kx500 specifics and 2-stroke theory

[riversbikes]

Hi all, am working on a KX500-powered roadracer. I have one specific question, and 2 theoretical ones. First the specific.
Has anyone ever experienced a big-bore 2-stroke revving uncontrollably with no throttle application? My KX did that 3 times yesterday. Methinks it is some sort of air leak past the throttle slide, that is artificially leaning out the mixture and tricking the engine into revving up. I actually had to pull off the HT lead to kill the engine, as it continued to run despite the kill switch being applied. That's compression for you! The local mechanic said he'd had that happen when the bike was starved for fuel on his YZ. Lo and behold, the tank was empty when I checked it, but there was still fuel in the floats... peculiar, but potentially deadly! Any help?

As for the theoretical:

1. Is there a minimum hole size for the core of a two-stroke silencer? A. Graham states 4mm in his book, but 4-stroke exhasts have more holes, albeit a bit smaller. Does it have to do with power pulses, or...?

2. What is the deal with boost bottles. They were all the rage for awhile, and i have one on my 1985 KX, but I don't see too many on any new bikes.

A lot of questions... is Eric Gorr lurking around out in cyberspace?

 

[MONKEYMOUSE]

I would really like to know more about the whole boost bottle thing to. As I have one on my bike and am not sure what it really does.

 

[PedroMx]

the revving comes from two sources
air leaking or low fuel level in the tank, run a leak test or check for cracks in the intake boot or manifold (rubber between carb and cylinder), for a leak in the crankshaft oil seal (magneto side) or for a leak in the gaskets (intake, cylinder base and crankcase halves - rarely).
Even if the floats appear to be full if there is no fuel in the
tank you will get in a super lean condition that will rev your engine up.
Either way you are risking a cylinder/piston so check

good luck

Pedro:)

 

[riversbikes]

bingo!!

Thanks to Pedro et al, that was exactly the cause. 1/2 full floats, EMPTY tank! Knowledge is power. Less than 24 hours on this ring and a mystery solved. Cool site everyone, thanks!!!

james

 

[cujet]

The silencer perforations can be nearly any size. While there is some affect on noise with various size holes. The major silencing comes from the packing. As a matter of fact, the outside diameter of the sliencer, in other words the thickness of the packing is the issue. If you are looking to keep the noise down, use a large oval silencer.

Boost bottles can help in lower RPM ranges. The difference is small, but can be measured.

Chris

 

[KAY DEE EXER]

http://power-mods.bizhosting.com/boost_bottle.html