main stack.
Small one is idle.

If you unscrew them - you can then get the numbers off the side.
Air jet it at the top.
Get some reading glasses or magnifying glass.
We need all three numbers. Main jet (bottom)/mixing tube (middle)/ Air Corrector jet (top with slot in it).

Sounds like your idle jet is lean.
Question - when it soft seized - were you just riding along - or had you just dumped off the throttle?

Calling Dr. Swiss.
Mon May 24, 2021 8:17 pm

Hooked
1959 Allstate w P125x Engine
Joined: 29 Nov 2020
Posts: 131
Location: Los Angeles
 
Hooked
1959 Allstate w P125x Engine
Joined: 29 Nov 2020
Posts: 131
Location: Los Angeles
Mon May 24, 2021 8:17 pm linkquote
SubEtherBASS wrote:
Soft seize... well done on pulling the clutch.
Now you know why most experienced Vespa riders have 2 fingers hovering over the clutch lever when knobbin it
"Hey Google, What does knobbin mean in Gringo?"
Hope everyone on a vintage bike does the two fingers.
And if you gun the engine between downshifts after knobbin you aren't relying on the idle jet to cool things.
Tue May 25, 2021 8:48 am

Addicted
'79 P200, '74 VBC Super, '80 100 Sport (sold to new home!)
Joined: 23 Jan 2012
Posts: 758
Location: 32 37' 40" N, 117 2' 53" W
 
Addicted
'79 P200, '74 VBC Super, '80 100 Sport (sold to new home!)
Joined: 23 Jan 2012
Posts: 758
Location: 32 37' 40" N, 117 2' 53" W
Tue May 25, 2021 8:48 am linkquote
Prob gonna need to pull the head anyway to see what happened in there, since the seize was "hard" and locked up the wheel. Get a look at the plug too, it may or may not give you some indicators. If there is damage then look to the causes like jetting. What is your pre-mix ratio and did it change after you opened your cases and did your fixes? Is your autolube just disabled or removed?

if the scoring is enough, you will need to hone and possibly go to an oversized piston.

I have hard-seized as a result of autolube fail, as a 15 yr old 2-up on my first Super at 50mph, and I have soft seized a couple of times on my P some years ago, even with a larger main jet. I ran the P for a couple years after the soft seizes before going to an oversized piston and honing the cylinder. How deep you need to go will depend on the scoring.

You will need to look, unfortunately, in addition to knowing your jetting. Order the Trail Tech CHT monitor, with the cable extension. its worth it to know your approximate engine temp, especially once you do an upgrade to two, (or five).

I have the temp gauges on both scoots and it gives peace of mind...but yes...2 fingers still hover over the clutch, and have since the incident at 15.

Pics also please. Cheers from San Diego!
Tue May 25, 2021 5:02 pm

Hooked
1959 Allstate w P125x Engine
Joined: 29 Nov 2020
Posts: 131
Location: Los Angeles
 
Hooked
1959 Allstate w P125x Engine
Joined: 29 Nov 2020
Posts: 131
Location: Los Angeles
Tue May 25, 2021 5:02 pm linkquote
modkuo wrote:
I have the temp gauges on both scoots and it gives peace of mind...but yes...2 fingers still hover over the clutch, and have since the incident at 15.

Pics also please. Cheers from San Diego!
Same here (but at 18). Still keep the fingers on that lever, even on my (twist and go) Fly 150. Doesn't hurt having a digit or two on the brake, right?
Another worthy habit is pulling the choke in different riding conditions. It should feel really crappy or you're running lean.
Tue May 25, 2021 8:19 pm

Hooked
'75 VBC Super
Joined: 05 Oct 2013
Posts: 124
Location: Santa Cruz, CA
 
Hooked
'75 VBC Super
Joined: 05 Oct 2013
Posts: 124
Location: Santa Cruz, CA
Tue May 25, 2021 8:19 pm linkquote
So what I am hearing is that there is always a chance of seizing? How does anyone enjoy the ride with that fear looming? I opened up the airbox and pulled the jetts. The large one has printed 160 at the top and E1 at the bottom. The small jett has printed 42. I wont be able to pull the head until Saturday to see what is going on there.


