rookie question

[honest ron]

ok,....all your informative posts embarrass me whilst i write this,..... cause im a rookie with no experiance but a thousand creative ideas roll thru my head every day !

anyhow,...... i was wondering why my engine has a higher top level of speed when its cold out ! its only a 125 engine 2 stroke.
i can get so much more out of it when its freezing out !

also,.... in garages, is there any point in buying the higher octane fuel if you have a low performance engine ,....?
i heard that its only for high compression engines ! true or false ?

[DAVID PATERSON]

Engines burn a mixture of fuel and air, cold air is considerably more sdense than warm air and thus, when it's cold you feeding more into the engine enablingit to make more power. At a drag race meeting you will see the cars will run faster times late at night than they do in the afternoon for this very reason.

Increasing the compression of an engine will increase the likelihood of pre-ignition (pinging). Higher octane fuels are more resistant to pinging and are thus required for high compression engines. I do not believe that using high octane fuel will have any significant benefit for low compression engines.

[enzo]

High octane fuel reduces the chance of pinging ( actually, the pinging is caused by too-rapid advancement of the flame front, and is generally called "detonation") by actually burning slower. Using it in a low compression engine can actually reduce power output as the fuel may burn TOO slow. so only use the octane level that you need to eliminate detonation.

[RWC]

Hi Ron! Don't be shy about asking anything here!Tech guys love to help others,i've found.Because it's important to get the fundementals right,they're keen to answer the simplest questions.With regards to the denser air -i can easily notice the extra power on both my bike & car.Actually because the air/fuel ratio changes in cold air,you will loose a bit of power from that but it's more than made up for by the heavier charge.
Keep the ideas flowing!

[honest ron]

yeah folks,....... thanks a million !!!!!!
it all makes sense,...... as before the winter i was on full throttle and the engine was losing power when i was near the top speed,..... and i felt it was an air/fuel mixture problem as i was trying to burn a combination that wasnt right,..... since the cold air arrived not only have i been able to reach my "top speed", but it seems to have an endless climbing ability in acheiving speed.......just keeps getting faster once i had the road length available !

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ok 1 more question then,..... my engine is supposed to take a B9es sparkplug,..... but after 2 days , that is fouled with excess oil,..... i then discovered that a B8es sparkplug would run perfectly ,.....but it was strongly discouraged by the mechanics to use it.....being the wrong size ! he says use it on short journeys only !
why would that situation have happened, in that my engine functions on the wrong size plug ?

[neilap]

I can only assume that the b8es is a hotter plug. Even though the numbers do not suggest it. Hotter plugs are just that, they dont cool off as much between cumbustion cycles. The hotter plugs will tend to burn off oil in your combustion chamber that come in contact with the plugs more easily. The drawback of that is pre-ignition. With the heat generated in the cylinders a hot plug might cause cumbustion to occur before spark is actually delivered to the plug. This can result in premature engine wear and even blown motors. I am not sure but maybe in this case higher octane gas might help. However if your vehicle is burning oil that much the best solution is to do the repairs.

[apguy]

>I can only assume that the b8es is a hotter plug. Even
>though the numbers do not suggest it. Hotter plugs are >just that, they dont cool off as much between cumbustion
>cycles.

Close but not quite. The numbers run 1->10 where 1 is a cold plug and 10 is a hot plug. The reference to hot and cold doesn't refer to its operating temperature - but rather to its ability to disperse heat.
Hence a 9 will disperse heat and therefore run cooler than an 8. In a race engine you might run a "hotter" plug (eg NGK BP9EV) to dissipate the heat better. Std road engines tend to run 7's.
As an 9 will run cool thats why the oil doesn't get burnt off and you get fouling. The only reason not to run an 8 is if it has a different "nose" length. Assuming there is no physical size difference between your BP9ES and BP8ES then you are quite safe to run a 8 plug. I'd seriously question why your mechanic is suggesting otherwise

[RWC]

Whichever way you say it:run hotter or burn off quicker,the result is the same.
I.E. the b8es will run a hotter tip than the b9es thereby burning off the oily deposits quicker.So the 8 may be just perfect for you....what happens if you go too hot-8,7,6 etc?
You'll melt a hole in the piston!OK,now that i've frightened you,how does one REALLY tell if the plug is right?Run the b8es for a few hours or more,then take it to a mechanic-he'll look at it & straight away tell you if it's ok or not(it just takes a quick look)He'll ask you how hard you've been reving it ,etc so he can make sure it has heaps of safety margin in reserve.
Hey what kind of bike is it?
By the way,you'll notice some plugs,like bosch have numbers like 21,24 27 etc.divide these by three to get the equivilant in other types.Cheers