low power 575 husky

[half_full]

I have a husqvarna 575 ( I know, I read all the threads/reviews) that is in like new condition. I got it as a parts saw that "needs a new top end". There was very, very little scoring on the piston and the machine marks were like new. So, I put in a new caber ring. Vac/pressure test, fuel line, filter all new. It runs like a dream until it hits the wood. Just no power to it.
Maybe a few tanks through it to seat the ring? I'll get a compression test later today. But, it was good after initial startup/cool down.
Thoughts? Other than scrap it...

 

[tlandrum]

are you sure its getting enough fuel?

 

[Guido Salvage]

Fuel or plug.

 

[nmurph]

Fuel line collapsing?

 

[HuskStihl]

Low compression. Pics of the cylinder?

 

[half_full]

Thanks for the replies! I just went to pick up the saw. A local saw shop sold it for me. The buyer hadn't run it since he purchased it 6 months ago. He's a trustworthy person and long time customer of the shop. The dealer tried adjusting the carb with no results. He called me to see if I'd take a look at it. I offered to give back the cash but he would like to see if I can get it going.

I'll check compression first and then look over the fuel lines. May pull the carb and try adjusting metering lever.

 

[half_full]

Compression is at 135 on my gauge. I know mine reads a bit on the low side. So, lets give it 140? New caber ring with about one tank of fuel on it. Would that seem like a normal compression reading? I know the 372's run a bit low on compression but not sure about the 575.

 

[nmurph]

It should be in the 165 range.

 

[half_full]

I'll pull the cylinder tonight. If the cylinder looks good, piston looks good, ring end gap is ok (I'll get that tonight) and decomp is not leaking (I'll put a plug in for testing) what else would cause low compression on a stock cylinder/piston/new caber ring?
I know squish could be adjusted by removing the base gasket. But, shouldn't be needed on OEM if I'm looking for stock numbers.

My comments earlier on the saw condition are no exaggeration. This saw looks new. Air filter isn't even dirty. Inside and out this is clean.

 

[TreeTangler]

What caused it to score the piston in the first place?

 

[nmurph]

I'll pull the cylinder tonight. If the cylinder looks good, piston looks good, ring end gap is ok (I'll get that tonight) and decomp is not leaking (I'll put a plug in for testing) what else would cause low compression on a stock cylinder/piston/new caber ring?

You may have some dips in the plating from the previous scoring that are keeping the rings from sealing tightly. I would slide the ring into the bore and use a light to check for gaps bw the ring and the wall.

 

[watsonr]

I think the strato saws run a little lower in the compression.. I may be wrong.

 

[hamish]

Most likely somebody decide to set the carb settings both at one turn out. The saw will run but unless you have a tach or a chunk of wood you wont know what its doing.

Initial High is 3, L 1 1/2.

Compression at 135 is fine considering you just put in new rings, ya gotta give them time to seat.

 

[CTYank]

I think the strato saws run a little lower in the compression.. I may be wrong.

Certainly not a general rule. My PS-6100 Dolmar, after a few tankfuls, cranked out 215 psi cold on a known-good gauge. I happen to see absolutely no reason why a "strato" saw should have lower compression.

And yes, that Dolmar is a civilized BEAST. Others have come to that opinion separately. It has nothing whatsoever to do with spec-sheet competition a la Norge. Way beyond that. Bone stock is just fine, thanks.

 

[HuskStihl]

When I re-ringed my 385 the compression immediately jumped to 155, ring seat may increase it a little, but it won't be dramatic. Carefully check the cylinder for scratches/gouges, and consider removing the base gasket. If the saw is really running fine, and 4-stroking appropriately, then the 135 compression is likely the cause of the perceived weakness.