Stihl 015L Carb Tuning Help???

[Kyle Corrigan]

I've been working on an older Stihl 015L top handle saw. It started developing a ping sounds and would stall out after running 30'sh seconds... turned out to be a worn crank bearing (possibly run too lean or vacuum issue?) that resulted in the crank slightly shifting, making the rod rub against the crank counterweight at temp. I replaced the bearings (gently used from a donor saw) and installed new crank seals. While at it, I installed a new piston ring (light grey scotch bright pad the cylinder wall... no notable damage) and rebuilt the carb. Has great spark.

Following the Walbro HDC 17A manual, I've started by setting the H & L jets to 1 turn out from closed. With the throttle lock on, 3 pulls on choke to get first cough... about 3 pulls later it's running rough (rich). Closing the H jet down to about 1/2 turn open (total), it runs great... quick throttle response... pulls through wood... but I can't get it to idle at all. If I drop off on the throttle lower than half, it dies. If I turn the H jet more rich and lean the L (trying to get balance)... high RPM runs worse and it won't idle... dies. I can't seem to find a setting where it will idle at all... but runs great full throttle with prior noted settings.

This is my first saw project. I've been reading this site for some time but my first post. I'm new to carb tuning. I'm hoping some experts have a few tips to share.

cheers!

 

[a. palmer jr.]

I've been hearing that those carbs are the problem. They're getting kinda hard to find, at least around here..
You can try setting the idle first, then if it idles well try the H side for full throttle running, then if you have problems with the transition from idle to high speed just richen the H screw slightly.

 

[Chainsaw Jim]

The main nozzle check valve could be failing. That would cause problems like that.

 

[Kyle Corrigan]

I've been hearing that those carbs are the problem. They're getting kinda hard to find, at least around here..
You can try setting the idle first, then if it idles well try the H side for full throttle running, then if you have problems with the transition from idle to high speed just richen the H screw slightly.

I'm a newbie... sorry for the dumb questions. Following the Walbro service manual, I have the Idle screw (top) set at mid point, and both H (high) and L (low) at one turn out from closed. I lock in my throttle open, pull with choke on (closed) until a cough... then open choke (with throttle still locked open) and pull until start. At that point, it will run really poor with lots of smoke (rich) and the only think that seems to help is leaning out the H jet (tightening towards closed about 1/2 turn). It picks up RPM and sounds like I'd expect.

How do I set the idle first? Try to start it without locking the throttle open (not sure it will fire)? Should I move off the 1 turn out default setting to try and get it to idle first?

Thanks for any help you can share. Sorry if I'm just confused...

 

[Kyle Corrigan]

The main nozzle check valve could be failing. That would cause problems like that.

Is that the small diaphragm/valve in the center of the carb body with the screen covering it?

Can you replace those or do you just have to get a new carb unit?

My carb kit didn't come with one... just the screens/gaskets/larger metering diaphragm/fuel pump/inlet needle parts. I'm probably over invested on the repair already. It's my father in law's saw I'm trying to resurrect for him but it might just be at the end of the road.

 

[Chainsaw Jim]

I'm not familiar enough with that carb yet to know exactly what type of nozzle it has.
Many members on these forums have one or two of these things laying around. Maybe one will offer a good one up.

 

[AnthemBassMan]

I've never dealt with Stihl before, but like all other 2-strokes, shouldn't you adjust the the Low screw to get the idle/low speed set? Get the saw running, then slowly back out the Low screw until the idles speed up then starts slowing down. Turn it back in until the idle starts to speed back up again. I leave mine on the richer side of the adjustment. From there you can set the High screw. I think the one turn out for both screws is to get it running, not a permanent setting.

L8R,
Matt

 

[Aggie 2012]

I'm suffering from a similar issue with my 015. It idles fine upon startup and has plenty of power in the cut.
The issue with mine is the transition from high back to idle. I have to partly touch the throttle to keep it from dying out. Especially when the engine is warm.

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[a. palmer jr.]

You should be able to start it normally, let it warm up a bit then set the L screw, along with the idle speed screw until the best idle is attained. Turn the idle speed screw down and try to get the highest idle speed with just the L screw. When you get it you should richen it up about 1/4 turn (counterclockwise) and see if it will still idle. If it does then leave the L screw alone and set the H screw in a similar way. Do not leave the H screw set at the highest speed, it needs to cut out a bit (4 cycle) when you have it at wide open throttle. It should run smoothly in the cut however.

 

[Kyle Corrigan]

Thanks you all for your input and help. I think I sorted things and thought I'd share my findings.

I tore down the carb for another complete cleaning (3rd time stripped and run through ultrasonic + simple green). I inspected the main check valve visually and using a small fuel line (suck/blow), it appears to work find... potentially I'd free'd it up in the process(?).

I also adjusted the diaphragm level again, a little lower. Following the Walbro service manual, I'd originally left it level to the carb body milled metal surface with the spacer gasket, making the lever aligned with the diaphragm plane. I later found a generic Walbro company carb troubleshooting video and they demonstrated setting it level to the metal housing plane (not adding the gasket) so I tried that this time. This basically lowers the lever the thickness of the spacer gasket below the diaphragm.

After reassembly, I set the H and L jet's at one full turn out from bottom (per Walbro manual) and attempted to start. I'd get a cough and eventually flooding. After a few days of attempting... drying out... modifying H/L + attempt... drying out... modify setting, I eventually got a rough idle. After letting it warm a bit, I was able to tune the L (down/lean) then work back to tune the H (down/lean). I ended up with L about ~1/3 turn out from bottom and H ~1/4 turn out from bottom. I have some fine tuning to do (WOT 4-stroking) but it's runs/idles really well now... feels like a new saw.

My best guess is that someone had buried/forced the H & L needles closed and pressed out the carb body (aluminum) mating surface, changing the opening and fuel ports. I think it was running way rich following the factory default settings and I had stumbled into an odd H/L needle setting to get it to WOT but not idle. By rolling the needles significantly lean (and following the above guidance to start with L and then add H... a must), I was able to get it running much better. Not only did the rebuild address the original issue (failing crank bearings) but the combo of new piston ring and fresh carb rebuild has it running better than ever... or at least the last 8yrs that I've had it (built in '78).

Anyway, I appreciate this kind of forum and the community help it provides a novice like me. For those that stumble across this thread down the road, I figured I'd circle back and share the outcome.

Now for a few hours of "test cuts"!

 

[Aggie 2012]

Good to know Kyle! Thanks for the update.

I have come to the conclusion that mine was basically the clutch. To keep the chain from spinning I was having to run way too lean. I'm still shopping around on eBay for a used one but have not come across what I'm needin for less than $30.

When I adjust my other saws I try to run the L in until the saw surges some. Then back it out to a smooth idle (chain will spin yet)
Then back out the LA (closes the throttle plate) until you reach the desired idle rpm. I like 2700 for most of mine.
Then go back to the L and run it in again then back out and re adjust the LA once more.

My thought process here is trying to close the throttle plate as far as possible so your not pulling from both the transition and main circuit at idle.

Does that sound right to all the pros out there or am I having the wrong thought process?




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