Witchcraft, voodoo, global warming? Odd ATC issue.

[nachop]

I had something really weird happen while taking my 85 250R out for a spin the other day. I bought this trike back in 85 and have owned it ever since. It is stock with exception of the Uni air filter. I am running Maxima Formula K2 at around 32:1 or 40:1, spark plug is an NGK BR8EV gapped according to spec(stock is BR9ES). I don't remember the main jet size, but I am running leaner main jet than stock 142 size (altitude is about 4500 ft). I am running the stock pilot jet with the needle on the 1st groove, and Boyeesen reeds (spelling?) It runs great. Like I said, I took it for a spin to run some gas through it. On a stretch of dirt road, I briefly ran it wide open. When I let off the throttle, it remained revving almost wide open. I thought the carb slide was stuck open but it wasn't. I hit the kill switch and it stayed running! I reached above the head and pulled the plug wire and it STAYED RUNNING! I thought it was going to blow up. I finally stalled it with the clutch. I let it set a while, started it, and all was fine. I rode it home at a pretty calm speed and I checked the plug, it looked fine, except for being a little wet. Now it does have a recent top end with very few hours on it. I run 90 octane, because it is all we have where I live. The manual recommends 91. Has anyone ever heard of something like this? What could have caused it. It could not have a hot spot due to carbon build up on the head or piston. I doubt it was a fuel/octane issue since it was fresh fuel. The only thing I can come up with is the spark plug. Maybe it got too hot and was igniting fuel despite the kill switch being off AND the spark plug cable being disconnected? I am at a loss. Thanks for any ideas.

[yaegerb]

You are too lean. Boyesen reeds like a richer adjustment. Can you post pics of plug? Do you have the ability to pop the head off quick and snap a pic of the piston?

Can you send your pilot, main, and which position is needle (one from top or bottom)?

Next time (if there is one), turn the switch to off and hold the throttle wide open. Sounds counter intuitive but it works. Essentially you are forcing maximum air in the cylinder which cools it down quicker and shuts down the "dieseling" effect.

[sweetip2000]

If you eliminated all electrical manually and it kept running could mean its still making an electrical connection contact somewhere. I would check that kill switch. It might be faulty. Your lucky you were able to think in a panic. Most riders
would freak out and get hurt. That's a very fast bike. Glad your ok

[Rob Canadian]

Interesting to find the hotspot on why it kept running and revved up. Due to a recent Top end. Maybe the headgasket(?) Piece sticking into the cylinder like a match... Guessing.

[nachop]

You are too lean. Can you send your pilot, main, and which position is needle (one from top or bottom)?

Next time (if there is one), turn the switch to off and hold the throttle wide open. Sounds counter intuitive but it works. Essentially you are forcing maximum air in the cylinder which cools it down quicker and shuts down the "dieseling" effect.

Thanks for the replies guys and thanks for the concern sweetip. The pilot is stock, which I believe is a 42. The clip is on the 1st groove from the top. I do not remember the main jet size, but it is leaned out because of elevation-4500ft. Interesting advice on the kill switch and throttle idea. Since the trike runs great, the plug was the correct color, and it smoked a little, I just made the assumption that it could not be running lean. I was under the impression, perhaps mistakenly, that if a 2-stoke did NOT smoke, then your jetting was lean.

[yaegerb]

Can a post a pic of the plug for s and g's?

[fieldy]

Would appling the choke in that same emergency situation cause the motor to die? Turning killswitch off then turning on full choke , is what i would have tried, as i believed that was what to do. It would be adding more fuel though.
I know choking is what to do if you have an over reving condition due to an air leak. Hmmm.
@ Nachop, glad you are ok. That had to be a scary.

[AK47KID]

Diesel maybe? Lol jk

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[fabiodriven]

No "lol jk", it was dieseling. Not a piece of head gasket or an electrical problem, you were low on fuel or high on air. That's what causes that. You've owned this bike since 85 and that's never happened before? They do it when they're running out of fuel. Once you switch to reserve it will calm right down. If you're absolutely positive there was enough fuel in the tank look for another reason you were either not getting fuel or sucking air. Clogged petcock, stuck float, loose or cracked carb boot, bad crank seal. Honestly I'm surprised at some of the suggestions here as this is two stroke 101. Everyone knows the death rev equals a lean condition. Now it's up to you to find it.


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[Hurley250R]

I bet you were low on fuel. I had that happen once after some hard riding, mine had 225lb of compression and all of a sudden it started revving very high. I switched it off, kept running, pulled the plug wire off, kept running. Finally dropped it in gear and killed it. Turns out fuel level was very low and it was dieseling. Rode it home on reserve.

[fieldy]

Handful of rocks in the fuel tank?

