Stihl 041 tuning issues

[sven556]

I've been working on this stihl 041 aveq off and on for getting close to a year now. I've replaced the crank seals, fuel line, impulse line, new episan piston and rings. I am pretty sure all that is good. This is about the first piece of equipment that I have tried to tune the carburetor on. I finagled my way through and got it to idle consistently, and have good throttle response. Put it in some wood and it bogged down in dried 7" hedge. Put it down for a month, tried again in 15" cedar. With the high needle at 1 1/4 turns out it will cut with about the same power as my 028 wb. at 1 3/8 turns out it cuts about the same with backfiring out of the carb. Leaning it out to about 1 turn out and it doesn't even want to rev up with any power.

Any ideas? After searching the forums for awhile, I'm wondering about a sheared flywheel key, or a plugged muffler.

 

[alexcagle]

What about the "L" side?
What carb # is on it?

 

[happysaws]

Did you clean and rebuild the carburetor?

 

[sven556]

Ok, I finally got back to this saw. I did clean and rebuild the carb. The low side is set at 1 1/16 turns out.

 

[a. palmer jr.]

Did you set the inlet lever correctly?

 

[sven556]

back at this saw again! I get frustrated and have to set it down for awhile! I bought an aftermarket carb and installed it tonight. It idled great, but bogs under full throttle with no load (no bar or chain).

Let's see if you guys can follow my logic on this saw: Earlier (with bar and chain) it would idle and rev up, but not have much power in the cut. Now, with new aftermarket carb it will idle but bog at full throttle with no bar or chain.

To me this says that the ignition is not breaking down at full throttle but the fuel delivery is the issue. I'm suspecting the new aftermarket carb has a bad high side circuit (cheap chinese carb?). I know I cleaned the oem carb and put in a rebuild kit, but I'm thinking maybe I didn't get something cleaned out well enough. So, I tore down the oem carb and am soaking it in a can of carb cleaner. I plan on putting it all back together tomorrow.

Any comments are welcome! I am getting frustrated with this saw!! When I cleaned and rebuilt this carb last year, I pulled the welch plugs, cleaned underneath and replaced the plugs. What are the symptoms if the plugs aren't sealing properly?

To answer some questions:
this is an Tillotson hs-138b carb
The inlet lever was flush with the bottom of the casting when I disassembled it tonight

 

[a. palmer jr.]

Kinda silly question but have you opened up the H screw any beyond the initial setting?
Also, a possibility your engine might have an air leak like mine did. Have you done a pressure test?

 

[HarleyT]

Clean and adjust the points, see if the performance changes.

 

[sven556]

This saw is electronic, so no points. An air leak is always a possibility. I did pressure and vaccuum test it earlier and it was good, but as many times as I've pulled the carb off now, there could be a leak in the intake stack.

I have opened up the H screw, it made a difference on the oem carb, not much difference on the aftermarket carb.

I think I'll put the oem carb back together and give that a try. If no go after that, I will go back to pressure/vac testing.

 

[HarleyT]

Just look at that stack of crap between the carb and engine, you'll find all kinds of problems there.

 

[pioneerguy600]

Air gap setting and or the EM itself?

 

[a. palmer jr.]

Air gap setting and or the EM itself?

Only 4 intake gaskets? I think my car has less gaskets than that...

 

[pioneerguy600]

Only 4 intake gaskets? I think my car has less gaskets than that...

Not the greatest design but they work well when airtight, the two I have left here are solid runners and the 3 I re homed are as well.

 

[a. palmer jr.]

I think when I put mine back together I may put just a bit of Motoseal on those gaskets to prevent a leak.

 

[Ted Jenkins]

It sounds to me that you have more going beside carburetor issues. If both carbs are are unresponsive then for sure some thing else is not just right. For me rule of thumb is to start with both screws out about one turn and start it. If everything is good it will start right up with the choke on then die once the choke is taken off. Turn the L or low speed screw out slightly more and try again until it runs fair at 1/4 or 1/2 throttle. Then pull the throttle to full and it will run , but bog down with poor response. Turn the H screw out in small increments until it starts to sputter just a little with full throttle after it has run full RPM cleanly. Remember that the motor will sputter just slightly from being a little rich until it has a full load on it. I have no idea what setting my 041 is set at because it gets adjusted until it pulls cleanly through the wood at full throttle. As far as idle goes it can not be adjusted untill everythings is dead on. The one turn out is just a starting point for final tune. Thanks

 

[sven556]

The air gap between the coil and flywheel was set with a business card. The OEM carb was somewhat responsive to H adjustments, it would rev up but it wouldn't have much power cutting (about as much as my 028). The aftermarket carb would not rev up at all.

Is there a way to test the electronic ignition? The saw will idle fine. The issues all seem to be at High RPMs. I thoroughly cleaned the oem carb last night but did not have time to re-install and test. Now I'm thinking I should pressure/vac test it first.

 

[a. palmer jr.]

The air gap between the coil and flywheel was set with a business card. The OEM carb was somewhat responsive to H adjustments, it would rev up but it wouldn't have much power cutting (about as much as my 028). The aftermarket carb would not rev up at all.

Is there a way to test the electronic ignition? The saw will idle fine. The issues all seem to be at High RPMs. I thoroughly cleaned the oem carb last night but did not have time to re-install and test. Now I'm thinking I should pressure/vac test it first.

I doubt there's an easy way to test the primary side. On the secondary you can check the continuity from ground to the spark plug terminal, shouldn't be shorted or open but should measure a few thousand ohms. The primary side has the trigger in it and probably couldn't be checked with a meter. The only sure way is to replace it with a known good one.

 

[sven556]

I vac tested the saw last night and it failed miserably. When I get more time I will try to find the leak.

 

[a. palmer jr.]

One place to look is the main seal behind the clutch...that's where mine leaked the worst..

 

[sven556]

I found a big leak in the intake stack. Surprise, surprise!! So, I cut some new gaskets from some thin cardboard, cleaned all the mating surfaces with acetone, and put it all back together with some permatex motoseal on all surfaces for an added measure. It holds vacuum now! I'll check things again in the morning before I put everything else back together. Hopefully everything will be good and I'll get to test it out some this weekend.