139qmb gy6 50/80cc starting issue
 

Hello all! I'm hoping you can help me out as I've been trying to fix up my little Chinese 139qmb gy6 scooter. Sorry if I ask something that has been posted before but I need all the help I can get! Thanks!

So I have a 139qmb engine gy6 scooter, it has been upgraded to a 80cc from a 49cc. I will list all performance and new parts below.
Performance free flow exhaust.
Performance air filter.
Performance un-restricted CDI unit.
New battery.
New starter motor.
New NGK spark plug.
New performance coil.
New 19mm carb.
Valves adjusted.
I have a pack of jets from #70 to #83.
Currently have main jet #83 installed.

The main problem I get is just trying to start it up. It use to take a while to start but now it won't start a tall unless boosted from a car battery. The battery is fully charged and still won't start. It is getting fuel to the carb and it does have a spark. Once started it idles perfectly and rides perfectly.
I've been working on this since November last year! It just will never start! Also the engine does turn over too but yet still won't start. I can't kick start it either as this is sticky when used and does nothing.

Is there anything else that I can do? Already spent a lot of money changing stuff so I'm getting fed up now.
Thanks for the help! Would appreciate it!

I don't know if you mean it has a weak cranking issue,;bad battery or weak starter.
Or if you mean it will not start on first startup in the morning.???
You might try a bigger pilot jet(#38) or the carb enrichener(fast idle solenoid).
Could try adjusting the mixture screw out a turn or two and see what that does.
Get that kick start fixed.

"Bigger" pilot jet might flood the carb, and should be unnecessary. Try a "Longer" pilot jet, #35 or whatever from AbsolutelyScooters.

Thank you for such a quick reply!
It has a brand new starter motor so that is fine!
Brand new battery so that's fully charged and perfect!
It just never starts unless jump started from a car battery so yeah not looking good as even then that takes a few times.

I don't see any point in fixing the kick start as I never needed really and I don't even know what's actually causing this issue too.
It use to start with this size jet (#83) before so I don't see this as the issue either.

Is there anything else that could be the problem?
Like would any of the performance parts be causing the issues?

Thanks for the help guys!

Hi
Welcome aboard
Pleased to meet you
I would check your engines compression. most likely its very high causing the problems turning it over
How many head gaskets did you use most when you did the install most of us when doing a bbk install use at least 2 to lower the compression
Very roughly, 100-125 psi is good, 125-150 psi is very good, and 150+ psi is great. most of my bbk builds are around 190 to 195 anything over 200 makes for a very hard to start engine as the starters are not strong enough to turn them over at such a high pressure
So do a compression check and let us know the results
Hope this helps
Take care and ride safely
Yours Hank

I do not own a compression tester so I will have to get one from someone and then I can post the results!
But I did not install the BBK myself so with answers regarding that? I will not be able to answer as I had a local garage to do that for me.

Hi
Seeing as the work was done by a third party I would ask them exactly what was done during the install and make them fix the problems that have happened since
Take care and ride safely
Yours Hank

I didn't have this problem soon as I got my BBK fitted.
This problem just randomly happened one day and its been like this for a few months now. Sometimes it does start up but that is once in a blue moon as now it seems like its give up all hope.

Have you checked your valve clearance? If a valve is tight and you are loosing a little compression then the jump with a lot more powerful battery and spinning faster could be why it starts then.

Yeah I have had the valves checked over and reset both on the intake and exhaust. So I don't think that this is the problem either.
Even with the car battery though (car turned on) it still doesn't start up first time either

It's probably due to high compression. My 83cc BBked 139 engine bike became super hard to start after it finished it's break in. This is not unheard of with BBKS, chances are you require an additional head-gasket. I added two additional gaskets and problem solved.

However the proper way to fix this is to have your engine and head milled by an automotive machine shop. Using multiple gaskets as spacers is a bad plan, and will lead to head leaking down the road.

Another simple thing to check would be to make sure the spark plug is not loose.

I have fixed many of theses scooters. The valves are not seated, Many have low compression from the dealer. Take a drill and put it in your side cover and your motor will start. If it starts reseat your valves

At the risk of being redundant, have you checked the selinoid?

I got one with the same issue... any updates ?

--Update:
Piston rings wornout at 5k miles, put in a 80cc bbk and a 90main jet, now its roaring.
The previous owner glued the cdi harness onto the cdi, i can't get it off to put on a racing cdi :(

Anyone know where i can get just the cdi harness and not the whole thing ?