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

[TRI955]

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?

This is the exact same problem that I'm having with mine, raising the needle lever did not help either....

 

[blsnelling]

This is the exact same problem that I'm having with mine, raising the needle lever did not help either....

You need to tune it richer. It'll quit leaning out once you get it rich enough. It's not an air leak.

 

[Log Hogger]

noob question

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

noob question: what is the "needle lever"?

I have a 445 that is behaving in a similar fashion. Fuel line and tank vent check out fine. The problem arose in colder weather after I richened the carb.

 

[Log Hogger]

Nevermind, I found it

it's the lever on the jet valve, right? Analogous to adjusting the float height on a regular carb?

How much do you suggest bending it?

 

[ronT2]

Here's the plan.

- Turn a .035" popup on the piston crown, leaving .100" crown thickness.
- Mill cylinder base .030", for a final squish of .018".
- 100° Exhaust
- 120° Transfers
- 80° Intake
- Widen intake & exhaust ports to 70% of bore, as measered on the curve of the cylinder wall. Some go across the chord, which makes it a little wider yet.
- Widen and angle rear transfers towards the intake port.

Brad, I see your exhaust and transfers came in where you wanted them to but didn't notice what you wound up with on the intake.

The reason I ask is that I just did a 372 BB kit to the #s in this thread and love the way it runs. Know I'm eye balling my 2150.

 

[HuskyMurph]

deflector

The deflector is PN 503 58 99-01 and costs me $8.74.

The spark arrestor screen is PN 503 40 56-01 and costs me $4.97.

The screws are from the hardware store.

i have this deflector on order. just installed my none cat muffler on my 346 xp. wheni put this muffler deflector on do i have change the settings on the carb idle screw or high and low.?? if so about how much. also will that deflector work for my 372xp??? thanks huskymurph

 

[blsnelling]

Might be temperature of the cyl assy. Try setting it up on a "warmed" up assy and see if it goes leaner with more cuts.

The tank vent may be an issue worth looking into.

I wanted to update this thread to post that the tank vent of the 346 does need some attention once ported. They aren't able to vent as quickly as the ported saw can burn the fuel. You will need to open up the passages in the vent path to provide for greater flow. Once you do this, the saw will quit going lean as you make repeated cuts. Thanks to Mike, aka Tri955, for finally sorting this out.

 

[TRI955]

Mike

 

[woodyman]

I wanted to update this thread to post that the tank vent of the 346 does need some attention once ported. They aren't able to vent as quickly as the ported saw can burn the fuel. You will need to open up the passages in the vent path to provide for greater flow. Once you do this, the saw will quit going lean as you make repeated cuts. Thanks to Mike, aka Tri955, for finally sorting this out.

So does that mean I have to mod the tank vent on my 346 Brad and if so how is that done?And that saw in the last vid looks alot like mine

 

[Log Hogger]

I'm interested to know as well

How does one go about opening up the tank vent passages?

Do I need a different tank vent for this?

 

[luvsaws]

opcorn:

 

[SawTroll]

So does that mean I have to mod the tank vent on my 346 Brad and if so how is that done?And that saw in the last vid looks alot like mine

Yes, you have to bore it out in the middle, streight trough the handlebar! :jawdrop::jawdrop:

On the serious side, I think they put the tank vent in an unconvenient place on those saws - actually my only complaint on them!

 

[blsnelling]

Sorry to keep you waiting Woodyman. I've been in bed all day. I don't know if that was your saw in that vid or not. Remove the tank vent and use a drill to open up the hole in the plastic parts. I'm not sure if you need to drill down into the tank or not. If so, that'll require removing the tank. I actually left the hose off on my 372 because of vent issues.