Large jett


Large jett lower


Small jett

Tue May 25, 2021 9:21 pm

Hooked
1959 Allstate w P125x Engine
Joined: 29 Nov 2020
Posts: 131
Location: Los Angeles
 
Hooked
1959 Allstate w P125x Engine
Joined: 29 Nov 2020
Posts: 131
Location: Los Angeles
Tue May 25, 2021 9:21 pm linkquote
Ray8 wrote:
"Hey Google, What does knobbin mean in Gringo?"
Hope everyone on a vintage bike does the two fingers.
And if you gun the engine between downshifts after knobbin you aren't relying on the idle jet to cool things.
Best translation I could find is "all balls."
Makes sense.
Wed May 26, 2021 2:48 am

Molto Verboso
2007 Stella 225
Joined: 02 Nov 2019
Posts: 1744
Location: Rochester, Minnesota
 
Molto Verboso
2007 Stella 225
Joined: 02 Nov 2019
Posts: 1744
Location: Rochester, Minnesota
Wed May 26, 2021 2:48 am linkquote
chilidog wrote:
So what I am hearing is that there is always a chance of seizing? How does anyone enjoy the ride with that fear looming? I opened up the airbox and pulled the jetts. The large one has printed 160 at the top and E1 at the bottom. The small jett has printed 42. I wont be able to pull the head until Saturday to see what is going on there.
The larger jet is three pieces, there is a main jet at the tip. Main jet pulls out of the tip.

Air corrector/ atomizer / main

160/E1/?
Wed May 26, 2021 5:54 am

Ossessionato
76 Sprint V, 63 GL, 62 VBB, 05 Stella
Joined: 16 Jun 2011
Posts: 3326
Location: Nashville
 
Ossessionato
76 Sprint V, 63 GL, 62 VBB, 05 Stella
Joined: 16 Jun 2011
Posts: 3326
Location: Nashville
Wed May 26, 2021 5:54 am linkquote
Is that a BE1 or an E1? (I don't recall the difference between the two, but I *think* the E3 is marginally leaner than a BE3).

Either way, OP, you're running 160/(B)E1/Too-Small.

The stock jetting on a 20/20 should be 160-BE3-100 (or 98, for later bikes).

You should also look for an air leak. The head-to-cylinder surface could be leaking and is where I'd start. You don't need to pull the head, just remove the cylinder shroud and look for any signs of leaking down from the topmost cooling fin on the cylinder. If that's the case, it'll be time to pull the head, lap it, and then re-install with some copper spray seal.

I've attached an example from one of my own bikes. In my case, the cylinder stud had come loose, causing an air leak at the head and a seize like what you experienced. I was doing about 60 when the rear wheel locked up, which is not something I'd care to repeat, either.


Extreme example, but it gives the idea of what you're looking for.

Wed May 26, 2021 8:50 am

Addicted
'79 P200, '74 VBC Super, '80 100 Sport (sold to new home!)
Joined: 23 Jan 2012
Posts: 758
Location: 32 37' 40" N, 117 2' 53" W
 
Addicted
'79 P200, '74 VBC Super, '80 100 Sport (sold to new home!)
Joined: 23 Jan 2012
Posts: 758
Location: 32 37' 40" N, 117 2' 53" W
Wed May 26, 2021 8:50 am linkquote
chilidog wrote:
So what I am hearing is that there is always a chance of seizing? How does anyone enjoy the ride with that fear looming? I opened up the airbox and pulled the jetts. The large one has printed 160 at the top and E1 at the bottom. The small jett has printed 42. I wont be able to pull the head until Saturday to see what is going on there.
Ha! Yes, the chance, however small depending on your setup and wrenching skills...is always there and once bitten...twice shy, right peeps?

I accept it as part of riding on the dark side. Enjoy what vintage gives you, and accept the trade offs which include f-e-a-r, apprehension, and friggin-frustration.

Ask Cotter-Pin guy

Main jet stack will come apart like this. Mine is 160/BE3/112 on a 20/20 with a kit and exhaust. I dont understand that voodoo too much either, but you will be dialed in soon, and have some new knowledge added as well.



