YACT yet another compression test thread. MS290, 105psi? Newish Poulan, 105psi?

[ham]

I snagged a free MS290 that the guy kept in the back of his work van. Case beat to hell and back from getting knocked around but apparently low hours. Rear handle is cracked and epoxy repaired, needs replaced. Has factory bar that doesn't show a ton of use. The guy retired, hadn't run it in years, was moving to old folks home and giving away a bunch of his junk.

So. I get it home, put in fresh gas, dicker with some fuel dumped in the carb, get it running great with no carb kit or anything needed. Cuts fine. Figure before I buy a new rear handle and go through the BS to replace it, do a compression test 105psi cold. Uh oh. Test a Poulan I have that I bought new and have babied, maybe 2 hours on it max. 105psi. uh not good. Use my compressor set to 125 psi to test the compression gauge it reads 125psi.

Is there anything I'm missing here? being that it already needs a new rear handle and is overall knocked around I'm hesitant to take the time to do a rebuild on the MS290. I don't know wtf the deal is with the poulan, it's tuned fantastic and has only has 50:1 stihl oil mix in it.

 

[cuinrearview]

Sounds like the hose is too long on your tester, and/or the valve isn't right at the tip. Most automotive testers have a lot of extra volume that isn't noticed on a larger cylinder.

 

[ham]

Cylinder looks smooth as can be

 

[ham]

Sounds like the hose is too long on your tester, and/or the valve isn't right at the tip. Most automotive testers have a lot of extra volume that isn't noticed on a larger cylinder.

https://www.amazon.com/BETOOLL-HW0130-Cylinder-Compression-Automotive/dp/B00SKSAB8U
That's what I'm using

 

[cuinrearview]

Without it in front of me I can't tell where the shrader looking valve is. Also, if you have to use any of the adapters that will add volume and falsify the reading. Compression testers as a whole are not a great tool to solely diagnose chainsaw health. This is a perfect example. If it truly had 105 psi it wouldn't run.

 

[ham]

Without it in front of me I can't tell where the shrader looking valve is. Also, if you have to use any of the adapters that will add volume and falsify the reading. Compression testers as a whole are not a great tool to solely diagnose chainsaw health. This is a perfect example. If it truly had 105 psi it wouldn't run.

The valve is directly next to the gauge. Also...... I know they're not great either, but the straight metal tube (no rubber hose) gives like 95-100psi

 

[lone wolf]

The valve is directly next to the gauge. Also...... I know they're not great either, but the straight metal tube (no rubber hose) gives like 95-100psi

Pics of the end of your tester.

 

[RED-85-Z51]

Does sound like a tester issue, but i will say that my new tester with only 1" of hose only shows 115psi on a freshly rebuilt 42cc poulan pro...its just all they blow. But the 290 is expect 140ish. Are you holding the throttle open and the choke is off?

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[cuinrearview]

Are you holding the throttle open and the choke is off?

Not necessary

 

[ham]

Pics of the end of your tester.

 

[cuinrearview]

Here's your problem

 

[ham]

Here's your problem

If so, why does it read accurately when tested with my air compressor (the compressor has two quality, matching gauges dead at 125psi with a good 25’ hose). Also, what can I do to fix it? If there’s some underlying issue with the 290 I don’t want to spent money and a lot of time swapping the rear handle

 

[cuinrearview]

But you said it runs good...

 

[cuinrearview]

Loading the tester with constant 125psi through the whole thing and cyclically pumping it are two different things.

 

[RED-85-Z51]

Not necessary

Its not a dramatic difference but there is a difference, here is no choke no throttle vs no choke idle. With no Schrader in the fitting its struggling to build pressure as it is

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[cuinrearview]

Its not a dramatic difference but there is a difference, here is no choke no throttle vs no choke idle. With no Schrader in the fitting its struggling to build pressure as it is

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Meh, that little difference could be a lot of things.

 

[RED-85-Z51]

Meh, that little difference could be a lot of things.

I tried to limit variables, first test was the no choke full throttle so there was no chance of any lube pulled in by more pulls or choking bumping up the number. Repeated the 1st test after the 2nd and got 120/121.

There is no reason not to expect that more air flow won't result in a higher static compression. The same way a 4 stroke will turn over a bit easier at idle vs full throttle

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[cuinrearview]

Lol you're trying to justify an unnecessary step with 2 1/2psi. Your 70:1 vs my 40:1 would cause a bigger difference than that man. Maybe you farted while pulling one of them over. The 2° difference in ambient between the two test could cause it.

 

[RED-85-Z51]

Lol you're trying to justify an unnecessary step with 2 1/2psi. Your 70:1 vs my 40:1 would cause a bigger difference than that man. Maybe you farted while pulling one of them over. The 2° difference in ambient between the two test could cause it.

Multiple tests back to back? Doubt it. Im running 32:1 in this turd...

Show me a manufactures compression testing guideline that doesn't say to ensure the choke is off and the throttle is open...


Also, thats 6psi.

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[cuinrearview]

Show me a manufactures compression testing guideline that doesn't say to ensure the choke is off and the throttle is open.

Like the ones that spec 50:1?