compression on a 650 4 cyl

[chipndale]

I have a 65Hp Mercury with Type II ignition system. S/N 2605193. I'm not sure what year it is. It is very sluggish to start with and then it will run about 27 mph and then slowly decrease and eventually die. I have used engine tune through the carbs and the cylinders and still only get 100 psi on 3 cyl's and about 98 on the other one. What should I be have for compression?

 

[mellowyellow]

Re: compression on a 650 4 cyl

are your readings from a hot motor?<br />btw, my 70 1150 starts with 292 ser# and I have<br />120-125 across all 6 cyl. (warm)<br />M.Y.

 

[chipndale]

Re: compression on a 650 4 cyl

The only heat was from the sun and the temp in the shade was ver 90 deg. I bought a new gauge with a hose on it so I could get to # 4 cyl and I got 100 psi.I just did it again with my old gauge and the same cyl's have 135 to 140. I can't get to #4 with this gage. I think I just need to keep running it because the compression seems to be increasing after I used some engine tune foam on it. What do you think?