Engine Trouble Another 'it died won't start' query!

Urban Fatbiker

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Engine: 48cc w/ bofeng carb, expansion pipe, bbr s1 ignition module & coil.
Drive: shift kut jackshaft low gearing.

Failure: while rounding up our turkeys, I ran it crossways over a plowed field, several ruts, and it died, now will not re-start.

Tests and checks:

Fire- measured over 12V from magneto, a significant pulse from plug wire to ground.
Have not done visual check with plug NGK BP6HS.

Magneto- checked mount. 1 screw loose. May have been a factor, maybe not. Removed mag, key is OK not sheared. Ground is good, continuity 327 ohms.

Fuel- checked carb float bowl (full) disassembled checked level ok, jet clear no debris.

Compression at spark plug feels normal.

Intake suction? I can't feel any, and it seems its pushing air OUT???

I'm lost unless ya tell me a cracked piston or crankcase might do that.

I'll let this stew a bit b4 I take it off. I do have another ready.
Hope my post a bit better than the 'won't start what's wrong' query, I've lived the other side of that question too long to forget to plug it in.
😳
 

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Chainlube

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Fuel- checked carb float bowl (full) disassembled checked level ok, jet clear no debris.

Did you check the float needle? Try it again now, maybe it settled down.
 

FrizzleFried

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I assume a rock didn't kick up and hit that header anywhere denting it? Before I looked at your photo I was thinking it sounded like a clogged exhaust (thinking you may have hit the ground with your stock exhaust)... seeing the photo, that's obviously not the issue (dirt clogging the exhaust that is)...
 

Urban Fatbiker

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I considered that but hadn't checked cause I can't see how.

Yet? Symptoms sure make sense, if crankcase had no suction...but it has pressure?

Gives me two checks anyways, I'll look over the pipe.

I still need to see a spark, guess a plug could fail maybe? Never seen it, yeah they foul and wear out but hard failure?
I did do a CDI swap while testing but not a plug.
 

Nickt919

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Before I did anything else I would try a brand new plug. They can fail at times you wouldn’t think.

An easy..easier… way to check the plug fire….
Lock the clutch disengaged.
Use 14mm socket on the magnet nut driven by a drill.
Do it slow with no plug in the head.
Don’t just use another plug and leave the one already in the head….Less resistance and stress on the crank threads by having the compression escape. Looking for healthy blue, purple spark.

This is easier than trying to push the bike around while trying to see the plug fire.
 

Urban Fatbiker

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Never got to the plug. I removed my drive chain so my cranks would turn it thru the jackshaft. Removed plug. Carb was already off. Loosened exhaust so I could hear it, cranked it slow, sounded like a pump.

Cranked it fast, spewed fuel everywhere out the plug hole. Flipped it over and cranked, it poured out. Crankcase full of fuel.

That wasn’t my shutoff valve leaking?? fuel line and carb were disconnected. Maybe...while running fast over washboard ruts chasing turkeys, I bounced a crapload of fuel in it and flooded the whole engine??? Or it leaked before, already had some in it? Me dunno.

Drying it out, checking it again with a new plug. Definitely not a crankcase leak it holds liquid a little too good.
 

Urban Fatbiker

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Betting I found it. No spark, and this time no voltage measured. Tried a different CDI, same. Then, unplugging it, the problem exposed itself.

Bet I flooded it after, trying to start it again in sad whiny desperation 🥺

Fixin' to fix it shortly. Soldering new ones on.
 

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Urban Fatbiker

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I must be getting flustered. I made 24 wire connections on my fatbike last week for a 12V lighting system, not one mistake.

I fixed it.
Still won't start.
I gotta check everything again.

Or, go ride my fatbike and say screw it I'll put my other engine on later! It has pretty blinkers now.
 

Wrench

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Betting I found it. No spark, and this time no voltage measured. Tried a different CDI, same. Then, unplugging it, the problem exposed itself.

Bet I flooded it after, trying to start it again in sad whiny desperation 🥺

Fixin' to fix it shortly. Soldering new ones on.
Secure the wires so they don't wiggle during the turkey roundup
 
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