What should the compression be on a tohatsu M25?

[55evinrude]

Hello everyone! I will be going to look at a 2008 "merc sea pro" M25 2 stroke and im wondering what should the compression be? 130?? anyways I will also be checking the color of the plugs, lower unit gear oil (make sure no water) all cables, prop shaft and the overall condition of everything. is there anything im missing? you guys let me know!

I will run it on the hose to hear how it runs and how it shifts. being that it's already 4 years old I am already planning on replacing the impeller if i buy it and removing the "restrictor plate" . hopefully it's good as the price is really good!

Nathan

 

[pvanv]

Re: What should the compression be on a tohatsu M25?

More important than the compression number will be that the compression is identical in both cylinders. If off by less than 5%, OK, if off by more than 10%, trouble. 2-stroke compression figures tend to read lower than 4-strokes. Obviously you don't want a reading of just 50 pounds, though.

 

[Sea Rider]

Re: What should the compression be on a tohatsu M25?

Should have near 100 psi when measured after engine has been warmed and throttle grip set to wot and with at least 4 rope pulls per cylinder, if planing to pass it to 30 besides changing 30 carb gaslet, probably will need a +5? deg timing advance for the carb to open fully.

Happy Boating

 

[55evinrude]

Re: What should the compression be on a tohatsu M25?

More important than the compression number will be that the compression is identical in both cylinders. If off by less than 5%, OK, if off by more than 10%, trouble. 2-stroke compression figures tend to read lower than 4-strokes. Obviously you don't want a reading of just 50 pounds, though.

Thanks pvanv!! I did know about the "no different than 10% thing". does anybody know what the factory spec for compression is for that motor though? thanks

Nathan

 

[55evinrude]

Re: What should the compression be on a tohatsu M25?

Should have near 100 psi when measured after engine has been warmed and throttle grip set to wot and with at least 4 rope pulls per cylinder, if planing to pass it to 30 besides changing 30 carb gaslet, probably will need a +5? deg timing advance for the carb to open fully.

Happy Boating

lol looks like we posted at the same time anyways. Thanks Sea Rider, I will check the compression and see what it is! now about the timing I was reading somewhere that some of the 25's are already set to 25 degree timing and some aren't?? anyways thanks!!

Nathan

 

[Sea Rider]

Re: What should the compression be on a tohatsu M25?

The new 2 stroke Mercury (Sea Pro) 25 HP sent here comes with just 20? timing, probably to justify price difference with 30 HP if both models are tested next to each other. Once you have installed the 30 HP gasket remove cowl, while throttle grip is at idle position, place lever to forward and full throttle, check if you have a 180? flat butterfly at wot, if not, will need to advance timing + 5? playing with stopper A to achieve flat butterfly and extra 5 HP at throttle end. Hole shot and top speed difference is outstanding.

Happy Boating

 

[55evinrude]

Re: What should the compression be on a tohatsu M25?

Thanks Sea Rider! I have decided to go with a brand new 2011 model sea pro as i am getting a good deal . when i get it will do everything to it. It all sounds pretty simple to do and i am mechanically inclined. once again thanks!

Nathan