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Old 09-20-2012, 02:04 AM   #16
PJay
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Sad to say, I think you on the wrong track.

The symptoms you describe are typical of (a) too much ignition advance and (b) a compression ratio too high for the ignition you're running.

As someone else posted, you have solutions looking for a problem.

Forget the methanol and water, and go back to basics for ignition timing and ignition system type. I'd also look carefully at whether your porting, head, and piston set-up make sense.

(FWIW, I've built TZ 250, 350, 700/750 Yamaha engines to produce - consistently - far more than the power the factory ever got out of them. None of the factories were stupid; it takes a lot of science to do better than they did.)
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Old 09-20-2012, 11:47 AM   #17
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Originally Posted by PJay View Post
Sad to say, I think you on the wrong track.

The symptoms you describe are typical of (a) too much ignition advance and (b) a compression ratio too high for the ignition you're running.

As someone else posted, you have solutions looking for a problem.

Forget the methanol and water, and go back to basics for ignition timing and ignition system type. I'd also look carefully at whether your porting, head, and piston set-up make sense.

(FWIW, I've built TZ 250, 350, 700/750 Yamaha engines to produce - consistently - far more than the power the factory ever got out of them. None of the factories were stupid; it takes a lot of science to do better than they did.)
i

550SENTA screwed with this post 09-25-2012 at 11:38 AM
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Old 09-20-2012, 08:54 PM   #18
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Originally Posted by 550SENTA View Post
i cant have problems with ignition!its electronic ignition,factory made(racing).i shortened the cillinder almost 20 milimeters because i installed a shorter biel that supports better high rpm than the stock one(long biel means morepower-couple but less rpm.when i run at high rpm it sounds like a boat or like as if its on nitromethane.all the changes i did to this engine are verry carefully studyed.when i ride my bike,it doesnt sounds like ,,brap brap brap,, it sounds like zzzzzzzz.for that.the compression is good,ignition also good,bad thing is that i cant find ,,good gassoline,, 4 it,i prepare high octane gassoline by myself adding naphtalene.the inconvenient is that after adding naphtalene to the gas i also ad a teflon oil that makes a lot of smoke(i cant drive with that on roads or in a city ;).
Ignition.

All your changes (and the fuel) mean that a factory ignition curve will be totally irrelevant.
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Old 09-21-2012, 12:59 AM   #19
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I would say that even with a digital ignition with 3D mapping possible, that other changes made to this motor will mean its only ever going to work at very high rpm, and may well need alcohol fuel.
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Old 09-21-2012, 05:38 AM   #20
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I would say that even with a digital ignition with 3D mapping possible, that other changes made to this motor will mean its only ever going to work at very high rpm, and may well need alcohol fuel.
i

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Old 09-21-2012, 09:01 AM   #21
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You will need a castor based 2T if you want to run alcohol fuel. If you dont want to use alcohol fuel, you will have to redesign the motor to allow it to work on pump fuel. 2T motors in very high states of tune, are not really practical if you want to use pump fuel, and reliability also tends to be greatly reduced, so these are things that are really only practical for serious race use, using the proper fuel, and rebuilds very frequently.
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Old 09-21-2012, 11:23 AM   #22
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Talking

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Originally Posted by Twin-shocker View Post
You will need a castor based 2T if you want to run alcohol fuel. If you dont want to use alcohol fuel, you will have to redesign the motor to allow it to work on pump fuel. 2T motors in very high states of tune, are not really practical if you want to use pump fuel, and reliability also tends to be greatly reduced, so these are things that are really only practical for serious race use, using the proper fuel, and rebuilds very frequently.
y

550SENTA screwed with this post 09-25-2012 at 11:39 AM
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Old 09-22-2012, 12:58 AM   #23
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If you have 16:1 compression, your motor will blow apart pretty quickly no matter what fuel you are using, unless its only being used for drag racing, running for a few seconds only each run.
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Old 09-22-2012, 02:02 AM   #24
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If you have 16:1 compression, your motor will blow apart pretty quickly no matter what fuel you are using, unless its only being used for drag racing, running for a few seconds only each run.
d

550SENTA screwed with this post 09-25-2012 at 11:39 AM
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Old 09-22-2012, 02:55 AM   #25
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Petrol does not pressure ignite. Only diesel does.honda experimented with petrol auto ignition, the bike was called the exp and was built for the dakar, the way that system works is that it purposely traps burnt exhaust gasses and mixes it with the new charge.

