Vito's Fat Bastard pipes

[Larry's Shee]

Warning !!
Boreing technical post !!​

Because I survived the 70s & 80s I had to do a little research to confirm my memory.

Think of two circles, one small (piston) one large (cylinder). Mathmatically the small only touches the large at one point. Lengthen them into cylinder shapes and the point becomes a line. So the piston is only touching at one point. But wait!! Hopefully you have a film of oil between the two, therefore the piston has no direct contact for the heat to flow from the piston to the cylinder wall. Not to mention the fact that oil absorbs heat easily but doesn't release it easily.

Exhaust temps range 1200-1300*F just past the ex port, with combustion temps of @1500*F.
But aluminum melts at 1220*f (siliconized al is a bit higher) The thermal properties of Al allows it to absorb heat quickly, but also disipates it quickly (luckily!! )

Enter the incoming air/fuel charge!!
First it cools the underside of piston (and lubes pin/bearing) Evidence of this is coked oil underside of well used piston.
Then when transfer ports open the A/F mixture enters cyl cooling the crown. Evidence of this is coking of oil on crown of piston.Evidence of proper jetting is by what is known as "piston wash"

With a 2s when you go from rich/safe/correct jetting towrads lean two things happen. Horsepower and temps rise (somewhat together) until you reach optimum. After that point power drops slowly but temps rise at an even faster rate, hence meltdown. This is why the run the best just before they blow up.

More can be read in books by Gorden Jennings and Grahm Bell. Might be something from Blair.

Opposing viewpoints, contradicting info all welcome.

https://www.google.com/search?site=...msedr...0...1c.1.64.hp..1.8.871.0.0DNi959XzGM

http://www.challengers101.com/ExhaustGasTemp.html

https://www.google.com/search?q=2+s...VKYrfsAX0u4HIAw&ved=0CB4QsAQ&biw=1440&bih=766

Jennings: http://www.amrca.com/tech/tuners.pdf

Bell: http://iheartstella.com/resources/manuals/tuning/Graham-Bell-Two-Stroke-Performance-Tuning.pdf

Blair: http://www.dragonfly75.com/motorbike/2StrokeDesign.pdf

 

[brian degand]

Quad is running way to rich with a 290 in it. So I'm thinking 245 or 250. ?

 

[Blaaster]

Plug chop!

 

[brian degand]

I did. Its wet black

 

[Blaaster]

Do you have a pic?

Should look a lot like this.

 

[Larry's Shee]

Safest way is to drop one size at a time. This is presuming float level is correct and main jet washer and slosh baffle is in place.

 

[jus_me]

I did. Its wet black

With a proper plug chop or just running for a while and pulling plug? Not trying to be rude but there is a huge difference.

 

[Blaaster]

Before you make the plug chop run it is important that the float level is correct, the idle is set correctly and there are no air leaks in the system, otherwise the smoke ring may lie about the AFR.


WHEN ALL OF THE ABOVE ARE CORRECT PROCEED WITH THE FOLLOWING.


Warm up motor to operating temp.

Fit new B8ES plug, ride WOT through the gears and hold WOT in 5th or 6th gear for 10 seconds, or as long as you can safely.

Switch off the motor and pull in the clutch, apply brakes to come to a stop quickly.

Take the plug out and replace the old one for the ride home.

Carefully cut the threaded end off the plug to expose the insulator.

There should be a smoke ring of a cardboard or biscuit colour around the insulator.

If it is non existant or a very light colour, you are lean and require a larger main jet.

If it is a lot darker you are rich and may go down a size in main.

I prefer to run a little on the darker side, I may loose a little power but it is worth it for the peace of mind that I won't need a rebuild so soon.

You have to get up a reasonable speed so that you can get the motor to pull strongly.

Then hold it Wide Open Throttle (WOT) for 10 secs or as long as you can.

The idea is not to get speed but to make it pull strong at full throttle to get onto the main jet circuit.

I find I can safely do it on a short run by applying the brakes some.

If you have not enough room you can use 4th or 5th gear with good results.