BOB.T

I know it's drivetrain related but it's not a scoob drive train

I run a mini moto, it's a 40cc two stroke. Normally I run it on NUL but have tried SUL in it and it performed better so I thought I would try some Optimax as it works wonders in the car

All was going well for a short while, it seemed to make a real difference but now, the thing just refuses to start It will run at random intervals but usually just dampens the plug and I'm gettin sick of wrenching the skin off my hands with the pull cord

I've cleaned the fuel tank out, replaced the fuel line, cleaned the carb, cleaned and gapped the plug, checked the lead, there's a good blue spark, and had a check in the cylinder, all ok. The fuel should be mixed 50:1, I mixed 100ml of shell two stroke oil with 5l of Optimax.

I'm at a loss really, my only thought is that Optimax may contain, lubricants, detergents etc that are making it too rich but can't help thinking that doesn't make sense

Anyone got any ideas, I might try changing back to NUL but then I'm stuck with the best part of 5l of fuel that's no good for owt

Bob

PS I'm not slagging Optimax, I'm sure the two stroke world wasn't a high priority when making it! Like I said, it works wonders in the car

CrisPDuk

All I can Suggest is that you might need to weaken the carb of withit being warmer at the mo' therefore less oxygen density. I know really small 2 strokes i.e. 100cc kart engines, are sensitive to air condition changes. That is all I can think.

BOB.T

hmm, I wondered about the jetting.... there is no adjustment screw as such. The bike has run in allsorts of conditions before, outside at about 30° and indoors at damn near freezing I've also tried starting it since having problems in both warm and cool weather, mostly cool at the mo

I wondered about a hotter plug too?

CrisPDuk

Possibly, but I'm afraid thats all I can think of. I'm not to hot on two strokes in general I'm afraid.

BOB.T

Cheers anyway

Odd things two strokes, I've been a mechanic nearly 9 years and still don't believe they work

NotoriousREV

Hmm, I wouldn't have thought using Optimax would cause the bike not to start, I know you've cleaned the plug, but I'd try a new plug just to be sure after it's been fouled. I think maybe it's another problem that has happened co-incidentally at the same time. How old are the piston/rings?

JackClark

I've used super and octane booster in my two stroke to no ill effect.

mike_s14

It doesn't make that much difference tobe honest
Tryed it in my GasGas 300....

BOB.T

I got the bike secondhand, it was a hire bike before I got it. The crank bearings failed shortly after I got it so it had, new bearings, all new gaskets, new plug, and a new piston ring. It's been running fine for just about a year now. I haven't had the piston out but I've had the top of the head off, there's no look of the piston burning out and the cylinder walls are perfect.

I've ordered a new plug and lead just in case. Gonna get some NUL today and rule out the Optimax, I'll keep you posted!

Cheers

Bob

davyboy

If the plug is wet its running too rich.

You should be able to lean the carb off a bit.

NotoriousREV

Maybe not, the plug will be wet from having being turned over without firing. If it was running and fouling I'd agree with you. I can't see that it ran fine last time and now the jetting is so far out that it won't even start. The new plug will probably work, unless it's something more sinister

BOB.T

Well, I put the NUL in and it started after a lot of messing about, it rode up the estate and back, it fired up time after time, all seemed well! I took it to the local race track, it fired up, I sat on, it stalled, never to start again, bugga! It can chuffin well stop in the garage and feel sorry for itself!!

Hopefully the new plug and lead will be here on Thursday, if that doesn't cure it I don't know what to do with it!

Bob

NotoriousREV

CDi unit? Do you know anyone else with the same model you can borrow a CDi off to check?

BOB.T

CDi, wassat then? The coil pack thing? I did wonder about changing that aswell, maybe see how the plug and lead goes first! Nobody has the same model as mine now, they've all sold up due to GF pressure I could see the chap where I bought it from perhaps?

Bob