Wed May 26, 2021 1:02 pm

Ossessionato
VSX, Stella 177, VNX1T, V9B1T
Joined: 20 Jul 2018
Posts: 3187
Location: Staten Island, NY
 
Ossessionato
VSX, Stella 177, VNX1T, V9B1T
Joined: 20 Jul 2018
Posts: 3187
Location: Staten Island, NY
Wed May 26, 2021 1:02 pm linkquote
charlieman22 wrote:
Calling Dr. Swiss.
Been in hiding aside from posting about my v100, and missed this thread. Dealing with lots of jetting/timing trials and struggles of my own for the past 2-3 weeks on my stella holding off until I had some conclusions.

Seems everyone has already helped OP realize his mj was too lean. If its a kit, I'd even suggest the 160 ac is too lean. What's the ignition timing set to? This could also be a major contributor and is the hidden root cause of all my problems which I've spent the last two weeks figuring out and starting to wrap my head around.
Thu May 27, 2021 4:04 pm

Hooked
'75 VBC Super
Joined: 05 Oct 2013
Posts: 124
Location: Santa Cruz, CA
 
Hooked
'75 VBC Super
Joined: 05 Oct 2013
Posts: 124
Location: Santa Cruz, CA
Thu May 27, 2021 4:04 pm linkquote
Some better pics of my main jet. Does 160/E1/102 add up that I am not getting enough fuel in my engine to cause the seize. Anyone can advise on a good place to get/order main jet pieces in the US?


Top


Middle


Bottom

Thu May 27, 2021 4:30 pm

Addicted
'79 P200, '74 VBC Super, '80 100 Sport (sold to new home!)
Joined: 23 Jan 2012
Posts: 758
Location: 32 37' 40" N, 117 2' 53" W
 
Addicted
'79 P200, '74 VBC Super, '80 100 Sport (sold to new home!)
Joined: 23 Jan 2012
Posts: 758
Location: 32 37' 40" N, 117 2' 53" W
Thu May 27, 2021 4:30 pm linkquote
what does the plug look like? Im no jet-setter, but usually the plug, in relation to the jet size, will give an indication of going to a bigger size or not. chocolate brown ceramic or a bit darker is good, grey or white-ish, is not.

I have no idea what the E3 or BE3 difference is, but seems most have a B. I only change the main jet up in numbers for my limited upgrades.

again...Im no authority on this but was taught from the NSM crowd.

Look up plug chop. More sagely advice will come from those more learned than I.
Thu May 27, 2021 4:57 pm

Hooked
'75 VBC Super
Joined: 05 Oct 2013
Posts: 124
Location: Santa Cruz, CA
 
Hooked
'75 VBC Super
Joined: 05 Oct 2013
Posts: 124
Location: Santa Cruz, CA
Thu May 27, 2021 4:57 pm linkquote
So I found this information about jets on Scooterworks.com website. Helps to explain the sections and their purpose.

https://www.scooterworks.com/blog/2012/08/30/carburetor-jetting-101/

I looked at my plug and it looks pretty clean even after my most recent ride. But I did clean it recently which before looked pretty oily.

On another note, looking at the plug. Is it possible that the plug could be causing the temperature in the piston?... just grasping at straws here.
Thu May 27, 2021 6:03 pm

Ossessionato
VSX, Stella 177, VNX1T, V9B1T
Joined: 20 Jul 2018
Posts: 3187
Location: Staten Island, NY
 
Ossessionato
VSX, Stella 177, VNX1T, V9B1T
Joined: 20 Jul 2018
Posts: 3187
Location: Staten Island, NY
Thu May 27, 2021 6:03 pm linkquote
Scooterhelp says stock jetting for your bike is:
160/e1/88.

http://scooterhelp.com/scooters/VBC.150super.html

So if your bike truly is a stock setup with stock carb 20/15 then you are rich on the main.. by a lot.

Your seize would most likely be from either ignition timing, an air leak or both. Possibly they went way rich to compensate for a small air leak that never got solved?

