My recently purchased 2004 Yamaha is in the shop, l posted the problem before on this site, but the mechanic calls me and says he did a compression test and all 4 cylinders had 110 psi, normal is 130, what could cause this, When l ran her for the first time it wouldnt pass 2200 rpms. Valve problem? cracked head? he also said the oil had no water in it. So rules out a blown head gasket

Could be a valve problem. Your piston rings could also be shot. Check those. If you're not getting the proper compression, your rings could be worn. Check your air filter too. You might not be getting the proper intake air.

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Just because there is no water in the oil does not mean the head gasket is good or bad. Do not chase a problem there.

110 psi on all four? Thats not bad at all. Did this mechanic do a wet test? (put oil in ecah cylinder & test again?), & did he also block open the throttle plates to allow air entry?

When doing a compression test, all that should be done. Values can be off as much as 30-40% before l worry IF ALL CYLINDERS ARE EQUAL. They guys gauge could be off!

If yours wo not run at full throttle, l am first checking fuel filters, & connections.

Your compression is fine.

My first question to your tech would be how accurate is his or hers comp. tester? To have ALL cylinders low is rare, and indicates worn rings, carbon build-up on the valves, or bad valve seals. This is just a shot in the dark, i'm a Merc guy. Keep in mind, 110psi is quite low for a 4/S, most are higher compression that a 2/S.

you have no problem. if all cylinders are equal, you're good to go. This guy just has a boat payment due or something and wants you to make it for him.

your WOT problem is clogged carbs, just rebuild 'em & go.