Calling stroker fans

[tj63]

I know it's not strictly a thumper, but I hope someone can help my son out with his bike.  He's got a Derbi GPR125, which has a Yamaha TZR 2 stroke engine in it.  He's recently (600 miles ago) rebuilt it with a new piston and rings, together with a thermostat and one or two other bits following an overheating episode.  It has been run in carefully, and was just loosening up nicely.

The only other thing he's done on it, about 80 miles ago, is replace the fuel hose.  Yesterday he got to a junction close to his home and the bike backfired very loudly then cut out.  Now, it won't start at all.  He says it sounds like it's going to go, but then backfires and stops.  He's flattened the battery trying to start it but all he gets are backfires.

Also, he says that when it is in gear, even with the clutch pulled in, he cannot push the bike forward.  It freewheels OK in neutral, but it's like the clutch is not working at all.  I don't know if the two are connected, but I thought it was worth mentioning.

Any ideas?

Thanks



Trevor

[guest27]

Eeek - not sure without looking.

Does the engine turn over in neutral?  Sounds like it does from your description.  If so it is not seized for some reason.

If it turns over does it have compression?

Is the engine kill switch OK?

If it does not turn over - pop out te spark plug.  Will it turn ove now and pump out a load of petrol?  If so carb leaking into the casing and locking the engine.

Spins but wont start could be many things, compression being one of them.  What caused it to over hear in the first place?  Was this cured or just parts replaced?  Could have overheated again holed piston, nipped up and scored bore etc all knocking out the compression.

Have you changed the plug?  If it has been running rich drinking too much petrol etc could have fured up the plug and this is the problem.  If there is compression etc try a new plug, make sure you are getting big fat sparks.

Should do for starters

Could be that the not starting and not turning over in gear are different things, a locked out clutch will not stop it starting and a seized engine will not spin over on the button.

R

[tj63]

Thanks for that, Rog.

He did change the spark plug recently, but up until last night he said it was running very well.

We think the overheating was caused by a faulty thermostat, which was replaced.  I doubt if it overheated last night, as he'd not gone very far from home (perhaps 1/2 mile) before the problem started. I got a bit more information on this and it seems he was still doing about 30mph when it coughed and died.

I've just spoken to him and he's going to whip the plug out and check for sparks and compression.  That's now he's calmed down a bit and isn't going to attack the thing with a big hammer.  I feel sorry for him, as he'd not had the thing long before the first breakdown.  Now he's only had it back on the road a couple of weeks and it's stopped again.

He's the only person I know who could fall in a barrel of roses and come out smelling like sh!t.


Thanks again.


Trevor

[guest27]

Let us know how it goes stinkwheels are fairly simple, but can be a bit of a git to sort.

R

[guest27]

Any luck?

R

[tj63]

He's pretty much decided it's a faulty coil, so when he's finished his batch of night shifts he'll be having another go at it.


Cheers


Trevor