And yes, if you have too hot a plug than what is standard that could also be contributing to the seize. The owners manual says plug should be a Champion L86 plug. Plug cross references to a modern NGK B6HS or Denso W16FSU.

A B6 plug is actually pretty hot so you are probably fine with the plug, but definitely check it's heat rating compared to the B6HS. B7 cooler, B9 coolest.

https://www.scooterhelp.com/manuals/VBC1T.VNC1T.manual/VBC1T.VNC1T.manual.pdf

Ignition should also be set to 22degrees before top dead center.
Thu May 27, 2021 6:35 pm

Hooked
1959 Allstate w P125x Engine
Joined: 29 Nov 2020
Posts: 131
Location: Los Angeles
 
Hooked
1959 Allstate w P125x Engine
Joined: 29 Nov 2020
Posts: 131
Location: Los Angeles
Thu May 27, 2021 6:35 pm linkquote
chilidog wrote:
So I found this information about jets on Scooterworks.com website. Helps to explain the sections and their purpose.

https://www.scooterworks.com/blog/2012/08/30/carburetor-jetting-101/

I looked at my plug and it looks pretty clean even after my most recent ride. But I did clean it recently which before looked pretty oily.

On another note, looking at the plug. Is it possible that the plug could be causing the temperature in the piston?... just grasping at straws here.
Buy a bunch of plugs. An old one won't help you see where you're at.
Not sure why you're experiencing this, tbh. Your setup isn't off the charts:
http://lfs.alexander-hepp.de/
Did your bike sounds like this video at 3:00?
This is the lean as hell sound, before seizing:
Thu May 27, 2021 9:08 pm

Hooked
'75 VBC Super
Joined: 05 Oct 2013
Posts: 124
Location: Santa Cruz, CA
 
Hooked
'75 VBC Super
Joined: 05 Oct 2013
Posts: 124
Location: Santa Cruz, CA
Thu May 27, 2021 9:08 pm linkquote
swiss1939 wrote:
Scooterhelp says stock jetting for your bike is:
160/e1/88.

http://scooterhelp.com/scooters/VBC.150super.html

So if your bike truly is a stock setup with stock carb 20/15 then you are rich on the main.. by a lot.
So I guess I should trust my current jetting? The scooter is really responsive, Quick off the line for being stock. It just has the little problem of the seize.
swiss1939 wrote:
Your seize would most likely be from either ignition timing, an air leak or both. Possibly they went way rich to compensate for a small air leak that never got solved?
So I failed to mention that it is 12v ac electric converted. I didn't know that timing could cause a seize so didn't think it was critical.
swiss1939 wrote:
And yes, if you have too hot a plug than what is standard that could also be contributing to the seize. The owners manual says plug should be a Champion L86 plug. Plug cross references to a modern NGK B6HS or Denso W16FSU.

A B6 plug is actually pretty hot so you are probably fine with the plug, but definitely check it's heat rating compared to the B6HS. B7 cooler, B9 coolest.
I have a NGK B7HS that I will put in and try out. I am still going to pull the head, check the piston and shaft, and also see if there are any signs of leaking. I am also going to remove the plastic shroud cover to try and get more air to cool the head. Could it also be a case of the air/fuel mixture screw too tight, making it lean(more air then gas)?
swiss1939 wrote:
https://www.scooterhelp.com/manuals/VBC1T.VNC1T.manual/VBC1T.VNC1T.manual.pdf

Ignition should also be set to 22degrees before top dead center.
This is great Swiss, thanks for the link.
Thu May 27, 2021 9:19 pm

Hooked
'75 VBC Super
Joined: 05 Oct 2013
Posts: 124
Location: Santa Cruz, CA
 
Hooked
'75 VBC Super
Joined: 05 Oct 2013
Posts: 124
Location: Santa Cruz, CA
Thu May 27, 2021 9:19 pm linkquote
Ray8 wrote:
Did your bike sounds like this video at 3:00?
This is the lean as hell sound, before seizing:
Hey Ray8,
I was in 4th with a low rpm which was probably putting strain without enough fuel coming in... that is when it seized. But the second time when I think it was attempting to seize again it did just that... cruising, started dropping in power. That is when I pulled the clutch before lock up and rev'ed the engine. But my head remembers a lot more wheel screech than in the video... like killing a cat and just trying to keep it steady and pull the clutch. That dude must do that often as he calmly pulled the clutch, took one hand off the grip and was fiddling the chock, rev'ed and kept going. I am not that skilled yet but give me a few more seizures. HA!
Thu May 27, 2021 9:27 pm

