Help me fix a 50cc two-stroke - AKA why i hate twostrokes - Pics now.

[takai]

Ok, so i have this old little Benelli scooter which i have been rebuilding for a friend and i finally have it all back together, new clutch pack, rings, and a cleaned carby.
After a bit of fiddling it starts well, and will idle nicely, and even go to full throttle, but it has diddly squat power. Like none at all, pretty much you load it up and it will stall instantly.

The engine has a fair amount of compression, and is getting fuel.
I simply cant figure out what is happening. My thoughts are that it is leaning out massively under higher throttle, and therefore stalling under load, but im not sure on how to test this one.

Anyone with a better idea of two-stroke engines that can give me a lead?

P.S. it has the smallest dellorto i have ever seen. Pics soon.

And here she is:

[oldcorollas]

correct mix of oil and fuel? or correct oil in squirter?

are there any adjustments on the carby? you could half block the carby intake to try and make it a little richer under load perhaps, see if it still stalls?

[takai]

The oil is a mix into fuel jobbie, but we have no idea of what it takes. The Benelli Aus distributor doesnt even have a mention of the bike at all, and the only other reference we can find to it is on Moped Army, which lists it as a 1970 Benelli.

The only external adjustment on the carby is the idle control, which is set to max, and a cold start choke. The choke automatically disengages on full throttle, so it doesnt help much.

Ideas on what sort of oil i should be using?

[joecoolmk2]

have you checked the spark plug? that'd give you an idea as to what the mixture is doing.

i'd say 40:1 mix would be good.

[takai]

True, i should check the spark plug, ill have to go buy a large plugtool tomorrow, mine was taxed a while back
Its running about 40:1 btw, 200mL of oil to 7.5L fuel. Premixed.

[joecoolmk2]

two strokes need to have a sealed crankcase, it hasn't got any leaks does it?

[takai]

Not that i know of, and i certainly cant see any when i tore it down and rebuilt it, did a check using carby cleaner while it was running, no bubbles or change.

[Vios-GT_07]

does the carbie have some sort of floater ? could be the float is stuffed...

[jeffro ra28]

basically, if its premix oil 2 stroke. lawn mower oil is what you need. Or similar. You can upgrade to fully synthetic but its eexxy and probly not necasary.
Has it got reed valves between the carby and barrel? These can often crack and cause very strange behaviour.

[SL666]

does it smell fuelly out the exhaust or anything?

have you got it warm before trying this etc?

[takai]

Yeah, it was definately warm while playing with it (after several runs up and down the street)
It didnt smell any more fuelly than normal, but that may be because my idea of normal is smelling the race car warm up in the morning.....
Ill play with it again tonight after dinner.

[SL666]

could just be that it sucks.. i mean 50cc pocket bikes don't go that well.. and probably rev harder..

i'd suggest finding out if you can get a carby kit for it (or if you are confident making your own gaskets) just pull it apart and give it a good clean out..

[takai]

Yeah, i pulled it apart last night and cleaned it up. Looks like it was rebuilt in the last few years of its life.
This thing certainly isnt a rev monster, but it did run up until about March. I do however remember the owner saying that he had changed the spark plug over, so maybe that has something to do with it. Ill laugh if its running a standard V8 copper plug or something. I never really thought to check it.

[styler]

id check the magneto is working well and providing a strong spark

[takai]

Point, will check that one too, going to be a pain to test, its hooked up solidly to the crank.