Poulan 3400

[countryhog]

Rebuilt this 3400 - new rings, seals, carb kit, lines, filters, etc. sucker ran sweet yesterday; ran well at high speed and gnawed on the wood like a beaver. Today it would rev up but would "oscillate" it's rpms. No amount of hi needle adjusting corrected it.
I'm guessing it may be the carb cause of a sudden many of my carb rebuilds are squirrelly. Any suggestions?

 

[Motorhead]

Sounds like your not done cleaning the fuel system

 

[Motorhead]

Don't forget the tank vent

 

[Digger's Dad]

I had an 028 I did a carb rebuild on some years ago that gave me fits after the rebuild. Ran great for the first tank and then started something like the oscillation you describe. It would hit top RPM then fade off, struggle, pick up, fade, rattle, on and on... Drove me nuts. Checked compression, vacuum, fuel lines, vents, re-rebuilt the carb twice all with no luck. Worked on it off and of for over a month. Finally took it to a buddy of mine who is a looooooong time Stihl dealer. He fixed in it 5 minutes.

The 028 has a spring that holds the choke open after you've started the saw. After many years the spring had weakened and would get pulled closed at high RPM causing the flutter problem. Once the RPM dropped it would open up and run great then shut down again.

Any chance that 3400 has a similar choke design?

 

[Wagnerwerks]

Dirt.

 

[P.M.P.]

Hate to say this but could have air leak somwhere.

 

[countryhog]

3400 has a mechanical choke. Gonna take the carb apart tomorrow, replace filter, check vent. Ok. Don't say leak

 

[5000+]

Did you run it without the air filter? The 3400 has chrome piston and unplated cylinder, are the rings supposed to be chromed?.

 

[5000+]

Does the carb have welsh plugs? Might have loose/leaking one.

 

[DrewUth]

Check the impulse line too. My Poulan 3000 acted similarly a few months ago- ran perfect one day, then super lean on top the next no matter how much I turned the H. Impulse line was cracked, massive air leak right into the crankcase.

 

[5000+]

Check the impulse line too. My Poulan 3000 acted similarly a few months ago- ran perfect one day, then super lean on top the next no matter how much I turned the H. Impulse line was cracked, massive air leak right into the crankcase.

No pulse line on these. Goes thru the intake block. Did you try a new spark plug?. Also try disconnecting the shut off wire at the coil. Sometimes the wire will intermittently short to ground behind the flywheel.

 

[countryhog]

No Welch plug. Will try other things

 

[countryhog]

Replaced new spark plug with another new spark plug. Voila! Thanks for suggestions.