Strange behavior of my Lambretta after riding ca 20minutes

[kejj]

It starts up fine. It idles fine, It runs off from stand still great, runs good through the gears and behaves great for a good 20 m minutes or so.
Then it starts acting up.

First, dies at idle, once in a while, always restarts at first kit. Feel like difficult to keep going, revs raised to keep going.

Then minutes later it needs throttle and revs at idle position even if I'm still running and just hit the clutch to make a turn.
Some minutes later it needs tons of revs to keep going. Eventually it doesn't move forward any much even at top revs in first gear and in the end it dies completely.

A brake for 30 minutes and its back to normal.

Any ideas? BGM CDI, rewired indian stator(DC). Indian Flywheel

[mick1]

Changing the stator would be my first though. Then cdi, plug, HT lead. basically it sounds electrical

[Timbo]

Definetly the stater breaking down I had similar a few years back..

[kejj]

Thank you for your suggestions.
I will try the electrics.

Could it be the clutch expanding with heat and causing major slippage?

[bazza3004]

The clutch wont make it cut out when idling etc .

[kejj]

Right.
Should I then bee able to take measurements of the stator and identify if it's at fault?

[coaster]

Right.
Should I then bee able to take measurements of the stator and identify if it's at fault?

All the measurements are in Sticky's Complete Spanners Guide but basically:
Red to earth - 95-115 ohms
Green to earth 450 - 530 ohms

Don't worry about the lighting coils but do check that stator earth wire (white) records zero ohms against the engine casing.

[Lambretta Sash]

sounds electrical, i would take multimeter with you and check the readings when it happens it may give an indication of what is failing. The other option is a plug cap where you can see spark to confirm its electrical.

[kejj]

White to maghousing, good
Red ot earth within tolerances
Green to earth, err, not good at all. Seems like I have found the problem.

[Ilango]

It starts up fine. It idles fine, It runs off from stand still great, runs good through the gears and behaves great for a good 20 m minutes or so.
Then it starts acting up.

First, dies at idle, once in a while, always restarts at first kit. Feel like difficult to keep going, revs raised to keep going.

Then minutes later it needs throttle and revs at idle position even if I'm still running and just hit the clutch to make a turn.
Some minutes later it needs tons of revs to keep going. Eventually it doesn't move forward any much even at top revs in first gear and in the end it dies completely.

Hello Kejj,
To me it sounds like no fault from the electrical side, because you said the engine starts, revs & runs good when cold. Hope this is a new rebuild. Had you followed the specifications on the gap to be maintained while installing the piston rings. The workshop manual recommends 0.2mm for my Vijai Super. Had this gap been too small, the ring tends to expand and create more opposition to piston motion as soon as the engine warms up. This in turn cuts off the engine at idle. Rewind back a little to recollect how much gap you set while rebuilding the engine.

A brake for 30 minutes and its back to normal.

- As the engine cools down the rings shrink back to a small size and hence friction is reduced. What is the % of 2T oil mixed?