Can't get motor to start

sami

New Member
Nov 8, 2008
9
0
0
Toronto
Hello,

I recently finished building my 70cc bike. I had it running great for two days and sadly as I was going along, I accidentally hit the kill switch as I was riding and the engine backfired and stopped. I have been trying for days now to get it going again with no luck.

I've followed previous posts closely and heres some of the things I've tried.

I have removed the carb and checked that fuel can flow and there doesn't seem to be any reason why it shouldn't. I've tested the spark plug and it works. The engine is still in the break in period so i'm using 16:1 gas-oil ratio with synthetic 2-stroke marine oil. I cleaned the exhaust and bolted everything back on tight. I've tried half-choke full-choke and all sorts of other combinations.

As I peddle the pistons move inside but the engine doesn't start. If I peddle hard, the gas inside will combust every 5 seconds or so. But after two minutes it totally floods. Gas drips out the end of the muffler. I've for days to get it running.

Any help troubleshooting would be great.
 

Motormac

New Member
Sep 23, 2008
108
1
0
Ontario Canada
Bypass the killswitch altogether and see if it starts. Wire blue to blue and black to black, cap off the white wire. See if it starts now, I think you have a defective or stuck killswitch.Sami I see you are from Toronto, good to know as I have not yet seen another M.B.er on the streets up here for more than a year!
 
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MikeBike

New Member
Oct 7, 2008
145
0
0
Palm Springs CA.
ok sound like my problem,

here is what you do

take off your clutch cover, and tighten your flower-nut.

what that does is tighten your clutch, to stop slipping.

see mine whould move the piston, but not enuff. it needs to be going at a good rate of RPM to start the spark plug timing right.

it took me three weeks and all the help in this forum to figure that out.

http://motorbicycling.com/f4/bicycle-engine-clutch-222.html

this should help
 

sami

New Member
Nov 8, 2008
9
0
0
Toronto
Hi Motormac, I tried eliminating the kill switch. No dice.
I'll give the clutch a go in the morning. And thanks for the suggestion on the oil.
 

Norman

LORD VADER Moderator
Jan 16, 2008
2,605
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pampa texas
Have you tried a new sparkplug? along with that check the plug wire make sure its screwed on to the cdi and screwed on to the sparkplug boot.
try a plug gap of 0.020 thousands. Some sparkplugs will fire when layed on the head and not under cylinder pressure but will not fire when under pressure from the compression of the cylinder.
Norman
 
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sami

New Member
Nov 8, 2008
9
0
0
Toronto
Hey Guys,

Here's an update. So I took my bike to a friends place who knows two-strokes pretty well and he seems to think the clutch is fine (remember the engine only has 2 days riding time). And I'm running out of ideas so I'm starting to think it's the CDI. Reason? Everything else works.

-There is compression
-There is gas flow
-There is a spark
-The clutch works well
-I've opened the carb 3 times and there's nothing wrong there
-I've tried for hours on many different occasions with all sorts of combinations of the choke (on/off/half/quarter/√3), no dice
-I have NOT looked into the engine chamber but its not likely I can find an issue there on a new bike

Now I can't determine how well it is compressing, flowing, sparking, etc but its happening at some level. Which means it should start up even if it only wants to give me a put-put-put.

Two-strokes are generally not this demanding. If anyone else has some other tips or fixes or thoughts on a new CDI that would be great.

Have you tried a new sparkplug? along with that check the plug wire make sure its screwed on to the cdi and screwed on to the sparkplug boot.
try a plug gap of 0.020 thousands. Some sparkplugs will fire when layed on the head and not under cylinder pressure but will not fire when under pressure from the compression of the cylinder.
Norman
I have replaced the spark plug and the plug wire is screwed well on to the CDI. However, I'm not sure how to adjust the plug gap. And, I do have a strong feeling that the plug is not firing properly in the cylinder, I just can't determine whether it is or not. How can I adjust the plug gap?

Cheers!
 
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MikeBike

New Member
Oct 7, 2008
145
0
0
Palm Springs CA.
spark plug gaping:

take it out, and take it to a local auto store, and they guy wouldnt mind showing and selling a gapper.

its easy, just dont go over bord, because to wide of a gap will give a weak spark.
 

Norman

LORD VADER Moderator
Jan 16, 2008
2,605
3
38
68
pampa texas
one more thing you can try take off the cover to the mag. take off the mag rotor and see if the woodruff key(looks like a half moon) is sheared if it backfired it might have sheared the key and with it sheared it will still fire but not at the right time.
The key is small and onery when you try to reinstall it use a drop of super glue to hold it in it place on the crank and then install the rotor.
if its sheared you can go to an auto parts store and buy a woodruff key that will be the right size or very close to the size yo need by using a file or dremel tool you can make a key or order one from one of the engine kit sellers.

to hold the rotor from turning remove the clutch side cover and use a rag jamed into the gears to hold the crankshaft from turning while removeing and installing the nut on the rotor.
 

sami

New Member
Nov 8, 2008
9
0
0
Toronto
I found the Woodruff key, I just dropped down as I took out the rotor. It does look like a half moon but how do I determine if it is sheared (or if anything is wrong for that matter).
 
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Bikeguy Joe

Godfather of Motorized Bicycles
Jan 8, 2008
11,843
237
63
up north now
Can you put it back in place, and slide the mag rotor over it O.K.? Does it look trashed? If you answered Yes, then no, that part is in good shape.
 

sami

New Member
Nov 8, 2008
9
0
0
Toronto
It looks okay. Since it ain't the magneto, I'm going to try the plug spacing tomorrow.

2 questions:
-Does anyone think it could be the CDI?
-What are the causes of the plugs not firing at the right time?
 

sami

New Member
Nov 8, 2008
9
0
0
Toronto
UPDATE:

In my madness to isolate every possibility, I uncovered something interesting. My fuel filter is completely damaged. I looked in my fuel tank and there are some impurities. So I rigged up an experiment.

I got a water bottle, filled with gas and put my fuel line directly into it. I took her for a ride and she rode for one minute. (the most I've gotten since this issue began). I'm picking up a new filter tomorrow and maybe that will help. I'll let you all know how it goes.
 

sami

New Member
Nov 8, 2008
9
0
0
Toronto
Cleaned the carb, tank. Put in fresh gas with the filter and no start. It gives a few but put-puts but thats it. I gave her for about 20 mins up and down my street but she didnt go. Maybe crap got in the cylinder and now its junk. Giving up for today.
 
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Technocyclist

Motorized Bicycle Senior Technologist
Jul 7, 2008
463
0
0
Asia
Try checking the wires and electrical connections if correct. Pay attention to the color of the wires
 

Motormac

New Member
Sep 23, 2008
108
1
0
Ontario Canada
Sami, crap may have gotten into your carburator but not the cylinder,did you get rid of the little screen filter in the petcock valve on the tank and replaced your inline filter? Do as Techno cyclist says and double check your wiring, make sure your white wire is not touching any part of the frame,it should be capped off completly. We here want to help you and if you follow our advice you will get it running.Dont give up,think of this as a great learning experience.
If you have changed your filter and gotten rid of the screen filter let us know and we will help you go from there. Mac
 
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