Author Topic: older 394xp runs well, lacks power  (Read 200 times)

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Offline burl

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older 394xp runs well, lacks power
« on: March 17, 2015, 10:53:59 am »
I have a late 90's Husqvarna 394xp that starts great and runs well, but is lacking cutting power - somewhat less than my much newer 372xp with the same bar length - 24". It produced 140 psi with a compression test. Just looking into the cylinder from the spark plug hole, it looks to me like it has light scoring. I'm not a good gauge of scoring, but that's what the guy at the local repair shop said when he took a quick look at it. I have tuned the carburetor with a tachometer to the best of my ability. Other factors that I should be looking at? Crank shaft seal? New cylinder? Or just rings? Carburetor? Anything else?

Thanks, Brian

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Offline aclarke

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Re: older 394xp runs well, lacks power
« Reply #1 on: March 17, 2015, 12:02:34 pm »
 Pull it down and inspect it. Probably be able to cleanup the cylinder scoring if it's not bad and replace piston and rings. Vacuum/pressure test the crankshaft seals or just replace them while the saw is apart. If it wasn't straight gassed, it likely has an air leak so that needs to be sorted out before reassembly. Adam

Offline wisecobandit

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Re: older 394xp runs well, lacks power
« Reply #2 on: March 18, 2015, 05:02:11 pm »
Be sure to check the plastic inlet manifold for cracks especially if its the white coloured 1 which can cause airleaks and mess with the impulse feed. It's a common fault with them.

Online srcarr52

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Re: older 394xp runs well, lacks power
« Reply #3 on: March 19, 2015, 10:30:02 am »
Be sure to check the plastic inlet manifold for cracks especially if its the white coloured 1 which can cause airleaks and mess with the impulse feed. It's a common fault with them.

Good call, I've had one crack on a friends saw and he didn't catch it in time before he locked it up.

Offline burl

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Re: older 394xp runs well, lacks power
« Reply #4 on: March 19, 2015, 12:01:43 pm »
Thanks a bunch guys. I'm gonna go ahead and tear into it, test the crank seals, and check the cylinder when I get a chance - probably not for a couple weeks. Good one on checking for cracking in the intake manifold too - I doubt I would have caught that. Please throw any other thoughts my way in the mean time. Thanks!

Offline adam32

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Re: older 394xp runs well, lacks power
« Reply #5 on: March 19, 2015, 02:56:52 pm »
Thanks a bunch guys. I'm gonna go ahead and tear into it, test the crank seals, and check the cylinder when I get a chance - probably not for a couple weeks. Good one on checking for cracking in the intake manifold too - I doubt I would have caught that. Please throw any other thoughts my way in the mean time. Thanks!

Port it ;)

Offline wisecobandit

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Re: older 394xp runs well, lacks power
« Reply #6 on: March 29, 2015, 05:00:56 pm »
I change crankshaft seals on most saws as a matter of course for how much they financially are if theres a thought in my head of a possible air leak. If your stripping the saw down to that point it only takes a few minutes to stick new ones in.
Ive seen more 394's fail a pressure test on the inlet manifold tho especially the earlier white ones (later are black) You have to remember plastic/nylon being bolted to a hot cylinder isn't the best idea and now with a bit of age behind them its almost inevitable they will crack at some stage.

Offline burl

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Re: older 394xp runs well, lacks power
« Reply #7 on: April 04, 2015, 03:54:16 pm »
Here are some photos of the piston from the muffler side of things. Any thoughts on the scoring? Muffler has small hole rusted through one corner, the outside/front face is a little dented, and the screen in the exhaust port is open on one side, but it otherwise seems functional. The white plastic intake does not seem to be ****. I'll pull to check the underside. Thinking about getting a vacuum/pressure tester for carb., crank seals, etc. What do people recommend? I've been looking at the Mityvac 8500.

-Thanks

Offline Eccentric

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Re: older 394xp runs well, lacks power
« Reply #8 on: April 04, 2015, 06:24:40 pm »
Looks like there's transfer from the piston to the cylinder.  It got hot/lean at some point.  Better tear it down and deal with it right.  As to why it got lean.......................could be seals.  Could be an air leak elsewhere.  Could also have been tuned too lean....
-Aaron

For older saws:
Tune the H side so that it 4-strokes (burbles) at WOT unloaded and just cleans up when under load.
When you lift cutting load, the saw should immediately revert to 4-stroking.  Fine tune the transition point for the wood you're cutting.

Offline alsled

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Re: older 394xp runs well, lacks power
« Reply #9 on: May 02, 2015, 09:26:49 pm »
Muffler screen plugged?

 

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