PW50 will not start properly or idle after servicing.

[minipeewee]

I bought myself a PW50 from gumtree for $650 (I was ripped off lol). Picked it up around night in the rain so I was unable to inspect it properly. I was too excited as it's my first mini bike and I let that get the best of me and I'm now paying the price. Guy started it, it ran. Tells me that he "big bore'd" it and tells me that the carburetor might need a clean. Had a go of it in his yard in the rain. Was a lot of fun and took off like a rocket. There's was much more wrong with it than I thought. Front forks were busted, ignition switch dead, steering bearings shot, throttle cable and fuel lines leaking yadayada. I replaced all those and cleaned the carby out today and here's the problem:

The damn thing won't start correctly anymore.

Just to clear things up, it always started on the first or second kick before I serviced it. You have to squeeze the throttle and after about 16 kicks or so, it starts but not properly. If you let go of the throttle, it dies. I set the ignition switch to start with max throttle, and the rear wheel does not spin fast at all. Choke already tried that. Nothing. It also blows lots and lots of smoke with a blue tint. I've confirmed that it's not anything to do with the ignition switch as I've disconnected that and started it with just the kickstart and it does the same thing. I can't help but thing it's the tranny oil I put in. 10w/40 4 stroke. I put about 200mls in. It's that castrol gold stuff. Doesn't say it's tranny oil, just 4 stroke 10w/40 and that it's good for lubing gears. I've been told that it would work. I did fiddle with the carburetor's adjustment screw on the outside and I'm wondering if it's the issue. The needle goes up and down the carburetor as normal and the oil pump works good. Throttle is nice and smooth. My old man says it's the read valve and wants me to check that but I doubt that's the issue. He thought it was a fuel delivery problem, so I checked the lines and fuel pisses out like it should. The carburetor seems to be perfectly fine, and it pissed fuel out of the float when I disassembled it. I can't help but think the top end is gone. The dude didn't install it properly? I dunno. I also accidentally started it without the oil pump and fuel tank connected prior to me fully servicing it so it was running on fumes. It ran for 30 seconds and died. Lots and lots of smoke and made a lot of noise probably because I removed the exhaust. I'm wondering if that damaged the engine.

What do you people think the problem is? I badly want to ride this thing! Help would be highly appreciated. It's my first motorbike and I'm 19 *lolol*. I'm determined to get it working. Couldn't afford a Z50, so I got this instead. I just needed to revisit my childhood!

 

[my67xr]

Welcome to Minirider's


Ignition switch is dead, they can be pulled apart and cleaned up internally on all the contact's then sprayed with crc/wd40 and most of the time come good again.

10W40 engine oil is ok, Yamaha list it as using 10w30 gearbox oil (4 stroke motorcycle engine oil is fine)
But the thicker 10w40 is all good.

Removing the exhaust wont hurt it as long as it wasn't run for 5 min's or more like it.

When you adjusted the carby, did you adjust the mixture screw?
The flat headed screw to the right of the idle speed screw (central screw with spring)
With it not starting easily and you needing to give it a bit of throttle sound's like you have turned the mixture screw in more than what it need's

China PW50 Miniky carby (Mikuni copy)

To adjust it properly, turn the screw in all the way till it only just start's to get tight, now back it back out 1.75 full turn's
This should be ok for it to start and run.
Try it out and see if it start's, if it does let it warm up for a few minute's just idling
Now turn the central idle speed screw in a bit till the rev's rise about 300-400 rpm's (slightly fast idle)
Next turn the mixture screw in 1/4 turn and let the engine settle for about 10 second's.
Listen to the way the engine is now running, you want to find the point where you get the fastest/smoothest rpm's
If when you turned the mixture screw in the idle speed went faster then that is good,
Try adjusting the mixture screw in another 1/4 turn and let it settle again, did the rev's go up again, or stay the same ?
If they went up try adjusting the mixture screw in a touch more.
If they didn't change then adjust the mixture screw back out and let it settle again.
Try another 1/8 turn out and see what it does.
You want the idle speed to be the fastest/smoothest you can get as i mentioned above.
When you get it close then you can lower the idle speed back down to a normal idle (via the central idle speed screw)
Now give the engine a couple of blip rev's and take note of what it does.
If it rev's sweet without a flat spot then you are good to try it out and ride it.
If it rev's but has a slight hesitation or as the rev's come back down they take a while for it to come back to normal speed it is a touch lean, so you need to richen the mixture screw a touch (turn it in about 1/16 of a turn) let it settle again.

