So.. the Spark Arrestor Conspiracy

[VintageBlueSmoke]

So I was laying there in a pool of sweat, feverous due to pneumonia, and started down a path of thinking that disturbed me even in my delirium. You engineers/specialists out there can correct/educate me further in due course.

So I was thinking, in the days before reed valve engines, a lot of fuel went wasted into the expansion chamber and out the exhaust as un-burnt or still burning fuel. In places like California, this was a potential problem with causing forest fires so someone discovered that if you put a metal screen over the end, it would get hot and ignite the un-burnt fuel. Genius in its simplicity really. This small screen kept millions of acres of land on the very brink of closure, open to off-roaders nationwide. But then came the reed valve. This ingenious device in 1974ish eliminated much of the un-burnt fuel flowing into the exhaust. Then in 1980ish came the exhaust valve or "Power" valve. In my mind, these two inventions together should have eliminated the need for the "Spark Arrestor".

So then there was a couple of hours (days, weeks?) I went on about how the spark arrestor is like and afterburner on a jet and wondered if there was any measurable "thrust" and how you would make a machine (dyno) to test it...but that is another story.

So dragging myself back to the original thoughts, I started thinking about why, if I was correct, do we still use this device and my thoughts turned dark. Did I just uncover a government/OEM conspiracy? Every one of us (in the know) knows that government motorcycle exhaust and spark arrestor approval is a racket. There is no (expensive) approval process for auto exhaust, only your states emissions and sound level test, but for motorcycles, there must be the government stamp and for Spark Arrestors, that includes the US Forest Service. To get authorization to use that stamp is an expensive process and your prospective customers HAVE TO PAY IT to ride on public land. Government and OEM's (to include any well funded aftermarket industries) built a business model around it and jumped in bed together. So much money changed hands that it would be silly to stop it just because is was no longer necessary. You know, like wired telephones, NTSC Television, or NASCAR. We, as a people are reluctant to change. (I'm one to talk, I've got 13 vintage motorcycles!)

So here I am, flush and weak, my bed smelling like a gym and me worse, banging on my laptop a small sample of what goes on in my head when most other people floating through time and space, seeing god, or visiting dead relatives. 

[Coop]

One problem with your line of thinking is you are stuck on two strokes. You have to consider 4 stroke engines into your thought process.

[factoryX]

Believe it or not, two strokes do not get hot enough to emit the so called "Spark"(Oil keeps things cool), and if they do spark there is a major problem with your motor.   So technically there is no real reason for two strokes to equip them, imagine that. As for the rotary valve, huh? The main issue here is the back firing 4 strokes. They do get hot enough, and will emit sparks/flame at any time.  It comes down to simple generalization that if you ride something with a motor, it can cause a fire. As for two stroke oil in the lakes/oceans supposedly from both marine engines and OHV's, most oil is now synthetic which is mainly food oil, and crude oil is natural occurring substance from decaying plankton. So either way its organic..

[SachsGS]

Spark arrestors originated with steam locomotives and why they are required on 2S I don't know,as Factory X stated,they are not needed.I've seen many a 4T with a glowing red header pipe.I've been checked many times for a spark arrestor while riding off road.

 As for that Flu,turn on Oprah and get some rest.

[ford832]

A well tuned 2t will blow red glowing sparks like a bastard.You just don't notice it in the daytime.I'm all for this law.It's a good idea.

[factoryX]

If your bike is running that lean, there is a problem. I've never seen two stroke emit sparks, even when my atc250r burnt a hole in the piston. And the glowing red sparks is probably heated fiberglass from the silencer, which is known to blow out when freshly packed, or your bike is running so lean that it igniting the carbon in the cylinder and pipe, which is melting piston territory..

[ford832]

My bike isn't too lean.I've never holed,seized or otherwise grenaded any of my two strokes-ever.Two strokes and four strokes both generate carbon.You can't ignite it in the pipe but a piece off the piston or one that comes back in with the backpressure wave will heat red hot instantly during ignition and can then easily blow out the pipe.I've seen it numerous times on my saw and bike both when it was dark or near dark.In every case I was working them hard but nowhere near the point of engine damage.Spark arrestors are a requirement for a reason and in the case of a turbine type,the effect on power is so negligible as to be almost non-existent.

[SachsGS]

Ford are you sure you are not just seeing fireflys? I've never seen a spark come out of any twostroke.
Come to think of it,I've been in more then a few 24 HR events and the 4T backfires you can see a mile away but I don't recall sparks coming out of 2Ts.

[ford832]

Maybe so  Always at dark or nearly so and always when working them.The last time was this past winter with my chainsaw with the spark arrestor screen removed-I put it back in when it's dry.Anyway,a big maple I was trying to get down before dark.Small for you guys out there but I had to plunge cut it then come in from either side with my 18" bar.The saw was working and was definitely shooting sparks-not like a grinder or something but one,then another and so on.It only takes one in the dry woods and doesn't necessarily have to be red hot to start a fire depending on what it lands on and wind conditions.I wouldn't want to take a chance on being responsible for burning down a good riding area or worse. 

[factoryX]

Now, chainsaws do spark, I've seen that. They run wot 100% of the time, so they are naturally lean and get very hot. The majority of chainsaws are two stroke, but are used completely different as to two stroke dirt bikes. The reason the oil mixture is extremely thick is so it can run at higher temps and not seize or melt the piston.

[ford832]

All my modern day saws have called for 50:1. I sometimes do that but often use the bike gas jug which is at 40:1.

[SachsGS]

On the subject of chainsaws,I'm busy cutting firewood with my new Dolmar PS6400.It's amazing how far saws have progressed,the throttle response,power and fuel economy of this machine is amazing.The Dolmar barks off the bottom like a 250 2T MXer and then instantly the saw is turning 12,000 rpm.Boy does the thing cut wood.

 I've seen sparks come off my chainsaws but it's off the bar during a heavy cut.

[ford832]

I've heard good things about the Dolmars but have never used them.I've also heard good things about the Echos.I guess I've just had such good luck with my trusty Jonsereds I tend to stick with them.
I've got a pile sitting the backyard awaiting my attention if it ever stops freakin' raining.If you show up with your Dolmar,I'll let you have a go at it
As for how far saws have come-this summer I was doing some light cutting so decided to fire up a couple of the oldies just to run a little fuel through them.
All my saws are well tuned and properly set.That said,the modern day somewhat modified 2156 worked very well as per usual running on a 40:1 mix of motul 800.
Using the same fuel/oil, the 1983 partner 500 screammed like a banshee as all the 500/5000's did,but it did give off a fair bit more of a 2t odour and a little smoke.Nothing unusual but the 2156 gives off almost none.
Same fuel/oil again,the 1967 R16 Partner worked very well too.It did have a strong odour and gave off a fair bit of smoke-which then reminded me of how I used to have a headache every night after using some of my grandfathers oldies when I was younger.
They certainly have improved.Though the old R16 doesn't look any bigger than the 2156,it's certainly heavier even with no chain break.
I think with their fixed jet hs jets and catalyst lean burn systems they have right now they are bordering on fragility.
My plan is to buy a bunch more from about 5 yrs old and back so I'll have enough to last me out.