 

[lotawood]

I modified the tank vent on a 346, but haven't been able to test drive it yet. I have pictures, but never have posted on the internet before.
What I did was
1-empty gas tank on chainsaw
2- take front handle bar off. This allows spreading the gas tank base from the top end
3- set chainsaw on flywheel side and look where fuel line, vent hose and primmer return hoses run to fuel tank in the gap between the carb area and the fuel tank ( on the right side,behind the pto and in the gap that you spread between the top end and the fuel tank base).
4- take needle nose pliers and pull the middle hose and white plug out.
The white plug has two different ways to limit fuel flow. It has a rubber dampener (?) and two discs that look like aquarium air stones.
The first thing I did was gut everything. But the problem was when I refueled the chainsaw gas would siphon into the carburetor throat quicker than I would want. The other end of the vent hose ends in the carb intake, under the air filter.
The next thing I did was to replace the rubber dampener and the dampener keeper. Now the keeper has a small cone pointing down and the black dampener has a cone shaped recessed area on one side. So that is the way I put it in. Same thing, siphoning fuel.
The last thing I did was to flip the black diaphragm/dampener over so the point from the dampener and the point from the white keeper were touching. No siphoning while refueling.
Put hose and tank vent plug back in. Put on front handle bar.
Like I said I haven't tested it yet. I was having concerns about the saw getting leaner after multiple cuts. This was after a muffler mod.

 

[bjorn773]

Here's the plan.

- Turn a .035" popup on the piston crown, leaving .100" crown thickness.
- Mill cylinder base .030", for a final squish of .018".
- 100° Exhaust
- 120° Transfers
- 80° Intake
- Widen intake & exhaust ports to 70% of bore, as measered on the curve of the cylinder wall. Some go across the chord, which makes it a little wider yet.
- Widen and angle rear transfers towards the intake port.

Brad, I'm not trying to hyjack the thread here, but am comparing your plan to what I currently have on my saw.

With my aftermarket cylinder, I have the following numbers with no gasket installed:

Intake 77 deg
Exhaust 107 deg
Transfer 130 deg

I have milled the cylinder .030" to achieve .016" squish when the .021" thick gasket is installed. Hindsight tells me I should have milled less and used a thinner gasket, but it's done now.

Should I be raising my transfers and exhaust for more duration. I wasn't sure how your numbers would compare since I'm not using a pop-up.

Here's a link to the thread for reference: http://www.arboristsite.com/showthread.php?t=114159&page=7

 

[blsnelling]

Brad, I'm not trying to hyjack the thread here, but am comparing your plan to what I currently have on my saw.

With my aftermarket cylinder, I have the following numbers with no gasket installed:

Intake 77 deg
Exhaust 107 deg
Transfer 130 deg

I have milled the cylinder .030" to achieve .016" squish when the .021" thick gasket is installed. Hindsight tells me I should have milled less and used a thinner gasket, but it's done now.

Should I be raising my transfers and exhaust for more duration. I wasn't sure how your numbers would compare since I'm not using a pop-up.

Here's a link to the thread for reference: http://www.arboristsite.com/showthread.php?t=114159&page=7

107 is quite low on the exhaust. If you raise it, I wouldn't go any higher than 100. If you do so, I would raise the transfers about the same, to keep close to 25 of blowdown. 77 isn't bad on the intake. I assume this was measured after lowering the cylinder?

Now, if you just widen the ports, you will see good gains. Have you ported a saw before? If not, maybe do this in steps, and start just by widening the ports. First time through, don't touch the transfers. Eventually, you'll have to widen them towards the intake to hold the RPMs in the cut. With the single ring, you can go really wide on them.

 

[bjorn773]

I'm still a novice. This is my third porting job. I did a simple intake/exhaust on my 350. Then got into my 365BB, milled it and did intake/exhaust and transfer porting. I never messed with timing. This one I've milled (prior to taking the posted measurements). I have widened the intake and exhaust to 70% of bore diameter, ported the transfers to match the crankcase, tapered/beveled the transfer ports toward the intake. I have not modified any timing yet, other that what resulted from lowering the cylinder.

 

[blsnelling]

I'm still a novice. This is my third porting job. I did a simple intake/exhaust on my 350. Then got into my 365BB, milled it and did intake/exhaust and transfer porting. I never messed with timing. This one I've milled (prior to taking the posted measurements). I have widened the intake and exhaust to 70% of bore diameter, ported the transfers to match the crankcase, tapered/beveled the transfer ports toward the intake. I have not modified any timing yet, other that what resulted from lowering the cylinder.

Well you're already ready for stage two then. Go for it!

 

[bjorn773]

I'll give it a whirl. Thanks.

 

[bjorn773]

Do you have any links handy for a good blowdown theory explanation?