Hello to all.
Well my misfortune continues as my Zongshen 250cc has eaten yet another starter. I've been working on starting this thing since i bought it last year cheap (thank goodness)
Replaced list : starter clutch
cdi
ign. coil including plug wire
spark plug
3 starters.
checked values from stator and cdi with my meter and all were within specs.
checked valve clearance 3 times intake and exhaust are now .008 and .009 .
Carby taken apart and cleaned
Had carby installed on a 110 atv to verify, it ran , albeit only while choked.

The thing is, it's always had this loud banging kickback kinda thing going on when i try to fire it up. It doesn't do it when the plug is out. It's only when I'm trying to fire it. It's backfired out the carb a couple times when i sprayed starter fluid but that's it. It keeps doing this loud metallic "SNAP" while cranking. Then i stop cranking quick.

So tonight, i thought i found a suspect ground wire from the stator. The one that grounds the trigger pulse (green/white). I fixed it.

For the first time , it was almost running. I choked it, I cranked it, It was kinda idling for a few seconds while still cranking until i gave it some throttle , and bang , another SNAP and then a grinding and that was it. Another starter gone.

Can anyone tell me what's happening? I'm so close but so frustrated. The wife wants me to give up and stop spending money on this thing. But i hate quitting .

Bye for now, and thank you for reading.

 

I'd be looking into the gears and such that the starter turns.

You know wives are always right.

 

Hi LT80 , thanks for replying. Yes I agree about looking at the gears. I have been looking at them because I've replaced the starter 3 times . It all looks good but I'm not sure what's going on in there once the covers back on. One question I have is about the gear that starter is first in contact with. That gear has a shaft , or pin , that's removable. That pin has a tiny little "nib" on one end. That nib can be orientated two ways, towards the engine, or towards the cover. I'm not sure which is correct and besides, it broke so now I just put the shaft in place and slide the gear on it. Not sure if this matters.

It still seems to me it's a engine kickback problem. I've heard of something called a decompression spring that some engines have. Supposed to help keep start up compression under control or something like that. Is it possible I have one that's not working properly? Why is it kicking back ? Got to get to work , bye for now.

 

So here is my wild idea:

Suppose an ignition spark occurs way too early on the compression stroke. The fuel air mixture ignites and drives the piston back down - spinning the engine violently backwards. This would be bad news for the starter motor.

The starter motor is geared way down when cranking the engine, and when the engine starts it goes from 600 RPM (cranking speed) to 1800 RPM (idling speed). The starter clutch disengages the engine from the starter (free wheeling) so the starter motor never sees this sudden and violent change in engine speed.

Now consider what happens if a spark occurs too early on the compression stroke and causes the engine to travel backwards back down the compression stroke. The starter is still trying to crank the engine in the right direction, but the engine violently goes backwards. In this situation the starter clutch will not disengage... It will stay locked up... The sudden backwards acceleration will try to spin up the starter motor in the wrong direction - all the while the starter motor itself is being forced by the applied battery voltage to go the right direction. Something has to give. Remember that when the engine is the driving the starter motor it is geared way up - not down.

I remember a similar thread with a 110cc quad with an E22 engine where the starter chain kept snapping. On this engine the starter drive the flywheel / starter clutch via a chain rather than direct gearing. I never saw a final resolution to this problem, though I suggested they change the CDI. But still this sounds very similar to your situation.

I once had a go-cart powered by a chain saw engine. It had fixed ignition timing at 25 degrees BTDC and had a pull rope starter. To start that machine to had to grit your teeth and pull *hard*. If you did it would start. If you didn't, the engine would backfire - driving the engine backwards. Same thing - something had to give. The pull rope mechanism disengages via dog and pawl clutch when the engine starts normally, but if the engine goes backwards it stays engaged. What gave was my arm. It felt like it was broken... When my friends and I went out riding we drew straws to see who was the luckless victim given the task of pulling that starter rope. [I just did some quick math - Wow - that was 41 years ago...].

I've reversed engineered a few CDI designs by removing the epoxy potting and tracing out the schematics. All the ones so far have circuitry in them to prevent the CDI from firing too soon. There is a closely spaced pulse pair from the trigger / pickup coil on the stator that goes to the CDI. The first pulse arms the CDI, then second pulse fires the CDI. These CDIs were copies from the old Honda design, and I'm sure that Honda put that "arming" circuitry in there for a reason. But I've also seen other CDI schematics posted that do not have this "arming" circuitry in them. These CDIs are vulnerable to rogue triggers causing problems as per above. Are people making and selling CDIs that don't have rogue trigger masking? I don't know. It would save a lot of parts if they were.

I really don't know what your problem is, but I'm throwing out this hypothesis. If I was in your situation this is the reasoning I would take...

Your starter motor is bad. I would buy another, install it, and crank the engine over and over with spark disabled. I would listen for any strange noises and troubleshoot those. If none detected I would replace the CDI (again) from a different and reputable source and then try and start up the engine once more.

I haven't been on this forum in a very long time. It may be a long time before I return. I'm working 7 days a week on a new and engulfing project and don't have much free time. I just happened to see your post and it intrigued me. I just wish I had more time...

 

Hello Lynn;
Thank you for taking the time and interest in my problem. Your hypothesis sounds very plausible and though a mechanic I'm not I was thinking the same thing. I've assumed I had the proper cdi but maybe not. And your right about cranking without spark. I've done that with no cranking issues. Only when spark is enabled does this problem exist. ( I should have mentioned that before). I looked at valves, and the T mark on flywheel with TDC, and carburetor issues etc. Could it be , the wrong cdi , all this time.? But a cdi gets its signal to spark from the stator that's within the flywheel which is cranking at the same speed as the engine? Is it possible to position the stator coil improperly within the flywheel thus creating a spark at the wrong time? I haven't messed with my stator/flywheel because my flywheel only goes on one way and the stator coil was just in there. I've never given it any thought. But spark timing does seem to be the issue . So now I need to figure out which cdi I need to buy and/or look into this stator coil possibility.
Thx again . I'll keep you posted with any progress.