Stihl 034AV

[Homer6679]

Hey Y'all, got around to looking at an old stihl today. My issue is that it will pop on start fluid but it there seems to be no fuel getting to the carb. New Fuel line and Fuel Filter. Is there a way to test the pump diaphragm in the carb or is the symptom of no fuel getting to the carb the test?

 

[jltrent]

I picked up an older 034 a couple weeks ago that looked pretty nice for $50. A new set of rings and compression was good, but the PTO side spun bearing was not nice. Actively on the lookout for a crankcase. It would start, but the air leak make it erratic running.

If you already bought the 034 I would put a carb kit in or at least check the diaphragm for pliability. What to lookout for in these saw is the air filter. IF the flox is gone on the air filter then the saw has ingested a lot of dust which will shorter the life of about everything in the saw.

 

[cscltd]

Pull saw rope with choke on with the choke butterfly facing down with filter off. Should see fuel residue on butterfly after few pulls. No fuel usually means fuel not coming from carb

 

[Homer6679]

Just did the choke test as mentioned in this thread. No fuel on butterfly, I pulled open the pumping side and there is no fuel on the pumping side either. The diaphragm is pliable I guess it’s not pumping. Time for a carb kit

 

[Lightning Performance]

Just did the choke test as mentioned in this thread. No fuel on butterfly, I pulled open the pumping side and there is no fuel on the pumping side either. The diaphragm is pliable I guess it’s not pumping. Time for a carb kit

Block off the carb inlet and give it some pulls then look for fuel. If you see none pull the carb apart and see if the fuel pump flaps are gummed up or curled or wrinkled. Wrinkled or curled will allow fuel to pass but it won't run long or right. If they were glued down from old oil that will cutoff the fuel supply.

 

[Homer6679]

The diaphragm doesn’t appear to be curled or wrinkled, however I haven’t seen one that is that color. It is almost a tan and white color. I’ll post some pics later today. Also would there be a way to bypass the pump diaphragm for testing purposes? For instance make rig up a gravity fed tank and run the saw on that to see if there are any other issues?

 

[Mad Professor]

There is a little screen on the passage from the fuel line. If that is clogged no fuel gets to rest of carb.

 

[Homer6679]

I know about the screen, fuel will flow to the metering side without the screen but with the screen it doesn’t flow. I tested it without the screen figured it wouldn’t make a difference just to see if it would run

 

[cookies]

check the fuel filter for clogging the fuel hose for holes and the impulse hose for tight fitting ends and hardness..it should be pliable. If the diaphragm is hard it will not deliver fuel at the needed pressure and volume to the fuel pump side of the carb body. The fuel pump check valve material your describing is the fiber style. You can try soaking the hardened pump diaphragm in dot 3 brake fluid for a hour or three to soften it up until a real kit comes., if it softens and becomes pliable it will not last and may tear quickly. Do not get brake fluid on the fiber check valve fuel pump. I suggest looking for a nos rebuild kit as the materials are much better and stay away from the blue plastic fuel pumps, the black butyl pumps are best but must never be used with E10 fuel.

 

[Homer6679]

New fuel filter and fuel line. The pump diaphragm is pliable. Could the metering side affect the pumping at all?

 

[cookies]

The metering side that impulse attaches to is the actual fuel pump

 

[Homer6679]

Pics of the metering and pump diaphragms. Both seem to be in good shape to my knowledge. Both are pliable

 

[cookies]

pump check valve finger looks lifted, it should sit perfectly flat on the carb body, lots of sawdust in the metering diaphragm meaning it could be in the carb body too if you pulled the screen then tried to run it. did you set the needle lever height at carb body deck height? check it for sticking and trash?

 

[SteveSr]

Pics of the metering and pump diaphragms. Both seem to be in good shape to my knowledge. Both are pliable

That pump diaphragm looks fine. I believe that white is teflon and should last almost indefinitely.

Your problem is elsewhere like a cracked impulse hose or crankcase leak. You should be able to see the impulse hose between the cylinder and the and the carb mounting flange on the tank.

Another way to check the impulse is to remove the carb and put a small dab of grease on the impulse port and pull the engine over. the grease should be sucked in to the fitting. If the grease doesn't move you have a leak somewhere.

While you are at it remove the muffler cover and post photos of the piston as viewed through the exhaust port.

 

[Bubster]

Intake boot would be something else to check.I have saw them split at the bottom.The saw will fire on a prime even through the boot,but no vac to pull gas.

 

[Homer6679]

Will post pics in a few, working on my dads husky 435 right now. Will a pressure test tell me if the impulse is leaking?

 

[SteveSr]

Will post pics in a few, working on my dads husky 435 right now. Will a pressure test tell me if the impulse is leaking?

Yes, if done properly.

 

[Homer6679]

Some pics of the saw and the cylinder as requested. I adjusted the metering lever properly and made sure it didn’t stick. All the ports in the carb are clean as I blew them out with carb clean.

 

[SteveSr]

Some pics of the saw and the cylinder as requested. I adjusted the metering lever properly and made sure it didn’t stick. All the ports in the carb are clean as I blew them out with carb clean.

Looks like you lucked out. Whatever killed the saw didn't take the piston and cylinder with it.

You likely have an air leak to find and fix. At the age of that saw I would also change the crank seals with OEM even if they aren't currently leaking.

BTW, those are the wrong fuel/oil caps but if they seal properly and don't leak...

 

[Homer6679]

I’ll be doing a pressure test when I get the time. What is the reasoning behind a leak causing the impulse to not work properly?