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2 stroke POWER-------- before blow up.

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I know this isnt exactly something that is specific to KTMs but I like the responses from this forum much more than I do from any other.

I have a compression tester and I use it often. I have NEVER blown up an engine. A friend just blew up his bike and I finished repairing it for him today. He asked me a question that I didnt have the answer to and was actually ashamed at this fact since I consider myself to be pretty knowledgable about all two strokes. He asked "why do two strokes run so much stronger when they are just about to blow up?". I thought about it for a minute and couldnt figure it out. They run leaner and have less compression when the top end is worn...so it wasnt a question that I could even give an opinion about since it doesnt make sense to me. I have heard this countless times but I have never witnessed it myself.

SO...how and why does this occur?

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you know I would like to hear that answer to,,,,you read on the internet all the dyno testing, and hp numbers, and how extreme rich mixtures make more power than lean ones etc... When I was younger i had a group of buddies I rode with, and one kid had a yamaha mx80, (oil injected little dog of a two stroke) well I had seen this bike run for 2 years, had took my share of little trial runs on it around our homemade track, well one day were all as usual smokin this kid on the track, all of a sudden out of nowhere here he comes, this little bike is screaming!!! I mean it is really runnin, right on the tail of our cr's yz's etc... So we stop were like what the hell is up with that bike, we all take turns riding it, can't believe it this bike has doubled in horsepower, 30 minutes later she froze up.... He had ran the oil injection tank empty..LOL!!!

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lots of oil in the mix seals the rings and piston better so it makes more compression

running real strong just before it seizes is a too lean condition, not enuf total fuel. Same happens just before it runs out of gas, sometimes revs up and wont slow down that last few seconds.

It wont real strong if the top end is worn out

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I would have to say in that situation, the little DS80 just got stronger due to a serious lean condition, as has been stated. For 2t's running pre-mix I have no clue why people would experience a stronger motor just before a blow out, that just does not make sense. The only thing I can think of is that something in the jetting caused a lean condition prior to the sieze.

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What do you mean by 'blow up' ? If you mean a lean seizure, then yah, it makes sense that it would run strong, because lean makes power. if by 'blow up', you meant shatter a piston or something, then i doubt it would really run any stronger before failing.

But I don't know, I don't own a compression tester, have never used one, ride 300 or more hours a year, and have never blown up an engine (knocks on wood).

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I would have to say in that situation, the little DS80 just got stronger due to a serious lean condition, as has been stated. For 2t's running pre-mix I have no clue why people would experience a stronger motor just before a blow out, that just does not make sense. The only thing I can think of is that something in the jetting caused a lean condition prior to the sieze.

When you run without 2T oil your air/fuel ratio is actually richer because it is all fuel now with no oil. Although that may not have been the case here because it is a oil injected system.

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having never blown up a 2T engine, I can't comment on if they "feel stronger" before they sieze? I sorta question the premise though ...

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Years ago I was roadracing an '89 FZR400 and I began to richen up all 4 of the needle jets at the race track as it was all I had to work with. Everytime I lowered that clip the bike got faster and faster. Pretty soon the bike became known for going real fast. In fact it would run dead even w/ F2s w/ me on it which should have never happened. I always just assumed it had a fully built race motor or something.

Then I needed some transpo so I stuck some lights on that bike and put it on the street. It was so rich in the midrange that it was unrideable. It would load up instantly (on the track it was always full throttle). So I dropped the needle several positions and it was ok in the mid but much to my surprise it stuttered real bad up top. It took about 2 sizes up on the main jet to get it to run right.

So I take the bike back to the track w/ "correct" jetting and guess what? It was WAY slower. I mean a lot slower than it had been!

So incredibly rich in the mid and very lean up top made this particular bike absolutely scream. Go figure?

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the extra power is due to a lean condition. meaning more air and less fuel, hence less lubrication, higher rpm, and uuuuurrrrrcchhhh! crap! sh#t. etc.

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