Crank seals? or worn reed valve, I had a bike with the same symptons as yours, was wear on the reeds.

Can an engine be siezed if it has still got super strong compression?

Because I'm about to take the barrel off to check for any scoring or wear.

I don't really want to be doing another top end after only having it for 2 months.

Air filter is cleaned every ride and is well looked after in general. Is not just left to rot in the shed.

I would do a few things (you may have done these before, but I'd do them again)

1. Sparking plug wet or dry when it won't start? (New plug?)

2. If dry, make sure adequate fuel flow through petcock, any filter and into float bowl. Also check vent hose in fuel tank and on carb.

3. If wet- then put a spark checker on it. Ones of the ones that you can extend the gap. Test against your brothers to see if sparks similar distance.

4. Very closely inspect wires- it could be a little crack in the pickup wire, or on the coil in the magneto that generates the primary. Swap if you can.

5. I think your secondary earth wires are a good idea, make sure good between stator and HT. Coil.

Thanks lotus.

When I have checked the plug it is went and smells of fuel. I get a spark when I hold the plug against the case.

Wiring all looks ok and have tried the regulator and coil on brothers bike and all was fine.

Took carb apart and cleaned it and checked the floats, all seemed good.

Not sure about the crank seals... Do these usualy go?

Hi there, I've been a bit busy this week or I would have come back to this earlier. What to look for on these wires.

Firstly check for continuity through both source coil and trigger. source coil should have same resistance in both directions, probably between 200 and 400 ohms.

Trigger may or may not have continuity in both directions - please post what is measurement of ohms with meter connected each way round.

Your symptoms are typical of a failing source coil.

Do you have a handbook that stating make and type of ignition system?

Hi dadof2.

Thanks for your reply.

I'm away from home for the week now and will be back to the bike next weekend.

I will check all the wiring and post back here when done.

Thanks again, Lee.

if its got spark and fuel it should go.

the fact that it worked, then stopped then worked points to something simple not serious.

The fact you "fiddled" with an earth and it re started tends to point to a simple solution.

That's the thing.

It's got spark, it's got fuel but it doesn't go every kick.

Like I said, a hard kick got it going again but it wouldn't stay running unless you give it some throttle. It just splutters out and doesn't sound like its running properly at all.

Have you had the flywheel off? Could be a sheared woodruff key!

TLTEL

Just to rule the possibility out completely drain and clean the tank, fuel lines and filters and refill with fresh fuel.

Other than dirty fuel carburation is unlikely to vary, as are mechanical items so that points to a wire intermittently shorting or going open circuit

Thanks for all your help guys!

I've managed to get home for the week instead I workin away so tonight I'm goin to get the barrel off just to make sure it hasn't siezed up.

I'm sure it hasn't but I'm going to rule it out anyway.

it can't be seized or no one could get t to run at all but a partial seize nipping a piston ring has in the past resulted in odd symptoms that are difficult to diagnose.

If you have'nt already, I would remove flywheel, check woodruff key. If it shears it can let flywheel move on crankshaft which will alter timing. it may be catching in right position sometimes to let it start then moves once running.

Had this happen to a moped years ago. (Garelli Tiger Cross).

If it's not the problem at least you can inspect, clean, or tighten up stator plate, also have a look at crank seal, you might see signs of leaking. In my experience its usually this side seal that fails as it runs dry.

Good luck.

TLTEL

Hi guys.

Think I've found the issue.

I took the barrel off and the piston wasnt moving freely. It was really stiff up and down but it hasn't siezed and rings were fine.

I could hear a dragging sound from the flywheel side so I took the flywheel case off for a look.

I found that the flywheel was rubbing on the case and once removed the piston moved nice and smooth and freely.

Is this just a case I the casing being tightened to much as I put the cover on from my brothers bike and it didn't rub at all or has the flywheel moved towards te casing?

There is no play in the flywheel at all.

Cheers. Lee.