49cc Motors driving me up the wall

[21Guns]

G'Day everyone. New to the forum and glad I found it honestly haha. I bought my sons two different brands of 49cc dirt bikes. I've replaced both pull starts, the flywheel on the one without plastics and put a new coil and killswitch on the one with plastics. Problem is no matter what I do the one without plastics is refusing to start and the one with plastics will start and run for a good while before seizing. I've made sure the carbs are adjusted (1 and a half turns each) and ensured correct oil/fuel ratios. I'm at the point of replacing these motors considering how hard they've been run. Any tips on how to get these things as reliable as can be for chinese engines would be greatly appreciated as the one without plastics is for my eldests birthday in April.

 

[my67xr]

Welcome to Minirider's,

What fuel/oil ratio are you running? eg how many ml's of oil are you mixing with how many litre's petrol ?

The bike that's not running, does it have spark when you try to start it ?
You are best off replacing the cheap china spark plug's with some NGK plug's too
And have you checked that the spark plug is wet after trying to start it?
Are you using the choke to start it ?


When you say the carby's are adjusted to 1 1/2 turn's out, most of them don't have a mixture screw
Is it the screw with a spring on the side/middle of the carby? If so it's the idle speed screw
I think you may have raised the idle speed up too much

Take the air filter off and while looking into the carby, wind the idle speed screw out until the slide stop's moving down.
Now wind the screw in until the slide has lifted about 1.5mm to 2mm above the bore of the carb.
This should be a good starting point to try it out.


That PY90 look's pretty clean in the background too!

 

[21Guns]

Thanks for the advice mate I'll give it all a whirl tomorrow if I get the chance. And you have great eyes! I've been trying to find out what that bike actually is for weeks. The naked and the PY90 came together from a woman who said it was an 80cc. And I honestly thought they were mixture screws haha.

 

[my67xr]

Jianshe make the PY90, also known as the JS90Y Wildcat
It's a chinese copy of the Yamaha PW80, but they have a 4 stroke engine in it.
Jianshe Australia | Jianshe JS9Y WildCat
I have a Jianshe PY80, a chinese PW80 2 stroke copy, there is a link to my build thread in my signature below this post, click on it to have a look.


One of the problem's i've found with those 43cc pull start engine's is the carby.
If it's been left sitting around for a while it'll have gummed up fuel in the bottom off the fuel, the main jet could be clogged up as well.
They also get blocked up at the fuel tap, take it off and check it for anything like dirt etc there too.
Luckily a new carby is cheap, or you could go for the performance version if you wanted too.
13mm Carby Carburetor 2 Stroke 47cc 49cc Mini Kids PIT Pocket Quad Dirt Bike ATV | eBay
HP Racing Carby Carburetor Adaptor 49cc Mini Pocket Chopper Dirt Quad Bike ATV | eBay

 

[21Guns]

The PY90 (as I now know haha) was driving me crazy too until recently. I had to fix the 5 pin comnector (wire had broken out so I soldered it back in) and the carb was gummed up badly plus someone had installed the float backwards on it. Now it needs a new throttle housing as the cables just sitting in too tight and revving hard when I started it. I'm mixing the fuel at a 1:25 ratio as my mate told me to do. I'll post up more later when I get to work on em so more.

 

[my67xr]

With the PY revving high when you start it, are you sure you didn't fit the slide back in the carby 180° out ?
The half moon notched side of the slide need's to be facing the air filter side of the carby
That will make them hard to start, and when they do they'll be revving real high.

The little pocket bike's you can run at 32/1, so 3.2 litres petrol to 100 ml's oil, 1.6 litre's petrol to 50ml's oil.
That will get rid of some of the smoke and help the spark plug to not foul up
When you finish using the little bike's for the day turn the fuel tap off and let them run out of fuel and stall.
That way next time you go to use it you shouldn't have to worry about the carby/jet's being gummed up

 

[21Guns]

Took your advice on the 49ccs and remixed my fuels got the plastic bike running like a dream and dialed in better as well as wired in a killswitch and new magneto. I'll start a proper build thread in the chinese section. Carb on the naked will be pulled and cleaned and the PY will get a proper going over soon. Thanks for the help

 

[headsmess]

good test is to pull the carb off, pour some fuel down the plug hole, and see if it fires up that way. if it does...its just a carb cleaning required.

when you pull the carb, make sure the reeds arent bent at the same time. or broken. they should make a strange sort of squeaking noise when air is sucked in, when turned over by hand. and there should be TWO distinct compressions with a two stroke...one up, and one down. cylinder compression, and crankcase compression.

check the exhaust isnt blocked...

if it refuses to start, worth popping the cylinder off and checking the bore for gouges. made sure it had spark first, yes? remove any and all wires from the cdi/coil thingy. except the main plug wire, obviously.

if plugs keep fouling, drop a number or two (if you are wise and run NGK plugs) and they will stay "relatively" clean. usually a good idea if the kids ride them around fairly slow most of the time. using a hot plug is only an issue when you run WOT for long periods.

 

[21Guns]

Thanks for all the tips mate. Im sure when my eldest blows his up after his birthday next week ill be referring back to this haha.

 

[Daniel D]

Hi all. I have recently come across a jianshe wildcat js90y. After starting I have noticed a small oil leak coming from a bolt that's around a thread on the oil cover plate near the oil filler hole just above the rear brake peddle. I tried tightening bolt but still leaks between the bolt and the thread. Does anyone have any info on why this would be happening? Any help would be much appreciated

 

[Daniel D]

Hi. I have just posted a reply to this about my wildcat js90y that I'm hoping you can help me out with. Thanks Daniel

 

[motodevo]

Mate you're gunna have to post a pic of it if you want a reply, your description is too vague and confusing

 

[Daniel D]

Mate you're gunna have to post a pic of it if you want a reply, your description is too vague and confusing

How do I post a pic? Sorry I'm new to this site

 

[Daniel D]

I think I've worked out how to post pic.

 

[motodevo]

Okay, so its leaking from the clutch adjustment screw/lock nut. There is an o ring on the outside of the cover for this which is probably shredded and thus leaking. It is 8 mm from memory

 

[motodevo]

Number 14 in this pic
View attachment 13268
Once you have replaced it you will have to re set the clutch. Here's a vid on how to do it
How to adjust Honda clutch - YouTube

 

[Daniel D]

Thanks so much for your help motodevo

 

[Daniel D]

Okay, so its leaking from the clutch adjustment screw/lock nut. There is an o ring on the outside of the cover for this which is probably shredded and thus leaking. It is 8 mm from memory

Will I have to drain oil prior to replacing o ring?
Would you know where I could get a workshop manual from?

 

[AntNZ]

Will I have to drain oil prior to replacing o ring?
Would you know where I could get a workshop manual from?

No, you shouldn't have to, oil level should be below that......prop the bike up at the front to get the oil to run to back of the cases if need be.

 

[motodevo]

Closest manual we will be for a crf50/70 for the engine (all chinese stuff started as a direct rip off of the honda 50). There won't be a manual from the actual manufacturer to be found unfortunately.
I would just lay the bike chain side down, if you hold the clutch set screw in place with a flat blade so it doesn't move, you can undo the lock nut with a ring spanner, take it off, take off the washer, remove and replace the o ring, put the washer and lock nut back on, if the set screw stays in the same position it was originally you wouldnt even need to re adjust the clutch adjustment.