taotao 50cc starting issue By ld9791 (Read 4,338 times)

[ld9791]

My joyess 50cc scooter is down.
I was travelling down the road at about 30mph and it died. Been working on it since (about 2 Weeks) I think I've narrowed the problem down, but would like a second opinion.
So far I have
Replaced the carb
Set air/fuel mixture screw to 2 1/2 out
Set valves at .004
Replaced spark plug (yes had and still have good spark)
Compression test is showing 30 psi
I pulled the gas line prior to petcock fuel flows fine
Pulled past petcock and it dribbles out while turning key
Removed airbox and sprayed starter fluid into airbox...when doing this scooter WILL start, but dies within 5 - 10 seconds even playing with throttle.

So after all this i'm thinking I have a bad petcock.

Any thoughts?

[tvnacman]

I'm not sure what the compression should be on a 50cc I'm thinking it is low at. 30psi.

John

[tvnacman]

I would recheck the valves. Then squirt some gas in the carb and see if it will run. You might want to check for vacuum leaks. If the vacuumed is low do to leaks it may not open the gas flow. There is a screel on the petcock it could be clogged.

Jogn

[ld9791]

Could a small break or crack in vacum line cause low compression?
Also
Any harm in bypassing petcock? Meaning run line fdom tank, to filter, to carb.. (capping of vacum line to petcock)

[tvnacman]

Jul 27, 2012 12:17:39 GMT -6 ld9791 said:

Could a small break or crack in vacum line cause low compression?
Also
Any harm in bypassing petcock? Meaning run line fdom tank, to filter, to carb.. (capping of vacum line to petcock)

You can bypass for a test. But replace the line.

When you did the compression test did you have the throttle wide opened?

A crack in a vacuume line will make you loose vacuume, enough to not be able to open the valve.
A cracked line will not effect compression.

John

[ld9791]

When I did compression test, NO I did not have throttle open. Was my first time ever foing it. (yeah i'm an idiot)
Will retest tonight along with a bypass test.
I have inspected the lines, saw a small crack at vacum line, but didn't look like it went all the way, nor any change when I covered it. Will replace anyway though

[ld9791]

How fast/how much of flow should come from the fuel line after the petcock. (line leading from petcock to carb))

[jct842]

When testing compression even if the throttle is closed you will get a whole lot more than 30# on a good motor. I would expect in the neighborhood of 150# on a good 50cc motor. (I just worked on a 50cc gy6 and got 150# on a 2005 motor with 2000 miles on it) If it had been running good and quit suddenly and has 30# of compression you have valve problems period. Unless a hole in the piston just popped up, you more than likely have a valve that is stuck partially open for one reason or another. You can squirt fuel into the carb all day long and with out compression it is not going to start. Vacuum leaks can be a reason the petcock doesn't let fuel through but you need at least 90# of compression to run half way decent/

[tvnacman]

Jul 27, 2012 12:44:01 GMT -6 ld9791 said:

When I did compression test, NO I did not have throttle open. Was my first time ever foing it. (yeah i'm an idiot)
Will retest tonight along with a bypass test.
I have inspected the lines, saw a small crack at vacum line, but didn't look like it went all the way, nor any change when I covered it. Will replace anyway though

I don't agree with the idiot comment. You here trying. .

John

[ld9791]

Yeah that was my fear. Replaceing valves/pistons level of difficulty? Cost? Special tools? And is it actually worth it for a 50cc?
I bought a 150cc and was going to keep the 50cc to play with, but to be honest i'm I little scared of actually getting that far into the motor.

[jct842]

What have you got to loose if you have a ride? Go slow, don't take anything for granted, and ask if not sure before you do it. If you stop for a week or so and just do some reading and watch a few videos and how too's you may just get some bearings on which way you want to go. The right tools are a must and most are not expensive. bash has a tear down here on a 150 which is very similar and the same principles on the whole engine. There is a leak down tester explained here some where and that would tell you where you are loosing the compression. You should be able to pin it down before turning a wrench. a top end (piston rings and cyl) is probably around $50-60 and head about the same and should not require both, just one or the other. read read read.

[Alleyoop]

Yes, just follow the procedure in this thread its for a 150 but it applies to your motor as well.
The difference is your motor is just smaller, but it has a head, cam, chain, rockers, pistion and rings. About the only thing difference on the 50 is it does not have a Starter Clutch inside the right case behind the stator. the 50s have the starter gear in the CVT and not inside the motor. But other than that it is Sameo Sameo as a 150 just smaler parts.
Alleyoop
www.scooterdoc.proboards.com/index.cgi?board=150cc&action=display&thread=6379