Loud Bang/Mini Explosion, Now it Won't Start

#1
Quick back story: I purchased my 11 year old son a Coleman CT100u for Xmas. He previously had a Razor electric bike that did 12mph so I could just ride my mountain bike with him. With the CT100u doing 20mph stock, I figured I needed something to keep up with him so I bought a CT200u-ex for myself. I recently did the governor zip tie method on both. My son is super skinny so his jumped up to 32mph, mine only went up to 25mph (I'm not skinny:rolleyes:), so I added a new carburetor, a straight pipe exhaust with muffler, and an air filter. Now mine does 34mph.

We were riding the other day for about 45 minutes, when we got back to our street, I went full throttle for about 8 or 9 seconds, and just as I reached my house there was a loud pop/explosion, and the bike shut off. I tried to restart it a couple of times with no luck. It had been a long day so I didn't troubleshoot it too much. I'm a Biomedical Engineer (I repair medical equipment), so I'm handy, but I've never learned much about automotive/bike engines.

Where should I begin troubleshooting this issue?

CT200U-EX.jpg CT200U-EX2.jpg
 
#2
Welcome. This is a great site. Sorry about your bike. Defeating the governor places a great strain on other components. The flywheel and/or connecting rod can fail in a big way. Hi strength parts are available for both of those applications and they are affordable. Drain the oil and see if chunks of metal come out with it. That might point to a broken connecting rod. Flywheel failure is visible from outside of the engine and it usually involves injury to your right foot.
 
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#4
Welcome. This is a great site. Sorry about your bike. Defeating the governor places a great strain on other components. The flywheel and/or connecting rod can fail in a big way. Hi strength parts are available for both of those applications and they are affordable. Drain the oil and see if chunks of metal come out with it. That might point to a broken connecting rod. Flywheel failure is visible from outside of the engine and it usually involves injury to your right foot.
Thanks for the welcome...and thanks for the suggestions. I'm traveling this week for job training, but I will take a look at the things you mentioned this weekend. I'll keep you posted.
 
#7
:DMedical equipment is far from clean (trust me, you don't want to know some of the things I see). My hands are always dirty, I'm just looking to be pointed in the right direction so as not to be doing unnecessary repairs.
If'n that's the case you'll do well here... just watch out for car three of the crazy train... there's a big hole in it and they throw all sorts of shtuff in on top of you... Your're slipping already ... Razor Electric and two Colemans! Yup Yup!

Great site welcome to the madness! Keep us posted and all sorts of quality parts available check @Hent.com 1st he owns this site! We support him where we can. Ya might wanna shy away from the "Zippy Wrappy Ties" jus'sayin...
 
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desert rat

Well-Known Member
#9
My guess is you popped a rod. Pull the spark plug and place a pencil or wooden dowel in the hole, slowly turn the motor and see if the piston is still moving. If not = bad rod. That would make that zip tie = $200.00. The other thing to check is the valves, pull the valve cover and rotate the motor. The rockers should not be overly loose at any time. Think less than a business card. If you find one that is sloppy loose you floated the valve and smacked it with the piston and now it is bent. There is no "hidden" power or rpms on these motors. Good luck with it.
 
#10
My guess is you popped a rod. Pull the spark plug and place a pencil or wooden dowel in the hole, slowly turn the motor and see if the piston is still moving. If not = bad rod. That would make that zip tie = $200.00. The other thing to check is the valves, pull the valve cover and rotate the motor. The rockers should not be overly loose at any time. Think less than a business card. If you find one that is sloppy loose you floated the valve and smacked it with the piston and now it is bent. There is no "hidden" power or rpms on these motors. Good luck with it.
Thank you. That's great advice. And yes, that would be a costly zip tie.
Now admittedly, most of my mini bike knowledge is from YouTube videos (I know, I hear myself and how dumb that sounds in retrospect), but are you saying that I shouldn't try to modify these mini bikes at all? Or, if I modify one thing, I need to strengthen other things to compensate?
 
#13
Thank you. That's great advice. And yes, that would be a costly zip tie.
Now admittedly, most of my mini bike knowledge is from YouTube videos (I know, I hear myself and how dumb that sounds in retrospect), but are you saying that I shouldn't try to modify these mini bikes at all? Or, if I modify one thing, I need to strengthen other things to compensate?
There is a lot of advice on YouTube. The problem usually is figuring out what is signal and what is noise.

I think the folks here will help steer you in the right direction.

I've only been tinkering with the inside of (much larger) air cooled engines for a few years. You need to appreciate where to apply force, and where a gentle touch is required. Tolerances of a .001" are a big deal inside most engines.

If you want to repair/build engines, attention to detail is key. Ask lots of questions and post pics to help you along the way.
 
#18
Pull the plug and see if she has compression. If it is the rod, you won't have anything. That is generally the first place to look if there is no visible rod hanging out the block.
 

toomanytoys

Well-Known Member
#19
Another 200 dollar zip tie! If I had a dollar for every post that starts with...I bypassed the governor and now my bike won't run post I could retire!

Everyone has offered good advice.

Only thing I can add...

If you do need another motor...and you want more power and more rpm...

Ducar 212 is my suggestion. Should spin about 5500 rpm out of the box. Pretty stout little guy and already had the proper flywheel if you decide you need more. Throw in a billet rod, cam and upgraded springs and you'll have a little screamer.

https://www.dynocams.com/item/ducar-212kit/
 
#20
If you get a new motor you will most likely need a new clutch. Most new engines are 3/4" shaft. The crankshaft on the 196cc HiSun on the coleman is 16mm. People say it is 5/8" but not exactly. Look on Facebook marketplace for a Coleman engine if you need one. People are always wanting to put torque converters on their bikes but the 16mm crank is hard to find parts so they just replace the engine. If you do need a new engine, the 212cc predator at Harbor freight is on sale. Basically find any engine with a 3/4" shaft. A torque converter is going to be one of you best upgrades. You can find one on Amazon for $65. Get one with a 3/4" driver and the sprocket for #40 or 41 chain. The torque converter will increase your takeoff and top end speed. To run one on the Coleman you need to raise the engine up about an inch. Use square tubing. Watch youtube videos but don't get all your info from 1 source. Watch a few and you will be able to sift through the BS.
 
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