4-stroke 125 scooter dies after 5mins ride and wont start until cold.

Hi guys and girls,
Im at the point of a petrol and match fix for m damn scooter. Lol.
I have a yiben gladiator 125 4-stroke and once started its ticks over lovely then when I set off on a ride after about five minutes it coughs splutters then dies and wont start again until cooled down.. someone said possible rings so changed piston and rings and no luck. Tryed changing auto choke twice but still the same.. so decided to check oil by draining it out (1litre) so measured out exactly the same amount and started to re fill but it only took just over 500ml, so I thought to myself "we have drained and changed piston so once fired up the oil will be pumped threw the engine and the oil level will drop allowing me to top it up" but no it hasn't dropped so could the over heating and cutting out be to do with a (pardon my french but) f**ked oil pump... Hopefully one of you scooter gurus can help me solve my problem..
Cheers guys.
4StrokeScooterFreak

 

first is it over heating,and seizing up or is it electrical as in coil over heating don't know your scooter so is it carb or injrction

 

@twodogs
It's a carb engine.
Sounds like fuel starvation, but as you have changed the piston, did you run it in properly or did you just fit and ride as normal?
Heat seizure, a soft seize, is also possible.
It could also be some crap in the tank, fuel vac tap faulty, fuel filter, carb jets, or even that the carb is shot. But thats just speculation.
If it was your oil pump, it would kill the engine completely.
Do a compression test when the engine is cold, note the reading.
Run the bike stationary until it dies and won't start again, then do another compression test. See if the readings are the same.
Let us know please.

Check the pipes from the engine to the vacuum tap for splits and holes; stupid little pin holes can stop the fuel flowing to the carb in the vac line. Check the manifold for cracks and splits and any air leaks around it.
Change the air filter.

With problems like this, it's a case of going through the motions to make sure everything is good before digging in deep and ripping things apart.
All the parts for your bike are available from CMPO in exeter.

 

running way too rich maybe?

 

+1 on Steves advice.

does sound a fuel starvation thing, to be safe just replace the vacuum tube with a new one, if your feel like getting dirty down pull out the fuel pump - undo the four screws on the rear and lift the base plate off, inside you will see a plastic sheet that is the diaphram and some chanels for fuel to pump round without removing the plastic diaphram just see if theres any large clumps of crud in it. - rebuild it back up and install to bike.

check the fuel filter to they tend to be an inline filter just before /after the fuel pump these can get clogged up fairly quick if there has been a lotta dirt get into the tank. if your unsure replace it for a hi flow inline fuel filter.

carb starter spray, just leave bike ticking over and spray a little fluid where the carb joins to the maniflold that leads to the engine its usually a point of leaks, if the engine starts to increase in rpm idle you have a leaky fitting and that when running is causing you to run very lean , the motor overheats and you get a soft sieze ( bike rpm falls aways speed drops and maybe stalls, a few mins after bike fires up like nothings wrong but again a few mins later it happens all over )

 

when you say it stops and wont start,do you mean it wont fire up or it wont turn over

 

Valve clearance?