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Craftsman 42cc chainsaw - Compression too low?

Posted by dougand3 Southeast TN (My Page) on
Sat, Mar 10, 12 at 10:11

Saw is from 2002. Light duty - sawing 3 cord per year. Starts and idles well. Bogs down on throttle up and with any load on 18" bar/chain. Compression is 75 PSI. Added 10 drops 90wt gear oil to chamber and got 95 PSI. Should it be 110 - 130 PSI? Does this sound like cylinder walls scored and/or rings stuck? Ready to be recycled? Thanks so much. Doug


Follow-Up Postings:

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RE: Craftsman 42cc chainsaw - Compression too low?

A quick ck is to pull the muffler.

1. You will basically be able to see the conditions of the cyl, rings and possibly a carbon issue.

2. If all looks well, troubleshoot compression, carbs adjustments/condition, fuel lines/filter, fire.

3. I h/n seen a comp/chart vs living by a rule of thumb of 100 psi or not being able to hold comp in with my thumb. I feel this could be different on newer engs easier to pull but runs great, like a low comp start.

4. Have you ever cln or adj your carb, ck the plug's cond, color of your spark? Fire/Fuel/Comp!

Good Luck and Please Share what you find. loger


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RE: Craftsman 42cc chainsaw - Compression too low?

Thanks, loger. I'll pull muffler next and see.


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RE: Craftsman 42cc chainsaw - Compression too low?

After the quick inspection with no signs of scoring?? I would suspect carb. too lean. I had that saw and 18" bar is too much for it IMO. Plus carb. needs adjusted from time to time anyway. Another thing oil mix might be in play? not enough? wear? wear equals low compression. I dought you will see wear without mic'ing piston and bore? Guess what I'm saying need alot more information and Questions answered to really have guest what could be wrong?


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RE: Craftsman 42cc chainsaw - Compression too low?

I looked at cyl wall and see some shallow vertical lines...does it rise to scoring? I dunno enough to say. Idle screw turned CW = no change. I'll try to figure out adjustment on High Speed Mix. Always used syn oil at 40:1. I have been testing without bar/chain, so, load is less. I keep thinking about: 75 PSI. Add 10 drops 90wt oil and get 85-90 PSI. But it idles fine. Thanks for replies.


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RE: Craftsman 42cc chainsaw - Compression too low?

Maybe you can let me know what I am missing. My Craftsman 36cc 16” chainsaw was bogging down the last time I used it. I cleaned everything down including the carburetor & spark arrestor . The diaphragm, gaskets were all good. It has spark and a new plug with compression at 89lb. It would not start. Then flooded. Then started but could not get it going again. I set the low & high screws at 1.5 turns out & went up to 2 full turns. Any ideas?


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RE: Craftsman 42cc chainsaw - Compression too low?

Joe, you might be in trouble due to adding to this post. Not by me since they are related. LOL

1. Check for a good blue spark again, even ck the old plug again. Firing and firing under compression are two different issues. You might need a spark tester that will check for spark with the plug installed (from your auto store, only if you need it or borrow it if they will loan). How many pulls was the 89 of compression showing?

2. The turns out from a light seat are too much IMO. I feel 1 - 1 & 1/8 or ¼ might get you started and eliminate flooding.

3. The flooding issue might dictate a carb’s issue as a bad diaphragm or possibly not installed properly. Did you check the metering valve for any debris etc.? Did you check the small fuel screen inside the carb? Did you rem all screws and verify all ports were open with compressed carb cleaner, fine wire, compressed air or Etc???


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