Stihl 036 possible seal leak?

Cam460 · January 30, 2019, 10:58:28 PM

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 · January 30, 2019, 11:22:22 PM

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 · January 30, 2019, 11:32:16 PM

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

doc henderson · January 30, 2019, 11:34:33 PM

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

Cam460 · January 31, 2019, 12:03:28 PM

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 · January 31, 2019, 12:15:40 PM

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

Cam460 · January 31, 2019, 12:34:42 PM

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

wild262 · January 31, 2019, 01:39:58 PM

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 · January 31, 2019, 01:59:03 PM

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 · January 31, 2019, 02:58:44 PM

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

doc henderson · January 31, 2019, 03:12:04 PM

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 · January 31, 2019, 08:28:43 PM

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 · January 31, 2019, 08:40:40 PM

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 · January 31, 2019, 08:59:02 PM

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 · February 01, 2019, 04:53:08 AM

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

ZeroJunk · February 01, 2019, 06:42:55 AM

Quote from: Cam460 on January 31, 2019, 08:59:02 PM
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 · February 01, 2019, 03:57:33 PM

Awesome thank you

welderskelter · February 01, 2019, 05:41:59 PM

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

wild262 · February 01, 2019, 06:19:12 PM

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 · February 07, 2019, 02:45:39 PM

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 · February 07, 2019, 10:37:47 PM

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 · February 08, 2019, 12:22:37 AM

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 · February 08, 2019, 06:07:02 AM

Quote from: smmyb123 on February 08, 2019, 12:22:37 AM
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 · February 08, 2019, 11:36:46 PM

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 · February 09, 2019, 01:09:40 PM

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?