[RubberSalt]

This is 100% diesel. The best way to kill it is to go WOT while trying to kill it with the switch. If that doesn't do it, shut the fuel off.

Do a Leak down test. I've got a strong suspension that you have developed a bad air leak (flywheel side crank seal?). 31 years old, and i assume this is the first you've seen this on this machine. Fuel doesn't typically change it's flow amount, unless clogged (filter). Air is more prone due to seal or gasket failure. These parts have vacuum, pressure, and age against them.

I experienced my first time dieseling when I was 20. It scared the crap out of me. Hit the kill switch, it kept going. Yanked the wire going to the coil off. Kept going. Shut the fuel off and ran away until it died! LOL I learned about leak downs and found several leaks on that engine. The engine was OK as far as internals go.

Typically, i'd say tear it down and inspect it, but I'm picky about the good machines. Now days, we have this for cheap (http://www.ebay.com/itm/3-5-5M-7mm-Android-Endoscope-Waterproof-Snake-Borescope-USB-Inspection-Camera-/262468118329?var=&hash=item3d1c51a739:m:mHZXuQlHTXd5cAHOY-sqOng). I own one. It's awesome. Video quality is alright. Plugs into your phone or your computer. The camera has leds on the end and you can control brightness. Has a few attachments to look around corners or side ways. Comes in a dizzying amount of lengths. Now you can look inside your pipes if get a long 1!

[keister]

They do it when they're running out of fuel. Once you switch to reserve it will calm right down. If you're absolutely positive there was enough fuel in the tank look for another reason you were either not getting fuel or sucking air. Clogged petcock, stuck float, loose or cracked carb boot, bad crank seal.

Winner!!!!

[nachop]

Once again guys, thanks for all of the information. I was actually quite calm. I had a carb slide stick wide open on me shortly after I first bought it. Yes, the first time it scared the crap out of me. This time I was just afraid for the engine. It was not a fuel delivery problem from the tank to the fuel line. It had a full, fresh tank of gas. Inside of tank and fuel valve are perfect. If it had a vacuum leak, would it not run erratic all of the time or can it show up only at certain times such as running it wide open? I will definitely be checking everything for leaks. I can only work on it on the weekends, but I will share what I find. Once again thanks to all.

[RubberSalt]

A leak down will tell you best..

If their are no leaks, then lean on fuel.

Had some machines that leaked only when hot. It was between the head and the jug. Put bigger studs in them, it warped the jug as they went in. After surfacing the top on some sand paper, it was fine.

[cr480r]

Since the trike runs great, the plug was the correct color, and it smoked a little, I just made the assumption that it could not be running lean. I was under the impression, perhaps mistakenly, that if a 2-stoke did NOT smoke, then your jetting was lean.

You can smoke like crazy and still burn up top ends when you run wide open.. Most smoke and slobbery silencer spooge is from the pilot circuit calibration. The premix oil builds up in cases and will pass thru and "clear out" during periods of sustained rpm.. Not a good indicator of main jets.. I think you are on the lean side and got a batch of bad fuel.. Just cuz it's fresh doesn't make it good. I get bad fuel at the pump all the time. I bet it's even worse at elevation. And what's up with 32 or 40:1? Which is it? Lol

[nachop]

I still haven't checked my trike, but if anything, I did learn something. I would NEVER have imagined that a lean condition could cause an engine to rev so high and to continue running with the kill switch off and the spark plug cable removed.

[AK47KID]

I still haven't checked my trike, but if anything, I did learn something. I would NEVER have imagined that a lean condition could cause an engine to rev so high and to continue running with the kill switch off and the spark plug cable removed.
Question.... did you get shocked when pulling the cap off? You might have a faulty kill switch and when you pulled the cap off (and let go) it was still giving spark through the rubber cap even tho it wasn't connected.

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[SteveCZ28]

sounds like it was dieseling due to an air leak.
like mentioned before, do a leak down test. and have a spray bottle of soapy water, and start spraying seal and gasket surfaces looking for an air leak which will show up with bubbles. you can make a leak down tester for about $12. depending on your materials.

I had a banshee stick w.o.t hit the kill switch, still ran its ass off. pulled choke to stall it out, made it worse. I didn't think to stall it out via dumping clutch and brake as it was screaming, and smoking horrible. I got off of it and then I literally watched my banshee blow up before my eyes. that was hard to watch. grenaded the left cylinder. upon tear down, I found a crank seal had a knick in it, which caused it to suck air, which then leaned out the fuel mixture in the left side (left side crank seal). my 2nd motor I learned about leak down test. youre looking for next to little, or no air pressure lost in a certain amount of time. most use 20-30 mins as an acceptable amount of time. I did mine over nite to be 110% sure I had no leaks. lol