When the carby was apart, did you remove the main and pilot jet's, and the mixture screw,spring and oring and blow the carby out with compressed air?
You need to blow air in through the 2 small prt's on the intake/filter side of the carby and check for air coming out one of the hole's in the base of the carby.
In the base of the carby where the smaller pilot jet screw's into, there is a tiny hole at the bottom of the thread's that goes through to the main carby bore.
If this hole is blocked up partially or fully the bike will be very hard to start.

It will pay to take note of the jet number's too if you pull the fuel bowl off again, when the big bore kit was fitted the carby should have been rejetted to suit.
What air filter are you running with it, and is the foam filer oiled with air filter oil ?

With the bike not spinning the back wheel with the switch set to start, that is normal, it's a safety thing so the bike doesn't take off with a little kid on it when they start it up.
With it doing the same thing when the switch was disconnected, then that may be because the mixture screw has been set wrong too
Once the engine is running, switch the toggle down from start to run then it's ready to go and ride


The smoke it was blowing, was it a grey/blue smoke or was it kind of whitish ?
Grey will be too rich (mixture screw), or white smoke is caused by a leaking crankshaft seal behind the main drive gear inside the engine.

Steering bearing's are the same as the one's used in a lot of push bike's so they're cheap and easy to replace.

Fork's bent/busted, you can buy a new pair of china PW50 fork's off ebay for around $100 inc delivery, just make sure you measure the size of your's first so you get the right one's

Check out my PW50 thread too, there's a link below in my signature, just click on it

If you need any help with it just ask on this thread and i'll try and help you sort it out.

Cheer's, Craig

 

[low_rb]

In all of that you havnt mentioned fitting a new plug, have you done that?

If gearbox oil is getting into the crank case you will know, it fkn stinks when its burning.

starting with throttle then stalling sound to me like a blocked pilot jet, did you pull the jets out and clean them?
or the idle screw is wound out to far,thats not the one you fiddled with is it?

 

[minipeewee]

Welcome to Minirider's


Ignition switch is dead, they can be pulled apart and cleaned up internally on all the contact's then sprayed with crc/wd40 and most of the time come good again.

10W40 engine oil is ok, Yamaha list it as using 10w30 gearbox oil (4 stroke motorcycle engine oil is fine)
But the thicker 10w40 is all good.

Removing the exhaust wont hurt it as long as it wasn't run for 5 min's or more like it.

When you adjusted the carby, did you adjust the mixture screw?
The flat headed screw to the right of the idle speed screw (central screw with spring)
With it not starting easily and you needing to give it a bit of throttle sound's like you have turned the mixture screw in more than what it need's

China PW50 Miniky carby (Mikuni copy)





To adjust it properly, turn the screw in all the way till it only just start's to get tight, now back it back out 1.75 full turn's
This should be ok for it to start and run.
Try it out and see if it start's, if it does let it warm up for a few minute's just idling
Now turn the central idle speed screw in a bit till the rev's rise about 300-400 rpm's (slightly fast idle)
Next turn the mixture screw in 1/4 turn and let the engine settle for about 10 second's.
Listen to the way the engine is now running, you want to find the point where you get the fastest/smoothest rpm's
If when you turned the mixture screw in the idle speed went faster then that is good,
Try adjusting the mixture screw in another 1/4 turn and let it settle again, did the rev's go up again, or stay the same ?
If they went up try adjusting the mixture screw in a touch more.
If they didn't change then adjust the mixture screw back out and let it settle again.
Try another 1/8 turn out and see what it does.
You want the idle speed to be the fastest/smoothest you can get as i mentioned above.
When you get it close then you can lower the idle speed back down to a normal idle (via the central idle speed screw)
Now give the engine a couple of blip rev's and take note of what it does.
If it rev's sweet without a flat spot then you are good to try it out and ride it.
If it rev's but has a slight hesitation or as the rev's come back down they take a while for it to come back to normal speed it is a touch lean, so you need to richen the mixture screw a touch (turn it in about 1/16 of a turn) let it settle again.

When the carby was apart, did you remove the main and pilot jet's, and the mixture screw,spring and oring and blow the carby out with compressed air?
You need to blow air in through the 2 small prt's on the intake/filter side of the carby and check for air coming out one of the hole's in the base of the carby.
In the base of the carby where the smaller pilot jet screw's into, there is a tiny hole at the bottom of the thread's that goes through to the main carby bore.
If this hole is blocked up partially or fully the bike will be very hard to start.

