NE 346XP - Affects of Cat Muffler & Muffler Mod - Porting & Popup To Come

[blsnelling]

Jimmy,

Start a new thread and put up some pics if ya can.

I'm gonna run to TSC tomorrow and will eyeball the snot outta thier saws to see what it is in there.

Stay safe!
Dingeryote

Thanks guys

 

[blsnelling]

Not necessarily a "jetting" issue unless the plug indicates lean burn.

What else in the fuel supply equation could impead flow?

If it is indeed an issue, then it's running out of fuel in extended cuts. I'm seriously suspecting the tank vent at this point. I think I'll remove it all together and see if that does it. If so, I'll have to come up with a proper solution.

 

[Article10]

Easy to go that route of increasing tank venting, then see if a change occurs in the correct direction. I know from working on GA aircraft in the past, when higher HP stc'd engines are installed, larger fuel lines and some times fuel tank venting fittings and lines are required.

if that accomplishes no change then it is worth looking at fuel supply system in detail.

 

[blsnelling]

Easy to go that route of increasing tank venting, then see if a change occurs in the correct direction. I know from working on GA aircraft in the past, when higher HP stc'd engines are installed, larger fuel lines and some times fuel tank venting fittings and lines are required.

if that accomplishes no change then it is worth looking at fuel supply system in detail.

I agree entirely.

 

[Article10]

Just another thought, do you go one heat range colder on the spark plug on any of the ported engines? With the increased fuel/air volume in the cylinder and corresponding increased heat generated, is that an issue on these engines?

 

[blsnelling]

Just another thought, do you go one heat range colder on the spark plug on any of the ported engines? With the increased fuel/air volume in the cylinder and corresponding increased heat generated, is that an issue on these engines?

No, I haven't ever messed with the plugs. Raising the needle lever seemed to help.

 

[sachsmo]

I know 2 strokes and 4 strokes have little in common, but the carbs still work off the same principle correct? Just saying when you get some real free flowing ports, your velocity drops, as does the venturi signal. Would this hold true for saw carbs as well?

 

[Tzed250]

I know 2 strokes and 4 strokes have little in common, but the carbs still work off the same principle correct? Just saying when you get some real free flowing ports, your velocity drops, as does the venturi signal. Would this hold true for saw carbs as well?

Better check that.

More flow=higher velocity=lower pressure=increased signal at the venturi.


.

 

[Terry Syd]

Carb

Last I checked the NE 346 had a 15mm venturi.

With this emphasis on EPA regs, it may be that the carb is restricted for fuel flow. Since the higher 'float' level seemed to help, it could be that the metering chamber is being drawn down too fast for the metering orifice to feed the chamber. You might have to enlarge the metering orifice under the metering valve.

You could check the size of the orifice with some of your other carbs to get an idea if it looks too small.

 

[stihlboy]

Here it is ported and about 1 tank of fuel through it. It's running great. It started in one pull this morning cold.

I've got a question for you carb gurus. You'll notice that the saw goes leaner and leaner the more cuts I make with it. It's not an air leak. Every 346 I've worked on does this. Even my 346 with a 357 carb does the exact same thing. I simply tune the saw to its leanest point and it's fine. But let it set a few seconds and it's rich again at first. Could the carb be having trouble supplying enough fuel? Do you think raising the needle lever would help cure this characteristic? Could the tank vent be having trouble keeping up in extended cuts?
It's hold about 11,800-12,000 in the cut, and 10,000 dogged in.

The saw comes back apart tonight for the machine work.

that don't sound good....you'll figure it out though..... who's saw is it? are they gonna use it for fire wood, limbing, bucking??? what is this saws primary use??

 

[blsnelling]

that don't sound good....

See post 106. Raising the needle seemed to do the trick.

 

[Hddnis]

Great thread, Brad, good work and I'm looking forward to more updates.



Mr. HE

 

[harrybeaver]

Can you describe what a pop up piston is? It sounds like you are trimming the top of the piston to make it more of a dome shape so it can increase the volumetric efficiency.

 

[blsnelling]

Can you describe what a pop up piston is?

The crown of the piston is machined such that the center sticks up higher than the sides. This is typically done on a lathe, but can be done on a mill. The idea is to have the "popup" sticking up into the combustion chamer, thus reducing volume. The net result is higher compression. When this is done, the base of the cylinder has to be machined as well to bring the cylinder down over the cylinder. You want to keep the squish around the outer edges of the piston crown just as tight as it was before you machined the edge of the piston crown down. If you didn't bring the cylinder down, you would actually be lowering compression.

There are a couple things to keep in mind when doing this. Make sure you don't lower the cylinder so far that you free port the cylinder below the piston skirt when at TDC. There's a slight negative affect in the you may be slightly covering the bottom of the transfers when the piston's at BDC. Also keep in mind that you'll be increasing intake duration by the amount that you lower the cylinder, since the bottom of the piston skirt isn't changing. All other port timing stays the same since both the edge of the piston and cylinder are coming down the same amount.

 

[Kansas]

Hey Brad, out of curiosity where would these muffler parts and oem coil be found I dont buy saw parts so I have to ask?

I guess for now I plan to do it at least the coil and muffler thats as far as I plan on going anyway just to let it breathe better.

I didnt see any used coils on ebay so is an aftermarket coil going to work and be rpm unlimited etc or should I just plan to get a new oem coil?

I rarely use AM parts on cars I fix I stick w/oem parts 95% of the time makes my life a lot easier so am very skeptical of these AM coils fwtw.

Btw thanks for the tips so far, this thread got me interested in mods finally

Kansas

 

[blsnelling]

I prefer OEM. Look for a black coil that fits any of the following models. 334, 335, 336, 338, 339, 340, 345, 346, 350, 351, 353, 357, 359, 362, 365, 371, 372, 385, 390, 570, 575. This is from a 455 or 460, but looks like it would work as well, LINK. Someone correct me if I'm wrong. Baileys does sell an aftermarket unit, LINK. You can get the muffler from Baileys too.

 

[Kansas]

Thanks I will get the Baileys coil.

Also where are the screen and deflector available from I have the muffler already on it?

I looked at grinding the deflector/screen etc off my cat and decided thats more trouble than its worth not impossible none the less.

I do want a screen on it what you did looks good better than what I would end up with grinding mine off.


Kansas

 

[harrybeaver]

Thanks I will get the Baileys coil.

Also where are the screen and deflector available from I have the muffler already on it?

Read post #44, Brad already answered this question. Thanks Brad

 

[wendell]

Have I told you how much I hate you guys?

I've been tempted to replace my 350 with a 346XP (and I have no reason other than CAD) and after this thread, think I'm stopping by the dealer tomorrow and checking one out. AAUUGGHH!

 

[dingeryote]

Have I told you how much I hate you guys?

I've been tempted to replace my 350 with a 346XP (and I have no reason other than CAD) and after this thread, think I'm stopping by the dealer tomorrow and checking one out. AAUUGGHH!

Yield to temptation already!!!

Then send it to brad.

Stay safe!
Dingeryote