Stihl 036 possible seal leak?

[Cam460]

Hi I am new to this forum and wanted to know if anyone had some advice. I rebuilt a stihl 034 last year (new jug, piston, (big bore/036) tank and some other small stuff) it ran fine for about 6 months but recently it will not hold a tune. When it first fires up it idles high and once warm will idle normal but after about a half tank of gas it starts getting boggy. Once I re tune it it will do the same thing last about a half tank of fuel. I have tried pulling the clutch and checking so play on the crank and it has none, I have also cleaned the carb and checked the jug to case gasket and that also seems ok. And suggestions? 
Thanks, 
Cam

[doc henderson]

check for crack in molded fuel line?  unless you can retune and finish the tank.  the crack may be at the half tank level.

[Cam460]

Thank you for the reply, I will definitely check this out but I can re tune and finish the tank. 
Thanks,
Cam

[doc henderson]

there are many chainsaw experts here who will reply soon,  good luck

[Cam460]

Update. I pulled the cylinder back off the saw thinking maybe there is an air leak between the jug and case. Just waiting on a new gasket to come in. All the internals look great since the rebuild no scoring at all! Any advise would still be greatly appreciated.

[limbwood]

spray carb cleaner around seals and gaskets while running it will rev when you spray by a leak.

[Cam460]

I tried this right before I pulled the cylinder. it did not have any affect on idle. Definitely an annoying problem! 

[wild262]

You have a impulse line as well.  Did you check that?  If it doesn't cause any problems till half a tank is run, than it could be the coil.  Coils don't always stop dead when they heat up.  If you have a spare, try that.

[Cam460]

Thank you for the advice, I checked the impulse line and it looks new but never thought of the coil. If the saw still acts up Once I get it back together I will put a new coil in it to see if that helps. 
Thanks, 
Cam

[limbwood]

might be water in fuel, have had a drop of water in carb bounce around and make it run wierd.

[doc henderson]

I have had large tanks with water, put into clear plastic pepsi bottles and then decanted off the gas and discarded the water that settled to the bottom.  could use a small glass jar, or look into gas jug and look for bilayer of water on bottom.  Also, if it acts up, could let it cool off without re tune and see if it runs fine cold.  I had the new 660 and had all kinds of trouble and gave it back to the dealer, and got the 880.  Sounds like you are quite the mechanic, so thanks for letting me feel like I was helpful. lol

[Cam460]

Thanks but I would rule out water because I run my saws almost everyday and am constantly mixing fresh gas. And I am far from a pro at this but try my best 😂

[welderskelter]

I have an 066 that always had issues with not idling for a long time. Finally done a crankcase check and bingo there was my problem. Runs good now. New seals done the trick. go for it.

[Cam460]

Yeah if the cylinder gasket doesn't do the trick that's my next step. Can you do the seals without splitting the case?
Thanks,
Cam

[wild262]

   Tank vent, fuel filter.  Did you check these out?

[ZeroJunk]

Yeah if the cylinder gasket doesn't do the trick that's my next step. Can you do the seals without splitting the case?
Thanks,
Cam

Yes.

[Cam460]

Awesome thank you

[welderskelter]

You will need a flywheel puller bolt and nut. You can get them on ebay .

[wild262]

              Just loosen the flywheel nut till its flush with the crank end, give it good square smack with a brass hammer, and it should pop right off. 

[Cam460]

Thanks for the info! I'm still waiting on the cylinder gasket to come in (you know how that goes :D). Guessing this won't solve the problem I guess it was worth a shot before diving into crank seals. 

[joe_indi]

A 034 is pretty old. If you haven't, replace all the diaphragms and gaskets in the carb. The diaphragms might be stiff. This could give you uneven running which might seem ok with a re-tune but never seems to stay permenant. OE repair kits (major and minor) are available.

[smmyb123]

There is a process you have to abide by when diagnosing a running condition issue on 2-stroke engines. Without sticking to the script you can run around in circles trying to chase down the issue.
Visual inspection: Check for any loose hoses, evidence of seepage or leaks, hot spots/melted plastic. Check spark with a real in-line tester to check the "heat" of the spark (probably not the issue here).
Fuel system: Drain the fuel tank and remove the fuel filter, pressure test the fuel hose to 10psi from the fuel filter end in the tank. This tests the integrity of fuel hose and carb inlet needle at the same time. It should hold 10psi indefinitely, if you notice any drop in pressure spray the fuel hose with soapy water to find the leak. No leak on fuel hose means leak in carb. Pick up a cheap vacuum/pressure tester to perform this, you will need it for the next step...
Crankcase Pressure Test: Remove the carb and push the impulse hose through the carb box towards the cylinder, the hose should be accessible from the clutch side with the top cover off. Now reinstall carb with rubber "blocking plate" sandwiched between carb and intake boot, ensure the entire port is covered. Remove muffler and sandwich a blocking plate between it and the exhaust port, reinstall. Ensure both carb and muffler are sealed tight enough to hold pressure and vacuum. Use the carb impulse hose to vacuum test the crankcase, crankshaft seals usually loose the ability to seal vacuum first. Vacuum testing should not exceed -.8 bar or -10 psi. If you cannot get a solid reading then you have a crankcase leak. Pressure test to 10 psi and use soapy water to track down the leak.

[Old Greenhorn]

There is a process you have to abide by when diagnosing a running condition issue on 2-stroke engines. Without sticking to the script you can run around in circles trying to chase down the issue............................................

