Ported my 181SE a bit

[Brmorgan]

Been thinking about doing this for a while, just had to get up the courage to finally do it. Here it is, $90 pawnshop find last year:

Needed a new fuel line & fired right up. The handle's second mount bar (behind the clutch cover) was broken so I spliced it with a piece of steel bar for now. I have a line on a new one.

Here's the exhaust port before:

And after:

I know it isn't a huge difference, but being my first attempt at this I didn't want to overdo it - I can always remove more later. I widened it by almost 3/16" per side and raised it maybe .020 at most, since I got rid of the head gasket.

I didn't do much to the transfers, just cleaned up the casting irregularities and smoothed out the transition towards the intake port:

The transition at that edge of the transfer ports were ~60° to the wall of the cylinder instead of being nice and smooth. The marks on the cylinder wall are from an extremely soft stone, and can't even be felt by hand but look awful in a photo. I didn't want to go too far towards the intake port though, because the ring ends travel in that area on one side.

Same goes for the piston, just cleaned up the casting in the window:

Once again the flash photography makes it look a lot rougher than it is, though it's MUCH better than before. There were prominent casting lines ~1mm high on the sides of the pin bosses and the whole area was rough in general. I didn't modify the piston at all other than that though.

 

[Brmorgan]

Now for the results.

I'm still having the same problem I had before modding it. I just CANNOT get it to rev out very high. Today I took it to my parts source and tried replacing the Tillotson #1 carb that was on it with a #5 (larger venturi) as he told me he thought it should've had a #4 anyway. Runs the same as before, though more smoothly. It seems like it starts to rev high, but then within a fraction of a second drops out and just chugs along at a lower RPM. I don't get it - I can close the H jet down to under 1/2 turn and it sounds EXACTLY the same, it just will not lean out.

However after first installing the new carb, I accidentally buggered the intake boot gasket during installation and it was sucking air there. Then it REALLY screamed and sounded more like I thought it should, but of course wouldn't stay running. Once I got that figured out it was back to the same ol' chug-a-lug. Don't get me wrong, it cuts strong as is but has never been able to rev out at WOT.

I talked to the mech at my saw dealer, and he told me that some of these carbs have an auxiliary fixed H jet opening, so that no matter how far you close down the main H jet it still sucks some extra fuel through the other one. This would explain how it's acting because it'll still scream if I run the tank empty. But I've never heard of such a thing. He said if that's the case to just take a piece of solder and shut the aux. hole off. Any ideas on this one, or how I can tell if the carb is in fact built this way? The main H jet on the bottom is ~3/32" - 1/8" diameter, and then 90° to the right of that on the side of the venturi there is another hole about 1/16" diameter, is that what he's talking about?

Something's messed up, because it has good compression (150lb, good but not great - needs new rings) and starts fine but is acting like it has a governor or rev limited ignition (impossible on this model, no?) on it.

 

[PES+]

Ok

I think he may be taking about the governor which is the brass plug looking piece right next to the choke shaft.

If the governor spring is weak it can open too soon or stay on after RPMs drop where it should close back off.

You need to remove the governor and seal the ball inside and then screw it back in.


ahhhhhh yes.....old trolling bait

good fishin in the early days

 

[Brmorgan]

I think he may be taking about the governor which is the brass plug looking piece right next to the choke shaft.

If the governor spring is weak it can open too soon or stay on after RPMs drop where it should close back off.

You need to remove the governor and seal the ball inside and then screw it back in.


ahhhhhh yes.....old trolling bait

good fishin in the early days

OK, I was wondering about that brass screw. The one on the original carb had clearly been tampered with because the slot was all mangled, but this one looks pristine. I didn't realize carbs could have governors (I know of fixed jets though :censored. I'll check it out in any case.

Dunno what you mean by "trolling bait"? Am I missing something? If you mean I'm trolling the forum, I certainly don't think so by my definition.

Also I re-tested the compression tonight as I was leaving the house earlier, now it's at 180 lbs. COLD! Can't complain about that. I guess the rings needed to re-seat a bit or something. I just figured they were worn out because I could just slip the cylinder over the piston without compressing them or anything, as if they weren't even there.

 

[Jacob J.]

Those thin-rings wear out fast. Even though you have a good compression reading it's likely you're going to need a new set.

 

[Brmorgan]

Jacob, I'm definitely going to keep my eye out for a new set to keep as a backup. They don't seem that easy to come by. I don't think Bailey's has anything either. For the record the rings are .025" thick. Anybody with a set for a reasonable price PM me, I'll be interested provided I have the cash (getting laid off). At any rate, this saw will likely only see a few hours of firewood cutting a year, or maybe as an intermittent slabbing saw for milling, but I won't be milling anything big with it. But if this P/C ever pack it in, it'll become a 288 I think. Easier to get replacements.

PES+, thanks so much! I did a search on the topic and ended up using the technique Brad Snelling used on his 076 - just punched a round from an aluminum can and put over the outlet hole at the end of the screw recess. It'll scream like a banshee now, but I wish I had a tach as I haven't worked on ported saws before and don't want to kill it. Now to go dig a log outta the snow to cut up tomorrow! Next up is opening the muffler and gutting it, the baffle inside is broken in two anyway and rattles like marbles in a tin can. Tried bending the pieces and pulling them through the port but it's too small.