Hooked
'75 VBC Super
Joined: 05 Oct 2013
Posts: 124
Location: Santa Cruz, CA
 
Hooked
'75 VBC Super
Joined: 05 Oct 2013
Posts: 124
Location: Santa Cruz, CA
Thu May 27, 2021 9:27 pm linkquote
modkuo wrote:
Order the Trail Tech CHT monitor, with the cable extension. its worth it to know your approximate engine temp, especially once you do an upgrade to two, (or five).
Modkuo - what temp are we talking about when a seize takes place? Looked into the trail tech, runs about $70 for the temp readout and sensor. When you see you are running hot, do you just rev the engine a few time to cool it? Thanks much for the help in troubleshooting.
Fri May 28, 2021 1:45 am

Addicted
'64 Motovespa 150S (177) , '66 Allstate SF, '65 VBB, '66 180SS
Joined: 27 Mar 2013
Posts: 881
Location: S.Salem, NY
 
Addicted
'64 Motovespa 150S (177) , '66 Allstate SF, '65 VBB, '66 180SS
Joined: 27 Mar 2013
Posts: 881
Location: S.Salem, NY
Fri May 28, 2021 1:45 am linkquote
" I am also going to remove the plastic shroud cover to try and get more air to cool the head."
Not sure about this.... it's the shroud that channels air over the head for cooling.
Fri May 28, 2021 4:34 am

Ossessionato
76 Sprint V, 63 GL, 62 VBB, 05 Stella
Joined: 16 Jun 2011
Posts: 3326
Location: Nashville
 
Ossessionato
76 Sprint V, 63 GL, 62 VBB, 05 Stella
Joined: 16 Jun 2011
Posts: 3326
Location: Nashville
Fri May 28, 2021 4:34 am linkquote
chilidog wrote:
I am also going to remove the plastic shroud cover to try and get more air to cool the head.
NOOOOOOOOOO!!!!!!

The shroud directs the air blown by the flywheel fan over the cylinder and head. That's what cools the motor. Removing it would be like draining the radiator of your car, then driving it around, and will have the same result.
Fri May 28, 2021 6:08 am

bodgemaster
63 GL, 76 Super (x 2), 74 Primavera (x 2), 06 Fly 150
Joined: 26 Sep 2013
Posts: 5925
Location: So Cal
 
bodgemaster
63 GL, 76 Super (x 2), 74 Primavera (x 2), 06 Fly 150
Joined: 26 Sep 2013
Posts: 5925
Location: So Cal
Fri May 28, 2021 6:08 am linkquote
Yeah, dont run it without the cooling shroud.

The jetting sounds fine for a stock Super with a 20/20 carb. Doubt that was the cause of your seize.

You said you split the case recently. Check for a possible leak at the head.

You might also remove the head and look for scoring in the cylinder, to at least confirm it was a seize.

Has the tank been out of the bike recently? Its possible your fuel line may not be routed correctly and be pinched, restricting flow. I see this a lot, especially on autolube bikes.

A CHT is only about $50. Conventional wisdom is to keep temps under 350F. Reducing the load on the engine, downshifting, revving, and dumping gas onto the piston can help cool it. When temps start creeping up around 400F, time to either pull over or go into the bike lane and just putt along until it drops.
Fri May 28, 2021 6:59 am

Jet Eye Master
PX221 MHR, O tuned PX200, PX125 and some motorbikes
Joined: 14 Jun 2017
Posts: 2813
Location: London UK
 
