What went wrong? Bike will no longer start.

[dlibs]

Hello,
First I would like to say thank you for allowing me to join the forum and become a member of the community. Motor bikes have been a hobby of mine for some time and I’m excited to be here.
Now down to business:
I cannot for the life of me figure out what went wrong on my motor bike. It’s a typical 49cc 2-stroke Chinese motor on a 2010 diamondback Sorrento mountain bike. I installed the kit back in October and the bike has run fine since (except for eating 4 chains, but seeing as it already has 1,082 miles on it I guess that can be expected). I have done regular maintenance on it (cleaning the carb, cleaning the exhaust, oil on everything etc). I was riding it to a price chopper to run some errands when out of nowhere the bike started backfiring like crazy. I started losing speed and the engine started to die so I pulled in the clutch and the engine returned back to its normal idle. As soon as I let go of the clutch it started backfiring again and died. After that it would not start again whatsoever. I originally thought it was the spark plug so I replaced that and that didn’t fix it. I also replaced the cdi box because that had cracked due to cold weather. Now it pops and occasionally jolts when you try to start it but no go. I also noticed a fair amount of fuel is leaking out of the exhaust. Is it possible I blew a gasket? I have a spare carb lying around I might try putting on to see if that will fix it but if it’s an engine problem I won’t bother. My only reason for trying a different carb is that the fuel in the fuel line actually bubbles like a fish tank when you try to start it. I tinkered with the carb currently installed but no amount of screw configurations seem to result in any kind of improvement. I hope I don’t have to replace the motor because it is welded to my frame (that would suck). Any ideas, opinions, comments, or suggestions would be appreciated and are welcome.
Thanks,
-Dlibs

 

[2door]

Remove the magneto cover, left side of engine and check to see if the magneto rotor (magnet) has moved on the crankshaft. Your symptoms sound like a damaged or missing woodruff key that holds the rotor correctly indexed to the crankshaft for proper ignition timing.

Also check your spark plug boot connection. If you're using the kit supplied plastic boot they are notorious for bad electrical connections which can also cause the problem you describe.
Tom

 

[DaveC]

While your inside the magneto cover closely check the wires soldered to the magneto coil. Many, many times that's the problem of suddenly not running. You can even test them with a ohm meter and there can still be bad soldering. A cold solder will mechanically hold the wire but not actually be "melded" to the wire. This can easily happen when on a production line not enough heat is applied to the solder joint due to the coil stack pulling off the heat and not enough heat for long enough to make a good solder. A 40 watt Weller solder iron will do a good job fixing this problem

 

[Al.Fisherman]

https://docs.google.com/document/d/1aBeJuoS--VQWwXysc07rpscTUbPzgc93xjiQBgsyFjc/edit

 

[rustycase]

WoW!!!

U welded ur engine into the frame???

WoW!

seems like u got plenty gud advice on ur sparky probs...
fish-tank bubbles in the fuel line?
Perhaps there is an internal flaw in the carburetor that has developed, or made itself apparent???
Stranger thing have happened....

Nice to have a spare carb handy to swap and see if that makes a difference.

I'm not really sure what the record is, or even what common life expectancy is...
my guess would be that a thousand miles on an HT engine would put it at a serious wear point on just about all the components.

crank seals would be a good thing to replace when u are checking the rotor key.
...I'd just replace the rotor key, mof...

Best
rc

...I recently got a sorrento added to the pile... nice looking mtb. How do u like urs?

.

 

[2door]

I completely missed that. Why would you even consider welding the engine to the frame?

Tom

 

[Al.Fisherman]

https://docs.google.com/document/d/1aBeJuoS--VQWwXysc07rpscTUbPzgc93xjiQBgsyFjc/edit

WoW!!!

U welded ur engine into the frame???
WoW!
Thought the same thing. Not smart.
fish-tank bubbles in the fuel line? Common, fuel bowl accepting fuel.
Perhaps there is an internal flaw in the carburetor that has developed, or made itself apparent???
I'm not really sure what the record is, or even what common life expectancy is...
my guess would be that a thousand miles on an HT engine would put it at a serious wear point on just about all the components.
crank seals would be a good thing to replace when u are checking the rotor key.
Best
rc

 

[dlibs]

Alright well I checked the magneto. I took it out and examined it and I couldn't find any reason why it would not work. I also ran the bike with the spark plug in my hand and it sparks the way it should (not a pleasant shocky feeling though!). The problem shouldn’t be electrical. I will try changing out the carb tomorrow and let you know how that goes.
Yes I welded the engine to the frame. I work part-time for a company that manufactures helicopter components for Boeing and Sikorsky so I had access to some heavy duty machinery to work on the bike with (a welder being one of them). I could take the engine off with a plasma cutter but the end result would not be pretty. I also used military-grade heat resistant epoxy on the screws so that they would not fall off or become lose while riding. I have to say doing both of these things is probably why this build lasted as long as it did with almost no problems. I previously had an engine kit on a roadmaster mountain bike but it fell apart every couple of miles or so and I snapped the engine mounts twice on both sides of the engine. It was a disaster and I ended up scraping it and the motor bike idea altogether until I was talking to my boss about it and he said he would help me out if I built another one.
The diamondback Sorrento is a great bike I love it with and without the engine. If I have to replace the engine on it I’ll see if I can take the old one off first and just keep the bike as a regular bike (but I will most likely try to stick another engine on it). The bike only had 400 miles on it before I put the engine on. With the engines miles plus the 400 the bike itself has roughly 1,482 miles on it. Despite everything that has been done to it and the stress that the Sorrento has had on it all the gears change fine and everything is still original, even the brakes!