It will pay to take note of the jet number's too if you pull the fuel bowl off again, when the big bore kit was fitted the carby should have been rejetted to suit.
What air filter are you running with it, and is the foam filer oiled with air filter oil ?

With the bike not spinning the back wheel with the switch set to start, that is normal, it's a safety thing so the bike doesn't take off with a little kid on it when they start it up.
With it doing the same thing when the switch was disconnected, then that may be because the mixture screw has been set wrong too
Once the engine is running, switch the toggle down from start to run then it's ready to go and ride


The smoke it was blowing, was it a grey/blue smoke or was it kind of whitish ?
Grey will be too rich (mixture screw), or white smoke is caused by a leaking crankshaft seal behind the main drive gear inside the engine.

Steering bearing's are the same as the one's used in a lot of push bike's so they're cheap and easy to replace.

Fork's bent/busted, you can buy a new pair of china PW50 fork's off ebay for around $100 inc delivery, just make sure you measure the size of your's first so you get the right one's

Check out my PW50 thread too, there's a link below in my signature, just click on it

If you need any help with it just ask on this thread and i'll try and help you sort it out.

Cheer's, Craig

Thanks a lot for the reply, mate. It's a lot of help.

>Ignition switch is dead
It couldn't be. It's a brand new one from ebay that I installed. When I do manage to get the engine started and hold down the throttle, I can flick the switch to "OFF" and the engine turns off with full throttle. I also tried the original switch which did work, and it's pretty much the same result. The original switch worked perfectly before I started service.

>When you adjusted the carby, did you adjust the mixture screw?
No, I don't think so, but I think my old man may have tinkered with it. I'll ask him. I did fiddle with the idle screw to the left of it. I did disassemble the whole carby and put it together correctly for a clean. My old man knows alot about bike carburetors. He opened it up today and said nothing looks wrong. We've come to a conclusion that it might be something else as the carby receives fuel and seems to be fine.

>To adjust it properly, turn the screw in all the way till it only just start's to get tight, now back it back out 1.75 full turn's
I'll give this a go.I'll try if I can manage to get it to idle without me pulling on the throttle. I'll report back the results.

>When the carby was apart, did you remove the main and pilot jet's, and the mixture screw,spring and oring and blow the carby out with compressed air?
Yep. It was pretty clean, but we carb gassed it anyways. My old man did a full diagnostic on it today. Took the jets out and did his thing. Said they were surprisingly clean considering the condition of the bike.

>With the bike not spinning the back wheel with the switch set to start, that is normal,
Yeah, I know. I've made a mistake in my OP. I was meant to say in the "RUN" preset it wouldn't spin it's wheel fast. Even with the switch completely disconnected. Sorry.

>What air filter are you running with it
The original air filter had no foam or mesh inside of it. It was just a plastic shell. I replaced it with a new one.

>The smoke it was blowing, was it a grey/blue smoke or was it kind of whitish ?
Oh, it was grey/blue alright. Smelled something nasty!

Yeah, I got new forks and bearings. Installed them and they fit nice.

I'll try all this tomorrow. Really is looking like it might be something to do with the mixture screw. If I can get it to idle, that will be good news. Thanks for your help.

In all of that you havnt mentioned fitting a new plug, have you done that?

If gearbox oil is getting into the crank case you will know, it fkn stinks when its burning.

starting with throttle then stalling sound to me like a blocked pilot jet, did you pull the jets out and clean them?
or the idle screw is wound out to far,thats not the one you fiddled with is it?

Yeah, I fiddled with the idle screw. And yes, it smells pretty bad. Gassed up the whole garage lol.

Spark Plug? I haven't tried that yet. I'll give it a go. Thanks.

 

[my67xr]

ignition switch dead,

I was just addressing what you had said about each problem/part

Have you had a chance to look at it yet ?

It might be worth checking for for leak's at the carby too, start the bike and let it idle, spray degreaser carby cleaner or wd40 on the join where the carby clamp's to the manifold.If the idle change's in any way then there is a vacuum leak there.
The bakelite/rubber seal's inside the carbys' clamp area can go hard, make sure you push the carby onto the manifold as far as it'll go to get a decent seal before tightening the bolt

 

[minipeewee]

I did what you said, and we managed to get it to idle by fiddling around with the mixture screw! That was definitely the problem. Unfortunately, things still aren't right. I pull the throttle, and the engine only rises slightly. The gold needle thingy is moving up and down correctly. It's most likely the settings on the mixture screw and the idle screw. With the mixture screw loose, the peewee starts on the first kick. With it tight, it takes lots of kicks. When we get it started with the screw tight, the wheel spins like it's supposed to. It's really fast, but the peewee is much much louder than it was originally. It conks out if you don't throttle with the tight screw setting.

