Suzuki AP50 Scooter 1998 (Two Stroke)Running Problems

I have just fitted a new standard 50cc piston and barrel kit because the original exhaust bolt sheered off in the barrel so for the price of a new kit I considered it would be a good idea to fit a new kit.
Since I fitted the barrel and piston the bike starts fine and ticks over when I take the bike out for a run after a mile when the bike gets hot the engine just dies with a rattling sound the bike will restart straight away and runs for a few minutes then dies again with a rattle.
The rattle is not there when the engine restarts.
Before changing the barrel and piston this problem wasent there.
Today I removed the barrel and piston and checked the gaskets and rings all was ok but I renewed the head gasket and base gasket the same problem is still there Im a bit uneasy about dissassembling anything else because the problem was not there prior to the new kit being fitted any help would be appreciated.

 

Circlip dropped down into the crank?

 

Hi
No definitely not that it only rattles at point of engine cutting out restart engine and it's quite until it happens again someone has suggested cdi unit playing up when warm.

 

Yeah could be ignition going out, either advancing or retarding to make it ping.

 

I've just changed the plug checked reed valve which is ok ride it out about 20mph it went about 3 miles before pinging and cutting out it restarted straight away half a mile and it pinged and stopped again I haven't checked carb yet I dont think its fuel related because it stops dead just like turning ignition off if it was fuel it would splitter before stopping.
The wire on the cdi unit that goes to the plug looks like it's been melted but I took the plug cap off and wire looks ok it's very strange what's going on it's a puzzle !!

 

Sounds like a mild heat sieze.

 

Hi
What would cause that I've had the head and barrel off today checked rings they are ok I've refitted the head and barrel with new gaskets but I still have the same problem do you think the cdi unit may be causing it ?

 

Heat sieze is when it hasn't been run in enough.
Can happen when you get close tolerance piston to bore clearance.
You should be running in for about 250 miles minimum on a 2 stroke.
Have you heat cycled the engine after re-build?

 

How do I get over this problem I have seen a good used barrel and piston for sale would it be better to go for that option or stick with what I have will it eventually be ok or will it keep seizing?

 

Stick with what you have.
Keep the revs down as much as possible, use a little 2 stroke in the fuel to help the lube, don't bollock it. On and off the throttle, not full bore, not full speed.
Gently gently catchy monkey as they say.
Keep an eye on the colour of the plug, it will foul with the extra oil added, plus make sure it runs rich and not lean.
You're looking between 200 and 300 miles for a decent run in period. Boring I know but better in the long term.

 

The scooter has a separate oil tank are you saying put two stroke oil in the petrol aswell ?
Also the mixture cant be adjusted only the throttle idle the mixture orifice is capped off the colour of the plug is light brown indicating mixture is ok.
If I keep riding will I be able to get more than 1 to 2 miles before the engine seizes more importantly would any more damage be caused as everytime the engine stops it rattles at the same time thanks for your help by the way its appreciated.

 

I guess your oil pump keeps it at 2% oil. Just ad some oil in the fuel tank so that you have a 3 to 4 %oil instead. So 2 centiliters oil per liter oil. Just until the cylinder is broken in.and dont give more than 3/4 turns of the throttle. Keep away from overtaking etc. Since the cylinder stills runs. Id keep with that.

 

I have managed to get hold of a second hand barrel and piston with new rings the bike runs fine but I have noticed if I go down the bypass at say 30mph for 10 miles leave the engine overnight the next morning the engine sticks as though the starter is jammed only for a second then the bike starts I have since added oil (4 capfuls 80ml to 5 litres of petrol drove 10 miles around country lanes 30mph max speed but variable speed the engine does not stick when cold if I do the same on the bypass the engine sticks when cold any idea why?
my thinking is that on the bypass the speed is a constant 30mph maybe I should vary the speed the top speed is 40 to 45mph not done that yet though ! The engine keeps going once started unlike the other barrel when the engine would cut out when hot.

 

Still sounds like a heat seize.
Too lean maybe on the main jet at a guess

 

Unfortunately I cant ajust the mixture as it is sealed and I cant get at it the plug is a nice brown colour so it indicates that the mixture is ok.

 

Mixture on the main jet, mixture screw is just for idle speed pretty much

 

The only ajustment on the carb is the idle I cant see any other ajustment .

 

Yeah. You need to take the float bowl off and swap the main jet for a bigger one.

 

Ok how do I know what size to get ? thanks

 

You need to read the number off the one it has fitted.