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Just taken my gp150 out for a quick run to knock up some miles on it as it needs running in. I was taking it easy but got caught in a headwind uphill so had to give it a bit more throttle in 3rd to get up the hill.

Once up it I was going round a corner and the rear wheel locked up and went from underneath me. I managed to save it and pull the clutch in and free wheel to the side of the road.

There was a little smoke coming from barrel area, I left it for about 15mins to cool down and it started straight away.

I then trickled home for 2 miles. Do I need to pull the barrel and head off? Or can I carry on running it in?

Not been a great weekend for me on the scooter front!!

Just to add its had new seals and and a new piston and rings on the original barrel.

I'd certainly take the barrel off and have a look.

I had a seize on the C2C last year on a Rapido 225, kicked it off after a 10 minute stop and completed the rally. Stripped it down the following week.....not a pretty sight. The rings were partially stuck and there were several score marks. Barrel needed a re-bore and a new piston.........bought an Avanti kit instead

Yeah I thought as much.

Oh well, it will have to wait I'm just doing the same thing with my lis125.

On Monday I had 3 working Lambrettas I now have one! Lol

If the compression is still good and it starts an runs of then personally I would continue to use it albeit cautiously until you have time to check it out properly. The main problem with a seize it the rings getting stuck in the grooves but if the compression is good then that won't have happened. It would be a good idea to investigate why it seized though, what was the plug colour like at the time and how hard were you pushing it?

I removed the plug just before I set off to check it and it was oily, so I cleaned it checked the gap 0.5 put it in and set off.


I only went about 7 miles in total and it was about 4miles into the ride when I was going about 30-35 mph sustained for about 3-5 mins and it locked up. It shut off immediately and I pulled the clutch in.

I left it for 10-15mins started first time with same compression and trickled the rest of the way home.

This is the plug now.

To lean what percentage of oil are you using?

Using 3% rock oil

With a heat seize i'd be more looking at the piston/barrel/ring clearance

I have just seen your question. I have just overhauled my GP 150 engine changing seals, piston and rings and other parts when found worn.
I have also used the same barrel as it had not done many miles and there was no wear mark where the top ring runs. I found out by asking the supplier I used what the + and - indicate in their parts list. Apparently there are slightly different size pistons in each main size and the barrel should have the same marking next to the inlet manifold, in my case a - . He suggested I try a + size which will give me room to hone the barrel if it is too large. Fortunately the piston clearance was ok and the ring gap was also good.
As you said you had recently done the same job on your engine I wondered if this would be any help to you.

Hi Dave.

I didn't do the rebuild unfortunately, Waddo who I bought it from did it. So would imagine it was correct.


I need to sort my other scoot out first then have a look at it.

That spark plug is too white indicating too lean a mixture. Nothing to do with oil. It is the petrol/air mixture that is weak caused by wrong jetting or an air leak. Left as is it WILL do it again.

CHRIS in MARGATE wrote:That spark plug is too white indicating too lean a mixture. Nothing to do with oil. It is the petrol/air mixture that is weak caused by wrong jetting or an air leak. Left as is it WILL do it again.

Got to be honest. I haven't had it apart I just bought it set up from Waddo, so I would be surprised it's set up wrongly!

Also wouldn't the spark plug be the result of the seizure?

Kristof Lammy pie wrote:This is the plug now.

that looks rather on the lean side Kris.The engine has been running lean and too hot
if you are running-in its much safer to run a litle rich for the first few hundred miles .You ought to consider increasing the size of your main jet and perhaps your atomiser bore too.
Its tempting to think it best to increase the % of oil to lubricate a new engine but in fact more oil means less fuel and a weaker mixture which in turn increases the temperature .
Did you check the piston to bore tolerance befor putting the engine back together / providing that was all right I'd just keep running it but avoid labouring the engine like going up long hills or staying at a constant speed or high revs for long periods.

The theory of additional or less oil to weaken or richen the petrol/air mixture is well proven and can be used to fine tune your engine but you need to be experienced and understand the effect.

Stick with your 3%, that's fine but you must try and richen the petrol/air mix. It's the air that burns too hot; the petrol has more of a cooling effect.
Keep checking the plug and aim for mocha colour

whenever I read 'mocha' it makes me hanker after a nice coffee
As the engine has/is seizing I think I might advocate erring on a slightly richer plug colour whilst running in . More like a digestive biscuit colour to go with the mocha coffee ooooooohh

Sorry that I've not contributed to this thread but, IMO, questions that still need addressing are carburation settings & spark plug manufacture & part number.

I agree,the fuel mixture could do with being richer,but that plug is far from being white.

Pulled the carb off this evening.

SH2/22 Dellorto carb

Mixture screw 3 turns out
Choke thread damaged so the choke is slightly wobbly
Slide unmarked Jetex with groove out of the back
Main jet 107
Atomiser 5899 - 4
Pilot jet 45
Starter jet 50
Float 5910 5gms