 

[my67xr]

You should never do up a mixture screw tight, it will damage the screw and damage the seat that it does up into.

So the pilot jet is blocked still,
or the pilot jet circuit is blocked somewhere between the small port on the air filter side of the carby and the pilot jet opening at the bottom of the pilot jet thread's in the base of the carby

Adjust the mixture screw like what i said above

 

[minipeewee]

We finally got the little thing running!

Turns out it really was nothing to do with the carb's insides. We fiddled with the mixture and idle screw together, and we found the correct settings. When we got the bike to start on the first/second kick with the mixture screw, we were onto something, so we stuck with that. The bike idles correctly and takes off like it used to before servicing. No more dying! These settings seem to be perfect. The bike feels like it's going at least 30k's an hour and really zips along fine. I'm a big 6"05 guy so that's pretty good for me.

I'd like to thank everyone in this thread for your help. It's helped alot.

 

[minipeewee]

Nevermind.. It's stopped working again. Stopped working with the stock head. We suspected it to be the top end gone, but we are wrong.


It will not start at all. Fuel leaks out of the exhaust manifold and the carby overflow valve so the cylinder is most definitely getting fuel. Plug gets wet. It's getting spark, but the spark looks weak. Cleaned the plug, nothing. Tested two plugs a brand new chinese one and the NGK one it came with. Sparks on both look identical and weak. They are blueish sparks but they are very short and thin. Is the CDI or magneto gone? I am about to buy a chinese PW50 cdi ignition kit on ebay. Also tried with the switch disconnected so that isn't the issue. We screwed around with the mixture screw beforehand with the stock piston and nothing. It also started bogging down after a few minutes of riding. Let it sit for a day and it will not start at all, so we redid the top end with a new kit.

We just rebuilt the top end with a real 44mm big bore. Piston's arrow facing down to the exhaust, rings in correctly, new cylinder screws, torque on head correct at 8ftib good compression etc. Kick has resistance, piston goes. Turns out it really wasn't big bored, so I bought a kit and installed it correctly. Stock piston was 40mm.

 

[my67xr]

Sound's like the needle and seat in the carby has dirt in it, and is sticking open
or that the float tab has been bent and the float level is now too high

The spark should be short, the gap from the centre electrode to the earth electrode/strap should be .6mm to .7mm max
Blue is a good spark, yellow is a weak spark


Have you measured the resistance through your stator to make sure the stator is faulty and out of spec ?

unplug the black w/red strip wire from your stator.
put the red lead from your meter, to the black w/red stripe wire from the Stator.
and the black lead from the meter, to the frame earth.
our PW reads 300 Ohms
now plug the black w/red stripe wire back in

now unplug the white with red stripe wire from the stator,
put the red lead from your meter to the terminal on the end of the white w/red stripe wire from the stator
and the black lead from the meter to the frame earth
ours reads .3 Ohms
plug the white w/red stripe wire back in

let me know what readings you get


Are you still running the ignition control box, if so try unplugging it and see if it will start after you fix the flooding issue
Top one is the ignition control box, bottom one is the cdi

 

[minipeewee]

Yep. We did all that.

The switch is not faulty according to the tests. We then discovered the source of the weak spark. The ignition coil was blown, so we got a new one, installed it and now we get a nice big spark. Bizarrely, that was not the issue! This thing is a piece of junk and needs some serious overhauling.

We installed the stock head afterwards with new gaskets to see if that would do something. Nope. Won't even sputter. Poured some starter fluid and petrol into the spark head. Nothing.. Compression it was getting with stock and the bore is terrible. We do not have a tester, but I think it's 10psi lol. Was getting this with the big bore head also. It should be getting 90psi. Checked the reed valve and that's good, so we put that back on. Put my finger over the valve, kicked it and it barely sucks at all. It did this with the stock head afterwards too.

We've ruled out the carburetor as it won't start with stuff in the spark hole and it's cleaner than a baby's bottom. Dismantled it again today. There is absolutely nothing inside of it. The float rises and whatnot correctly.

We're thinking there's a leak in the engine, possible crank seal broken or something really, really serious. I still have absolutely no idea at all why it started several times on the first kick before we started servicing it. I cannot help but think it's the 4 stroke tranny oil I poured into the tranny bay, but that can't possibly be the issue. I poured about 150ml into it.