Porting my trimmer

[Fly By Night]

It was lean before, I don't think the thing has 20 minutes of run time since I did the mm. I experimented with diffrent jets without much luck. This unit has a wyj series carb, a wyk is identical but has an adjustable highspeed! I should probably bite the bullet and order one.

Thanks Delimber, I'll try to split the case tonigbt and snap some pics.

You are right on doing it just for fun, not to mention stuff with more power is just more enjoyable, it doesn't matter if it's your truck, saw, snowmobile or string trimmer!

 

[Chris-PA]

If the muffler mod is not so extreme as to be pulling extra oxygen back into the cylinder through reversion, then it will actually enrich the mixture, not lean it. Increasing the air velocity through a carb without air corrector jets gives a richer mixture, which is why saws "4-stroke" when you lift. These barrel valve carbs are not corrected either - the needle varies with throttle position, not air velocity like in a CV carb.

 

[1Alpha1]

Keep it simple, it's only a trimmer

That's what I used to think about chainsaws.......until I became a member of this forum, and learned that many think otherwise.

 

[stihlaficionado]

That's what I used to think about chainsaws.......until I became a member of this forum, and learned that many think otherwise.

Before long they'll be a modded trimmer forum

 

[1Alpha1]

Before long they'll be a modded trimmer forum

With chainsaws, because of their inherent danger, I'm very careful and take my time when cutting. I'm never in any hurry to cut.

But, when it comes to weeds, I'd wouldn't mind at all if I could get it done faster.

 

[Fly By Night]

Before long they'll be a modded trimmer forum

I think it's time to start a new section on this forum. "High performance grass eaters" most everyone on here would probably end up doing theirs out due to being addicted to aluminum shavings

 

[cali6construction9]

He's right I've used the hell outa the stihl fs 80 and I love it theirs no comparison to the cheaper brands/models.. so you're pry like me and just want to hotrod what you got see what you can make it do.. Hell Yeaa motor aside you'd be amazed what just going from a single string head to a dual string head it seems to carry more momentum and never ever buy that round string stick with the hexagon or really anything with an edge.. that round crap doesn't actually cut the grass it just tries to power through it hints you'll get a cleaner cut with edged string to

stihl 026 husky 300xp mac 610 efco 132s craftsman 170 mac 1635

 

[Fly By Night]

Oregon gator line square .095" is the way to go. It's clear/grey If you've never used it and see some, grab it, you'll be glad you did.

 

[Fly By Night]

This is my tnc-260pfl next to a shindy home pro 22t

 

[Fly By Night]

Here is the case and jug, it looks like they made it crank case volume as tight as possible. The ducts feed from the bottom of the case. I don't see any reason for it, unless it's to help suck fuel/oil out of the bottom?

 

[cali6construction9]

Yeah pry for better circulation

stihl 026 husky 300xp mac 610 efco 132s craftsman 170 mac 1635

 

[Chris-PA]

As I said up thread, I suspect it is an exhaust delayed scavenging design. Exhaust pressure pushed down into the upper transfers, but not down into the long case runner feeding it. The arrival of the fuel/air mix is delayed so that less fresh fuel is lost out the open exhaust port.

This is similar in concept to strato engines, but there the upper transfers are filled with fresh air that will be used in the next combustion rather than old exhaust. But it's simple and cheap.

 

[Fly By Night]

I'm tempted to whack a chunk out of the case to the lower transfers, my concern is that the piston has the area pretty well covered on the lower part of the stroke.

 

[Chris-PA]

I'm curious what the port timing is. I'll bet the blowdown angle is small.

 

[Fly By Night]

If I had a degree wheel I'd love to check, I may have to break down and buy one.

 

[Fly By Night]

As I said up thread, I suspect it is an exhaust delayed scavenging design. Exhaust pressure pushed down into the upper transfers, but not down into the long case runner feeding it. The arrival of the fuel/air mix is delayed so that less fresh fuel is lost out the open exhaust port.

This is similar in concept to strato engines, but there the upper transfers are filled with fresh air that will be used in the next combustion rather than old exhaust. But it's simple and cheap.

At which point is the exhaust drawn into the transfers? I cant think of a way it would get sucked in there.

 

[Chris-PA]

At which point is the exhaust drawn into the transfers? I cant think of a way it would get sucked in there.

When the exhaust opens the combustion pressure starts to drop, but it doesn't go to zero instantly.

The transfers open a little bit after the exhaust port, with whatever pressure has been built in the case as the piston comes down. The direction of the flow will depend on the balance of pressures.

In this design the fresh charge will be forced out of the small channel with good pressure/velocity, but that opens to the large volume of the upper transfers. My thought was that if the residual exhaust pressure is greater for a moment after the transfers open, then that upper area will fill with exhaust gas before being purged by the fresh charge coming out of that narrow runner. A lot would depend on muffler back pressure and port timing.

 

[jughead500]

So thats what the pure fire engines consist of.interesting.i thought they stuck "pure fire" on them because of the cat mufflers.

 

[jughead500]

Just as soon as i find a tbc260 pfl im going to be doing a base gasket delete on the 340.

 

[Chris-PA]

So thats what the pure fire engines consist of.interesting.i thought they stuck "pure fire" on them because of the cat mufflers.

Perhaps it is! I could see the saws labeled "pure fire" had removable transfer covers and quad transfers but I wonder if they have that lower transfer channel? It's sort of interesting but I like the strato concept much better - it offers performance improvement too while this does not.