Sorry for a second "won't go" post in a week. Hoping there are some people who know a bit about 2-stroke engines.

Engine is in a goped aka scooter with an engine. It's the standard 'strimmer' type, 35cc I guess, with a centrifugal clutch and reduction gearbox.

It starts up and runs fine, will rev up and spin the rear wheel, but as soon as any load is on it it dies. At first I thought it was a mixture issue but try as I might I can't get it to produce any power.

Is this a sign that the engine is knackered? eg not holding compression or something like that? Or should I think about changing the carb perhaps?

Could be exhaust blocked with carbon. I used to have to clean exhaust out with caustic soda now and again, You could try it with exhaust of just to check.

Worth a shot I guess! Thanks.

Any other suggestions?

Chris

Piston rings or head gasket. My 100cc was the same, start, rev but no power..

New piston and head gasket and ring ring off we go..

Stale Fuel or possibly crankcase full of fuel or crankshaft oil seals dried out (if its stood a while)

Alfie

[Edited on 27/5/15 by alfiebeard]

Thanks everyone.

Exhaust isn't the issue. It's just as gutless without the exhaust and also upsets my neighbours!

Stale fuel is out - I replaced the fuel tank and put fresh fuel in it

Rings, gasket, oil seals etc, yeah could be. I've no idea of this thing's history.

Just been out and tried fiddling with the mixture again. It's better, turns out I had it far too lean before, but it's still hit and miss. One minute it will go (quite well actually) but the next it just bogs and dies when you put load on it.

I take it a weak spark couldn't be the cause? I had to take the coil (with integrated magneto) and flywheel off to drill out the fuel tank mounts that the previous owner had snapped off. I only guessed what the gap should be between the flywheel magnet and the coil.

Chris

The Gap between the coil and the flywheel could cause rough running what I usually do is get the coil as close as possible without touching the flywheel then if it runs well leave it there if not move it in 10 thou increments until it runs best. if its too far away from the flywheel it will effectively alter the ignition timing by a small degree or two. also just another thought it has got an air filter of some description on hasn't it? if not the mixture at high revs will be too lean.

Alfie

Set the coil-flywheel gap to 0.4mm, any closer and the flywheel will rub the coil at high rpm. Check the in tank pick up, quite often they get blocked up restricting fuel flow (not cleanable, fit a new one). Check the clutch, if the spring is very week or broken then it will bog/be flat.

Could also be a tired piston ring as mentioned above but from your description it's less likely than one of those.

Ian

If it runs well but then suddenly losses power it's most likely a blocked jet causing a weak mixture when you try to accelerate. Compression issues don’t come and go and neither do ignition ones unless something’s falling off.

Lean mixtures are hard to ignite, if the mixture is leaning out it could be showing up a weak spark.

Thanks guys. I'll give the carb a good clean out tonight and see if that makes any difference.

Chris

Ok, I think I sussed it.... I had the carb on back to front. I think that's it anyway - it seemed a lot better with it turned around the other way but was getting a bit late to test it properly.

Will report again tomorrow.

Chris