........................................Pressure test to 10 psi and use soapy water to track down the leak.

This is a pretty rock-solid reply and technique, too bad we can't make it into a sticky or create a collaborative thread on these troubleshooting issues. SO many of them come up over and over.

[Cam460]

Thank you guys so much, I really appreciate the time it took to write this. The cylinder gasket came in today so I got the saw back together tonight and ran it not under load. (Didn't want to pith off the neighbors too much ;)) I re tuned it, let it cool off and re started it. It doesn't have a high idle when cold anymore which I'd say is a good sign, I'm going to be falling all day tomorrow and I'm going to bring the saw to see if this solved the problem   If not my next step is carb rebuild than pressure test if that doesn't work. I will keep you guys up dated thanks again for the advice this is really a great forum!
Thanks,
Cam. 

[Cam460]

Update. Ran the saw today and it is still doing the same thing, half tank of gas than needs to be retuned. Is there any chance the carb adjusting screws are vibrating causing me to lose my tune?

[doc henderson]

you can run them all the way in and count your turns, or mark the slot in the screw with a sharpie, but that sounds unlikely.  i still am hoping for you it is something simple.  Please don't take this the wrong way, but it seems you are going for the big stuff.  So just refilling with fuel does not solve the problem, and letting it cool off does not solve the problem?  The fuel line as you probably know, is a molded engineered piece of the machine, that often gets a crack at the bend, that is hard to see, costs about 5 dollars to repair.  It is so common that my stihl mechanic told me after a description over the phone of the problem, that it was most likely the problem.  In fact his name is Sylvan at fairveiw service in Pleasant View, Ks if you want to give home a call.  Or better yet call your local dealer if they have a mechanic that does only Stihl power equipment for 40 years.  Trying to help!  Sounds like you have other back up saws as well.

[joe_indi]

Update. Ran the saw today and it is still doing the same thing, half tank of gas than needs to be retuned.........

Oh oh, I think what I typed was deleted by my over enthusiastic Keyone :(
What you mentioned above could happen if the tank vent is blocked. A low pressure will be created in the tank to the point that the pump is unable/difficult to draw fuel.
It's very easy to check this. When you reach the half tank level and the rpm starts playing up, just open the filler cap and then close it. This will equalise the pressure if the vent was indeed the culprit your saw should run normally again

[Jsawyer]

Sorry if I missed it...did you do a pressure test/ vacuum test? It should hold 10 psi and at least 6 or 7 inches of vacuum. I blocked off my 034 with some fender washers and and some 1/6 rubber. You can test thru the impulse line. I had similar problem with my 034AV thought it has seal leak but it was the Reed valves in the carburetor and the fuel line and filter.

[knuckledragger]

036AV, rebuilt the saw and had high idle trouble as well. This 036 never would idle down. I went through all the simplest causes of this symptom and all checked okay. Aggravated I put the saw on the shelf and there it stayed for close to 90 days. When I cleaned my bench off one day I decided to give myself another shot at being smarter than the saw. Turned out to be a leak in the crankcase via the seal on the flywheel side. I replaced the seals on both sides since I had the saw that far down. That 036 schooled me on saying out loud that I had rebuilt a saw that I really hadn't totally rebuilt. Oh, the 036AV was purchased shortly afterwards. The boy that bought the saw is still running it. I looked back to see when he got it, 11-18-2017.

[oldred]

if its runs normal cold then bogs down warmed up it could be ignition/electrical issues, fuel tank cap or incorrect carb adjustment. could be seals but it would run lean if the carb its properly adjusted for the big bore. 

throw in a new ngk bpm7a spark plug. test your coil. pressure/vacuum test your seals and cap. if you got it ripped down to the case, throw in some new seals theyre cheap and itll give you piece of mind.

[oldred]

..that is if i'm understanding you correctly. "bog" to me means its running rich or slowing down.
also if you havent rebuilt the carburetor, rebuild it. specially since theres a new top end on there, it has to be adjusted specifically to the bigger bore. 

[Cam460]

Alright guys so here's where I'm at I put a new set of crank seals in it thinking that solved the problem. The old seals were pretty brittle. So I re tuned it just to have the same thing happen the only thing I can think to do is a total carb rebuild. 

[Mad Professor]

Seals, intake, fuel line , vent all O.K.?

The carb ,besides rubber, can have things like a piece of crap in it. Besides a carb kit, not a chinesium kit, a sonic cleaning can get crap you'll never see out.

It's worth fixing, my 036 saws are my favorite for firewood < 20".  Pretty easy to fix in most cases. They are stihl all german parts.

[Air Lad]

Alright guys so here's where I'm at I put a new set of crank seals in it thinking that solved the problem. The old seals were pretty brittle. So I re tuned it just to have the same thing happen the only thing I can think to do is a total carb rebuild.

If you're going to pull the thing down the carb kit/impulse line/fuel line are things that are worth thinking about while you're at it
Just sayin

[oldred]

rebuild it entirely, not just the gaskets. dont worry about the welsh plug.

if it still dont work check to make sure you got the right spark plug then start testing everything electrical.

[wild262]

And make sure the plug wire is not arcing or touching the cylinder anywhere.  Did you ever check the coil?

[limbwood]

when you are about to give up, put saw under pressure and put it under water and watch for bubbles, small leaks hide sometimes.