why is my saw running?

[cgarman]

I'm just curious, but where exactly is the check valve located on your comp tester? It you see 145 on the gauge at any time, it should lock it there unless it see a higher pressure, or you hit the pressure release.

Maybe a pic of your comp tester would help. We all Love pics around here!

There's a check valve at the end of the rubber hose where it screws into the plug port. The bleed valve is seen by the gauge.

I (being a small to average sized human) pulled it to 120 after 4-5 tugs on the starter. A friend (pulling much faster) also got to 120, but was able to make the needle bounce higher to 145 a few times. It was almost like he was bumping it as he pulled the cord. It kind of reminded me of a pressure gauge on a noisy compressor - bouncing as the motor runs. In both cases, it held a steady 120 for several minutes.

 

[Ax-man]

Something is definately not right here and the type of gauge being used is suspect or there is a procedure problem. The gauge pictured is the right one to have. A saw with only 60 lbs compression on my gauge won't start. It wouldn't even cough.

Compression 101.

Get the right gauge first.

First pull on a saw in good condition will jump right up to 75 lbs. 100 lbs is really good.

Second pull should get around to 110 to 125 lbs or a little more like 130.

Third and fourth pull will get up to 140 to 150. This is a cold reading. A saw that is warm will be about 10lbs less.

150 lbs is a very good number and about average for a saw in good shape on the top end. Some model saws will go higher sometimes as much as 180 to 200 lbs.

A reading of 125 lbs or less means the top end needs attention. The saw may run fine but will be doggy and slow and lacks snap when cutting wood. You can tell the difference in a saw if you were to run the same model that had 150 lbs. verses one around 125 to 130.

Four to five pulls is about all you need to do for a compression test. Most saws fire in this range when they are cold. Anymore than that your just wasting your arm strenth. Doesn't matter weather the throttle is open or closed. A sufficient amout of air will pass by the throttle plate in the carb in the idle setting.



Age makes no difference either. I have an old vintage 770 G or gear drive Homelite with a good piston and cylinder it tests at 150. Same with my vintage or almost vintage little 020's. They also test out at 145 to 150 lbs. Again these are cold readings. Size and age makes no difference.

Compression testing is only a guide not an absolute. Some saws with really bad looking pistons and cylinder can test out within the acceptable range. The intake side of the piston is just as important as the exhaust side of the piston. Visual inspection is always the best way to go.

 

[cgarman]

Sorry - I'm not following. You said the type of gauge being used is suspect. Then you said the gauge picture is the right one. Did you mean to attach a photo, or are you referring to mine?

A little more detail - my crappy abused 46cc Poulan hit 145. My friend's Dolmar 7900 hit 165 - both with the same setup.

I just bought this saw used, and the guy said it pulled 145. Should I be worried that I can't get the same numbers?

 

[boutselis]

Sorry - I'm not following. You said the type of gauge being used is suspect. Then you said the gauge picture is the right one. Did you mean to attach a photo, or are you referring to mine?

A little more detail - my crappy abused 46cc Poulan hit 145. My friend's Dolmar 7900 hit 165 - both with the same setup.

I just bought this saw used, and the guy said it pulled 145. Should I be worried that I can't get the same numbers?

I think he was getting some of mine and some of yours mixed up. My guge is the one thats suspect and the one you showed in your picture looks right (I believe)

I am getting a different gage.

 

[Ax-man]

I think he was getting some of mine and some of yours mixed up. My guge is the one thats suspect and the one you showed in your picture looks right (I believe)

I am getting a different gage.

Correct, your gauge is suspect. Cgarman pictures of his compression testor is very similar to mine and is the correct one to use . IN my opinion it is the right one to use anyway. Opinions will vary of course.