Jet Eye Master
PX221 MHR, O tuned PX200, PX125 and some motorbikes
Joined: 14 Jun 2017
Posts: 2813
Location: London UK
Fri May 28, 2021 6:59 am linkquote
chilidog wrote:
So I failed to mention that it is 12v ac electric converted. I didn't know that timing could cause a seize so didn't think it was critical.
I wonder where you set the ignition timing? Points and electronic don't run the same advance. Electronic on a stock VBC should be 18 degrees max. 16 degrees to be very safe. This could easily be the whole problem.
Be sure to make your own timing marks and check with a strobe lamp. Check everything more than twice. 1 degree over is too much on a 2 stoke engine.
Fri May 28, 2021 9:30 am

Molto Verboso
2007 Stella 225
Joined: 02 Nov 2019
Posts: 1744
Location: Rochester, Minnesota
 
Molto Verboso
2007 Stella 225
Joined: 02 Nov 2019
Posts: 1744
Location: Rochester, Minnesota
Fri May 28, 2021 9:30 am linkquote
Jack221 wrote:
I wonder where you set the ignition timing? Points and electronic don't run the same advance. Electronic on a stock VBC should be 18 degrees max. 16 degrees to be very safe. This could easily be the whole problem.
Be sure to make your own timing marks and check with a strobe lamp. Check everything more than twice. 1 degree over is too much on a 2 stoke engine.
I have to echo what Jack said about timing. I got a real surprise on my motor, that like yours has a mismatch of parts. With a two stroke timing light, I was off by off 6+ using the factory marks, I used a piston stop and digital indicator to mark "0" or TDC. I had to check twice being so far off I thought it was me.
Fri May 28, 2021 8:35 pm

Hooked
'75 VBC Super
Joined: 05 Oct 2013
Posts: 124
Location: Santa Cruz, CA
 
Hooked
'75 VBC Super
Joined: 05 Oct 2013
Posts: 124
Location: Santa Cruz, CA
Fri May 28, 2021 8:35 pm linkquote
chandlerman wrote:
NOOOOOOOOOO!!!!!!

The shroud directs the air blown by the flywheel fan over the cylinder and head. That's what cools the motor.
So it isn't a good idea... I will take a look at it tomorrow and see if it gets proper airflow. I will also check the position of the stator, take some pics and get your thoughts on position.
Sat May 29, 2021 11:41 am

Hooked
'75 VBC Super
Joined: 05 Oct 2013
Posts: 124
Location: Santa Cruz, CA
 
Hooked
'75 VBC Super
Joined: 05 Oct 2013
Posts: 124
Location: Santa Cruz, CA
Sat May 29, 2021 11:41 am linkquote
Disassembly in progress... for timing, here you can see how I have setup the BGM stator. I recall when I installed the the instructions booklet didn't say much on timing setting. Any thoughts on this are appreciated. Runs good other than the seize so thought it was timed correctly.




Setup

Sat May 29, 2021 11:47 am

Hooked
'75 VBC Super
Joined: 05 Oct 2013
Posts: 124
Location: Santa Cruz, CA
 
Hooked
'75 VBC Super
Joined: 05 Oct 2013
Posts: 124
Location: Santa Cruz, CA
Sat May 29, 2021 11:47 am linkquote
Pulled the head. Didnt see any leaks there, but there is wear in the main.




Right side


Left side


Close up of right side. Running my finger over th there is some slight valley and hills.

Sat May 29, 2021 1:53 pm

bodgemaster
63 GL, 76 Super (x 2), 74 Primavera (x 2), 06 Fly 150
Joined: 26 Sep 2013
Posts: 5925
Location: So Cal
 
bodgemaster
63 GL, 76 Super (x 2), 74 Primavera (x 2), 06 Fly 150
Joined: 26 Sep 2013
Posts: 5925
Location: So Cal
Sat May 29, 2021 1:53 pm linkquote
Yup, it seized.

Doesnt look too bad, can be cleaned up.

Did you make the circled mark on the case? What does it represent?

Regardless, Id suggest setting the timing again from scratch. Do you know how or would you like help?



Sat May 29, 2021 6:18 pm

Hooked
'75 VBC Super
Joined: 05 Oct 2013
Posts: 124
Location: Santa Cruz, CA
 
Hooked
'75 VBC Super
Joined: 05 Oct 2013
Posts: 124
Location: Santa Cruz, CA
Sat May 29, 2021 6:18 pm linkquote
SoCalGuy wrote:
Yup, it seized.

