034 surging

[PowerWagon]

I have a stihl 034 that is having a lot of surging.... idle is poor and at times exhaust note sounds softer. Surges like hell at Wot no matter the tune.

I have replaced the crank seals with oem, cleaned carb, tried a eBay Zama carb that made it run worse...

I'm wondering if anyone has ran into this , stock carb just not wanting to cooperate. Thinking on trying a tillotson....

 

[procarbine2k1]

Does it surge at idle? Did you check the impulse hose?

 

[Mad Professor]

Needs a pres/vac test. Impulse line, intake boot, fuel line (not pres/vac) , are likely culprits. Check cyl bolts and case halves/gasket.

 

[PowerWagon]

It tends to idle for a bit and then slowly die. I replaced lines/ case gasket when I did crank seals. No change after all that. Which is why I'm thinking carb issue.

In the cut, it will surge between running crisp and blubbery rich. Trying to tune it leaner just makes it bog out when snapping the throttle.

 

[PowerWagon]

But yes I need to try a vac test before another carb.

Thanks

 

[Poleman]

Have you changed/checked the fuel filter? They can cause issues like that.
If you have, what have you done to the carb? Clean, kit? It sounds to me like it's carb. If you've rebuilt it does it hold pressure? Replace needle? Welch plug reseal/replace.
It sounds like intermittent fuel delivery.

 

[Wood Doctor]

I ran into this same issue with an 028 Wood Boss. The fuel line was so old and weak that it was closing up when the carb tried to get more fuel at WOT, so it starts running lean, surges, and then has no power in the middle of the cut because it becomes starved for fuel. I replaced the fuel line (not easy, see service manual). The pickup body (fuel filter) was surprisingly OK.

The fuel line is straight down inside the tank and when old, it gets weak and will squeeze closed when the carb tries to pull in fuel at WOT. Newer Stihl fuel lines are commonly S-shaped and heavier construction.

 

[dswensen]

Just a thought - I had an 038 that had a choke flap in the air filter. When I went to WOT, it would suck the choke flap closed until the RPMs fell off, the choke flap opened and it ran up again until it sucked the choke flap closed - repeat, repeat, repeat. Surging just as you say.

Does your choke flap reside in your air filter?

The poor idle and the softer sound at idle might be a partially clogged muffler screen?????

 

[drf255]

Run it sans air filter for one cut and see what it does.

How's the spark screen in the muff look?

 

[PowerWagon]

All I did was clean the carb, I will double check needle/fuel lines. It really does sound like a fuel delivery problem to me too.

I'll take a look at the filter also but I dont think there is a choke flap.

Muffler is modded and flows well.

 

[drf255]

There is NO choke flap in an 034. 024/026/028/038 do have them.

 

[PowerWagon]

Had to run it yesterday, didn't want to but my Jonsered 670 was acting up, would not upcut. Cuts downwards strong but trying to upcut it just blurbles. Don't know what would cause that??

Anyway the 034 ran half decent for me, bit of a bog I had to feather through but did ok in the cut.

Made two loads and it was about all my trailer could take....

 

[drf255]

Too rich would do that. Clogged airfilter too.

The more load you put on a saw, the fatter it wants to be.

 

[Poleman]

When you said it cuts good from the top but issues with an undercut......you may wanna check your intake boot. I found a torn boot when a saw acted just like that other than in reverse. It was on a MS390....it would undercut great but top down it wouldn't.
Worth a look see maybe?!

 

[PowerWagon]

Dragging this up again,

Pulled the cylinder, inspected intake boot thoroughly, replaced impulse line, same issue.

Saw fires right up on choke but lean surges and dies right away if you don't feather it to keep it going(even then way too lean) Adjustments make no difference.

I'm going to pull the pickup line/filter next.

 

[Poleman]

You may possibly check your impulse connection as it comes from the case to the back of the upper carb mount area. It attaches to the back and feeds through a hole and into a hole in the boot to the carb impulse. It' possible the rubber boot isn' sealing against the back structure and carb. The boot itself is used as a gasket to seal the impulse chamber. A leak here could cause your leak condition.
I worked on a saw where it was leaking there once and was hard to find as saw pressure/vac tested good, carb tested good, the fuel line and impulse were new. I found it by spraying carb cleaner around while saw was running. You, know when you find the leak as the saw will pick up.

 

[president]

You may possibly check your impulse connection as it comes from the case to the back of the upper carb mount area. It attaches to the back and feeds through a hole and into a hole in the boot to the carb impulse. It' possible the rubber boot isn' sealing against the back structure and carb. The boot itself is used as a gasket to seal the impulse chamber. A leak here could cause your leak condition.
I worked on a saw where it was leaking there once and was hard to find as saw pressure/vac tested good, carb tested good, the fuel line and impulse were new. I found it by spraying carb cleaner around while saw was running. You, know when you find the leak as the saw will pick up.View attachment 611570

Darned Right,someone jammed the wrong gasket against the boot to carb contact
and it messed with the sealing surfaces there Stihls are different from the older huskys
that draw impulse through the heat blocks

 

[PowerWagon]

That sealing surface did look clean but maybe it is just mashed down to thin?

I will take another shot at that. Maybe some loctite 518.

Thanks!

 

[Poleman]

I don't think 518 will work since its anarobic and only sets up with no air. Something more like Dirko, Moto seal, 1194 may work better.

 

[PowerWagon]

I have an activator for it. SF7649

Makes it set up quick.