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Discussion Starter #1
Hello all,

I have the exact same bike as in the picture. I used it a couple of time, every time I found starting the bike very hard. I even broke a couple of pull starts already and I just think it doesn't make sense.

I am trying to understand where the problem is and why the pull start is so jerky, so this is what I know so far:

  • Trying to start the bike, the pull start feels very jerky and fairly hard
  • Rotating the flywheel by hand, it still feels very jerky and hard
  • With the plug out there is decent spark
  • With the plug out, the flywheel is very easy going and smooth, no jerkiness whatsoever!

I'm no expert, but my assumption is that if with plug out and the flywheel rotating smoothly, it means nothing is wrong with the piston? Do I have the right assumption?

If so, then what's causing the jerkiness? I've placed back the plug and I tried a couple more things:

  • Disconnect the exhaust from the engine outlet - the flywheel is still very jerky. I placed my finger softly inside the exhaust outlet and felt the piston moving with no problem.
  • I also took the carb off, and tried the flywheel and it still feels hard and jerky.

The last thing I can think of is that maybe the reed valve is blocked? Does that make sense? What's the best way to troubleshoot this?

I know it's a long post, any help appreciated!!!!
 

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Remove the pullstarter and make sure the coil has plenty of clearance against the flywheel...It needs to be a true business card thick which works out to .020" of airgap..............

If all checks out remove the reeds and have a looksie at the crank.............Good Luck
 

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When the piston goes up it compresses the air inside and it gets hard to turn till your passed TDC and going down and the exhaust port open.
 

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CAM said:
Remove the pullstarter and make sure the coil has plenty of clearance against the flywheel
There's some gap, I have pushed the coil unit as back as possible. Also, I can definitely see a spark on the plug. The only concern is that the flywheel has to rotate really fast. With the plug out I have secured my cordless drill onto the flywheel, and I only get a spark if the drill is set to fast mode.

EPR said:
When the piston goes up it compresses the air inside and it gets hard to turn till your passed TDC and going down and the exhaust port open.
Perhaps I'm making the wrong comparison but my chainsaw for example, although it's only 25cc (so half the size of the pocket bike), has a very smooth pull start.

So what are you saying? That it should really never get a smooth and easy going with the plug is inserted in?
 

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There's some gap, I have pushed the coil unit as back as possible. Also, I can definitely see a spark on the plug. The only concern is that the flywheel has to rotate really fast. With the plug out I have secured my cordless drill onto the flywheel, and I only get a spark if the drill is set to fast mode.
Alright so refer to the second half of my suggestions...It sounds like you have rusty needle bearings in the crank ,,rusty crank bearings or a scored-up cylinder................remove the reedplate and look inside...........
 

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Alright so refer to the second half of my suggestions...It sounds like you have rusty needle bearings in the crank ,,rusty crank bearings or a scored-up cylinder................remove the reedplate and look inside...........
Sorry if I persist with this but I really want to understand how it all works (this is for me more than just fixing the bike but also a learning experience).

If there was any issue restricting the piston moving, as you suggested - needle bearing or a scored-up cylinder, wouldn't that result with a jerky pull start even with the plug is out?

Because with the plug out, the flywheel is moving really smooth and so does the piston.

Thanks!
 

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When the sparkplug is installed, as the piston moves upwards it compresses air/fuel inside the combustion chamber. Without the sparkplug, the combustion chamber is left wide open allowing any pressure to equalize outside of the engine. It sounds like you have decent compression which is good. Try re-gapping the coil and put some gas down the sparkplug hole. It should start up then die as the fuel inside the engine has been burnt up. If this all works out and you re-install the carb,, if it's a no-go, then you need to figure out why the carb isn't working. These lessons are usually learned one at a time mostly from experience, but most of times a description of why things are happening do well to supplement.... I myself am still learning about these small engines. Good luck and let us know what happens! :D:thumbsup:
 

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Sometimes the new $10 China carbs are bad from the factory.
 

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Sorry if I persist with this but I really want to understand how it all works (this is for me more than just fixing the bike but also a learning experience).

If there was any issue restricting the piston moving, as you suggested - needle bearing or a scored-up cylinder, wouldn't that result with a jerky pull start even with the plug is out?

Because with the plug out, the flywheel is moving really smooth and so does the piston.

Thanks!
Youre the one saying you have an issue with the way it feels and you eliminated most of the suspected pronblems and dont want to finish the steps required to troubleshoot the problem and want total clarification on what I say????...Maybe its you that has the problem and not the engine......

You dont take the time to inspect and just run the engine chances are the parts will gall so badly theyll be rendered trash.......Everybody knows that youre supposed to remove the redplate to inspect the reeds and the crank.....If the reeds are gummy from thich oil theyll give ya problems by not allowing proper air to enter the cylinder but youre the grand whiz on engines over me I guess..........

If you take the time to do what every normal person who doesnt want to blow their shiz up would of just took the reed plate off just to see..........but I see youd rather argue than take 15 mins to be safe than sorry ...........I guess there isnt really an issue then...........

But then again.....What do I know.Follow my 16,000 threads...Ive built more engines than youll ever own in 5 lifetimes....Engines in a realm of power youll never wrap your mind around so Good Luck with the imaginary problem dude..........
 

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wo, ease up Cam the almighty.
this poor guy just wants to know why its jerky turning over. Not that your ideas aren't good.
he didnt know about fuel mixture compressing causing the jerks. now he does.
nobody knows everything (except you and your 16,00 threads) and come here for help
 
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