Doesnt look too bad, can be cleaned up.

Did you make the circled mark on the case? What does it represent?

Regardless, Id suggest setting the timing again from scratch. Do you know how or would you like help?
That circle mark was made many years ago from when I had someone help me time it when it was setup for 6v points. I agree with you that it seems like I need to reset the timing-
I don't know how to do it and any help in this area is greatly appreciated!

Also, what should I do about my cylinder marks? What is the best way to hone those smooth again? Will it require new rings for the piston?
Sun May 30, 2021 6:51 am

bodgemaster
63 GL, 76 Super (x 2), 74 Primavera (x 2), 06 Fly 150
Joined: 26 Sep 2013
Posts: 5925
Location: So Cal
 
bodgemaster
63 GL, 76 Super (x 2), 74 Primavera (x 2), 06 Fly 150
Joined: 26 Sep 2013
Posts: 5925
Location: So Cal
Sun May 30, 2021 6:51 am linkquote
Ok first things first. A hone is going to require you to take the cylinder off. Are you able to do that? Sorry, I dont know what tools you have or what your mechanical skill level is. Its not difficult, just trying to get a feel for how deep you want to go.

While a hone would be good, you can probably get by without one. Ive seen much worse cylinders. Up to you.

You can borrow a hone from your local Auto Zone. Its basically a set a grinding stones on springs that you attach to a drill. Use it to lightly scuff the inside of the cylinder. You dont need - and wont be able - to get all the scratches out. You just want to knock down any ridges and give the surface a light cross-hatching. Takes about two minutes.

New rings probably arent necessary, but once the cylinder is off, inspect them for damage. You can remove scuffs on the piston using 800 grit wet sandpaper and oil.

Clean everything squeaky clean, and lets see what it all looks like before you put the cylinder back on and set the timing.
Sun May 30, 2021 9:21 am

Style Maven
74 50s x3 78 P200 x2 84 Cosa PK50XL2 58 AllState 68 Sprint 80 50special '66(?) Super125
Joined: 22 Nov 2010
Posts: 8205
Location: seattle/athens
 
Style Maven
74 50s x3 78 P200 x2 84 Cosa PK50XL2 58 AllState 68 Sprint 80 50special '66(?) Super125
Joined: 22 Nov 2010
Posts: 8205
Location: seattle/athens
Sun May 30, 2021 9:21 am linkquote
charlieman22 wrote:
Ok - well - its hard to know what damage was done from the seize.
What often happens is - the aluminum from the piston melts over the top of the ring - pinching it - so it can't expand and seal properly.

Know that's not what you want to read...
But in any event - job one right now is to get the jetting sorted.
If you have to pull the cylinder and put new rings in/clean up the ring slot on the piston, in the end, it wont be nearly as bad as splitting cases.
In fact - plenty of YouTube videos on doing it right on the bike - so engine stays on

....
For the price of a set of rings and small hassle borrowing the hone, I gotta agree with Sir Charles here. It's what I did when it happened to me 7 or 8 years ago and bike still runs fine after. But before deciding, first pull the cylinder(just undo the muff and it's easy) and let's see your piston showing the rings and ring grooves where it seized. BTW, I don't think that's a stock head there...
Sun May 30, 2021 12:07 pm

Hooked
'75 VBC Super
Joined: 05 Oct 2013
Posts: 124
Location: Santa Cruz, CA
 
Hooked
'75 VBC Super
Joined: 05 Oct 2013
Posts: 124
Location: Santa Cruz, CA
Sun May 30, 2021 12:07 pm linkquote
Not the first time pulling apart and putting back this engine. Just not too savvy on the corrective actions when something needs adjusting.


Cylinder pulled and a better picture of the main damage


Using the borrowed honing get-up I was was able to clean up the grooves decently.


After honing. There are deeper scratches that wouldn't come out. Not sure if I should keep at it or if they can be lived with? I sprayed it down with carburetor cleaner.

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