Mechanical help needed - poor starting and running

[casper]

Hi , never tried any of these forums but here we go.
I am a Kiwi living/working in China.
i bought a Chinese Zongshen bike 80cc, 4 stroke , it's about a year old.
When it is cold it starts no problem but after about 30 sec it starts to lose power more and more and then dies , after this it does start but not easily.
It may do this two or three times , then it will run but with very reduced power until it runs for 15 or twenty minutes the power will slowly increase , so now at the lower speeds it is ok but at the higher end it still has little power.The carburetta and petrol tankhave been striped and cleaned.I live in a small city and believe me not one of the many "repair shops" has any idea what they are doing , please help,

[CrazyCarl]

When diagnosing a problem like this you've only really got three choices...spark, fuel or air.

Off the top of my head I'd say it sounds like a fuel starvation problem. The carb may have been cleaned but did you check for proper operation of the fuel supply cut off valve? Also, any chance to pinching the fuel line? Is the idle set too low? What happens when you open the throttle?


If you're 100% sure the carb is okay, then check the boot between the carb and head. I've had weird air leaks there that caused all kinds of crazy problems. Just make sure everything is tight and not cracked.

Also, some scooter carbs have an "auto choke". If equipped, check for proper operation or unplug it and see if that changes anything.

Sparkwise, take your plug out and check the quality of spark. Maybe your plug is fouled?

Did the scoot suddenly start running poorly or did it get gradually worse over time?
CC

[casper]

Hi crazy carl,
Thanks very much for your reply.
I understand everything that you say , but what's got me baffled is that it does get better and stops cutting out after a time , so if it was an air leak it would surely not improve with time but do it all the time.It does have a lack of power all the time.
The plug has been replaced.
After they striped & cleaned the carb & tank it did stop cutting out for a short time but still did not have it's normal power , this did not last long & it reverted back to cutting out after a day or so.
It is a lesson in frustration as I cannot speak Chinese and I don't know if my wife translates what I am trying to say correctly.
These road side repair people have no testing equipment at all & I just know they don't know what they are doing,but I also they are just trying to earn a living so I can't be too hard on them.
I will disconnect the auto choke as this reacts from the heat of the engine & maybe the mixture is wrong this is why it never has no power.
Any more thoughts from you ?
I will let you know how I get on.
Regards Casper.

[CrazyCarl]

It ain't necessarily so. If it's an air leak and has to do with rubber, it will expand as it heats. Either way, it shouldn't be so bad that the scoot will stop running.

My wife and I had a Jialing 50 cc scooter in Chengdu before we left and it had all kinds of weird problems running and starting which ended up being a problem with the front variator. I would check inside the drive case and make sure the belts and pulley are all okay.

CC