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I have just rebuilt a series 3 LI 150 engine. New seals etc, clutch, piston and rings electronic ign, plus and leads. Timing spot on 24 before TDC (also tried at 19). Good spark and fuel ok. Wont fire up and plug comes out soaked. The engine had a 3 ring knackered piston which I changed to a 2 ring as the only 2 ring I could find was for an LD. On kick over the compression feels 'wooly', a bit like it needs clutch adjustment (there are no cables attached at the moment). I can also smell a stink like burnt engine oil. I have restored several Lammys but this has me beat. Any sane suggestion would be much appreciated.

You need only 3 things.
Ignition... good spark?
Fuel ..... new petrol. Keep throttle shut when kicking
Compression .... woolly you say? Do you know anybody with a compression tester? Invaluable.

Did you measure ring gap?
Is the clutch ok?

Try a squirt of Easy Start.... that will start a WW1 tank!

Check the cylinder piston clearance, I recently built a 200 with 6 thou clearance thinking it would be ok for a run around but it would hardly start and when it did ran badly.

I measured it with feelers with the cylinder removed between the piston skirt and the cylinder at the bottom of the stroke.

I put a newly bored top end on and it went first or second kick so my cylinder has been sent for rebore.

It started easier with air filter removed and also if I held it flat out with fuel and choke off.

CHRIS in MARGATE wrote:You need only 3 things.
Ignition... good spark?
Fuel ..... new petrol. Keep throttle shut when kicking
Compression .... woolly you say? Do you know anybody with a compression tester? Invaluable.

Did you measure ring gap?
Is the clutch ok?

Try a squirt of Easy Start.... that will start a WW1 tank!

Got good fuel, great spark good compression with my finger stuffed in the plug hole. New clutch which was soaked for 4 days ring gap is fine, piston to bore gap fine. Tried starting it with carb clean but didn't want to know. Think I will take the pot back off and get it checked at the engineering shop. Either that or introduce it to a box of matches ! Thanks for your suggestions.

Have you got a good spark at the p;lug when out ? have you tried Disconnecting the Green from the loom to the cdi as the Ignition / Kill switch may be earthing out when plugs in the scooter ? just a thought

piston wrong way round ?

stator breaking down under load ?

Compression/leak test a good call.

Swann Vesta matches preferred make

I'm a bit confused are you saying you've used an LD piston ?

How do you know the timings spot on ? Wouldn’t you need the engine running to check the timing with a strobe gun? That said as long as you’re somewhere near it should still start.
If you couldn’t find a 2 ring piston why not just fit the top 2 rings to a 3 ring piston.
If it feels like the clutch is engaged I would guess that the compression not great.

I had a non starter, it had a spark when out of head but it failed under compression. Faulty CDI ?

The engine had a 3 ring knackered piston which I changed to a 2 ring as the only 2 ring I could find was for an LD.

not got the wrong piston in there have you ?
i remember a mate building a engine from boxes of bits he bought, it wouldnt start for love or money when we took the cylinder head off and turned it by hand over the piston never came to the top of the bore , cant remember if he used a series 1 piston in a series 3 barrel

try putting a squirt of oil down the bore and turning it over a few times to seal piston to bore then put plug in and try again

sunrisemac wrote:try putting a squirt of oil down the bore and turning it over a few times to seal piston to bore then put plug in and try again

I'll get the cylinder honed tomorrow, shove a squirt down there and give it a go.

St George wrote:I had a non starter, it had a spark when out of head but it failed under compression. Faulty CDI ?

I swopped this engine with a runner so cdi is good. cheers.

martyn dwane wrote:The engine had a 3 ring knackered piston which I changed to a 2 ring as the only 2 ring I could find was for an LD.

not got the wrong piston in there have you ?
i remember a mate building a engine from boxes of bits he bought, it wouldnt start for love or money when we took the cylinder head off and turned it by hand over the piston never came to the top of the bore , cant remember if he used a series 1 piston in a series 3 barrel

I've gone dipshit! The only 3 ring 150 piston I could find was for an Ld. needless to say, I wouldn't fit that. Is there another 3 ring 150 piston for an Li?

It won't matter if it's 2 or 3. If the bore is worn a new piston won't cure your problems. You will need to have the barrel rebored and fit an oversize piston. There are lots available. Best to get the oversize piston and ask a machine shop to bore to the appropriate size.

57.2, 57.4, 57.6 are available.

CHRIS in MARGATE wrote:It won't matter if it's 2 or 3. If the bore is worn a new piston won't cure your problems. You will need to have the barrel rebored and fit an oversize piston. There are lots available. Best to get the oversize piston and ask a machine shop to bore to the appropriate size.

Cheers, that's where i'm going.

pg42 wrote:

CHRIS in MARGATE wrote:It won't matter if it's 2 or 3. If the bore is worn a new piston won't cure your problems. You will need to have the barrel rebored and fit an oversize piston. There are lots available. Best to get the oversize piston and ask a machine shop to bore to the appropriate size.

Cheers, that's where i'm going.

Strictly speaking the machine shop should hone the bore until all areas of wear are removed and then keep going until they get to the next oversize. I made the mistake of ordering a +.25 piston and THEN asking for a machinnr shop to bore the cylinder to fit only to be told the following day that it needed a +.5 bore to remove all the wear.

I'd tell your machine shop what piston oversizes are available and ask them to bore to the smallest oversize possible and Then order the piston

Agreed but better still, find a scooter repair shop that rebores and stocks pistons.