 

[nightcruiser]

Since you mentioned fuel coming out the exhaust, maybe something got stuck in your needle valve and is holding it open?

 

[maniac57]

Sounds like a timing problem from the backfiring. Check the mag and cdi first.

 

[vachon644]

Something similar to that happened to me on a scooter engine; the carburetor main jet had loosened up and fallen inside the float bowl thus allowing the carburetor to flood the engine. That could explain why your exhaust has gas flowing out. In these situations, be careful when turning the motor over because you could bend your piston connecting rod if gas in liquid form blocked your engine head (liquid does not compress) while you pop-started your engine. Try to check the carburetor first.

 

[dlibs]

So the mystery continues…
I examined everything everybody suggested so far. Everything seems fine and everything seems to be in relatively good condition, but it still would not start. I went ahead and replaced the carb, and when I did the bike fired up right away. I was happy and I thought my troubles were over. 15 minutes of running the engine later the motor started backfiring and seizing just like before. I turned it off with the kill switch rather than let it die on its own. When I tried to start it again it would not start at all. This has to be the most bizarre thing I have ever experienced it’s like my bike is bi-polar. Has anybody ever heard of a motor ruining carbs? That seems to be what is happening.

 

[nightcruiser]

Sounds like it could be a flakey magneto? Did you check the solder joints on it, and perhaps pull it off and sand down the bottom so it makes a good ground connection where it mounts to the motor?

 

[dlibs]

yeah I already took the magneto out, checked to make sure all the wires had solid connections, and put it back in and made sure everything was tight. Everybody keeps suggesting that it's the magneto but I am more than sure its doing its job. The magneto looks brand new and every time I test it the spark plug fires the way it should. I don't think its electrical I thinks its a matter of the carb flooding the engine with fuel hence why the exaust leaks fuel everywhere, but how is it possible that this problem could develop with two carbs in such a short period of time? The only answer I could think of to my own question is that there is crud in the fuel tank clogging the carbs. I will check the filter on the gas tank to make sure there is nothing in it, empty the tank, clean it out, and put new fuel in again and see if that makes a difference (again). Ill also take the carb off the motor and clean it out. I'll post again to let you know if any of these things worked.

 

[nightcruiser]

Yah, crud in the fuel tank could screw up two carbs in a row. Also, make note that the angle the carb sits when mounted might have effect, a carb may work perfectly when mounted level on one bike and flood out the motor on the other if the carb is on an angle. The float adjustment would be what you would use to compensate for the angle the carb is mounted. I have found the float adjustment has a huge effect on this sort of situation. Although I have the CNS carb (I think you said you have an NT?), when my float was not adjusted properly my motor flooded like all ****....
Try this, get her running and when she is about to start to run crappy and die turn off the fuel valve before it dies, if the motor comes back to life then you probably need to do a float adjustment (or clean out crud that got under the needle valve).
Again, a carb could work perfectly well mounted on one bike and not so well mounted on another bike, depending on the angle it is sitting, doesn't mean the carb is "bad", just needs adjustment to match its running condition.

 

[vachon644]

When problems occur after a certain period of time, in most cases they're related to something overheating. I can be the CDI box or even the engine itself. If you have fuel problems it could create a lean mixture which would in turn overheat the engine, it can take seconds or minutes depending on how badly lean is the mixture. Try to check wheter the problem occur with the gas tank cap unscrewed, check for leaks (most of the time around the carb/intake manifold), start the engine and spray WD40/Quickstart ether/etc around the possible leaks to see if the idle changes.

 

[dlibs]

All fixed!
I cleaned out the gas tank and checked the filter, and both were clean. I took off the carb and ran hot water through it, and while I was doing that this nasty goopy funk came out onto my hand. I was not really sure what it was at first seeing as the gas tank and gas tank filter were clean, but then it hit me. The goop was actually deteriorated rubber from the fuel line. The gas must have eaten away at the rubber tubing while it sat in the tubes when the bike was not used. My suspicions were confirmed when I disconnected the fuel line from the fuel shut off switch and the fuel line actually tore apart. I guess the rubber tube that came with the kit was not a very high quality one (not that anything in the kits are ever of high quality). I was going to order another rubber tube, but I decided that I would not like to go through this mess again at some point in the future. What I did instead was take a pen, cut off both ends of the pen, and use the pen tube as a fuel pipe connecting the fuel line valve and the inline fuel filter. I than used another pen tube to connect the filter to the carb. Not only is the bike now running great, but I actually noticed a slight performance increase (seeing ass the fuel flows right into the carb through the plastic tubes instead of flowing through a maze of rubber tubing). So, for anybody who ever has this problem, REPLACE THE FUEL LINE THAT COMES WITH THE MOTOR BIKE KITS. Thank you everybody for helping me troubleshoot this problem, the help was appreciated.
-Dlibs

 

[2door]

Keep a close eye on your "fix". Most pens are made of a plastic that will be attacked by gasoline. You'll be back to square one in a hurry.

Just go to a local auto parts store/ hardware store and buy a foot of 3/16" I.D fuel line. You might get by with 1/4" I.D tubing but it will be a loose fit and require clamping to keep it from leaking at the tank and carburetor. Most auto parts/hardware stores will have a lawn mower section or go to a lawnmower or motorcycle shop.
I promise you, your ball point pen idea is going to come back to bite you.
Tom