Detonation is caused by a pressure and heat wave that the end gasses cannot resist, the pressure wave and heat wave is caused by the initial spark event not by pressure ignition.

250 4t motocross bikes run 14:1 (static compression) and they still use a spark plug.Remember in a 2t the compression ratio rises as you reach pipe resonance frequency so 16:1 may become 19:1 or even 20:1.

Even those 4T motocross bikes that run 14:1 are on the limit, a bit higher and detonation occurs and that detonation occurs at about 10:1 dynamic compression ratio.

I know you probably dont want to hear it, because you have invested a lot of money and love in this bike. But i recon you should look at a big bore sleeve or kit or something and reducing compression to make the desired power while running at normal pump fuel.

Also as i understand it, when you increase compression you increase low down torque but top end suffers and viceversa.

What bike is it?
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Old 09-22-2012, 03:32 AM   #26
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Petrol does not pressure ignite. Only diesel does.honda experimented with petrol auto ignition, the bike was called the exp and was built for the dakar, the way that system works is that it purposely traps burnt exhaust gasses and mixes it with the new charge.

Detonation is caused by a pressure and heat wave that the end gasses cannot resist, the pressure wave and heat wave is caused by the initial spark event not by pressure ignition.

250 4t motocross bikes run 14:1 (static compression) and they still use a spark plug.Remember in a 2t the compression ratio rises as you reach pipe resonance frequency so 16:1 may become 19:1 or even 20:1.

Even those 4T motocross bikes that run 14:1 are on the limit, a bit higher and detonation occurs and that detonation occurs at about 10:1 dynamic compression ratio.

I know you probably dont want to hear it, because you have invested a lot of money and love in this bike. But i recon you should look at a big bore sleeve or kit or something and reducing compression to make the desired power while running at normal pump fuel.

Also as i understand it, when you increase compression you increase low down torque but top end suffers and viceversa.

What bike is it?
h

550SENTA screwed with this post 09-25-2012 at 11:40 AM
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Old 09-22-2012, 04:00 AM   #27
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This thread is entertaining
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Old 09-22-2012, 05:28 AM   #28
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hehe.4 stroke running 14 to 1 compression?i think they just want to imitate 2 strokes but they will never act like 2 strokes.what walves do they use ?and at how much rpm?i think they could work at low rpm ,like diesel engines but not at high .detonation occurs because of overheating and pressure.if the engine is hot and has high compression ratio i think that gassoline could burn without a spark plug.i had an electric waterpump mounted on the bike and because of too much heat the plastic on it has melted.the resonator its important at what rpm compresses the gasses into the cillinder.i have a fantic xm 125 liquid cooled.to get rid of this problem with compression i could just mount a bigger head gasket.now i run only 100 cor gassoline with naphtalene added(a tea spoon at 5 litters) and full sinthetic oil mixed with a teflon additive,it makes a lot of smoke(because of the burned teflon aditive) and has power only at verry high rpm(thats because of naphtalene).
The 250's produce max power at about 11 000rpm and rev to 13 000 to 14 000 rpm. The super single 250 class bikes (250 4t single cylinder road racing) rev to 16 000.

The 450 mx bikes rev to 11 000 to 12 000 rpm and can be made to rev to 13 000 and 14 000 rpm

They use hollow stainless valves filled with sodium or titanium valves and titanium valve springs.

Petrol does not pressure ignite, its a fact. It is to do with the properties of the chemicals the fuel is made of. All the liquid chemical fuel that usually burns with an open flame does not pressure ignite. diesel can only be set alight by pressure or an directed flame like a blow torch.

Hp is a function of torque and rpm so to make high hp numbers you have to rev or make a lot of torque. on a 4t to make more torque at low rpm's you ether have to go turbo, supercharger or nitro and that is no feasible on an light weight mx bike so the opt to rev the thing to produce the wanted amount of power.

A 2t an the other end does not need to rev because its expansion chamber acts like a turbo producing a torque boost witch interns producers more hp at lower rpm's.
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Old 09-22-2012, 05:29 AM   #29
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This thread is entertaining
Sure is..................I wonder why the link to a video of a Simson moped though?
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Old 09-22-2012, 05:46 AM   #30
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This thread is entertaining

Yep,.....in a 2 stroke trainwreck kinda way !
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